what type of pistion for supercharged engine..

johnnyboy · 06-23-06, 10:38 PM

hello all,
i am building a 331. in on of my research mags i stumbled across a 331 build where they suggested what type of piston to use if you intend to add a supercharger in the future. would it be domed or dished. i guess with the dome you would add compression. whereas the dissed would lessen compression. help!!!!!!!!!!!!

Bill D · 06-23-06, 11:53 PM

To answer your question directly, a dished (low compression) piston is required when using a supercharger.

Now, if you are planning on building a GT40, a SC won't fit. At least not easily.

Bill D

johnnyboy · 06-24-06, 07:52 AM

thanks bill,
im actually building a diablo replica but im using my ford engine. plenty of room

.
thanks again

Howard Jones · 06-25-06, 01:29 AM

Pumped motors, either turboed or blown, in general have about 8 to 1 compression ratios at about 1 bar. BUT that is so general in nature that ...well.... it's a gererallity. The main thing is to decide of the fuel you will be using, then how much boost you want to run, call up a few piston manafactures and begin your education on compressed motors.

Cams will also have a lot to do with this a will timming and fuel management. I assume you will be running a electronic FI system.

This is a subject that always ends in the same place in my head. Why not just build a big motor. 450 CI's or so and keep it all simple. 700HP is fairly easy to achieve with 450CI's and not all that expensive. On the other hand 700Hp from 300 inchs is going to cost some real money. The FI system alone is going to run up to about half again the cost of the motor, not to mention the cost of the blower.

Anyway get on the phone to JE pistons, Ross pistons, Keith black etc. and start asking your questions. I'm sure they will want to help you with your project.

Buy the way, what are you going to use for a gearbox?

johnnyboy · 06-25-06, 02:14 PM

700hp is a little much. i would love to run that ,but the transaxle i have will have limitations. im currently using a upgraded audi 5000. however if i add the supercharger a porsche g50 will be instaled. the car is being built to do some light road racing so bottom end excelleration is the main factor. this is my first build so please excuse the lack of knowledge, but so far so good.

the more imput the better. thank for the the imput sofar.
thanks guys

JohnC · 06-25-06, 04:53 PM

Why not call the various piston manufacturers and ask their engineers which pistons they would recommend for your application? I've found the people at J&E and Wiseco to be very helpful. They can also give you the best recommendation for a good ring pack, since rings for a FI application are going to be different than for a high compression NA application.

If you're new to the forced induction world and want to learn more about superchargers, there is a good book by Corky Bell entitled "Supercharged" which is a very readable introduction on the principles and applications of different types of superchargers. This will help you decide how much boost you want to run, and how much compression you can get away with.

John

StuartB · 07-05-06, 11:57 PM

It also depeneds on the size of the blower and the amount of boost you want to run. You can run mild boost on a high compression motor but just don't let it start to detonate and don't try to then run the small blower faster later on to make more power, you'll just create a lot more heat, not good and no extra power to be had.
Small blowers on high comp' motors have good acceleration but lack the top end power, big blowers on low comp' motors have big power up the top end but pickup is slower.
Piston shape's itself isn't so important if your not going all out racing, but make sure you use forged pistons, nothing else will do.
The piston compression hight is one of the factors that dictates compression ratio so you'd be best advised to see what's available for your motor `off the shelf` first.
If you do want to run big boost and can't find the right pistons (at around 8:1cr) look at what forged pistons are available and see what you can do by `mix n match` with whatever rod, crank and head combos will fit to get the compression ratio down.
This is where the dedicated forums help so much as there's a lot of truth in the saying `it's all been done before` so a little looking in the right place can work wonders, good luck with it.

Jim c · 07-10-06, 10:06 AM

Johnyboy

It doesnt sound like your going to go nuts boost wise.
All the pistons that the guys have mentioned Have all been used in projects I have done for customer cars never had a problem with any of them.
Have pumped up to 32psi on some of these brands.

The only thing I would definitly make shaw of is if a low comp piston is supplied that the squish band ( if the engine you are using has one) is not removed.
Thats the part of the piston that comes close to the head usually within .040" or so.

If it is removed to lower comp it will generally induce detination prematurely.
Good luck

Jim