I have an idea, first off I have 63cc iron heads, a 383 forged scatt crank,
I want to turbo charger it and run a 7.7 to 1 or lower compression,
due to the iron heads,

My problem no one makes pistons that can lower my compression to 7.771 with a 383 and 63cc heads,

i am thinking about using the small 400 connecting rods, the 5.56 lenth and standard 383 piston (the ones disend to use 5,7 rods)

I was wondering what would be compression with flats top (made for the 383 with 5.7 rods)pistons, on my 383? with the 5.56 shorter Rods.

Please tell me if this will work or will my compression be to low?

Thank you,
slow boy

 

If it's possible it would drop you about 3 pts.

Go to any online CR calculator, enter in your current setup....then change piston deck heigth by .14 (5.7-5.56)...i/e f .025, then make it .165, and recalculate

 

KB pistons makes a 383 piston with a 28cc d dish. KB#121

If you were to modify your 63cc heads by opening up the combustion chambers with a die grinder to 69cc, and modify the pistons d dish to 31cc's and install them in a standard block (.025" deck height) with a 5.7" rod usign a .051" thick felpro gasket you would have a compression ratio of 7.72:1


If you were to use Water injection on your turbo motor you could run a 8.5:1 compression ratio using as much or more boost and make more power safely without detonation an be able to use the same KB121 pistons without haveing to modify the heads or the piston dish. With a standard .039" gasket 63c heads and 28cc dished pistons your cr would be 8.46:1 in a standard block. (.025" deck clearance)

Do a search for water (methanol) injection on the net. There are many companies that make good water injection systems..

Kb hyper pistons will work fine on a turbo motor but require much larger top ring gaps. Wrere talking .030"-.032"

 

Ok lets say I am looking for a forged pistons only.

Hyper piece of crap! Will never go in side any of my motors. There to weak and brittle.
The only reason that there used in cars today is that are are Dirt cheap to produce. Even cheaper the cast!
If you ever cut on in half you see what I am saying the hyper are filled with air pockets from the sylcon particals in the pistons,
Ive got a couple of enginer freinds that work in the gm and they say they use the hyper pistons in gm cars becasue they are half the cost as cast, which adds up to Millions of dollars saved to gm!

Its all sales marketing about the hyper piston and I feel bad for any of those people who fall for there bs about how good the salses peop[le say the hyper,
If i was u and cannt aford forged go with CAST pistons over hyper junk.
And on a side almost all cars from the Cars with boost from there manufactures come with Cast pistons.

Thank you,
Shane

 

Don;t make the mistake of comparing the stock hyper cast piston that GM installs in there assembly line and crate motors, to a hi performance hyper piston from KB or Federal Mogul. The GM pistons are made of an entirely different alloy and are not *T-6 heat treated*.

Hi performance hyper pistons are about as tough as nails ( you have to really try and break one in a motor.) They will stand up to moderate NOS or boost (10lbs) and some moderate detonation. Just like a forged piston. Any piston will fail of subjected to severe detonation and lean out.

A company like Aries or Ross can make you a set of CUSTOM Forged racing pistons with the dish size you want. They will not be cheap. It will actually be cheap er to sell off your heads and get new ones with larger chambers.
Do some more research on what it takes ot make a turbocharged street motor last on the street. Detonation is what kills pistons wether cast or forged. The water injection system will keep the motor out of detonation on street pump gas with 8.5:1 and a good amount of boost with less or no ignition retard or exessive rich mixtures required.

 

Get a set of custom Forged pistons made.....all good piston companies make customs...Diamond, Ross, Aries, TRW, etc....They'll be between $600-up usually.

 

Water injection... What about alcohol, like I hear a lot of the turbo Buick guys do? TTA motors (not a V8, but hey) run 16.5 PSI, but they have like what - 8:1 compression. Premium gas is a must, that and an intercooler.

 

Alcohol (methanol) is part of the brew used in a water injection system. Usually a 50-50 mix is best.
U can use Ethanol or denatured wood alcohol also, but methanol is the most effective from a standpoint of detonation suppression and specific power output.

The alcohol provides a high octane suplimental fuel with excellent cooling properties. Just increases the effective volumetric efficientcy and power output (allows more boost/ timing advance) of a motor then uses a water injection system.

 

What heads do you have on it now? I second the using the KB with 28cc dish, and combine that with some Water injection, check out the GN forums, last kit i saw was ~$450. Honestly i do not like the idea of increasing piston to head clearence, ruines the quelch effect, the close the piston to the head, the better the quench, better the quench the more effecient the combustion chamber is, and also limits the chance of detonation, due to rushing air, and its ability to basicly blow out the hotspots in the chamber. Last engine masters i read, had a recomendatoin of .040 for a street motor, so thats your deck hight + compression thickness.

What CR do you have in it now, im going to be in the same boat as you someday, im going to be running a 383 with Forged Probe 20.4 CC dish pistons, with the Vortec heads, that are 63-65cc (havent checked yet, after milling for flatness, and polishing the chamber im not sure where its at) But ill be chaning over to AFR 190's with the 74-76cc chamber, that will drop me to around 8.45, but being an aluminum head, its like running 8.1:1 or lower.

BTW im getting my pistons from CNC-Motorsports.com, for $480 w/ rings, dont know P/N on rings yet, waiting for a reply from CNC, said to be Total Seal rings, im hopping for some of the gapless sets

 

I think JE or SRP makes a -31cc dish piston for the 383.

 

Maxx,

Is the motor you are planning going to be a blower/turbo motor? If so why in the world would you run gapless rings? If you get ANY detonoation w/ that be prepared to buy new pistons when it sheers off a ringland.

I need to find the article they did w/ gapless rings and rings w/ gaps where the gapless rings made less power than gapped ones. I got it laying around here somewhere. The gap is needed, and its definately not a bad thing... I know these companies claim big numbers from the gapless, but at what costs...

 

I would REALLY like to see that article now, I've only seen the gapless ran on N/A motors, and thats only been a handful. Just to be clear on the design, the rings im talking about is where the top one is made up of two rings, with the end gaps set at 180* of eachother, and then normal second and oil rings.

 

Total Seal, gapless all the same basic design. Designed to have no gap on the top ring. I am not a fan of the design b/c of things I have read, and a few tests I have seen that showed no power loss from actually having a gap, and IIRC there was actually a slight power gain. I need to find that article now that I am spewing these words out of my mouth.

I would in no way run them on a boosted car that I built though. I just think you are asking for problems. w/ the drastic cylinder pressures that you have w/ the SC/Turbo, I don't think its a good idea. Am I scientifically correct... who knows. That is just my personal opinion.

 

thanks for the heads up, ill do some more reasearch on them.

 

Here are a few posts...

https://www.thirdgen.org/techbb2/sho...hlight=gapless

https://www.thirdgen.org/techbb2/sho...=gapless+rings