thrubbinv8 and 10secty so is it safe to say with a say 10:1 compression runing on pump
gas runing low boost will make the same amount of power as a lower comp engine running
high boost so which one of these engine will be suitable for every day use and have less chance off detting need to know which route to go because this topic is very conteverisal

 

I don't think it works that way, berty. Again, running low compression is purely for detonation resistance. If you extrapolate that out to running 12.5/1 compression and 0 boost, then it obviously wouldn't make more power than 8/1 and 20 psi.

 

engineermike SO WHAT DO YOU THINK WOULD BE AN IDEAL CR TO USE ON PUMP GAS
FOR MAINLY STREET USE AND WOULD I EVER GET CLOSE TO MY GOAL OFF 700/800 RWHP BY
USING TWIN SC 61 JUST NEED SOME SERIOUS INPUT FROM SOME ONE WHO AS TRIED THIS COMBO ON A SBC 383

 

I run a 406 sbc with 8 to 1 comp and twin pt-61's in a 3400lb camaro with a glide and 3.50 gears. Its made over 800hp with only 20psi, here's the link to the vid https://www.theturboforums.com/smf/index.php?topic=55638.msg575133#new

It drives like a n/a car with no shortage in low end grunt without boost, but when the boost kicks in its a different animal. I chose a lower comp setup only cause I did not want to depend on running race gas all the time or having to buy a meth inj kit to be streetable. I can run my 9psi springs and shitty cali 91octane pump gas all day without a hint of detonation

Hope this helps

 

There is a guy who has a 1200hp 427 sbc with 22lbs of boost on 8:5:1 compression.

He has alot of pretty neat stuff. 18 degree heads and the like. Pretty neat.

www.montygwilliams.com

 

I saw that vid about 2 months ago. that engine is simply awesome with all high buck parts. Maybe low comp. and massive head flow is the way to build a street motor????

 

Great subject,
I've just finished my sbc twin turbo project. 355 ci, twin turbonetics to4e/ t3 57 trim, smog heads( 882 chev heads). Made 1014 hp and 960 ft/lbs @ 6100 rpm. Engine still made 950 hp @ 7000 rpm. Engines has approx 24 deg timing, runs @ 7.6: 1 static comp, 24 psi boost.
eagle rods, and crank, trw pistons.
Fitting it to a 1800 lb altered t- bucket, drag only.
Do not know how to post pics, email me to see dyno stuff and engine
ash

 

As mentioned elsewhere I dont think a point of CR is equal to Xpsi of boost.

Its certainly true to say a very low compression motor could be lousy off boost... although cubes can often offset this.

Basically its a matter of what you want. If its a street car then surely drivability it more important than peak hp. If this is the case, very low compression / high boost should be left alone. Its generally accepted that 8.5-9:1 is nice for a mildly boosted application. You need to ask yourself if its worth the hassle of changing CR for the sake of a boost or hp figure you've decided you want. Perhaps running low boost with your current setup would be best... then if you are prepared to sacrifice off boost drivability for more power then drop the CR and raise the boost accordingly. Its always a compromise whatever route you take.

Remember that boosting your current motor will result in pure bonus power over NA. When you start dicking around with CR then you are losing in order to gain elsewhere.

 

I have a question about pistons on the corvetteforum and he posted pics of his pistons and their full dish, so the quench characteristics arent ideal. From everything I have read says that better quench = less detonation.

There is a guy running 20 psi on 8.9:1 compression, but he had his pistons and chamber ceramic coated.
http://airflowresearch.com/articles/article21/A21-P1.jpg

There is alot to be said for modern chambers and some attention to detail.

 

I'm running out of the box AFR 210 w/ 76cc combustion chambers, 28cc dished pistons and a .060 head gasket. I'm pretty sure my quench area is not ideal to say the least, but it still pulled 800+ on the Dyno and ran a 9.5@149mph at 21psi with no signs of detonation(40deg initial 28deg total under boost)

 

holy crap that is low compression.

