Cam Choice For 500Kw Rb26

[BMYHOE]

Forget high compression if you want big boost... waste of time. The small amount of hp you will make lower off boost will not offset the amount you could make by winding the boost up further and not having any issues.

Lower compression and no quench for big power and high boost.

id rather higher CR with lower boost.

of course you need a good tuner & E85 to make it work

it is a street car so this thing would be so much better to drive with higher CR...

Edited October 9, 2012 by BMYHOE

[WMDC35]

try kellfords, see what they recommend?

[Sub Boy32]

I bought a set of Kelford 280 10.55mm lift cams, They do them as an off the shelf item. My turbo isn't anywhere are big as yours (B/W EFR 8374 .91a/r) and make 460kw at the hubs, full boost (20psi) at 3400rpm, it is a RB30 however.

Edited October 9, 2012 by Sub Boy32

[rob82]

Forget high compression if you want big boost... waste of time. The small amount of hp you will make lower off boost will not offset the amount you could make by winding the boost up further and not having any issues.

Lower compression and no quench for big power and high boost.

Well that's definately a different way to look at things.... When was the last time a high performance car manufacturer reduced compression ratio or quench in a newer model?

Higher compression will make the engine more efficient everywhere. Now couple that with a highly knock resistant fuel and you will have a good engine. You need to look at your compressor map and see where the turbo needs to run and then choose the compression ratio based on the fuel and boost you need to run.

[GTR_JOEY]

I bought a set of Kelford 280 10.55mm lift cams, They do them as an off the shelf item. My turbo isn't anywhere are big as yours (B/W EFR 8374 .91a/r) and make 460kw at the hubs, full boost (20psi) at 3400rpm, it is a RB30 however.

Why only 20psi mate?

Is that in E85?

How have you set your cam gears up? Response/power

I only ask as I'll be having me 83/75 tuned very soon

[jet_r31]

to the thread starter ..thats a lot of turbo for 500rwkw..lol

cheers

darren

[Lithium]

Just because it seems it can be months between Sub Boy's posts (sorry Chris if you pop back in soon) his car is on 98, and 20psi was a limit they hit with the internal wastegate setup.

[GTR_JOEY]

Ah ok

Cheers for that Lith

[bigmikespec]

Well that's definately a different way to look at things.... When was the last time a high performance car manufacturer reduced compression ratio or quench in a newer model?

Higher compression will make the engine more efficient everywhere. Now couple that with a highly knock resistant fuel and you will have a good engine. You need to look at your compressor map and see where the turbo needs to run and then choose the compression ratio based on the fuel and boost you need to run.

You answered your own question... OEM's are tight quench, high compression engines for a whole bunch of reasons not directly related to big horsepower. Efficiency across the whole rev range, emissions, etc

In terms of making big horsepower in a boosted application it is far from different. No quench and lower compression (lower is very subjective) and obviously high boost pressure is favoured.

I can see the appeal that the OEM's go for and also what others do on here with their builds; but for 500kW throw that approach in the bin.

[scotty nm35]

I totally agree Michael, there comes a point where you have no choice but to lower compression, high cylinder pressure will kill your engine very quickly.

After modeling a few high comp builds with my tuner just last night, I can say that a 500kw engine must have low compression to survive, no matter what fuel or internals you run. I wish it weren't the case but cylinder pressure rises exponentially with power.

[Lithium]

I wish it weren't the case but cylinder pressure rises exponentially with power.

What were you using to "model" different engine setups? My understanding is (no doubt could be wrong... but I'd like to be convinced on that fact) that it actually doesn't increase exponentially at all. I would have thought it would take no time to blow a motor up when increasing power if it did. There are ways of gaining torque without (or hardly) increasing peak cylinder pressure.

[rob82]

You answered your own question... OEM's are tight quench, high compression engines for a whole bunch of reasons not directly related to big horsepower. Efficiency across the whole rev range, emissions, etc

In terms of making big horsepower in a boosted application it is far from different. No quench and lower compression (lower is very subjective) and obviously high boost pressure is favoured.

I can see the appeal that the OEM's go for and also what others do on here with their builds; but for 500kW throw that approach in the bin.

What would car manufactures know about building engines.....

Every new model needs to make more hp, less emissions and better fuel economy. Changing to a higher compression ratio is not an easy change considering the extra thermal loading on turbo chargers and catalytic converts coupled with the potential for higher NOx levels and less resistance to knock. They usually run high quench zones to promote central flame propegation and the fact that detonation usually propagates at the outer edges of the chamber. Look at the 335ci engine or L3T mazda engine or VW golf they are all running high compression ratios couple with Direct injection.

