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Old 03-03-2012, 12:35 PM
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Horse power and pump gas

Today I just got back from a well known local engine builder. This is a full machine shop builder with high HP experiance in buisness for 30 to 40 years. I went there to pick his brain about building a sbc engine that would not exceed 400hp for my 81 Vette. We talked quite a while about todays pump gas fuels in old engines with carbs. In a nut shell his opinon, was "Your not going to build a engine with a carb that will make 300hp with the junk gas coming out of the pump. Go fuel injection and modern electronics and I can make you any haul butt motor you want." He also told me that if it where him he would not exceed 8.5 to 1 compression on any engine with a carberator because you'll have to take out so much timing to keep the motor from detination. We all know what retarding the ignition does for HP. So ponder this info from a guy that built engines for some well known NASCAR drivers here in the NW and still building some really fast motors for folks from Seattle to LA

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Old 03-03-2012, 01:22 PM
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There are many things you can do to keep the detonation off your back with pump gas. THey are tight quench distance, cold air induction, keep the engine cool running as possible, careful timing selection, rod lenth, etc. Many things come into play. Were running a vortec 350 with 10.5:1 compression on 93 octane pump gas and it has full timing. It has RHS Vortec heads and the Vortec chambers are far better than the old school bath tub chambers. It has a tight quench distance and a short duration roller cam. We used to run this much compression on a 350 with old school camel heads as well. If it's done right you can get away with compression in the 10:1 range without issue.
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Old 03-03-2012, 01:34 PM
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Doctor the gas

you can make high octane racing gas by adding Touline or acetone to reatard the speed of the gas inghiting. We for years made our own racing gas for Dirt tracks 5 gallons of touline to 50 gals of reg gas. These are regular paint driers found at any reputable paint store.
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Old 03-03-2012, 01:34 PM
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Nothing to ponder. My sbc made over 550HP on pump gas with a carb when it was a 383. Timing was 21* initial and 38* total. Compression was around 11:1. Too many examples to count. His point is flat out wrong.

40 years experience? Maybe Alzheimer's is kicking in.
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Old 03-03-2012, 01:58 PM
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Was he drunk or just full of crap?
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Old 03-03-2012, 02:03 PM
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Find a different engine builder.
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Old 03-03-2012, 02:21 PM
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trying to sell fuel injection

dont like carbs
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Old 03-03-2012, 03:57 PM
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Quote:
Originally Posted by 1957plymouthhemi
Was he drunk or just full of crap?

Well I dont think either. I really found it odd that he was so negative about guys like me with moderate street engines with carbs. I mean really, there are a ton of hot rods out there with all kinds of configs of old school design.
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Old 03-03-2012, 04:00 PM
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Quote:
Originally Posted by F-BIRD'88
Find a different engine builder.

I was'nt looking for someone to assemble a engine, just free info. I did have a nice chat with the guy but I think he deals with mostly the racing community.
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Old 03-03-2012, 08:15 PM
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Quote:
Originally Posted by spikebot 81
just free info.
I bet that's your answer right there. Some people don't like sharing information for free and he definitely didn't give you good information. I'll bet he would have been more than willing to SELL you a 400 hp engine that would run just fine on pump gas.
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Old 03-03-2012, 10:41 PM
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Quote:
Originally Posted by spikebot 81
I was'nt looking for someone to assemble a engine, just free info. I did have a nice chat with the guy but I think he deals with mostly the racing community.
You got what you paid for.
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Old 03-04-2012, 12:51 AM
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If you want to run regular grade fuel and the best timing curve, I agree with him.
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Old 03-04-2012, 06:49 AM
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I think he makes a good point. You can't travel two hundred miles in the midwest without dealing with a different fuel cocktail. Plus, there's no way that you can predict what kind of regs the epa will foist upon us next week or month. EFI offers on the spot automatic adjustment to varying fuel and weather conditions that carbs can't. If you want to be building street engines for a living 5 years from now, where would you invest your R&D dollars?
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Old 03-04-2012, 03:44 PM
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Quote:
Originally Posted by spikebot 81
Today I just got back from a well known local engine builder. This is a full machine shop builder with high HP experiance in buisness for 30 to 40 years. I went there to pick his brain about building a sbc engine that would not exceed 400hp for my 81 Vette. We talked quite a while about todays pump gas fuels in old engines with carbs. In a nut shell his opinon, was "Your not going to build a engine with a carb that will make 300hp with the junk gas coming out of the pump. Go fuel injection and modern electronics and I can make you any haul butt motor you want." He also told me that if it where him he would not exceed 8.5 to 1 compression on any engine with a carberator because you'll have to take out so much timing to keep the motor from detination. We all know what retarding the ignition does for HP. So ponder this info from a guy that built engines for some well known NASCAR drivers here in the NW and still building some really fast motors for folks from Seattle to LA
You either got a lot of disinformation, happens a lot with guys building race motors, or the guy is not with technical changes to cylinder heads since 1996, happens a lot with old farts like me.

