xsspeed Posted March 9, 2023 Share Posted March 9, 2023 Also, and sorry to fact check,are your numbers right for mean piston speed? I was just doing calcs last night for my rb, using mps=2×stroke x (rpm/60) Top end revs should see around 25m/s give or take. 4500fps is like 1300m/s? Or am I misinterpreting what you're showing? Quote Link to comment Share on other sites More sharing options...
Roman Posted March 10, 2023 Author Share Posted March 10, 2023 12 hours ago, xsspeed said: hey dave whats your estimate on weight diff between the 3s and this? I thought you had said something like 50kg but wondered if youd started weighing anything? Not too sure, havent weighed anything. However gut feeling is that it wont be meaningfully lighter than a 3S setup. Was using this calculator. Was using feet per minute as the units. Sorry if mislabeled it somewhere. https://www.omnicalculator.com/physics/piston-speed RB20 has a nice short stroke and a pretty good rod ratio. 1 Quote Link to comment Share on other sites More sharing options...
xsspeed Posted March 10, 2023 Share Posted March 10, 2023 where 4500fps come from then? for a 4gr with 77mm stroke at 10,000rpm youre looking at 25.6m/s, or 82ish fps Quote Link to comment Share on other sites More sharing options...
Roman Posted March 10, 2023 Author Share Posted March 10, 2023 It's just a number I pulled out of my ass to show a comparison of engine rpm at that piston speed. That was somewhere around max rpm for each of those types of motor. As it seems a more meaningful comparison than the other way around (comparing piston speed at a fixed rpm) And yes I see I labelled it wrong, should be FPM. 1 Quote Link to comment Share on other sites More sharing options...
xsspeed Posted March 10, 2023 Share Posted March 10, 2023 duh i should have just checked dividing it by 60 Quote Link to comment Share on other sites More sharing options...
xsspeed Posted March 10, 2023 Share Posted March 10, 2023 also you'll be pleased to know i went down a rabbit hole on engines last night, spotted a contender for someone to tap potential, for a nondescript v8 the 1urfse (lexus ls460) looks like it has potential to apply similar 1nz/4gr logic too assuming those things can translate, geometry is a bit more 2GR so not as rev happy with heavier pistons at 94mm, but 11.8:1 CR, D4S, RR of 1.77 2 Quote Link to comment Share on other sites More sharing options...
Roman Posted March 10, 2023 Author Share Posted March 10, 2023 Yeah another thing in favour of 4GR is keeping max torque down a bit so a J160 wont explode behind it. However that now seems a bit of a moot point that it'll need a gearbox adapter anyway. However it'll still be nice to use the J160 as it's got good ratios, and, I've already got some to use. I'd rather not go to a bigger heavier box if I can help it. 1 Quote Link to comment Share on other sites More sharing options...
Hyperblade Posted March 10, 2023 Share Posted March 10, 2023 Stick with J160, becoming more popular which is good for parts and some amount of crossover with other variations of it is good. It's a good box. And if worried about torque just do the fix the Silvia guys do something internal which I can't remember specifics of. 1 Quote Link to comment Share on other sites More sharing options...
HumberSS Posted March 10, 2023 Share Posted March 10, 2023 Throw some nice big rads on the bottom of inlet runners where it meets the base flanges for your final print, just to reduce the stress razors there. This is such a cool build, one of my favourite cars too. 1 Quote Link to comment Share on other sites More sharing options...
shrike Posted March 10, 2023 Share Posted March 10, 2023 6 hours ago, Hyperblade said: Stick with J160, becoming more popular which is good for parts and some amount of crossover with other variations of it is good. It's a good box. And if worried about torque just do the fix the Silvia guys do something internal which I can't remember specifics of. @Romanits the circlip mod as a base line 500nm or around 400hp, shotpeening is also involved https://neatgearboxes.wordpress.com/2014/04/16/nissan-silvia-s15-6-speed-gearbox-circlip-mod/ Neat do it over here but im sure someone in nz would 1 1 Quote Link to comment Share on other sites More sharing options...
GARDRB Posted March 10, 2023 Share Posted March 10, 2023 Just convert it to mild hybrid and use the alternatory/drive thing to start it rather than dicking around with starters. Then you can run KERS too Quote Link to comment Share on other sites More sharing options...
Stu Posted March 11, 2023 Share Posted March 11, 2023 Crank handle start... 6 Quote Link to comment Share on other sites More sharing options...
Rhyscar Posted March 12, 2023 Share Posted March 12, 2023 Loving your progress on this. Happy to provide 2gr doorts for motivation. They go REAL good 1 Quote Link to comment Share on other sites More sharing options...
keltik Posted March 12, 2023 Share Posted March 12, 2023 On 11/03/2023 at 11:21, GARDRB said: Just convert it to mild hybrid and use the alternatory/drive thing to start it rather than dicking around with starters. Then you can run KERS too Genius. A modern mans Lucas starter generator 1 Quote Link to comment Share on other sites More sharing options...
Yowzer Posted April 13, 2023 Share Posted April 13, 2023 The clear option for your valve issue is to throw the 4GR in the trash and run the 2GR, just as nature intended. 4 Quote Link to comment Share on other sites More sharing options...
xsspeed Posted April 13, 2023 Share Posted April 13, 2023 Keep going, I'm dreaming of 4gr altezza track hacks now What were valves like in the 1nz, obviously a small bore there too, was there any concern there? Yet again comparing this to rb20 (sorry) this is still a big bore, and 20s will happily rev high (maybe not make more power) so I'm guessing the engine characteristics of small light piston and rod ratio/short stroke count for more in pure rpm stakes, and the valves do enough seeing its smaller air volumes per stroke. Hanging out tonsee how this goes Looks way smaller with covers off! Edit: added pic of one of my rb20det heads, looks like 4gr valve setout was rb inspired puhuhu 1 Quote Link to comment Share on other sites More sharing options...
kpr Posted April 14, 2023 Share Posted April 14, 2023 2gr with 4gr crank. 4 Quote Link to comment Share on other sites More sharing options...
xsspeed Posted April 14, 2023 Share Posted April 14, 2023 would be interesting to see if you could, I'm guessing either the cranks are mounted higher in a 4gr or the piston compression height is significantly different between the two (or both) to account for such stroke difference. solution is only a custom set of rods away if need be Quote Link to comment Share on other sites More sharing options...
Yowzer Posted April 14, 2023 Share Posted April 14, 2023 That would give a sweet revving 3.2L. How much do ya reckon you could bore out the 4gr? Quote Link to comment Share on other sites More sharing options...
Yowzer Posted April 14, 2023 Share Posted April 14, 2023 I do like how the engine is barely in the car and we're already discussing extensive engine modifications 5 Quote Link to comment Share on other sites More sharing options...
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