SU or Weber Carburetors? | Answering a timeless question

It’s an age-old question—and sometimes fuel for an argument: Which carburetors are better, SU or Weber? The answer is elusive. Everyone has an opinion, but no one seems to be able to offer definitive proof. 

We set out to find some concrete answers by measuring a couple of mule engines equipped with various popular Weber and SU configurations on a dynamometer. We’ll even spoil the surprise by skipping to our conclusion. Which one is better? We have three answers: either, neither, and it depends.

How can this be? Well, it turns out that both choices make about the same power, neither choice is a silver bullet, and the answer really depends on the application. The way your car is built, the way you drive, and even your own cosmetic preferences can help you make the best decision.

Clockwise, from left: We tested four setups on our MGB engine: 11/2-inch SU HS4 carbs on a factory MGB intake manifold, a Weber 45 DCOE carb on a Pierce intake manifold, a Weber 32/36 DGV on a Pierce intake manifold, and 13/4-inch SU HS6 carbs on a Maniflow intake manifold.

The Numbers

We’ve made thousands of dyno pulls in our time. While we’ve rarely tested SU and Weber carbs back to back, we can tell you that it’s been clear through these pulls that either carb combination can make similar power numbers. We figured you’d want more proof than that, however, so we finally performed some thorough tests to show that both setups work well.

For our first set of tests, we used a 1978 MGB fitted with a bone-stock 1.8-liter B-series BMC engine. We compared dual 11/2-inch SUs, dual 13/4-inch SUs, a single side-draft Weber DCOE, and a single down-draft Weber 32/36 DGV. The venturis in each test were sized to logically suit the volumetric efficiency and displacement of the engine/carb setup being tested. We dynoed all of the combinations on a chassis dyno and came up with the following horsepower numbers at the rear wheels:

For our second set of tests, we turned to our Modern Midget’s more radical 1380cc A-series BMC engine. This engine features a well-ported cylinder head, higher compression, more cam, and many other performance tricks. It makes good power throughout a big rpm range.

We tested three setups on this engine: the dual 11/2-inch SUs, a single 13/4-inch SU, and a Weber DCOE. Each one was tested on an engine dyno, so our numbers represent the horsepower at the engine’s crankshaft. (The chassis dyno figures always include driveline loss, hence the lower figures for the MGB.)

As the numbers show, each carb setup shines slightly at a specific rpm point, but on average they’re all nearly identical. Nitpickers may say that the Weber DCOE is the best, but in our book it’s only by a hair—a one- or two-horsepower advantage doesn’t make a clear winner in our book. Context is king when choosing a carb setup.

It Depends: Like We Said, Context Is King

The MGB testing was done on Baker Engineering's Dynojet 248 chassis dyno.

So, the numbers show the Weber DCOE winning by a hair, but each setup produced nearly the same numbers. Which do you choose: One or two SUs, a side-draft Weber DCOE, or a downdraft Weber DGV? Here’s how we decide.

First, we’ll consider our budget and skill set. Ifa we already have SUs on our car as well as the tools and skills needed to rebuild them—or the carburetors are in good shape—we’ll usually keep them. We’ll just make sure that they’re properly dialed in. 

If we think that a professional rebuild is in order—that alone can often cost $400 to $800 per set—then we’ll start thinking about a switch. We’ll also consider a swap if we just don’t have the right carburetors on our car. (Picture a rubber-bumper MGB fitted with its original single Zenith-Stromberg.)

Next, we’ll think about drivability features we like. If a manual choke is viewed as a pain for those who drive the car, then we’ll look toward the downdraft Weber DGV as it’s available with an automatic choke. The DGV can be purchased with a choke that’s either heated by water or operated by an electric circuit. If manual chokes are okay, then the DCOE or SUs are on the list.

Accelerator pumps make for good throttle response and can also influence our decision: Webers have them and SUs don’t. As a result, many people feel that a properly dialed-in Weber provides slightly crisper throttle response. We’ve been unable to prove this on a proper dyno, but our seat-of-the-pants impressions agree.

Another drivability consideration is our ignition system. SUs and Weber DGVs work well with vacuum advance distributors. Meanwhile, DCOEs are less suited for them; most kits don’t even have ports for vacuum advance, so custom work is involved and the results can be mixed. 

