I need more RPM from my sbc. Looking for advice.

Recon1342 said:

bwh998 said:

In reply to Recon1342 :

The 55 vette and bel air were both cars though... 

And neither were known for being high RPM screamers... 

Unlike, say, the DZ302, which was an unashamed high RPM engine.

Like Ford's BOSS 302, they were deliberately underrated so that only racers would buy them (why would you buy a 290hp 302 when you could have a 396 or 390 that made more?) but both engines were 400+hp and 7000rpm+ in stock form.  That's the beauty of being a homologation special, when the regulations in both production car and racing were lax enough that the SCCA could mandate production vehicles for road racing.  (Too many genies have been let out of bottles for that ever to happen again)

The DZ302 was the first SBC to have floating wristpins from the factory... you don't do that with an engine that makes peak power at 4800 like Chevy claimed.

Actually, it wasn't.  It made peak power at 6200 rpms.  But they set redline at 5800.  Just because GM dynoed it one time at 7000 doesn't mean it will live at that RPM.

It also had a very short 3" stroke and a smaller journal crank (which meant more meat in the block).  They came with no warranty, and the only reason chevy did it was homologation rules for T/A racing.  Even at that, the true output (in gross HP) in 1969 was 350 hp at best.  It's not the wild child everyone thinks it is.  It is a destroked 350 stuffed in enough cars that they were allowed to race it.  There again... the RACE versions sometimes buzzed to 7000, but there were no heads that would flow well enough to make power above 6500 or so.

So all the hype you hear about the 302 is mostly internet myth and nostalgic old-school folks who remember seeing a Camaro with a 302 beat a Charger in a street race 50 years ago.

It's a 302.  It isn't magic.  It is a small SBC.

Wasn't the LT5 a high RPM engine?  Asking for real.

I didn't see RPM numbers in the article, but I skimmed it quickly. 

It really seems like Chevy was trying to make the Coyote engine back then.

OP needs a Cadillac.  A 500 @ 5600 is moving the same air as a 350 @ 8000.  Theoretically.  And it isn’t a whole whole bunch heavier either as one would assume.

bwh998 said:

In reply to Knurled. :

Yeah the ls swap would definitely make more sense, but i really want to keep this one sbc. World products does have an iron smallblock thats cast to accept LS heads though...

What hilarious circle track rulebook lead somebody to dream that up?

A lot of really silly engines have been built to sneak around rules. Doing it just for the hell of it isn't something you should be doing if you have to ask how.

In reply to bwh998 :

If you have a known CI and HP, then the RPM and head flow can be determined. 

If you have CI and RPM, then the Head flow and HP can be determined.

If you have CI and head flow, then the RPM and HP can be determined. 

When you answer the questions about combo parameters...you can 1. select the correct cam to match. 2. Determine the correct compression ratio to match. 3. Buy the correct carb to match.

Always always always buy quality valve springs and get the valve train geometry right. 

Marched combos run way stronger, for way longer and cost the least in the end. All the parts can be matched for engine speed and load. The weakest parts break. Matched parts last. 

A 401 CJ said:

OP needs a Cadillac.  A 500 @ 5600 is moving the same air as a 350 @ 8000.  Theoretically.  And it isn’t a whole whole bunch heavier either as one would assume.

He won't like the extra 25 lbs though.

I had to sleep on it but I think I figured it out.

OP doesn't want to put "100lb" of extra turbo stuff, but wants the engine to rev to the moon. A turbo big enough to weigh 100lb is going to be huge and spool very late, thus requiring 14,000rpm to reach boost before he can decimate all at race wars. Dude just needs a regular sized turbo. Easy.

Daylan C said:

bwh998 said:

In reply to Knurled. :

Yeah the ls swap would definitely make more sense, but i really want to keep this one sbc. World products does have an iron smallblock thats cast to accept LS heads though...

What hilarious circle track rulebook lead somebody to dream that up?

Luddities who wanted LS head flow but thought for some damned reason the SBC bottom end was superior.  As far as I've seen it's a drag racer/street warrior thing, not circle track.  Circle track is much better at banning or limiting LS engines.

There are people online who insist that GM failed by not making an intermediate engine with LS heads on the SBC bottom end, for reasons they can't really explain other than "I want to buy cheap junkyard heads that flow good on my 350"

barefootskater said:

I had to sleep on it but I think I figured it out.

