Learn Me Intake Manifold Design

I've dug around on this quite a bit and it's probably smartest for me to simply port the stock intake manifold. I understand, honestly.

However, porting the stock manifold makes a really boring, not very instructional class project and so I'm building a new manifold from the ground up.

The plan is to make the manifold as adjustable as possible, since we are unlikely to be able to design it correctly first try. To do this I was planning to build it in three pieces:

a) A base with weld-on injector bungs and a place to bolt the fuel rail.

b) Four round tubes that bolt onto the base plate.

c) A plenum that will mount a vacuum block and bolt to the four round tubes.

With this design I can swap the tubes any time I like for different runner lengths. Maybe even end up with a torquey street set and a higher rpm track set.

Does this sound like an intelligent approach?

Should I just copy the plenum volume of the stock manifold or is there a rule of thumb for plenum sizing?

I've seen three styles of plenum on four cylinder engines. A sort of blob that looks like this:

A log style manifold like this:

And finally, a sloping log like this:

There are also snail type manifolds, but I lack the tools and skills to build them.

Any ideas on which type of plenum I should use?

There was some interesting design info listed at at the bottom of page two in the current VQ30 thread. Feel free to give it a look.

Yeah take a look at the VQ thread. Some good stuff to start off there.

Yah, I saw that. I think I understand the basics of resonances and runner lengths, and just looking at those stock VQ30 manifolds you can see they don't flow worth a damn.

What I'm really stuck on is how to design the plenum and the feasability of making the runner length adjustable.

http://www.youtube.com/watch?v=YZhSgwYs08k

That's friggin awesome!

Depends on how often you want to change the runner length. I built an IR manifold that used lengths of steel reinforced industrial hose. Cylinder head side was a flat flange (basically a copy of the intake manifold gasket) with round stubs welded on. Plenum was from a Ford Escort, which already had round runners. Used machined barbs/beads to retain the hoses, conventional radiator hose clamps. Loosen and slide for small length adjustments, or different hose lengths for large adjustments. The hose (look for 'mine spray hose' in McMaster, etc.) is rated for high temp, high pressure, oil/gas resistant. Slightly flexible (6" bend radius), so can make routing/fitting a bit easier.

Carter

Carter, do you have pictures?

This ^^^^

Adjustable was done a while ago, it looks pretty hack, but it could be repeated very easily and cheaply today... I think this one performed pretty well...

Here are some older pics, from my Flikr account, I hope that the links work OK. I built a prorotype set of adaptors and hoses for Jeff McNeil's 'Mrs Jones' Spitfire. It used quad Kiehein carbs, so no FI bungs were fitted.

Parts for cylinder head adaptors: http://www.flickr.com/photos/13867611@N04/1516956573/in/photostream

Tube with machined hose barbs: http://www.flickr.com/photos/13867611@N04/1517808056/in/photostream

Completed adaptor (2 required): http://www.flickr.com/photos/13867611@N04/1516957701/in/photostream

Front view showing inside taper: http://www.flickr.com/photos/13867611@N04/1516957863/in/photostream

Adaptors fitted to Jeff's Spitfire: http://www.flickr.com/photos/13867611@N04/1516961925/in/photostream

Spitfire with quad Kiehein carbs: http://www.flickr.com/photos/13867611@N04/1517811570/in/photostream

I've since continued with my original project, to fit EFI on my Spitfire, using Escort bit's and pieces. The Escort manifold is brazed together out of thinwall aluminum tubes and 2 castings. The thinwall tubes are perfectly round, perfectly sized for my application at 1-1/2" OD. I've cut them off about 1-1/2" from the plenum, plenty of grip for the hose. I used a common table saw and carbide tipped blade (with a dab of cutting fluid) to cut the manifold tubes and castings.

Escort manifold: http://www.flickr.com/photos/13867611@N04/1517807584/in/photostream

Have not taken many pics of my own work since I built Jeff's set, but I'll try to get some and post them.

Jeff ran this setup for a few years before selling Mrs Jones. AFAIK, no issues with the reliability or robustness of the hoses.

Carter

Taiden wrote: http://www.youtube.com/watch?v=YZhSgwYs08k

OMG!!!!

In reply to tuna55: Great picture of the method an a V-8!
No, I certainly cannot make any claims.
I think I first saw the method used back in early 1970's on a TR-6 racecar that was fitted with huge Lucas mechanical fuel injectors. TJ Kelly raced that car in the SCCA Florida Region, and elsewhere I'm sure.