We’ve long been fans of vacuum advance on street cars, as it adds a bit of economy. Most importantly, a vacuum advance increases cruise and idle drivability as well as engine smoothness. For this reason, we’d say that the DCOE is a little less than desirable for street use. 

Next we’ll move on to our tuning needs. If we plan on dialing in things in once and then basically forgetting about it, any carb is fine. However, if we like to tweak our tuning, the DCOE is probably the easiest to service. The SUs come next, with the DGV bringing up the rear. 

The DCOE and DGV have easy-to-reach idle mixture screws. Some SUs (HIF and HD models) have screws, too, but they’re not always as conveniently located. Other SUs (H and HS models) have their idle mixture controls hidden underneath the carbs, so reaching and adjusting them can be an exercise in contortion.

Further mixture work with the DCOE comes through the removal of a wing nut followed by a few turns of a screwdriver—the process is very simple and fast. SUs are nearly as easy: three screws to remove the carb top followed by another screw to change the needle. 

DGVs are probably the least convenient to service. To change the jets, the air cleaner as well as the whole top of the carburetor must first come off. 

Emissions are another factor. SUs can easily be equipped with factory PCV systems and work with the evaporative loss systems that absorb fumes. Many Weber setups lack provisions for these things. If keeping smells and emissions at bay is important to you, you’ll have more work to do if you select a Weber.

Another thing to consider: Who do you know? If your friends in the sports car community are Weber people, maybe you should follow their lead. That way you can freely exchange knowledge and parts with each other. The same is true if you hang out with SU people. 

The last consideration, whether you want to admit it or not, deals with aesthetics. Maybe you like the look of polished dashpots. Or maybe you need two—or three!—Webers with velocity stacks. Don’t discount this concern as silly. After all, you pick your paint colors and accessories for aesthetic reasons, so maybe your engine compartment choices should follow suit to some extent.

Looking for some concrete answers? Both SUs and Webers have their strengths and weaknesses. Either is good and neither is perfect. The things that matter the most to you in the context of your car, your tuning expectations, and your drivability priorities will make the choice for you.

Size Matters

Okay, so if you’ve been paying attention, you’ve figured out that any choice can be a good one if made in the right context. However, making a good choice isn’t just about SU vs. Weber. When shopping induction setups, you also have to pick the right size and number of carburetors.

Many people oversimplify the carb’s job. They see it as a piece of equipment that simply gets fuel into the engine. That’s true, but it’s only a small part of the equation. The carb also gets air into the engine and, of course, properly mixes it with the fuel.

Carbs are “sized” by the amount of air they can flow, and this sizing should closely match the engine’s needs. The engine’s capacity is one factor of this sizing, but its maximum rpm and volumetric efficiency are also important. For example, a large engine running at low engine speeds may need less carburetor than a smaller engine running at higher speeds.

The bottom line is that an engine’s CFM needs are determined by this formula: 

If we assume 80 percent volumetric efficiency for a stock engine, we’ll see that a stock MGB (roughly 1800cc or 110 cubic inches) needs 153 CFM at 6000 rpm. A stock Triumph TR6 (approximately 2500cc or 152 cubic inches) needs 211 CFM at 6000 rpm. 

If we add performance modifications to either engine, we’ll see the VE increase—along with the CFM needs. Likewise, if we raise or lower our maximum rpm, the CFM needs will also be affected. This chart shows several of these scenarios:

Note that a normally aspirated engine will rarely achieve 100 percent volumetric efficiency. However, with forced induction, 100 percent or greater is more easily obtained.

Now that we’ve figured out the math regarding our engine needs, we turn to our carburetor choices. This chart shows the flow potential for our common carburetor choices:

Note and disclaimer: This data was taken from multiple sources, some averaged. Flow numbers may vary slightly due to testing conditions and methods or tools used. Nonetheless, this information should be useful in carb sizing decisions.

Now it’s time to put this all together. Once we know the CFM needs for our engine, we can pick a carburetor size and setup to match it. It’s better to go a bit oversized than undersized, but don’t go too far. Installing too much carburetor will reduce power at lower engine speeds and allow the fuel to fall out of the air/fuel mixture. 

