10.0 to 1 compression..... how much boost can i run without worrying about blowing up my engine??

Nick

 

That is a very broad question since boost itself isn't the only thing that could blow up the engine. Anyways, I would say 8-12psi if you have an intercooler of some sort, 4.5-6psi if you don't.

 

i am running 15lbs of boost on 10 to 1 but am running 100 octaine fuel from sunoco . could run on 94 and booster on the street.thats with custom programming and no fmu

 

Do a search - most will agree 8psi intercooled is about as high as they'd run on stock internals, and even then, you will break a piston. Sometimes it's 500miles, or 20,000... 12psi on stock internals is asking to blow the motor or lift the heads unless you're doing it very carefully, have a strong motor, and run race gas or close to it.

The worry is NOT the dynamic compression of 10:1 multiplied with 8psi of boost (it is with 12psi though no matter what). The worry is that if you detonate hard or run lean, the stock hypo pistons are too weak to handle it. You can easily run 6psi intercooled on the street with 93-94 octane, and get a little more longevity out of it... but unless you can easily afford to blow the motor within 5k-10k miles, it's a tough choice, and a lot of guys blow the motor with 8psi intercooled.

Even then, "How much boost?" is an impossible question to answer, because boosted motors with high CR are ticking time bombs. ALL of them. It's just a question of how long you want it to last. Even if the bottom end is 4340 forged alloy, 4bolt mains, etc, you could lift the head with too much boost, you could melt a piston be running lean, or detonate just right, blow the piston, rod, or crank... If you dont know how much boost you can run safely, assume conservative, and always have tuning/fuel mods before slapping on the blower.

My stock internals at 145k mixed with 1.6rr, headers, CAI a 218/230 114lsa cam alone(NO BOOST OR NITROUS)... Ran like a bat out of hell, but the stock injectors actually ran a little lean with the cam at 6500rpm. Mixed that with a stock oil pump that was really tired, I ran hot, blew the headgasket, and rod bearing on #8 ground away. Now I'm rebuilding the motor... after 500miles with the cam...

 

Sorry, where did he say he had stock internals?

 

Another thing to keep in mind is the cam. If you bleed off some cylinder pressure with overlap, then the motor doesn't "see" as much boost. Of, course, it doesn't make as much power, for a given boost level.

In my case, I ran 12 psi boost (measured at the intake) on stock pistons, and 93 octane. 10.5 compression. Saving grace was the Hot Cam bleeding boost out the exhaust.
After heavy abuse I pulled the heads to do some upgrades, and the pistons look new. But it only made 405RWHP.

Lots of factors goin to figuring the age old "how much" question!

 

well typically, even with a cam that bleeds off some boost, you will make more horsepower because the motor is processing more air, up to a point. now whether that power is usable in your application is another story.

It is almost impossible to tell you straight up what the max amount of boost you can run on a particfular engine is, but a rough estimate can be given with a certain combination. Something I haven't seen talked about a lot on here is combustion chamber design, and I feel this has a lot to do with how and when the motor will detonate. But there are other factors. Stock pistons on an LT1 car aren't a good combo with boost. If you are running good forged pistons, then your chances of killing the motor drop tremendously.

 

The supercharger is on a ZZ4 engine. It has forged connecting rods, 4 bolt main, etc. Here is a link to the specifications

http://www.westcoastsportscars.com/zz4.html

As far as mods, I have MSD pro billet distributor, 6AL ignition box, blaster 2 coil, SLP 1 3/4 ceramic coated headers, Demon 750 double pumper carb and of course the Weiand 144 CID supercharger. No internal work done yet, but the stock cam lift is .575/.510.

Right now, I am more concerned about the health of the engine before about how much boost/power I can get out of it.

Thanks for all your help so far. kepp the suggestions coming if you still have any. I'm sure none of you would want to see a ZZ4 engine crap the bed. =)

Nick

 

With a roots blower, the idea seems to be to keep the boost to a minimum and make your power with the motor. Because you probably don't have an intercooler, your inlet temps are going to be higher, plus the fact that you have a small blower, the motor isn't going to like too much more boost than just a couple pounds, say...5-6ish? That is if you are running pump gas with no alcohol/water injection. I'd say look toward your cam for more power. A solid roller, or even a bigger hydraulic and a good valvetrain will lower your boost pressure, then you can gear up the blower to keep the same boost, but make more power because your flowing more air. Just some thoughts.

-Kenneth

 

Man- you guys make me wanna crank my boost with a race tune and gas, so I can get an 11 second timeslip on a stock motor.

$$$- gotta stop spending it. lol

 

hey racr4jc.....

I was planning on eventually doing the cam and the roller rockers over the winter. What brand/specifications would you recomend? Anything else you would recomend while I am at it??

If anyone else has some suggestions, please feel free to comment.

Thanks

Nick