The great thing is the hoses allow you to easily connect things without custom tubing bends or worrying about alignment, and you can even twist and turn the pieces to fit under the hood, or around steering shafts, etc as needed. Also, for carbs, it isolates them from both heat and vibration from the motor, which can enable more accurate and consistent fuel delivery.
Another thing, you could have different volume plenums to try, for tuning at different courses, and easily swap them during test/tune sessions to measure the effect.

Heck, use long hoses, and you can easily create a reverse 'tuned length header' for the intake side.

Hah, you could tie the hoses in knots if you wanted to. ;)

Carter

erohslc wrote: In reply to tuna55: Great picture of the method an a V-8! No, I certainly cannot make any claims. I think I first saw the method used back in early 1970's on a TR-6 racecar that was fitted with huge Lucas mechanical fuel injectors. TJ Kelly raced that car in the SCCA Florida Region, and elsewhere I'm sure. The great thing is the hoses allow you to easily connect things without custom tubing bends or worrying about alignment, and you can even twist and turn the pieces to fit under the hood, or around steering shafts, etc as needed. Also, for carbs, it isolates them from both heat and vibration from the motor, which can enable more accurate and consistent fuel delivery. Another thing, you could have different volume plenums to try, for tuning at different courses, and easily swap them during test/tune sessions to measure the effect. Heck, use long hoses, and you can easily create a reverse 'tuned length header' for the intake side. Hah, you could tie the hoses in knots if you wanted to. ;) Carter

I wasn't trying to be too smartass, that's called the "high and mighty", a car put together for drag racing by engineers to be adjustable for all of that, so they were definitely tuning for intake runner length. It worked pretty well.

Yah, I get it, no prob. (and anyway, isn't 'smart-assery' on this forum considered a virtue? ;)

erohslc wrote: Yah, I get it, no prob. (and anyway, isn't 'smart-assery' on this forum considered a virtue? ;)

Nope. Definitely not. That's how to be declared a shiney happy person

From what I've read, using an exhaust header works great as an intake manifold as well. Something about the reverberation of the intake charge and all that good stuff. Apparently it works friggin FANTASTIC on forced induction applications where velocity isn't as important.

For NA, you have to realize that the longer runners build velocity at lower RPMs and thus you get more low end torque (look at truck intakes). The short runners are for higher RPM power. The trick most people settle for is medium length runners, but they're only OK at both extremes. We used to modify the intake runners on the NA DOHC Cobra's for shorter runners. Sounded cool and worked great at higher RPMs for road racing and all that stuff. Didn't really hamper the lower end power that much, maybe 10-15hp IIRC. The middle and top end more than made up for it. I can't recall the numbers at the moment.

You COULD do something along the lines of a vacuum actuated runner. Make an ITB intake and take the middle section and make a sleeve that goes around it. you could probably seal it up with an o-ring or something, but I doubt it really matters. LOL Now you'll want to get a vacuum actuator that will pull or push the runners to vary the length according to engine vacuum. Now, if you REALLY wanna get cool, you could use an electric servo to do the same thing.

Just an idea...

In reply to Conquest351:

I actually have a very specific target, peak torque at 4500 rpm. I would love do the electronic servos, but I think that's more than I can do in six days with kids. That's why I was thinking more like a pile of aluminum tubes that we can swap in and out in 5 minutes.

In reply to DaewooOfDeath:

Understood. Flange them and use bolts, or, like previously mentioned, get some hardcore reinforced hose and get after tuning those runner lengths.

The servo stuff would be really rad though...

I was going to say use a lot style... would allow you to cut and install hoses (similar to what tuna posted)... you could even go with some motorcycle ITB... in my mind I picture a factory manifold cut so it could still use the factory injectors and then weld a flange or something to mount the "adjustable length runners" and at the end of those runners mount the ITBs to em (in reality you could use some old motorcycle carbs and remove the fuel portion)

what engine are you planning on using for this project?

I like the log style idea from a logistical standpoint. I like the bike carbs idea too. I'm electronically retarded, so pardon me if I'm being ignorant, but how would I connect de-fueled carbs to a TPS?

The engine is a GM/Daewoo/Suzuki/Opel 2.2L DOHC I4. Basically the big brother to the Aveo engine.

DaewooOfDeath wrote: I like the log style idea from a logistical standpoint. I like the bike carbs idea too. I'm electronically retarded, so pardon me if I'm being ignorant, but how would I connect de-fueled carbs to a TPS? The engine is a GM/Daewoo/Suzuki/Opel 2.2L DOHC I4. Basically the big brother to the Aveo engine.

I have always wanted to do a project with some bike carbs...