Of course, there’s still one more factor to consider: Just because a carburetor flows a certain amount of air doesn’t mean it will flow that much when it’s on the engine. Why? The manifold between the carb and the cylinder head has to flow well, too. Some designs flow better than others. This is another reason why you’ll want to pick a carb that flows a bit better than you need—you can probably expect losses from the manifold, especially if it’s a stock piece. (On a related note, we’ll get into some head-to-head manifold comparisons in a future issue.)

Tune It Right

Here’s a harsh reality when it comes to carburetors: Time and time again we’ve seen people worry and fuss about which setup to install, only to spend little or no time on the jetting required by their particular engine’s needs. 

The right carburetor setup teamed with the wrong jetting will lose power and potentially damage your engine. Make sure your jetting is correct or call in an expert. We’d go so far as to say that an incorrectly sized carburetor that’s properly jetted is better than the right carburetor that’s not properly jetted. 

How do you correctly jet a carburetor? First of all, understand that there is a difference between setting the idle mixture and the mixture under load. That second one involves the all-important main jets. 

In the case of most carbs, the idle mixture can be tweaked with a screw (or jet nuts on some SUs), but the main mixture is adjusted by changing jets or needles. While the idle mixture can be adjusted while the car is standing still, adjusting the main mixture requires the car to be running—and usually moving—under a load. The details of main mixture adjustment can easily fill many pages, but we do have three tried-and-true methods. 

First, if your engine features a fairly straightforward combination of parts, there’s probably a chart or expert you can consult that will get the jetting very close to your needs. We’ve found factory manuals as well as Internet sources—try Teglerizer Engineering and Consulting (teglerizer.com) or Pierce Manifolds (piercemanifolds.com)—that can offer great charts and recommendations. Any reputable carburetor vendor or installer will be a good resource for a personal consultation, and they should be rewarded with your business. 

Second, you can use the proven reading-the-plug method to determine carburetor jetting. If following this route, don’t do it after the car has been idling—you’ll just be reading the idle mixture off the plugs. Here’s the best way to go about it: Make an acceleration run in a remote, safe area before immediately shutting off the engine and coasting to a stop. Now read the plugs.

The third option is probably the most accurate: Use a chassis dyno fitted with a wide-band oxygen sensor. We usually use our first method to get a baseline tune before doing the fine work on the dyno. 

You’ve probably noticed that we’ve suggested spending a few hundred dollars on tuning, ideally via a dyno session. We’re consistently surprised when people don’t heed this very important advice—they’ll spend extra on a carburetor setup they may not need but will skimp on the tuning. Money spent on a good tune is always economical. 

Now What?

If we’ve done our job here, then we’ve settled the SU vs. Weber debate: They’re both good, but neither is an overdog. 

Here’s where we want to leave you: First, don’t worry so much about which carburetor is better, but rather which setup best fits your application and tastes. Next, make sure to size the setup to your engine needs. Finally, spend the time and money to tune it right.

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wspohn
wspohn SuperDork
8/13/20 1:19 p.m.

Good article. It is particularly true that on siamesed port engines the benefits of Webers are low and given that new Webers come set up for some other application and the tuning to your engine is a combination of experience and science that most owners lack, it really isn't that attractive a mod except to those who desire the look of the Webers for bragging rights.

 

Go to one intake port per cylinder and things shift a bit more toward the Webers and it becomes worth the exercise to fit and tune them for a street performance car or a race car (I have always used Webers only on my race cars powered by MG engines).

MG engine with after market 4 port crossflow head:

MG engine with factory DOHC head:

dougie
dougie Reader
8/13/20 11:10 p.m.

Would have been nice to see some test results on the SU 2" HD8's. Tuning on the dyno is the only way to accurately tune any performance motor.

https://youtu.be/8CmGFL54VlA

Sam12693
Sam12693
8/14/20 6:13 p.m.

I've worked with SU's and Webers.  Lucky enought to live close to Pierce Manifolds for my Datsun 240Z setup.  Webers let me tweak settings as I add modifications or change my driving style.  Jets x 6 are not cheap, so getting good advice from folks running similar modifications saves $$ and time.

wspohn
wspohn SuperDork
8/15/20 2:37 p.m.

Dougie - the BMC factory was in the habit of speccing too large SUs for racing. The Healey didn't need 2", nor did the race MGB, nor the street Rover 2000 TC. They even tried them on the factory MGA Twin Cam race cars.  Flow is too slow at part throttle and they don't run well except on wide open throttle, and even then only when tuned exactly right.   I have tried them on my race cars (up to 1950 cc MGB motors) and prefer the 1 3/4" . It gets you little to have a horsepower or two more at top rpm if you lost time getting there.

