I'm building a motor with my Dad. He said he would finance a motor for my Camaro if we built it together and I concentrated on college. Anyway I wanted to build a nitrous motor, but he wants to build a straight natarully aspirated motor. And since hes paying for it he kind of gets final say. This will be race only motor so pump gas doesnt matter (Dad doesnt believe in street/strip go one way or the other)

Anyway he read somewhere that its useless to go over 12.0:1 compression but I say since its all N/A wouldnt it be better to go like 14 to 1? What do you guys think how much would the extra compression be worth power production wise.

Rough layout of the motor would be a 4 bolt 350 with 3.75 crank .060 domes, all roller, with 67cc Trick Flow aluminium heads if it makes a difference to you.

 

Usually I see 12:1 thrown around a lot in reference to street engines because anything above that will require you to run race gas. The local guys that build race engines usually go well over 13:1, but I read something about 16:1 and up being a waste. Sorry I can't help too much Not much actual experience here yet

 

Well you do get more HP/TQ from higher compression numbers, but as you go higher you see a diminishing rate of returns. For example, going from 11:1 to 12:1 might get you a 3% increase in HP, but an increase from 16:1 to 17:1 would only get you a 1.6% increase. However, this can still add up. Say you have a motor that will make 480 HP with 11:1 compression - if you increase that compression to 17:1 it might make 550 HP. However, there is a limit to where you could get this to run reliably and you would have to pay for top grade gas. You'd have to do the math to see if it'd be worth it for your application. You can use a program like DesktopDyno to easily get an idea of how a compression change would affect your power level.

 

I've got money on a static vs. dynamic compression discussion about to kick up again along with the "you could but why" grey matter area.

 

Those are 2 separate discussions. Static vs dynamic CR is just a question of what you can get away with on pump gas or whatever…

WRT power relative to CR, it’s a curve that essentially as you go higher in compression you do not gain as much power. In other words, the gain going from 8-9:1 is about the same as going from 10 to 13.5:1… as you go higher it gets harder to make more power.

Above about 12:1 the gains start getting so small that it most cases it’s not really worth it to go higher. That being the case and that racing a car on $1.50/gallon gas is much cheaper then $5/gallon, even if it never sees street use, plus assorted chamber geometry issues I’d probably stick to a lower compression, whatever I could get fairly easily with a flat top piston.

 

Higher compression means more horsepower period!
To make serious H.P. you need to at least start at 13.0 compression for all out drag strip racing.
Just look at what the pro stock class runs...

 

Well, my Dad wants to run 12.5 to 1 which I guess would just be able to limp along on the 93 octane gas here in FL. But I wanted to go 14:1 since hes adament on seeing what we could do on just motor. When I get the car away from him Im going to add a nitrous kit anyway so I guess it doesnt matter.

 

"Just look at what the Pro-stock guys are running".....yeah, they also run mushroom cams, and a lot of other race-only goodies, it's a total package affair to get high comp to run well.
"
"When I get the car away from him I'm gonna add a nitrous kit so I guess it doesn't matter anyway." --Oh yeah it does, you're talking about adding serious additional pressure to the combustion chamber when you juice. Takes a lot more to run safe @ 14:1 than it does to run @12.5:1. A nitrous "hiccup" would probably be a lot more serious on the 14:1 setup......Mindgame?

 

My thoughts exactly, thats why I said it didnt matter. I ment I wasnt gonna push my high compression ideas on him. i suppose I should have clarified that. When we order parts ill just make sure I get forged everything, and serious rings. Plus when I buy the stall convertor Ill buy a nitrous one.

 

Well you have to decide what kind of gas you want to use. Is it for street driving or race track only???

If its a street car I wouldnt go any higher than 11:1 compression unless you running a solid roller cam setup. With a solid roller you "should" get away with 12:1 but I dont konw on the regular old 350 blocks. I doubt you can run 12.5:1 on pump gas without some serious cam.

