Jump to content
SAU Community

Recommended Posts

They are as relevant as a 7000rpm limit on the std crank.

100% agree on the point you're making, but I'm trying to make a different one :)

my standard rb30 crank goes to 9000rpm no probs so yeah I really do understand what you're saying :(

Nice to see the 3.4lt project is coming along still.

Im just guessing, but if the compression heights are kept to a lowish 28mm and the custom rod length is about 152mm to suit the RB30 block, the rod ratio works out to 1.6:1.

I've just run a few numbers on my engine calculator and for a street application with a degree of reliability 8000 rpm would be the absolute upper limit (including a missed gear shift). 8500 rpm would be pushing the limit of what the rod bolts and pistons will tolerate and 9000 RPM will break a conventional designed forged pistons as piston speeds exceed 46m/s.

Also at 9000 RPM the acceleration away from TDC/BDC is 54.5 m/s ^2. Numbers like that are only seen in all out drag engines. ie... engines built entirely from top shelf custom parts the likes of carillo/pauter with wmc5 bolts and special piston designs. Titanium rods would go a long way to improving high rpm reliability as the rotating mass and rod big end loads are considerably less due to less inertia during the acceleration/deceleration phases of the engines rotation.

post-26553-1261660079_thumb.jpg

Nice to see the 3.4lt project is coming along still.

Im just guessing, but if the compression heights are kept to a lowish 28mm and the custom rod length is about 152mm to suit the RB30 block, the rod ratio works out to 1.6:1.

I've just run a few numbers on my engine calculator and for a street application with a degree of reliability 8000 rpm would be the absolute upper limit (including a missed gear shift). 8500 rpm would be pushing the limit of what the rod bolts and pistons will tolerate and 9000 RPM will break a conventional designed forged pistons as piston speeds exceed 46m/s.

Also at 9000 RPM the acceleration away from TDC/BDC is 54.5 m/s ^2. Numbers like that are only seen in all out drag engines. ie... engines built entirely from top shelf custom parts the likes of carillo/pauter with wmc5 bolts and special piston designs. Titanium rods would go a long way to improving high rpm reliability as the rotating mass and rod big end loads are considerably less due to less inertia during the acceleration/deceleration phases of the engines rotation.

Do you feel like running the numbers for a std stroke rb30 for a comparison?

They are as relevant as a 7000rpm limit on the std crank.

Well rob @ rips revs his engines past 11500rpm and this is with the factory rb30 crank and making over 1400hp. Need i say anymore?

Well rob @ rips revs his engines past 11500rpm and this is with the factory rb30 crank and making over 1400hp. Need i say anymore?

yeah I think you've missed the point aswel mate

my standard rb30 crank goes to 9000rpm no probs so yeah I really do understand what you're saying :)

For a few dyno runs, with lazy driving for 10k-km's or are we talking a SOLID 30,000km's with the ass wringed out of it for streeter duties/drag days? :(

There is a... sizeable lets say... difference between the two.

BTW - i know the point you are making, not covered in the above i know :P

Sorry but Im not so good at making graphs. Ive got one other table that shows piston speeds and acceleration through 360 degrees crank rotation, and the comparison of the tomei to the HKS kit is really very little when comparing the two engine setups. Really the 119.5 rod was only made as an option to allow the use of a thicker crown piston that uses a conventional RB26 30mm compression height. Its well known that the 2.8 kits are safe for 10k so I didnt bother calculating the 8500rpm values.

Ive attached the rest of the table. You might recall the Racepace 2.9 spaced block engine that used a 84mm crank and SR20 rods as well.

At 9000 RPM the piston acceleration for a RB30 is 47.5m/s^2.

The most important thing to keep in mind is the whole point of having a stroker engine is that you dont have to rev the hell out of the engine to make reliable power. That extra 400+cc of capacity will do for the RB30 what the RB30's displacement does over the RB26, if that makes sense.

