I am building a 357 CI LT1 for forced induction and I have already purchased the Cola forged 3.50 inch stroke crankshaft, Manley 5.7 inch forged H beam rods and now I am trying to decide on my pistons. I am torn between the Diamond Blower/Turbo Dish piston that is a -22cc dish and the JE Extreme Duty forced induction piston that is also -22cc dish. I will be using AFR LT4 210cc heads that I have puchased bare and will have ported so both pistons are going to give me the same compression ratio. I talked to JE and they say that the JE piston will take 20 to 25 pounds of boost and the Diamond site says their piston is for up to 20 pounds. I will probably never run more than 20 pounds but I want to build the motor to take more than I am going to give it. Speed, INC. said the Diamond piston is the same one that they are running in the INTMD8 LT1 SS car and they are running 24 pounds and nearly 850 RWHP and 9.80's. The JE's are the most, $682.00 is the cheapest I can find and the Diamonds are $559.00. If the JE is truly that much of a better piston, then I don't mind saving for a while longer but why spend the extra money if the Diamond is just as good as quality. Maybe I am over-analyzing but any input or experience with either would be a big help.

 

JE's are without a doubt one of the nicest pistons you can get. I'd say save the extra money and buy them!

 

JE and not the lighter SRP pistons. JE are full lightweight race pistons. It's not just about cost. A JE and it's cheaper SRP piston are almost the same however the JE pistons are designed slightly different and are much lighter. You always want a lightweight piston. This of course means everything HAS to be balanced and if the pistons/rods are very light, mallory weight will need to be added to the crank (more money) to get everything balanced but it's worth it in the long run.

 

Education request...

Why a 357 with 3.5" stroke in particular?

 

Well these are the two off the shelf choices. If I was looking at customs I would take JE right out of that all together, and look at Diamond or CP. (Diamond for price and CP for engineering and technology) BME and Mahle are also in there but we are not at that level here.

In your situation mass is probably not as important as where the mass is. RPM is usually not the problem here is my guess, most guys don't want stupid RPM on blower motors, in fact most of the ones I see guys are shy to go 6500rpm.

Anyways......

I would suggest the pistons with the smallest bore possible here. The JE and SRP's are both available for a 4.020 bore, You can get the Diamonds changed from a off the shelf piston for $30 more so you can get a 4.000", 4.010" or 4.020" piston.

As for the mass of the pistons.....

Diamonds 4.030 x 5.700 x 3.500 = ?g 2.950" long pin
SRP 4.030 x 5.700 x 3.500 = 492g 2.750" long pin
JE 4.030 x 5.700 x 3.500 = 508g 2.950" long pin

So I guess money doesn't buy the lightest piston here.

I actually have a set of SRP's and a set of JE's in the shop right now, just got the SRP's in today and looked them over and compared them to the JE's. I really can't see a huge difference in the pistons (in fact they look like identical CNC programs) and I personally don't like paying the extra money for the JE's since they seem to be overpriced because of the name.

The Diamonds and SRP's are the same price and you can get the Diamonds in a 4.010" bore for $30 more. The Diamonds have a longer pin (2.750" vs. 2.950") so they are a better choice in the strength department since the loads on the pin are not as high since there is more pin to piston contact.

Other part of this is the rest of the strength of the system here. Crank looks like it's good enough, Manley H beams are proven to be strong rods. The only real question is block strength, which is always the issue in LT1 motors. Any blower motor I do I want a good amount of hard block in the water passages and the mains need to have a very tight tolerance on the journal diameter. The spec is normally about +/-.0005 from journal to journal where I would rather see +/-.00025 instead. Don't run stupid big clearances here and you should be ok.

Bret

 

Who knows but he should take it down to a 353 and keep the cylinder wall thickness.

Bret

 

I just happened to get a really good deal on a 3.50 inch stroke crank instead of a 3.48 inch. I did not want the added expense and headache associated with building a stroker so I went with something smaller. The 3.50 inch stroke with the 4.030 inch bore comes to 357 cubic inches.

 

Gotcha.

Thanks for the response.

 

I tend to agree with Bret on the wall thickness. I am going to run a .020 over piston and hard block in mine.....and at least a 200 shot