ok, so currently my car is a stock bottom end LT1 with a vortech ttrim making about 6-7psi, just added a snow performance water/meth kit, heads are ported, cc305 cam, 42lb inj, 255 pump. i was getting some blowby and with the stock pistons and rods hitting 125k i took it in for a rebuild before it got any worse. so its in the shop now getting rebuilt basically. so were gonna bore it out to a 355, callie compstar rods and mahl pistons, 1.6RR, gonna delete the A/c while its apart also. builder recommended keeping the stock compression, i dont want to get to serious with boost on this car so my question is with stock compression and the forged internals AND the meth, whats the MAX i could hit for boost with still keeping things safe? what kind of HP to the wheels you think it will make, built auto, 3k stall, and PCmforless is gonna tune it?. FWIW on the stock bottom end and without the 1.6RR and meth, it supposedly made 450 to the wheels on 6-7psi of boost with the previous owner, not sure if this is true or not cause i wasnt there to see it but..

 

Why wouldn't you lower the compression to take advantage of the ttrim if you're gonna buy pistons anyway??? The whole idea with rebuilding a motor with boost in mind is to lower the compression and allow the blower to do the work

 

well this is the first motor ive dealt with rebuilding plus its supercharged on top of it so its all kinda new to me. this car isnt gonna be hitting a drag strip or anything, just street/weekend use, and when i took it in i said im happy with the power of 7-10psi ( this is going off of what the car is making before i brought it in, which feels powerful to me) and i think thats why he recommended stock compression?? nothing has been bought yet so changes can still be made. whats the recommended compression for boosted LT1's? again im not trying to go all out and make as much HP as possible, id be comfortable with 500WHP

 

I understand what you want, but stock compression pistons will be harder on the rotating assembly. I think you should use 8:1. Like I said, allow the blower to do the work. I'm pretty sure if you use the same pulley with the .030 overbore then the boost pressure is gonna drop a tad bit. I too only want a reliable cruiser but I haven't gotten to the rebuild yet and I'm only working with an s trim

 

well i know the guy building it said if i drop the CR the pulley would have to be changed, not sure with the bore tho? i dunno ill have to talk with him more on it and see. he said it should def be able to handle like 10psi with stock CR but wouldnt push much more then that. like i said if i can lay down about 500WHP and not be PUSHING IT, id be happy.

 

From what I've read here most guys use lower compression pistons when they rebuild. Did u check out the sticky threads at the top of the forced induction page?? I'm no expert but I think 10psi is gonna be high for stock CR, but I could be wrong.

 

I would tend to agree with everyone else here posting. stock compression ratio is going to be great for power at your level but you're going to be pushing it, risking blowing head gaskets, and it leaves you no room at all if you want to up the boost to take full advantage of that t trim. If you're looking for something more reliable, I would tend to believe going with a more pump gas friendly 9:1 area is going to be safer and leaves you room to let the blower do more work. Also, i would invest in some 2618 alloy forged pistons vs. 4032 alloy, as recommended by many boost built applications. Do some more research before you buy parts, theres a wealth of good info here in the forced induction section.

 

A lot of guys on tech say the best CR for a street blower setup is between 9.1-9.5 that way you maintain a little more of the down low throttle response.

 

If you drop your compression down to 9:1 you won't notice anything when you are driving the car normally. This will also allow you to increase your boost to 12-15psi without any kind of worries.

Even if you don't want to increase the power now you will have it for future expansion if you want to.

Given that this is a weekend driver then I would keep the possibility that you will want one that has an extra 100+hp over what you have now. Dropping the compression will allow you to do that later if you want to.

 

ok, def sounds like i want to go with the lower CR. anyone have any ideas were to start off with pulley size to be making close to 10psi after the build? i mean right now its making about 7 but from what im understanding im gonna lose a few psi after the build, vortech says to do a trial run after the build and go from there?? curious if anyone has a similiar setup and what pulley and belt your using and what psi?

 

I don't know anything about which pulley you should use, but I agree with this guy...judging by your comments about your goals, I think 9-9.5 is the way to go for your CR. If you run stock compression, you really should run racing fuel and have a really really good tune to be safe. A PCMforless tune is not generally considered a "really really good tune" since it is a mail order. Not that they do bad work, but a knowlegeable tuner who has your car on the dyno is going to be a better bet.

 

yeah i talked with the guy building it were gonna do 9:5 compression , and im goin with PCmforless cause the shop doing the work mainly does LSx powered cars and doesnt have the software for LT1's but mite get it so he can dyno tune it, although bryan from pcmforless seems to be pretty good at tuning even through mailorder.

 

Just to give you something else to keep in mind is the amount of boost you are going to see is going to depend on the cam.

 

well it has the cc305 in it

 

also what about ARP head studs or bolts for what i plan on runnin, no more then 10psi. ive herd alot of leaking issues with studs and to the point i read alot staying away from them on a street car unless some serious boost. so there bolts shoud do fine for low psi? and is ARP rod bolts a must when doing compstars forged rods?