The beauty of the larger displacement AND the shorter rod ratio is that while the engine doesnt need to (and shouldnt) rev as much as another type of engine, the faster piston accelerations from BDC and TDC mean better cylinder filling making for a more torquie engine. The cylinder pulls into a vacuum faster on induction cycles than a higher ratio motor will, so the engine breathes more efficently.

I agree with Marko's comment that there is nothing wrong with the strength of an RB30 crank. Rob @ RIPS certainly has proven that time and time again. I do wonder what kind of rods and pistons are in his 11,500RPM engine though, im guessing aluminium/titanium and some very fancy pistons. The inertia loading of chromoly rods and pistons at that engine speed would be increadably high. Acceleration factor of an RB30 crankshaft at 11500 rpm is 77.5m/s^2. That is a 1/2 again as much as the RB30 at 9000 RPM.

post-26553-1261665231_thumb.jpg

Ash I think it's just not coloured correctly?

Yes thats it. I always was better at maths than I was at art, especially past 12am.

New table attached.

post-26553-1261700716_thumb.jpg

Edited by GTRNUR

My point was that this setup was never designed to be a big rever.

It was designed to ( compared to the equivalent setup in an normal stroke RB30 ) to make considerably more torque, bring boost on earlier and make same power with less boost and less revs.

So if it makes the same peak power as my current RB30/25 with less boost and less revs, and more torque and comes on boost earlier - Ill be happy.

If it revs to 7500 rpm then it realisticly should make more peak power than my current setup as that is what Im revving it to now, due to the increase in capacity.

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now



  • Similar Content

  • Latest Posts

    • Ok i will get those 310mm. I found one but on a different site. This is the description on those...is it ok? Technical parameters: - Axle: front. - Disc type: ventilated. - Number of holes: 5. - Disc diameter: 310mm. - Total height with center: 54mm. - Thickness (new/min.): 30/28mm. - Designed for brake calipers manufacturer: Sumitomo.
    • You Gregged a whole racetrack!?
    • Look for broken wire or bad connector at the motor. Might not be it, but is worth starting there, as it is easy.
    • Hi everyone, I’m having an issue with my R32 GT-R. Sometimes, when the car goes over a bump or experiences some vibration, the 4WD warning light comes on the dashboard. When I check the code from the control unit in the trunk, it shows Code 19 – ETS Motor. However, everything seems to be working fine — if I turn off the engine and restart the car, the light goes away and everything functions normally. Has anyone experienced this before? Where should I start troubleshooting this issue? Thanks in advance!
    • I'm back from the dyno - again! I went looking for someone who knew LS's and had a roller dyno, to see how it shaped up compared to everything else and confirm the powerband really is peaking where Mr Mamo says it should. TLDR: The dyno result I got this time definitely had the shape of how it feels on the road and finally 'makes sense'. Also we had a bit more time to play with timing on the dyno, it turns out the common practice in LS is to lower the timing around peak torque and restore it to max after. So given a car was on the dyno and mostly dialled in already, it was time for tweaking. Luis at APS is definitely knowledgable when it came to this and had overlays ready to go and was happy to share. If you map out your cylinder airmass you start seeing graphs that look a LOT like the engine's torque curve. The good thing also is if you map out your timing curve when you're avoiding knock... this curve very much looks like the inverse of the airmass curve. The result? Well it's another 10.7kw/14hp kw from where I drove it in at. Pretty much everywhere, too. As to how much this car actually makes in Hub Dyno numbers, American Dyno numbers, or Mainline dyno numbers, I say I don't know and it's gone up ~25kw since I started tinkering lol. It IS interesting how the shorter ratio gears I have aren't scaled right on this dyno - 6840RPM is 199KMH, not 175KMH. I have also seen other printouts here with cars with less mods at much higher "kmh" for their RPM due Commodores having 3.45's or longer (!) rear diff ratios maxing out 4th gear which is the 1:1 gear on the T56. Does this matter? No, not really. The real answer is go to the strip and see what it traps, but: I guess I should have gone last Sunday...
×
×
  • Create New...