There are a lot of ways to control detonation without putting so much lead in the gas you can use it for fishing line sinkers. Actually the addition of lead was the result of looking for a cheap solution to the detonation issue, not necessarily a better technical solution. this can be gotton too with organic chemistry it just costs more. The removal of lead has forced the fuel blenders to start with better feed stock, today's fuels are a quantum improvement over the sulfur ridden, lead injected swill of the 1960's and 70's. The 10% ethanol pump gas we get in Washington state pretty much everywhere except on the Indian reservations is fine for a well hopped street engine, It is quite possible to build a near 400 horse 350 that'll run on 87 unleaded with no problems if you know what you're doing. And it's no big trick to run a 350 up into the 420-430 area and keep it streetable with a not too hot cam and 92 octane pump gas. you can go even further on E85 if you know how and can afford the fuel bills.

The return by the manufactures to the Ricardo combustion chamber (1930s technology) which pretty much coincides with the introduction of OBDII emissions and fuel mileage standards in 1996 is what makes a 400 horse carbureted 350 possible with unleaded, 10% ethanol fuel. At Ford these are GT40 (P) heads, Chrysler call's 'em Magnums, Chevy calls 'em Vortecs actually only the L31 fits the technical description. The word Vortec in that camp is somewhat more an advertisers name than techncial description so it doesn't always get you what you want, use caution with that word. Ford has a similar problem with the GT40, if you want the really good 5 liter heads you need to say GT40P. The other term used loosely at GM is Fastburn, the real Fastburn heads a Chevy guy is looking for is the GMPP Gen I engine version of the GEN II reverse cooling LT4 head. The Fastburn is might good, if costly, choice

The Ricardo head didn't just suddenly happen at GM there is period of evolution starting in the mid 1990's that leads toward the LT1, LT4, L31, and Fastburn. One can see the evolution in the L98 head which is currently still used on the ZZ series of 350 performance crate engines. The L98 was also made in cast iron and found it's way onto lower rated TPI 350 Camaros and Impalas as well as TBI powered Buicks. The TBI truck and some passenger cars also got the Swirl Port head. This is actually a cousin of the iron L98 head with a vane put into the intake pocket to stir the mixture with the goal of improving lower end performance, mileage and emissions. Yes, the vane can be ported out.

OK; a 1980 Corvette motor is going to be a first generation SMOG motor it, therefore, is going to suffer with those large chamber, low compression emissions heads over top a set of circular, deep dish pistons that further lower compression and wipe out anything remotely like squish/quench. For an engine of this era; the pistons and heads are a must to change. Then we can think about the cam and carburetor. But first lets think about emissions testing, I see a Vancouver location which probably means a 1980 is done with emissions testing. So we can proceed with that as a non-goal but the engine will be plenty clean anyway.

If you're looking for a decent performance Corvette that won't be embarrassed by Smart Cars and PRIUS's you can get by with a moderate rebuild on the 350.