Now when you have a higher octane fuel - in order to achieve the full affects of a highly knock resistant fuel is to increase the compression ratio. I dont see the point of running "big boost" when all your doing is running the turbocharger outside of its effciency range.

And average cylinder pressures dont increase expotentially with power... You would probly find that a well setup 400kw car would have similar cylinder pressures to a 500kw car, its just the 500kw car has higher cylinder pressure at a higher rpm.

[bigmikespec]

What would car manufactures know about building engines.....

Every new model needs to make more hp, less emissions and better fuel economy. Changing to a higher compression ratio is not an easy change considering the extra thermal loading on turbo chargers and catalytic converts coupled with the potential for higher NOx levels and less resistance to knock. They usually run high quench zones to promote central flame propegation and the fact that detonation usually propagates at the outer edges of the chamber. Look at the 335ci engine or L3T mazda engine or VW golf they are all running high compression ratios couple with Direct injection.

Now when you have a higher octane fuel - in order to achieve the full affects of a highly knock resistant fuel is to increase the compression ratio. I dont see the point of running "big boost" when all your doing is running the turbocharger outside of its effciency range.

And average cylinder pressures dont increase expotentially with power... You would probly find that a well setup 400kw car would have similar cylinder pressures to a 500kw car, its just the 500kw car has higher cylinder pressure at a higher rpm.

But they are not building race engines... they are producing OEM products with strict guidelines, regulations and laws.

If you choose your turbocharger poorly then yes you might be outside its efficiency, not if you have a compressor map and can design the package effectively.

[scotty nm35]

What were you using to "model" different engine setups? My understanding is (no doubt could be wrong... but I'd like to be convinced on that fact) that it actually doesn't increase exponentially at all. I would have thought it would take no time to blow a motor up when increasing power if it did. There are ways of gaining torque without (or hardly) increasing peak cylinder pressure.

It was an engine design engineering application, not sure of the name but it calculates accurately if modelled correctly. We were hoping to run 11:1 on a 2.5L VQ, at any more than 15psi the cylinder pressure would spike. Power was made more easily with the compression at 8.8:1 with lower cylinder pressures. As we are designing it for track we decided lower compression was a must and turbo response less critical. Street applications you could argue the opposite I guess.

Increasing the engine capacity was the easiest way to increase torque and power output without affecting cylinder pressure, but we are trying to keep it under 2.5L, and looking for 700hp+.

[BMYHOE]

I guess your best to talk to your engine builder & tuner on the compression ratio and whatever he / she is comfortable with

[brad 110]

Rob 82 is all over it. Have a look at your Dyno graphs how many of these graphs maintain targeted torque values. Lets say the engine can withstand 850 nm then how many of these tuned engine generate that targeted torque then maintain it to the rev limiter. Who says these high comp engines need to run 25 psi at 4500. Map the boost if you don't have flyby wire throttle mapping to maintain the cylinder pressure the engine will cope with happily. If this requires 17 psi at 4500 increasing to 30 psi at 9000 who cares nor will the engine!! Assuming we are using the fuel of quality that rob82 suggests then 11:1 and boost is no issue.

[BMYHOE]

+1 ive owned a 8.5:1 400Kw RB30 & 9.5:1 500kw RB30

and all i can say is the 9.5:1 is so much better to drive in every way on the street.

[Tyranus]

Thanks for the great information fella's. Will be bringing up the CR topic with mech and we'll go according from there on. I'll be updating my build thread cheers.

[Lithium]

We were hoping to run 11:1 on a 2.5L VQ, at any more than 15psi the cylinder pressure would spike. Power was made more easily with the compression at 8.8:1 with lower cylinder pressures. As we are designing it for track we decided lower compression was a must and turbo response less critical. Street applications you could argue the opposite I guess.

The cylinder pressure spike would be (if it is a good simulation) detonation - that'd be due to being octane limited. Cylinder pressure would go up exponentially if you went driving past the point of being knock limited on the mission for more power, but gaining power using controlled combustion should not be anywhere near exponential.

[bigmikespec]

Assuming we are using the fuel of quality that rob82 suggests then 11:1 and boost is no issue.

Sure you will run boost... how much based on the fuel is the limiting factor.