Im looking at a Scat 4340 crank with scat q-lite 5.7 rods and srp -31 cc pistons w/ stock ported heads flowin 26x for a boost build. Probably plan on about 8 psi at first with a small sc I already have and maybe later hopefully about 20 psi. I also plan on hitting it with 100-150 shot. I dont think im going to run an intercooler at this point, probably water/meth injection. What do you think of this rotating assembly?

 

For less than $100 additional you can get a Compstar crank, which I would much prefer. Same with the rods. The SRP is a 4032 alloy piston and I would only run a 2618 on boost plus nitrous. If it was just one or the other and not a lot of either the SRP would be fine. IOW, I can't advocate any of those choices. I would call Callies for a complete balanced RA with the Compstar crank and rods and the #2618 alloy pistons of your choice. It will not be much more $$$ than what you are thinking of and will be a lot better.

Rich

 

yea dont use srps, mine let go on spray alone, they are VERY sensitive to detonation

 

Yeah, they are forged but use the high silicon #4032 alloy. Depending on the exact alloy, up to 13.5%. They are fine for NA use but NOT for anything more than trivial nitrous or boost. #4032 melts at 995F, #2618 at 950F.

#2618 Aluminum

• Copper 1.9 - 2.7
• Iron 0.9 - 1.3
• Magnesium 1.3 - 1.8
• Nickel 0.9 - 1.2
• Silicon 0.25 max
• Titanium 0.04 - 0.1

#4032 Aluminum

• Chromium 0.1 max
• Copper 0.5 - 1.3
• Iron 1.0 max
• Magnesium 0.8 - 1.3
• Nickel 0.5 - 1.3
• Silicon 11 - 13.5
• Zinc 0.25 max

I am no materials scientist, but I believe that #4032 is a "eutectic" alloy, add a little more silicon and you have the dreaded "hyperutectic" alloy that is used in the stock pistons, which are FINE if detonation can be avoided. The high silicon alloys make the metal harder and more thermally stable, which is fine for longevity and allows tight piston to wall clearance. This in turn reduces noise and oil consumption. But these alloys are much more brittle and should not be used in a race, high boost or nitrous environment. I guess JE/SRP use this alloy in the piston you are looking at to be competitive on price, but it is not a good material for the purpose. Note that even in the SRP line they use #2618 for the high compression dome pistons. The JE version of this piston (#2618 alloy) is ~$200 more.

Rich

 

Damn, some of my posts are superb. Someone ought to make a book out of them

Rich

 

Agreed

 

thanks Rich, I was hoping you would chime in. Ive been beating this horse for quite awhile and its almost dead. I considered an eagle setup at first but after doing research I looked elsewhere. Ive read pretty good things about scat components, BUT I wasnt sure they could handle what im planning either. As for the SRP pistons, I wasnt aware at all of this info you've given and thought these pistons really would hold up. Good thing I asked. So Im looking for a 2618 alloy instead I guess? Would you recommend staying away from je/srp all together, or just that specific piston I was speaking of? I was hoping to be able to use the light rods to save rotating mass as they weren't that expensive, but I know in saving weight im going to sacrifice reliability pushing the assembly to its max with nitrous and boost. Would you recommend staying away from lightweight cranks and rods, as most of them ive seen are rated between 500-650 hp?

I just looked at JE pistons and they have a -31cc piston like you said for $200 more, but it doesnt say what its made from? Actually, neither did the srp piston. Ive also noticed alot of mahle pistons are 4032 as well. Sticking with the stock ported heads is limiting my choice of off the shelf pistons because I need that large dish. Any suggestions, besides getting different heads or custom pistons, that would kill my budget.

 

I'd buy the book!

 

If you were looking at the JE extreme duty blower piston they are the 2618 material. Look into Diamond and Ross, they both have some pistons that are slightly cheaper if you have to get them custom.

 

The JE version of the -31cc "blower" piston is the desirable #2618 alloy. Essentially all "race" psitons are this more expensive alloy and from what you are planning, you do need it. That is the LAST place I would skimp on a blower + nitrous combo. You might get away with the cheap rods and the SCAT crank, but the good pistons are a must, IMHO. As mentioned, there are other brands such as Diamond and ross to consider. Again, you might want to call Callies about a complete RA.

Rich

 

Me too.
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Look into what Probe Industries has also.They make good stuff and if it's not on the shelf they can/will make it for you.

http://www.probeindustries.com/index.htm

Like Rich said--The bottom end on thias type of set up is NO place to cheap out.
You are going to NEED a good block also.

 

 

And not only am I talented, I am humble!

Rich

 

 

Damn, maybe you should give yourself an award?


David