OP doesn't want to put "100lb" of extra turbo stuff, but wants the engine to rev to the moon. A turbo big enough to weigh 100lb is going to be huge and spool very late, thus requiring 14,000rpm to reach boost before he can decimate all at race wars. Dude just needs a regular sized turbo. Easy.

The weight of a turbo system is not just the turbo(s).  The exhaust manifolds are heavier, and you need to either stick some intercoolers way out in front of the radiator or you need a water/air heat exhanger, which trades better polar inertia for extra weight.  And then there are the other cooling factors involved, since a naturally aspirated engine may be just fine living at 230-240 degrees water temp but a turbo engine may not be.

100lb may be an exaggeration but it is more rounding error than hyperbole.

Knurled. said:

There are people online who insist that GM failed by not making an intermediate engine with LS heads on the SBC bottom end, for reasons they can't really explain other than "I want to buy cheap junkyard heads that flow good on my 350"

I thought L31 heads were the answer for that. 

Pretty much everything Curtis said in one link.  LS, destroke, big bore:

https://www.hotrod.com/articles/4-8l-crank-ls3-block-how-to-build-an-8000-rpm-ls-stroker/amp/

Easy money

I don't get using an outdated antique drivetrain (350 and th400) for anything that isn't a stock restoration or period correct build, especially when it's for arbitrary restriction reasons rather than a particular racing class. 

Guys quick question, I would like to build a d15 to 300 hp. Now for my own specifications I want a 5000 rpm redline, no bore or stroke increases, no turbos, superchargers, or nitrous. Unlimited leafblowers may be used, but the engine has to weigh less than stock.

Catatafish said:

Guys quick question, I would like to build a d15 to 300 hp. Now for my own specifications I want a 5000 rpm redline, no bore or stroke increases, no turbos, superchargers, or nitrous. Unlimited leafblowers may be used, but the engine has to weigh less than stock.

Simple!

Gunpowder.  Fill it with gunpowder.

Catatafish said:

Guys quick question, I would like to build a d15 to 300 hp. Now for my own specifications I want a 5000 rpm redline, no bore or stroke increases, no turbos, superchargers, or nitrous. Unlimited leafblowers may be used, but the engine has to weigh less than stock.

15:1 compression and mechanically injected nitro methane.  Let us know how long it lasts.

JesseWolfe said:

 

  Let us know how long it lasts.

A little longer than the 8000 RPM sbc/TH400.

I can't believe this thread made it to 3 pages

In reply to Hungary Bill :

I can understand how some folks might want to go this route for reasons but an LQ4 and a turbo kit seems a lot cheaper. 

Guys

what if OP just posted a dumb idea to steal Curtis's and Knurled's secrets

The local junkyards by me can't seem to get rid of their 5.3 iron blocks and at least the local PnP that I'm heading to this weekend is doing a 40% off all engines/trannies.

Just sayin'. Might be a bit easier/cheaper to achieve what you want with a junk truck engine a few years newer.

bwh998 said:

In reply to Curtis :

8k isnt asking much from the bottom end, i sometimes even see the cast crank 602 crates spinning close to that. I have the 604 which uses a forged 4340 piece.

A crate motor is RPM limited by valve springs is it not?

Suprf1y said:

JesseWolfe said:

 

  Let us know how long it lasts.

A little longer than the 8000 RPM sbc/TH400.

I can't believe this thread made it to 3 pages

This brings to light the largest concern with the idea:  Making a torque converter live at 8000rpm.

It is possible,  but you will be hemhorraging money making it work.

This is 100% why there is not an automatic in both of my RX-7s.  I have a stack of automatics for them, but torque converters that can live at high engine speeds (10k+ in my case) are recockulously expensive.  Cheaper to just replace manual transmissions on a regular basis.

In reply to bentwrench :

By my understanding: Sort of...

you can upgrade cam and valve springs to the point that the bottom end becomes the limiting factor. I am unaware of a stock SBC casting that will survive at that kind of RPM...

bentwrench said:

bwh998 said:

In reply to Curtis :

8k isnt asking much from the bottom end, i sometimes even see the cast crank 602 crates spinning close to that. I have the 604 which uses a forged 4340 piece.

A crate motor is RPM limited by valve springs is it not?

In the case of the 602 and 604, probably not.  It's limited by the fact that at 6200 RPMs and high cylinder pressures, the forces seen at the crankshaft like to physically rip the bosses out of the block and make very expensive explosions.  It makes messes and gets you banned from tracks.