boost limits on stock block

[MikeH686]

Ok im about to hand my car off to the body shop together some rust removed ... and I can focus more on my motor ... im gonna definitely boost it more then likely turbo so my question is what can the stock block with 10:1 compression handle in means of boost I know 500hp is the limit but can anyone tell me the psi limit im looking to boost around 12psi I may lower compression to keep from blowing head gaskets thanks for amy input

 

[VibrantRedGT]

Exact psi will be impossible not given your current combo. I ran 455HP on the stock block with 12psi fine until one day the motor leaned out for some reason which toasted a ring on #5. Took the head off and Happy Birthday to me a piece of piston ring. After you put everything together get it dyno tuned right away.

 

[txstang84]

Exact psi will be impossible not given your current combo. I ran 455HP on the stock block with 12psi fine until one day the motor leaned out for some reason which toasted a ring on #5. Took the head off and Happy Birthday to me a piece of piston ring. After you put everything together get it dyno tuned right away.

+1...the "how much boost" question is kinda irrelevant. Boost is a function of restriction anyway, so you can have 12psi on a stock engine, change cams and drop down to 10psi, but make more power. Same thing goes for heads. That being said, if I'm not terribly mistaken, the stock bottom end should be good up to around 500 before you start splitting the block. But, like vibrant said-proper tuning is a necessity.

edit-I just paid attention to what you said about your CR...10:1 is kinda high to start with a turbo...might wanna think about using either a centrifugal supercharger or dropping the compression a little.

 

[Bullitt347]

If you can keep the engine from detonation, over 12 psi is easy, but rattle it once and your done.

 

[bentley429isBAC]

I've seen 19-20 psi stock shortblock iron heads around studs with a turbo. 18 psi with a s trim.

 

[MikeH686]

I will plan on dropping it to 9:1 or does anyone think lower would be better? I mean I know tuning is key afterwards my setup now is stock bottom end eagle h beam rods probe 10:1 forged pistons custom lunati cam which im gonna change out to either a crane or comp cam edelbrocj performer heads 1.6 roller rockers forged pushrods hollee systemax upper and lower 70 tb with a 74crane it'd 75 maf I can't remember off top of my head

 

[Mr. Rustypwnz]

ive hit 24 psi for an entire night or racing, by the end of the night it had pushed some coolant. 15psi is about it for daily driving and making it last.

 

[srtthis]

some where between 450-500hp most of the time...

boost = what ever makes that power....

 

[MikeH686]

Oh ok I know with like n/a subarus boosting them the block can only take 8psi but thanks for all the quick responses

 

[1991notchbackLX]

Oh ok I know with like n/a subarus boosting them the block can only take 8psi but thanks for all the quick responses

How do you boost an n/a motor exactly?

 

[txstang84]

I was kinda wondering the same thing, but I guess if he means putting a turbo on an engine that was originally n/a...?

 

[RacEoHolic330]

How do you boost an n/a motor exactly?

Just like Bubb Rub and Lil' Sis. Woo Woooooooo

 

[90 lx convert]

Well, in 2009 my car was making 411hp to the tires, 11.4 a/f, 11psi of boost on the stock block with a girdle. At an NMRA race at Maple Grove it split the block right up the middle through the cam bearings. So just for my experience I'd say 450- to the crank was enough to trash mine. Mike

 

[rbonella]

Your CR will limit the amount of boost you can run safely with pump gas....Id probably limit it to 6-8psi or so depending on how it reacts when you're tuning. you'll probably be in the neighborhood of block splitting power any ways. I boosted my 357 with 10:1 CR and Iam glad I didn't lower the compression. I have great low end power still, I don't have to spin the blower too hard (8psi) and I'm making good power for my application (street). I have a feeling this low heat/ conservative boost level will make for a street motor that should last a long time with great consistency. Made more than enough power, but I know my Novi2000 is begging to be spun higher which is always an option with race fuel, methonal, or a drop in compression

 

[MikeH686]

Yes by slapping a turbo on is what I meant ... and everybody has a different story now 20 its fine then 6-8 is too much then 11 is fine ... weird I wonder why that is .. bad material in the casting of the blocks?

 

[FastDriver]

Just like Bubb Rub and Lil' Sis. Woo Woooooooo

LMFAO! I wonder if anyone else gets this.

 

[FastDriver]

No, it's because you didn't specify things like whether or not you intend to run race or pump gas, and some people are missing the fact that you're running 10:1 compression. When you say "stock block," it doesn't really work that way. The block itself can take more boost than is feasible on pump gas as long as the power is kept in check, but boost is only a means to an end. The truth is that it lies completely in the tune, and the only sure-fire way to do this is to increase the boost incrementally and tuning as you go until you're not picking up power anymore. Then back it down a couple psi and a couple degrees ignition timing.

I think for what you're trying to do, I'd only run 6 or so until I dialed it in with a good tune. I think you'll have a hard time pushing 12 on pump without detonation or without lowering the timing so much that upping the boost is ineffective for producing more power.

 

[90stang5speed]

Im no expert on this but, like a lot of people have said, tuning will be very important. 10:1 compression might limit the boost psi but, you can also look into methanol or water/meth injection as a way to cool the intake air charge and raise octane to help with avoiding detonation. check out snow performance for the meth injection. it has worked real well for my buddy and should for me too if I ever get mine back on the road again.

 

[txstang84]

No, it's because you didn't specify things like whether or not you intend to run race or pump gas, and some people are missing the fact that you're running 10:1 compression. When you say "stock block," it doesn't really work that way. The block itself can take more boost than is feasible on pump gas as long as the power is kept in check, but boost is only a means to an end. The truth is that it lies completely in the tune, and the only sure-fire way to do this is to increase the boost incrementally and tuning as you go until you're not picking up power anymore. Then back it down a couple psi and a couple degrees ignition timing.

I think for what you're trying to do, I'd only run 6 or so until I dialed it in with a good tune. I think you'll have a hard time pushing 12 on pump without detonation or without lowering the timing so much that upping the boost is ineffective for producing more power.

The only thing we're not factoring in here is inherent casting flaws...which would make plenty of sense if-just for argument sake-two people have the exact same setup, and all variables were the same. One guy is able to consistently run an entire year without any issues, and the other guy has a cracked cylinder, or split the block after only four months. Otherwise, I'm in agreement with you to an extent. But, regardless of whether he runs race 104 or pump 93 and, intrinsic flaws to his specific block will wind up determining just how much he's "safe" to run. I witnessed a stock blocked, forged gut 331 with mild cam, AFR 185s, and a Novi make 460rwhp on tuning conservative and safe enough to run our local 93 octane or 91 in a pinch...a few months later, it cracked a cylinder. It took a while to finally diagnose it, but the block was lost due to a casting bubble. Tuning is of paramount importance, but there are some things you just can't factor out...and they usually rear their ugly head at the most inopportune times...

 

[FastDriver]

That would make sense "IF" you took two identical motors. Still, your anecdotal evidence is the exception, not the rule. I ran 420 rwhp at 10 psi for 4 years without an issue. I bent a connecting rod when I decided to be a jackass and do a "rule of thumb" tune when I decided to push the boost up to 12 psi. For every 1 casting flaw that causes a catastrophic condition in a 5.0, I'll show you 99 tuning mistakes that caused the catastrophic issue. The bottom line is that this guy has what he has, and shouldn't concern himself with the minimal possibility of casting issue. Instead, turn the boost up as you watch power output and keep the timing and AFRs in check.