Rb26 Cams

[JH32]

I've asked this before but couldn't really get much of an idea as to what the benefits/downfalls are of having different cam duration on the inlet side to the exhaust side.

If you had an RB26 with a GT35 on it, and you put 264deg inlet cam and 272deg exhaust .... what pros and cons would you see? Other mods would be bigger injectors, AFM's, Power FC and all that sort of stuff.

Or is it better to go for same duration inlet/exhaust?

[Fitzpatrick Speed Works]

Tough question Jimih and its understandable why you havent had straight and complete answers. As a personal preference I dont believe in miss matching and have only seen benefits to it on lower level cars ie. 256 and 264!!! However I cant give you alot of definative answers as I have only done one car with differnent cams the ones I have already mentioned and didnt change to the same both side for a direct comparison. The advantage of this setup is suppose to be you can run a good size duration on the exhaust side to help your turbo spool and boost harder but not sacrifice idle and low down torque due to the smaller inlet side. This is good in priciple but the time you get into the higher numbers like 264/272 there is enough cam duration overlap to cause the "lumpiness" anyway, which is alway pretty minimal even up to 280's in a rb series engine. I dont think there are any real cons to the setup the only being on a 264 cam the biggest lift you can run is the JUN 9.7mm due to running any bigger the japs have found at the lower duration causes problems with the ramp rates on the cam, so if you are wanting more lift which does give more peak power you are limited wheras with 2 272 yu can run the big lift on both sides. Sorry dont know how much this has helped, but I dont want to talk on heresay!!

[Cubes]

My understanding is..

Say you had a 260 inlet 260 exhaust..

Drop a 272 exhaust in and it will give you more top end and smooth out mid range torque, make it easier to launch out of corners and give a little more throttle control. Basically make it softer.

Drop a 256 or something in the exhaust and mid range will ramp harder. Making it much harder to pull out of corners.

For example a race setup.

An experienced driver would possibly want the smaller exhaust duration as he has better skill through the corners and can control accleration better.

A noob will want the bigger duration exhaust as it will help him with regards to throttle control and help with a little more top end speed to make up for the slower cornering.

[JH32]

Guys thanks very much for the info, it is very much appreciated!

So from what you guys are saying, if I didn't want to go for too much lift and wanted to try to increase spool without sacrificing too much idle ... then I should perhaps try a 256 (or 260) inlet/264 exhaust?

I don't necessarily want to go too high in duration as I'm not aiming for huge horsepower or anything ... just something that will spool reasonably quickly and be a bit of fun on the street.

[Fitzpatrick Speed Works]

Sounds like a 256 odd and 264 combo would suit your requirements perfect!! As cubes said the smaller cams provide alot more punch mid range, however they will still be a hell of a lot etter than the standard item in top also!!!! Keep in mind also anything over 9.5mm lift will require head mods so to keep it simple and still get huge gains go a 262 or smaller setup it will also provide more mid range over a standard setup or a bigger duration setup which is important on a street car. Let me tell you a little secret, a high average power on a street car will always out perform a peaky car that might have more peak power. EG. a car with 70 odd horspower more from 4000-6000RPM and will always feel faster and be faster on the street than a car with 70 more horspower at 7500-8000RPM!!!! So your cam choice would be spot on!!!

[JH32]

Thanks again for the help s13drifter

I think I'll definitely go the 256/264 combo as that sounds as though it's going to suit my purposes. Hopefully it'll give me decent average power! I'll let you know how I go once they're in and it's tuned etc