Sam - we are lucky to have local shops that specialize in Italian cars and keep full sets of jets that they will charge a fee for plus whatever it costs to replace stock once you know what you need. I am lucky that I never had to do anything but fine tuning on my V12 Lamborghini, but that would have been the way to go.

IIRC the Datsun wasn't homologated with Webers but with Solex PHH 44s, but that's pretty much the same thing except for jet availability. We had local racers that got them properly set up and they were one sweet set up once they got them optimized!

dougie
dougie Reader
8/17/20 9:03 p.m.
wspohn said:

Dougie - the BMC factory was in the habit of speccing too large SUs for racing. The Healey didn't need 2", nor did the race MGB, nor the street Rover 2000 TC. They even tried them on the factory MGA Twin Cam race cars.  Flow is too slow at part throttle and they don't run ell except on wide open throttle, and even then only when tuned exactly right.   I have tried them on my race cars (uop to 1950 cc MGB motors) and prefer the 1 3/4" . It gets you little to have a horsepower or two more at top rpm if you lost time getting there.

Sam - we are lucky to have local shops that specialize in Italian cars and keep full sets of jets that they will charge a fee for plus whatever it costs to replace stock once you know what you need. I am lucky that I never had to do anything but fine tuning on my V12 Lamborghini, but that would have been the way to go.

IIRC the Datsun wasn't homologated with Webers but with Solex PHH 44s, but that's pretty much the same thing except for jet availability. We had local racers that got them properly set up and they were one sweet set up once they got them optimized!

That hasn't been my experience, I'm very familiar with all the Healey Works and BMC prepared competition cars. With modern cam design, true technical head porting, and a few additional American tuner tricks the period factory teams couldn't do, didn't have knowledge of or have time to install and test, I've achieve performance far beyond any Healey they prepared for road racing. It was easier for them to switch to Webers, then to do additional testing & tuning with the 2" SU HD8's.

wspohn
wspohn Dork
8/18/20 12:43 p.m.

Well done if you have managed a triple 2" set up that has good transition through the rpm range. I don't think that could ever be done with the twin 2" on an MGB engine.

My favourite set up on the C series was a triple 1 3/4" intake that resolved all of the problems with the end cylinders that the stock twin carb set up caused (I think I've posted a pic before). The flow rate on those totals 630 cfm.

I beleive that Vizard said that a 2" SU can flow 330 cfm on the bench and I would think that a 3 liter pushrod C series would be hard pushed to need 990 cfm at red line

wspohn
wspohn Dork
11/2/20 12:18 p.m.

PS - for those times when really large capacity is called for SU had these racing carbs (DU6) that presumably had the capacity of two 1 3/4" SUs.......  420 cfm per carb?

 

 

 

Torqued
Torqued New Reader
6/1/21 11:52 a.m.

Very interesting article and comments too!  The power figures for the four different carbs are so close that I'd bet that a proper statistical analysis would find them indistinguishable. Then the choice comes down to the other factors -tuneability, drivability, convenience, ...

mdawley
mdawley New Reader
2/17/22 5:52 p.m.

I use a 45DCOE on my MGB "FrankenB" for all the (good) reasons described by all. But one of the most important items to me after 45 years with the set up is the lack of any attention needed over those years. Rebuilt engines have been required in the car every 150k miles or so and when changed the carb and manifold were laid assembled on a blanket on the windshield without even diconnecting the throttle cable (same type situation for the Pertronix dizzy...). I have never rebuilt it as the car gets continuous use so gas degradation is not an issue. It comes off in about 10 minutes as well. Then there is the issue of float bowels over exhaust manifolds on a B; a real issue in summer stop and go city driving that the DCOE does not seem to be affected by. The final positive to me is potential fuel line leak points; 1 connection on the Weber. how many on a set of SU's?

wspohn
wspohn SuperDork
2/19/22 11:50 a.m.

But one of the most important items to me after 45 years with the set up is the lack of any attention needed over those years.