I am running 12:1 compression on my 383 stroker LT1 which has reverse cooling. And this is borderline for pump gas here in FL. I also run Nitrous but I have all forged internals and a very strong valvetrain with a huge 110 Lobe seperation Solid Roller cam, shaped and polished combustion chamber and some custom shaping of the surface of the pistons to reduce some of the cylider pressure so I can use pump gas....GOod Luck

 

You didnt read far enough into my post. It says this is a race only motor, so pump gas doenst matter. Im a going to use a roller cam but not sure about solid lift yet.

 

I say, since it's a race only engine, defintely look at +14.1 compression, a solid roller cam, and DFI (because the LT1 computer will only support up to 7200 RPM's). Build the bottom end as stout as possible, use shaft mounted roller rockers, hydra-rev kit. Great oil system, bigger radiator. And you'll be In Like Flint. At least a 550 RWHP engine combo.

I'm making about 402 rwhp & 380 rwtq with a 355, that's running 12:1 compression on a hydraulic roller 232/242 .610 lift cam. I can run 91, but the computer will pull massive timing out, and make considerably less HP and way less Torque. Just to give you an example of HP.

 

Nah dude, Carberation. Fuel injection is a pain in the ***. Maybe I'll start messing around with FI later on, but this is my first MAJOR project and I want to keep it simple. I'll try to convince my dad to go solid lift, but Im not sure about it. He has a grudge against it. He says he had one before and he constantly had to re-adjust the valves.

 

Man, is this coming just this side of annoying.

If this is really a no compromises ‘race’ engine, pick the best parts and build the best setup that you can that fits within the rules.

Realistically, to me it sounds like you and your dad are building a nice toy… not really a serious all out race engine, but more serious then a lot of people would like to use on the street. If that’s not what you were building you wouldn’t be using the heads that you’re using or asking the questions that you’re asking.

Now to answer your basic questions, if you’ve got 67cc heads you’ve pretty much decided some of your limits already.

For the most part, domed pistons suck… they disrupt the flame front and quench and in many cases hurt power production as much as the compression increase helps it. With flat top pistons and a quench distance on the tight side you won’t see roughly 10.5:1 compression. Even if you mill the heads down to say 62cc’s you’ll still have roughly 11:1 compression. And if you use say a 12cc dome you’re still only at 12:1. FWIW, 14:1 is out of the picture unless you get heads with smaller chambers.

WRT to the solid lifter cams… If this is a race engine, how much are you really going to be driving this thing around anyway? It only takes 20min to adjust valve lash once you get used to it, and most people that are running solid rollers on the street are adjusting them at roughly 5-12K mile intervals… Doesn’t seem like that big a pain to me for the advantages…

 

Really? I didnt know that about dome pistons. And one of the reasons I liked the trick flows was the fact that they had the 67cc chambers. Most of the other fairly serious heads I was looking at in catalogs had even bigger chambers 72cc+

And I totally agree with you about the solid lift. And I said I would work to get it in the motor. But my dad has a think skull, once he gets it in his mind he doesnt like something its hard to get him off of it.

I would aprreciate more posts from other people about pros and cons of dome pistons. Not that I dont believe you its just your the only person Ive ever read mention that.

And about what you said earlier, the car really became race only because I bought a newer truck to dirve everyday, and I cant afford insurance on a Camaro, and a new truck at 19. Much of my interior was i poor condition anyway, so I decided to strip it out see what I could do about getting it tubbed, and build the toughest engine we could with what we could afford. Thus my reasoning to want to build a nitrous car, but Dad gets in the way here says he doesnt want to do that yet. And I cant afford to throw $3000+ away on one part for a blower, so I go looking for other sources of power. Therefore here I am asking about compression. So if it doenst seem race only to a seasoned vetran Im sorry for the misunderstanding. I appreciate the statements you gave about dome pistons, I didnt have that information. But Im doing what I can with what Ive got so dont question my motives.