- Bore the block .030 to clean things up
- A set of D dish hyper eutectic cast pistons
- A set of Scat forged I beam rods, I don't like to reuse high mileage rods and along that same thinking don't see the sense in rebuilt rods that have so much fatigue life already used up.
- A pair of L31 Vortecs
- An Edlebrock Performer intake
- A carb of 600-650 CFM be it Edlebrock/Carter or Holley or it's many clones
- A comp XE 258 or 262 cam
- A decent set of 1-5/8ths long tube headers into real duals with a across over.

This will generate around 380 hp with a strong bottom end, decent mileage and if you're running an automatic it won't need a higher than stock stall converter. By the way if you're running an automatic you will find the replacement of aTH350 that's probably in there with a 700R4 with a locking converter and a 3.08 rear gear set to improve both out of the hole and cruise performance.

If you want to bust into the 400 plus club, this is easy to do with a few parts changes.

- Instead of cast hyper pistons run forged, here we're going to add some cam so going to a flat top piston will work better to get the Dynamic Compression up.

- Instead of L31 Vortec heads run GMPP P/N 25534421 or 25534431 these are big and bigger versions of the L31 that take more lift and provide more casting meat than the rather lightweight L31. Or look to the aftermarket. Certainly aluminum is a consideration as performance desires go up, it's nice to get the power with a 50 pound weight reduction as well. Back cut the valves with a 30 degree blend to the seat cut, add 1.6 roller rockers.

- Replace the Performer intake with a Performer RPM model.

- Grow the carb to 700-750 CFM

- Substitute the cam with comp XE 268 or someones equivalent.

This will build you a 400-430 horse engine, depending on heads, on a 350/355 that is still very streetable.

With the heads and pistons you want to make a tight squish/quench area (something missing on your first generation smogger) when the piston closes on the step of the combustion chamber. Say with a clearance close to .040 inch a little less is even better but don't get under .035. At the other end don't get over .060. Keeping this tight forces the mixture from the far side (sounds like a cartoon) toward and in front of the spark plug, putting more molecules here improves the chance of a light especially when combined with a high energy, multi-spark ignition, which eliminates misfires and speeds the burn. Later, when the burn gets back to the far side it encounters a space with lots of surface and little volume that sinks excess heat out preventing an explosion (detonation). These two functions speed the burn, make for a more complete burn and reduce detonation without having to raise the fuel's apparent octane level. This improves power, mileage, and reduces emissions.
Mind you the engine still has all the cylinder to cylinder mixture distribution problems of a carb on a manifold that fuel injection doesn't have. But you'll find this to be a quantum improvement over what you've got. The Edlebrock intake, especially the RPM does wonders to improve these old distribution problems with factory intakes the Edlebrock is well worth the cost of admission.

Then of course there's always a 3.75 inch stroker crank, as long as your screwing around with new rods and pistons, it isn't too far of a reach to bump it up to 383 inches. This is a whole new playing field guaranteed to put a smile on you face and a dent in your wallet.

Bogie
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Old 03-05-2012, 06:29 AM
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Thanks for the great info Bogie. The dent in the walet has already raised its ugly head. You must be a mind reader as to the direction I'm headed. My budget is scary close to going over so I'll have to cheat alittle but I think this engine project is going to work out just fine.. Gosh its been since early 80s since I was heavey into hotrods so things sure have changed over the years. The good news is the engine is a fairly fresh rebuild by the P.O. and by checking all the specs I'll save some coin on parts. Block is going out today for zero decking and hone. As it stand now pistons are 4 valve releif flat tops in a .040 hole and .040 below the deck. No signs of wear. Crank journals have been undercut .010 and mic out great. Havent bought any parts yet until the block comes back from the machine shop. The 882 smoggers are in the trash as is unkown cam and lifters but I must say with all talk of wiped cam lobes this one sure was in great shape.
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