Actually, SUs rarely give problems if left alone. I built a custom set of triple 1 3/4" for my MGC, tuned it and never looked at them for the next 20 years. SUs suffer from 'fiddlers' - people that automatically assume that poor running must mean they should tinker with the SUs even though they don't know what they are doing (and the problem is very often ignition in the first  place).

Extra brownie points if you can guess what I made the MGC intake from - it is 1 1/2  intakes from a 4 cylinder engine heliarced together.

 

 

Streetwiseguy
Streetwiseguy MegaDork
2/21/22 4:08 p.m.

Back when I was seeing a lot of B20b Volvos, I solved a tremendous number of carb problems with some ignition work.

frenchyd
frenchyd MegaDork
2/22/22 1:25 p.m.

In reply to Carl Heideman :

Racing Jaguars with SU's I was given  the opportunity to swap Webers in place of the SU's    I was at 310 hp at 6000 rpm on the SU's then we removed the manifold and replaced it with Webers it took us 9 pulls to reach and pass the SU's  By 15 horsepower   @ 6000 rpm ( and a few torques, don't remember but not a lot)    
If you look at the intake manifolds you can see exactly where that difference is. The Weber manifold is just about straight in while the SU manifold has sweeping curves going into each cylinder. 
     When I bolted the SU's back on I still had enough time to do a a little more testing. This time the difference was down to 12 horsepower.   Looking at the air density I richened the SU's one flat.   And the difference dropped to 11 horsepower.    
  We were out of time and I didn't want to spend enough for another hour.  Which is what we figured it would take to get the SU's off and Webers on then adjust them.  
   The difference between the two carbs though is the ease of adjusting the SU's imparted to switching jets and air correction  on the Webers. 
   While you might be able to change Webers in 10 minutes ( with a helper )  SU's can be adjusted in 2 minutes or so.  

wspohn
wspohn SuperDork
2/23/22 9:52 a.m.

They are remaking the DU6 double barreled SUs I posted a pic of above, but they are not cheap! A couple of thousand per, quite often.

sir_mike
sir_mike Reader
5/4/22 10:00 a.m.

I like my Webers.Twin 40s one and single 45 on the other.Yes they can be a pain but you have to make sure the rest of the cars systems are correct.

MGWrench
MGWrench New Reader
5/4/22 11:38 a.m.

In reply to wspohn :

TR4 intakes?  I've got a triple intake manifold for my MGC-GT, do you think three 1 1/2" SUs, HS4s or HIF4s, on a mostly stock engine would be appropriate?

wspohn
wspohn SuperDork
5/4/22 11:58 a.m.
MGWrench said:

In reply to wspohn :

TR4 intakes?  I've got a triple intake manifold for my MGC-GT, do you think three 1 1/2" SUs, HS4s or HIF4s, on a mostly stock engine would be appropriate?

Almost - TR4A, which used the longer runners and had smaller diameter runners (which came in handy when I had to grind them out asymmetrically to match the MGC port spacing).

I think that you can make triple 1 3/4" carbs run just fine on a pretty stock MGC engine with little or no modification.  I built my engine with a mild cam, and home built headers, which with the new carb set up removed most of the things that hampered performance.  The result was to move top speed from the stock 120 to 130 and still rising when my road ran out.

tolyarutunoff
tolyarutunoff New Reader
5/4/22 4:29 p.m.

on both my early miura, 4.2 maserati indy, and 4.7 bora the cars cruised on the idle circuit to well over 60mph!  on the bora a couple plugs kept fouling.  i'd switch holes with a clean plug and go 1/8 turn lean on the idle screws of the offending cylunders.  after 3 adjustments i could trundle thru town at barely over 1000rpm in 5th...not that i did that very often!

frenchyd
frenchyd MegaDork
5/5/22 10:38 a.m.

Where the Webers and SU's are nearly identical is the mixture requirements for any given application. 
 On a SU just look at the needle for that  application. It's never a straight line. A smoothish curve is about  the best you can hope for. But getting there is so much simpler then the Weber. The trick to meeting the fueling requirements for a Weber  is the air correction selection. 
  That's probably why Ferrari's, Alfa's etc. don't respond as well to modification other cars do.   The balancing act between air correction, accelerator pump, and Jets that Webers  have is far harder to learn and understand. Even so called experts are guessing at this point. 
 

