Gain from cam gear Vs. gain from camshaft

[frankiman]

^^you fail at pic posting

[mikes_ca]

Pic doesn't work, anyways, post-cam tune hp was 489, pre-cam tune was 494, but torque increased from 389 to 407 with the cam tune. And the curve looks damn pretty, can't wait to drive it, in 5 months

Mike

[Skym]

Cams and turbo engines are slightly different to NA engines with cams. With cams on turbocharged engines, you have to take into account turbo.

Say you have a turbo or turbo's that produce full boost at 4000rpm and doesn't drop off until 7500rpm (peak hp) on stock engine. You find a cam that produces torque, hp to match turbo (4000rpm-7500rpm), which would be a 260 duration cam with 9mm or so lift on stock head. That's why some say those cams suit that turbo. Most tuners in Japan have worked this out, so sell turbo kit with cams, etc, up to 1000hp+.

Then say you add longer length extractors, upgraded intake design for race use, which shifts power to mid to high on stock engine. You design head to suit with oversized valves, larger ports, aggressive cams, etc, which gives engine more mid to high powerband. Can gain 100hp+ by doing this on a 2 litre 4cyl head.

On RB20DET, this gives you a 2000rpm or so powerband, so have to drive it like a diesel engine. Basically drop down to lower / correct gear to keep engine in the 2000rpm powerband. Same goes for dragracing, where holding onto gear (keep engine in powerband), not shifting up before 1/4 mile line produces a faster 1/4 mile. This dragracing trick applies to GTS, GTR, etc. Can go from low 11sec to high 10sec just by doing that with GTR.

Most cam manufacturers ask for turbo specs, runner length, diameter, etc when designing cams, as they play a role in where torque, hp is produced in powerband.

This is an example of what a cam manufacturer asks you to provide (info comes from engine builder that gives it to cam manufacturer) -

https://www.capella.co.nz/sites/kelford.co.nz/design-shop/

Factory aim for wide powerband and focus on bottom to mid range for daily driving. That's why turbo's are small and duration, lift is low on cams, ports, valves are smaller, exhaust manifold runners are shorter, etc.

Cam timing shift's the powerband. For example of HKS Vcam on a RB26 vs RB28 without Vcam, both running similar size turbo's, 264 duration cams -

http://1.bp.blogspot.com/_vhpEGyEVhes/TNDTTwynRSI/AAAAAAAACdM/BAFDs2gYWks/s1600/Vcam26+vs+28+-10.jpg

Get full boost alot earlier -

http://4.bp.blogspot.com/_vhpEGyEVhes/TNDTUbxUzCI/AAAAAAAACdU/jx7ASpDvBwc/s1600/vcam26+vs+28+-10+boost.jpg

Note the RB26 can have more hp, torque down low, but lose peak hp. Or can set it the other way, where you lose bottomend, engine takes longer to reach peak torque, hp, but gain more peak hp.

Or have more hp throughout powerband, as shown on this RB20DET dyno graph -

http://www.uniqueautosports.com/Dyno/yx32gtstdyno.gif

As shown in above link, adjusting exhaust cam gear gives engine more peak hp. Combined with adjusting intake camgear, gives engine more hp throughout powerband and full boost is produced earlier. I think that's without touching tune on ECU, where there are gains from playing with ignition timing, etc. Also done with stock cams.