One more time BUILD THREAD I must be stupid
02-02-2019, 01:42 PM
#22
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I haven't seen the data on the V2's, but i remember Tony was targeting 420 cfm. Assuming a bit of port work, likely they are similar to the BR7 273. Flows 420 on 273cc runner. i don't know if he had to open them up any to gain the extra flow or if it is just mad wizardry in the bat cave.
02-02-2019, 02:06 PM
#25
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02-02-2019, 04:43 PM
#29
For my last two engine builds I have run JE asyemmetric pistons which have tiny skirts and are extremely light. These pistons come in a 4.155 4.1 stroke off the shelf.
But wiseco offers a 4.155 4.125 stroke off the shelf and i assume the wisecos weigh a little more. Pricing is pretty similar.
I wonder what is more important, 4.1 vs 4.125 stroke or the weight of the pistons.
my old je's weigh 420g in a 4.08 4.0 stroke and matching wiseco's weigh 490g
But wiseco offers a 4.155 4.125 stroke off the shelf and i assume the wisecos weigh a little more. Pricing is pretty similar.
I wonder what is more important, 4.1 vs 4.125 stroke or the weight of the pistons.
my old je's weigh 420g in a 4.08 4.0 stroke and matching wiseco's weigh 490g
02-02-2019, 09:43 PM
#31
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I haven't seen the data on the V2's, but i remember Tony was targeting 420 cfm. Assuming a bit of port work, likely they are similar to the BR7 273. Flows 420 on 273cc runner. i don't know if he had to open them up any to gain the extra flow or if it is just mad wizardry in the bat cave.
02-04-2019, 06:17 AM
#33
I’d go 4.185”/4.0”. Keep the rod to stroke ratio decent and the slightly taller pistons will be more stable in the bores. Less ring flutter is a good thing Piston speed gets really high when spinning over 4 inch stroke stuff. At your power level I really don’t think the engine cares about 50 grams of piston weight. On a restricted low power circle track engine it’s a big deal but not in your case
Your heads and that cam seem really good and I’m betting the nosing over you speak of was a push rod and or valve spring thing more than the profile being wrong
running an air pump will be huge on an engine this size
Your heads and that cam seem really good and I’m betting the nosing over you speak of was a push rod and or valve spring thing more than the profile being wrong
running an air pump will be huge on an engine this size
02-04-2019, 09:01 AM
#34
The Dart block has much longer sleeves though. They are 5.800" or longer, I can't recall exactly. But the 4.125" stroke is supported better in that block than a 4" stroke is in a production block. I would have zero issue running the bigger stroke. It will make more power with more stroke. Even if the RPMs come down a few hundred RPMs. That's where having a better intake manifold and more cam timing gets the RPM back (and in turn more HP)... But the 4.185/4 is probably the best option for a high revving really powerful engine.
03-04-2019, 09:06 PM
#35
Im still trying to get everything figured out for my new engine.
I keep wondering if i should go crazy on the stroke like 4.25 and keep my rpms down? Maybe better on the oiling system
At what point does increased piston speed and extra friction come into play. I know there is no replacement for displacement but alot of these big hp motors have relatively small displacement.
But what is actually faster at the track? bigger displacement or more rpms and hp.
thoughts?
I keep wondering if i should go crazy on the stroke like 4.25 and keep my rpms down? Maybe better on the oiling system
At what point does increased piston speed and extra friction come into play. I know there is no replacement for displacement but alot of these big hp motors have relatively small displacement.
But what is actually faster at the track? bigger displacement or more rpms and hp.
thoughts?
03-04-2019, 10:07 PM
#36
Bigger inch engines always make more power but are less efficient. Parasitic frictional losses stack up. Sixty percent of an engine’s rotational friction is from the rings. Long strokes drive the piston speed (feet per second) of linear travel up
smaller engines with large bores to breathe through big heads will twist high with shorter strokes and always make more horse per cube.
Heres a funny exercise. Figure the feet per second of the big ends of the rods. The heaviest part of the bob weight (two per journal) at like 8000 rpms. Do a 3.622” and compare to a 4.125”. Huge difference
smaller engines with large bores to breathe through big heads will twist high with shorter strokes and always make more horse per cube.
Heres a funny exercise. Figure the feet per second of the big ends of the rods. The heaviest part of the bob weight (two per journal) at like 8000 rpms. Do a 3.622” and compare to a 4.125”. Huge difference
03-05-2019, 10:53 AM
#37
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Another consideration in High RPM longer stroke engines, specifically shorter rod/stroke ratios. While they accelerate quicker
providing more torque in the low and mid-range, at higher RPM they contribute significantly to increasing friction
due to piston/ring side loading against the cylinder bores.
I would choose the 4.155-4.185" Bore X 4.00" Stroke for a NA build it will still make all the torque you can use
in all but the most all out strip builds and maximize Head Flow.
All depends on the combo and application.
providing more torque in the low and mid-range, at higher RPM they contribute significantly to increasing friction
due to piston/ring side loading against the cylinder bores.
I would choose the 4.155-4.185" Bore X 4.00" Stroke for a NA build it will still make all the torque you can use
in all but the most all out strip builds and maximize Head Flow.
All depends on the combo and application.
Last edited by NAVYBLUE210; 03-05-2019 at 11:01 AM.
03-19-2019, 07:24 PM
#40
Unfortunately, i think im gonna have to put this build on hold. Just found out I have another kid on the way. I have decided im gonna go turbo 5.3 until i have more time and money to finish building this new engine. Good news is my headers will work for turbo manifold flipped around. I have a gtx4294 turbo that should work good on a stock 5.3