With SU's as you get away from stock it's easy to see where things go lean or rich and adjust accordingly. Since most changes require additional fuel,  a needle chucked into a drill will quickly polish down with a piece of 1000 grit emery paper.  If you're  anal you can then measure that spot and keep a record of the changes you made. 
  I pinch the needle where it's running lean. Stick a sharpie in and mark that spot on the needle and Bob's you Uncle. 

wspohn
wspohn SuperDork
5/5/22 11:44 a.m.
tolyarutunoff said:

on both my early miura, 4.2 maserati indy, and 4.7 bora the cars cruised on the idle circuit to well over 60mph!  on the bora a couple plugs kept fouling.  i'd switch holes with a clean plug and go 1/8 turn lean on the idle screws of the offending cylunders.  after 3 adjustments i could trundle thru town at barely over 1000rpm in 5th...not that i did that very often!

This was my Islero engine - V12 with 3 DCOEs per side.

It was (obviously) finicky to tune from scratch but once done I could floor the accelerator in 5th gear at 1200 rpm, and it would pull smoothly away and could have accelerated without drama to the 170 mph region  (I only tested it to c. 100 mph, being marginally sensible).

Like your Maseratis, once the tuning was done, the watchword was 'hands off'. More cars have been screwed up by people meddling with carbs when the problem lay somewhere else. 

There are some amazing carb guys around, or at least there were.  I was at Laguna Seca having an issue with the smooth running of twin 45 DCOEs on my MGA Twin Cam race car and this guy that looked like a street person came over to watch. He turned out to be a Weber guru, pulled the jets and showed me one out of 4 air corrector jets that someone had for some reason lightly countersunk the entry hole of.  Swapped out for another one and the issue was cured.  Likely never would have found it without that guy.

There are SU magicians out there too, and also for American cars ( I was lucky enough to find one when fine tuning a car I owned with a big block Chrysler with sixpack).

frenchyd
frenchyd MegaDork
5/5/22 12:38 p.m.
wspohn said:
tolyarutunoff said:

on both my early miura, 4.2 maserati indy, and 4.7 bora the cars cruised on the idle circuit to well over 60mph!  on the bora a couple plugs kept fouling.  i'd switch holes with a clean plug and go 1/8 turn lean on the idle screws of the offending cylunders.  after 3 adjustments i could trundle thru town at barely over 1000rpm in 5th...not that i did that very often!

This was my Islero engine - V12 with 3 DCOEs per side.

It was (obviously) finicky to tune from scratch but once done I could floor the accelerator in 5th gear at 1200 rpm, and it would pull smoothly away and could have accelerated without drama to the 170 mph region  (I only tested it to c. 100 mph, being marginally sensible).

Like your Maseratis, once the tuning was done, the watchword was 'hands off'. More cars have been screwed up by people meddling with carbs when the problem lay somewhere else. 

There are some amazing carb guys around, or at least there were.  I was at Laguna Seca having an issue with the smooth running of twin 45 DCOEs on my MGA Twin Cam race car and this guy that looked like a street person came over to watch. He turned out to be a Weber guru, pulled the jets and showed me one out of 4 air corrector jets that someone had for some reason lightly countersunk the entry hole of.  Swapped out for another one and the issue was cured.  Likely never would have found it without that guy.

There are SU magicians out there too, and also for American cars ( I was lucky enough to find one when fine tuning a car I owned with a big block Chrysler with sixpack).

Absolutely there are real magicians out there who know the shorts cuts to dealing with ( actual) carb problems.   
  But far fewer with Webers than SU's or American cars.   It's just a matter of numbers rather than any bias.  
  Even racers who use Webers tend to try to find one of those and just leave it alone.  
   Which is a pity because the air is always changing and the skill of adjusting for that is where the power is. 
   EFI spoils us.  It adjusts instantly and constantly.
      But if you watch Sprint car racing. You'll often see the crew chief pass a signal. ( some get really clever, adjusting their hat. Holding an elbow, leaning one way or the other.  Then the driver will reach down and move the dial a jet. 
   I saw Steve Kinser come from 5 positions back to win after such a signal.  ( that's when I invested in my own Air density meter). 

wspohn
wspohn SuperDork
5/6/22 11:24 a.m.
frenchyd said:

   Then the driver will reach down and move the dial a jet. 
   

