startingstock

iTrader: (3)

I am ordering custom pistons tomorrow, and am curious about compression. Motor will be 438ci (4.175 "× 4" ). It is for a street car and I dont need more than 1k hp. I probably dont need that much, but..... So from what I have read, 14.7 Lbs. of boost basically doubles the power output of the motor. So I was thinking 10Lbs would be plenty. So high can I go on compression ? I have been told by one machine shop that 10:1 is a good number. 10.5: 1 by another reputable builder. And anyone have any idea what kind of power I would be looking at off boost with a very conservative cam ? Maybe I dont even need 10 Lbs to hit my target. The car is purely street. I dont mind an intercooler, but would like to stay away from meth. 93 octane is all I would use. Any input would be awesome. Thanks. Oh, and I have Ls7 heads.

jordoza

If your staying on 93 then go with 9.5 to 1 and youll have a more forgiving tuning window. You cohld 10.5 to 1 but the window gets smaller. Honestly with a 427 to 438 it will ahve plenty of power out of boost. Do why narrow your tuning window.

startingstock

iTrader: (3)

9.5:1 ? Seems kinda low for only 10Lbs. Is that cause the block is not aluminum ? I've got holley efi and a decent tuner. I know the window will be smaller, but I was under the impression 10Lbs wasnt alot of boost. Especially with an intercooler. But I'm no expert. I appreciate the input. Anyone else have an opinion?

jordoza

Its not alot of boost. Boost is addictive. It will be 10 pounds for 3 to 6 months then 12 for a month or two. Pretty soon your knocking on 20. I have done it multiple times. Maybe your the one guy who wont turn it up but you would be the only one i know. Personally ive run 11 to 1 and 18 pounds on 93 before. It really depends on the tuner and combo.

startingstock

iTrader: (3)

I will probably be that one guy. I've never been to the track, and would never be able to put it to use. And I will be 40 this year. And tires are expensive, especially with 3 kids. Heck, I probably wont be able to use half of what I end up with, but it is more about a personal milestone. I appreciate the responses though.

973800CamaroRS

iTrader: (3)

the lowest I would go would be 10-1. there is a lot of power and spool to be had with higher compression. If you ever plan on e85, flex fuel, or meth injection you could go even higher

jordoza

I get you. Im 49. 3 kids. A wife that doesnt understand my sickness. Anyway if you absolutely are gonna stay at 14 pounds or lower with the ls7 heads id go 10.5 to 1. If you might go e85 then yes you can go higher. What turbo you going to go with.

jordoza

Is there a reason your going with a wierd bore size requiring custom pistons. If you we 4.155 or 4.185 you could do shelf pistons and save a good amount of money.

NitrOmm

iTrader: (1)

I'm 55, kids are out of the house but still bleed us when they need (but I'm happy to do it). My wife wont even get into my scetchy bitch & she certainly cant grasp the sickness & symptoms related to this disease.

10:1 on my 416 feels perfect. Its peppy, powerful & never feels sluggish out of boost. I do spray meth/H2o for safety. At the power level of your goal & If you you are dead set against meth (want only pump gas) I'd stay at 10:1 ( my $0.02).

startingstock

iTrader: (3)

To jordoza :
I bought the block from a member and I was under the impression the bore was around 4.120+. It so happens that the last piston in there was a 4.170. 5 thou will get me perfect and I was hoping to have a rebuild if I ever need it. I see alot of guys saying 4.185 doesnt leave much meat for boost. I have read some horror stories about people boosting the LSX454. I got a deal on the block, no matter what the bore was, so I decided to keep it. And thanks for the input fellas. I ended up working late and will be ordering the pistons tomorrow. I guess I'll be shooting for 10:1. I'm just hoping I am at least 550 at the wheels off boost. I havnt picked a turbo yet. Any suggestions? I'm just looking to run a single. Hopefully I wont need anything huge since I dont need alot of boost.

ddnspider

iTrader: (26)

Good Lord, your 40, you're not dead! If you're going to build a 1000hp car, you should NOT be caring about tires. Either do it and have fun with it or don't do it. You don't have to run a certain number or make a certain power number. Build it, drive it, enjoy.

TrendSetter

ive had really good luck with 93 over the years. with a decent intercooler and good tune, i dont see why you couldnt get away with 10.5:1 on 10psi. those ls7 heads are VERY efficient though so keep an eye on your timing. na guys are making power in the low low 20s advance. i saw an RPM video where he made a lot of na hp on a hci 427 and he claims it was at 19.5 degrees....

jordoza

Is this an ls7 block?

startingstock

iTrader: (3)

Lsx bowtie

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iTrader: (3)

And I'm not too worried about tires. But I prefer to go forward instead of jogging in place. I've got almost 600hp now on my sbc daily driver and no2, and I've had fun. I just dont think I will get more traction with more hp on the street. But, who knows. The on and off ramps of I95 is where I have my brief moments of fun 2x day. Once on the way to work and once on the way home. I'm sure it will pull harder in 3rd/4th

ddnspider

iTrader: (26)

With a setup like that boost by gear and rpm will allow you to feed the power in to help with grip.

white01ss

iTrader: (37)

Since you're sticking with 93 and you don't expect to turn it up then keep it below 10:1. Heck, you could run 8:1 and turn up the boost and still make sick power. I'd shoot for 9-9.5:1 so you have a margin of safety in case you decide to turn it up later.

startingstock

iTrader: (3)

I didnt want to start a new thread, but I have another question. I an looking for an idea of turbo size. Looking for quick spool and I probably never go above 6500 rpm. Just curious the smallest turbo I can get away with for 1k hp. Doesn't need to be the cheapest, but dont want to spend 3k if I can help it. Is there an affordable t4 that would get it done for around $1500 ? And when a turbo is rated for 900-1200 hp, do I lose efficiency if I am at the high or low end of the bracket ? Do I shoot for the middle ? Mind you, it's for 438 cubic inches. Any advice is appreciated. Thanks

startingstock

iTrader: (3)

Beuller........

Beuller........

Beuller...............

AwesomeAuto

T4 and 438 cubic inches? Only if you plan to run twins.

The absolute smallest you should use would be a VS billet 88mm in a 1.32 T6.
It does seem like a lot of turbo, but you have a lot of engine, and need something to keep the backpressure ratio in check.