Putting together a solid 355 and trying to pick out a piston. Do I need to go with a 2618 alloy and H13 pins or would 4032 with H13s get the job done on a good tune.

Bore - 4.030
Stroke - 3.48
Rod Length - 5.7
Head cc - 54
Piston cc - -2.5
SCR goal - 12.5:1

Will be running an LS 411 PCM, Jesel shaft mount rockers, stock crank, 2 bolt mains, half fill, ported stock castings with 2.02/1.60, and a prayer. Cam TBD once piston is selected.

 

How much do you plan on spraying? A well designed 4032 piston could likely take up to 250 with good tuning. 2618 would be safer from there on up.

And why tool steel pins? I guess it depends on manufacturer, but an average aftermarket pin will likely outlive your main bearings with 2-bolt caps. You'll need main studs and a line hone at minimum but splayed mains aren't that much more and a ton stronger. 4-bolt mains are recommended with a real solid roller motor unless you want cap walk.

The fill also seems unnecessary.

 

Check out cp bullet pistons there 2618. I'm running them in my 355 on 200 shot with no issues. I also running 6in rod for weight.

 

250 will be the starting point and will be going up from there. I agree that splayed mains would be preferred and I haven't ruled it out at this point. My issue is that the block has already been line honed. The 2 bolt mains have already been studded and we were planning to half fill just to give the bottom end a little extra strength. I asked the builder about the H13 pins and he basically said that they may not be necessary but he uses then on all his big nitrous motors spraying 400+. I won't be going there but it seem like the cost of pins wasn't too high and I might benefit from the added strength.

 

Thanks, I'll check those out. I ran a set of 4032 JEs in my old setup with stock rods, stock crank, ARP hardware, and a 200 shot. That motor lasted 15 years and pushed me into the 10s. I'm hoping this setup might live at least half as long spraying 300-350.

 

what made you abandon the vortech option as i read your other post in favor of this sr nos combo?

 

The Vortech and the motor were going into another car. I decided to put that car back to stock and sell it and sell the supercharger. This will fund my new SR nitrous build for the car that I've had forever.

 

What heads are goin on it? As well what's ur et goals? Just Curious

 

I'm undecided on heads but have been looking at AFR 210, TFS 23degree 195s, or their 21degree 185s with AI port work. I may try to see how far I can go with the stock castings first. So far, I've run them to 10.80 @ 128 with a 1.5 60' on a fat tune and 200 of nitrous. Those heads are ported but still stock valves so I'm considering more port work and upping the valves to 2.02/1.60.

If I could get it to run a high 9, I'd be happy.

 

I've had great luck with le 21* trickflows. He is little bit cheaper than ai. They pushed me 6.2s in the 1/8 so far on 200 shot.

 

That's good to hear. The 21* seem to be more recommended for nitrous combos but I wasn't sure why since they didn't come in a 195, just 185. Do the 185s have a thicker deck? How would you compare the 21* 185s to the AFR 210s?

 

I'd say ported trickflows are the same or little better than them out box 210s. If the afr were ported then they would out perform them hands done.

 

The AFRs outflow the LE ported 21* TFS heads on paper, but the AFR numbers are likely inflated. I would imagine the Race Readys are pretty much even but the Comp ports probably have a slight edge. The real benefit of the AFRs is they their valves are pretty light and the springs are already suited to a SR cam.

People say the 21* TFS heads are better for nitrous because the shallower valve angle means a more concentric and efficient chamber, but the AFR Eliminators seem to like the same amount of timing from what I've seen. Also, the AFR decks are 3/4". Don't think you could wrong with either.

 

I'm really leaning towards the TFS 21*. So, with all the info in mind....355 SR, 300+ direct port, stock crank, 2 bolt mains....should I spend the extra for the 2618s and H13 pins or just go with 4032s and standard aftermarket pins?

 

I'd go with the 2618. They would give u a bigger tuning window on 300 shot.

 

Would there be any pros or cons of going with a flat top piston and a 54cc chamber versus a dome piston with a 68cc chamber to achieve the 12.5:1 ratio? Does heavy nitrous use influence the choice?

for example...
an AFR 210cc head with 68cc chambers and Ross #99571 pistons (14cc dome)
an AFR 210cc head with 54cc chambers and a flat top -5cc piston

 

After some research I found the following reply to someone posting a similar question. I follow the logic but this would also depend on having a head with a small chamber and a thick deck to support cylinder pressures the motor will see with nitrous. You wouldn't want to start with a 68cc chamber, mill down to 54cc and expect the deck to hold up...necessarily. You would want to start with a 54cc chamber that has the deck as thick as possible.

A flat top piston design will give you BOTH a larger quench area, and a smoother combustion flame front travel ...... than either a "dished" or "domed" piston.