The race organizations that I ran with tended to make rules that strangled modern measures (this was vintage racing) so they came down on people like a 914 that ran with me who was tuning his engine from the cockpit while driving using an air/fuel gauge and a cockpit control from the ECM.

I fitted an MSD ignition early on but hid it under the dash and also utilized a knock sensor on the engine coupled with a cockpit accessible control to vary ignition advance. I only used it in practice and then covered the gauges up so they weren't visible when going through tech.

Did it go faster with the maximum possible advance on a given day?  Possibly, but my intention was to find the maximum safe advance wit the fuel in the tank and prevent potentially very damaging detonation by backing of a tad from that.

frenchyd
frenchyd MegaDork
5/9/22 10:23 a.m.

In reply to wspohn :

I'm thinking the reason to limit in-motion adjustments is to reduce the cost of engine development  in Vintage racing.   Although to be fair I was using the dial a jet back in the 1980's. With the open cockpit and a study of the weather patterns I could open my visor on the straight away and feel the weather on my face adjusting the jets accordingly.  
     Technology is so advance now that some cars have the potential  to even in relatively stock configuration greatly exceed original performance.  
 With little more than a reground camshafts and a $100 EBay turbo charger Calvin was able to take a stock engine from a junkyard wreck with 175,000 miles on it and improve the horsepower from 290 to 824 horsepower.  
  He did that without removing the head or touching the bottom end. 

wspohn
wspohn SuperDork
5/10/22 11:28 a.m.

As rules are liberally applied. there is a lot of 'variance' in mechanical spec locally.

All the Alfas I used to race against at Seattle, were carrying 1600 - 2000 cc engines - it was like the original 1300s had somehow evaporated. The early 911s used whatever they could get in there from a decade after they were built (I recall there being some line past which the substitution would have been too obvious, but don't recall what that line was - I think that the original 2000 cc engines 'grew' to 2.4 or so.

No trophies to win, no championship points, so why should the Bugeye owner run a grenade 948 cc engine when they could run a mild tune 1275 lookalike with around the same or more power and have it last indefinitely?  And there were a few early Jag XKs that had engines that had somehow stretched to 3.8 or even 4.2 while retaining the appearance of a 3.4.....

frenchyd
frenchyd MegaDork
5/15/22 1:50 p.m.

In reply to wspohn :

Then there is the Chevy small block.  So many of them started out with 283's and suddenly they were racing with 350's stretched to 400's or yes I even built a 430 for one of my customers. 
    The problem is with all those engines. Is it's so easy to tell a 948 from a 1275 or Various Porsches,  Jaguars,  etc. 

     But yes I'm guilty of it.  A 283 I built I put a Target master (350) in it.  And it was reliable enough to win 12 out of 13 races that season. But a  2nd instead of first  justified  going all the way to 430 ?   

wspohn
wspohn SuperDork
5/16/22 10:08 a.m.

In reply to frenchyd :

A friend of mine owned a Ford GT40 - a real one, not a clone.  He attended a get together of them and his was the only one that still carried a 289 engine - the others were all larger variants.  And when was the last time you saw a Mk 1 Sunbeam Tiger with a 260 in it? They all have 302 and up (original 289 cores are apparently hard to get now).

frenchyd
frenchyd MegaDork
5/16/22 2:35 p.m.

In reply to wspohn :

Even with original 289's. The aftermarket is flooded with aluminum heads that flow massively better. Electronic ignition hidden inside distributors and all sorts of cams etc.  Chevies are as bad or worse. Since you can legitimately run a .060 overboard engine , 500  inches is normal for 454. With original blocks coated in cosmoline and stored away  and modern looks similar engines in place 1000 hp is possible. 

sardigarmi44
sardigarmi44 New Reader
5/18/22 9:23 a.m.

I beleive that Vizard said that a 2" SU can flow 330 cfm on the bench and I would think that a 3 liter pushrod C series would be hard pushed to need 990 cfm at red line

mobdro apk
 

 

frenchyd
frenchyd MegaDork
5/18/22 9:56 a.m.

In reply to sardigarmi44 :

You are right.  The 3.8 DOHC Jaguar doesn't use all of the carb even when highly modified.  
3 Weber DCOE 45"s  only make 15 more horsepower than the 3" SU's HD8's  and that's purely because the Weber manifold is straight in while the SU's are curved. 

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