 

yeah, I know. Whats funny is there is no lack in low end grunt, believe me thats what I was worried about, the car is all steel and glass full interior only missing a hood. Plus its got a glide in it with a fairly tight converter, I honestly thought it was going to be a dog down low.....go figure

 

Damn that is some good power for a set of 882 heads! Those have the worst exh. port design on the planet with the port filled in around the guide and dual heat crossovers. All hail the boost gods!

 

A lot can be said for a good cam huh.

 

I'm running 6-7psi on a stock 350 sbc with 9.25:1 cr, with std unleaded UK fuel. I'm pulling the ignition back to about 25' - but i think i can increase it now that i'm running a chargecooler. I think i should be able to get it up to around 9psi on that standard (cast pistons!) engine - if i can get the box to hold.

Intrestingly I ran a Victor Jnr when i first converted to efi, I hated the loss of low end torque and swapped back to a performer RPM.

 

I find it interesting that some people are framing this as a question of how MUCH compression is streetable instead of how LITTLE compression is streetable! My understanding is that the power increase with forced induction is a product of the base HP and the denisty ratio (read that more boost more top end HP). This is what I want: max HP /torque with still decent off boost streetability. Noone in their right mind would think that high compression and low boost would be the optimal situation. You want to run the most boost (without pulling excessive timing) that you can pull on your fuel octane rating. Obviously, the less compression you run, the more boost you can run, UNTIL you turn it into a low compression slug. The discussion should be how LOW can the compression go (on the street) until you have unacceptable off-boost response, IMO. Every pound of boost that you can run after that point is gravy. It's just a higher density of air that you can force into the engine. Correct me if I'm wrong.....

 

well i think the ideal compression ratio for a street driven car is somewhere in the area of 8.4:1 (Stock GN ratio) to 9:1. Personaly i would still stay in the 8's if you want to make massive power without running race gas or meth injection. My plans are for a 800 RWHP motor to run on jsut intercooled boost on 91 octane (best gas you can get here)

 

the main reason that i made this post so i could get alot of info on diffrent peoples ideas and input

and another reason is that i have a 383 already built with 10.7 pistons and getting info on how to pursue this with low boost without having to spend another 300 bucks on 8.1 pistons..

i have read alot of post and replys and have come to the conclusion that 8.1 pistons with 15-21 lb of boost is good for 500-800 hp depending on aplication (cam...heads..induction.. ect)on pump gas

and 10.7 comp with low bust around 3-5 lb of boost is good for around 400--700 depending on aplication (cam...heads..induction.. ect)on racing fuel 110 to 112 octane

tim

 

I've read over the years that a drop in compression of a full point is an overall horsepower reduction of 3%.

Say I have an LS1, and a stock 2002 LS1 M6 will dyno 305rwhp. Add heads and cam, other stuff... headers, underdrive pulley. Let's say I am at 390rwhp with stock compression.

Now remove 2 points of compression (10.1:1 down to 8:1).

Am I suffering?

6% of 390rwhp is 366rwhp.

In 2000, I went 11.6 with 375rwhp on a 1.57 short time.

Of course dropping two points in a 6 cylinder or something would suck more but let's at least base some of the numbers on real stuff.

I went with 8.25:1 with my LS1, simply from running the math, and to leave more headroom for detonation. Putting a street/strip car at 10:1 with C16 and a lot of boost is probably going for max power, but I'd rather make less power and not worry about the tune as much.

I'm impressed with that 1st gen Camaro running 9.5@149 on 91 pump, is that correct? Tell us more about the car!

 

Yeep,
torched the first set on the dyno, got to keen and was leaning it out, egts went to about 1300 after the turbo and 13.1 on A/F meter.
once i got a " new" set of heads from the junk yard and put more fuel in... 11 to 11.5 A/F meter and got egts down to 1050 approx, went good...

ash