Piston selection for SR 355, direct port combo?
Piston selection for SR 355, direct port combo? 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.
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.
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.
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.
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.
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.
On The Tree
Joined: Feb 2015
Posts: 159
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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.
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Verdad Gallardo 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.
If I could get it to run a high 9, I'd be happy.
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?
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.
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?
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
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.
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.
