Camshafts and how they work.

[NerdJuice]

Possibly a bad choice of title.

I'm looking to get some new cams and cam gears for my GTR, but I'm not exactly sure what all the numbers do when selecting a cam. I know how cams work, and what the lift and duration refer too, I'm just not sure how they'll effect the power band.

What would a larger duration or lift do? Lift? What's the maximum lift and duration a stock head can accommodate? Ideally I'd like a cam that gives more low-mid range gains then higher end.

Thanks.

[Skym]

From what I understand duration affects hp, lift affects torque. But both play a role in hp, torque.

With higher lift, more duration on both cams (Tomei Type-B cams), get more of a crossbow look at bottomend of powercurve. Once you increase boost level, this crossbow look at bottomend is more noticable. But to tell the truth, don't notice it too much by seat of pants. Also increase in mid range, higher rpm hp. Stock cams are more for a wide powerband and focus on bottomend to midrange, but still can be improved upon.

Factory cam specs (factory cams are similar with specs to Tomei Poncam Type-A cams, but Tomei cams are more aggressive) -

http://www.tomei-p.co.jp/_2003web-catalogue/e090_camshaft-specs.html

Also you need to match cam to turbo's on turbocharged engine. For example, turbo's produce full boost, peak torque at 4000rpm and say peak hp at 7000rpm and you select cams to match. Actually there's more to it than that, but that's basically what you do on a turbocharged engine. When the cam, turbo's work together, it makes the car very quick on racetrack.

I think once you go over 10mm? lift on GTR head, need to do some clearance mods. But someone else should be able to confirm the max lift before clearance mods need to be done.

You want Tomei Poncam Type -A cams, as mentioned in this link below and stock, N1, HKS GTSS, HKS 2530, Garrett GT2860-5 turbo's -

http://www.tomei-p.co.jp/_2003web-catalogue/e070_cam_RB26.html

Also cam timing plays a role in increasing boost response (builds full boost earlier or later, depending on how it's set) and where you want power, torque in powerband. Most stick to 0? or factory specs for camgears, as Poncams are like copies of stock cams, but with more aggressive specs, so work best with factory specs for camgears.

[NerdJuice]

Thanks Skym, there's a fair bit of info there.

I neglected to mention I won't be running stock turbos any longer. I have a pair of HKS GT-RS waiting to go in. Since they are larger I'd like to get them to spool quicker as I don't have a 2.8 or anything yet. So the type B would be better?

Also are they HKS cams any better or worse? I'm rather partial.

[Bignoga]

I have a set of hks cams if you need. BNIB

[Skym]

If HKS turbo, use HKS cams or similar spec aftermarket cams. I saw a HKS 2.8 with HKS cams in R34GTR a while ago with HKS GTRS turbo's. I'll see if they mentioned the cam specs. I think the 2.8 litre engine is matched to work with GTRS turbo's. HKS have gone to the trouble of working out cam specs to match their turbo's.

To get more down low, HKS sell Vcam (similar to VVT on stock RB25DET) that helps to produce more hp, torque down low (more than RB28 engine).

[Super_Dude]

A v-cam won't beat out a 2.8. Your best option is obviously going to be the most expensive. Look what dirty garage in australia with a 2.6 and gtrs's. He did a ton of head work and big cams. His powerband would put most to shame.

He is still missing lots of low end. It's a 2.6l l6. It doesnt matter what you do your not going to have much low end. Good headwork can make the mid range killer but it will still be gutless down low. Cams will male this worse.

[Skym]

Look at this dynochart of RB26 with HKS Vcam step 1, 264 duration cams (dotted line) vs Tomei RB28 engine (dash line) and both have similar size turbo's -

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

Boost -

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

Note RB26 has more down low, but less up top (due to way Vcam is set and extra capacity helps).

There are hp gains with VVT. It's one of the reasons why RB25DET is better with bigger turbo's than RB20DET. Even R35GTR engine benefits from it with more hp down low.

HKS Vcam + RB28 + HKS GTRS turbo's = best combo.

[Super_Dude]

The rb28 is running -10's and the vcam car is running 2530's. If they both had the same turbos, the 2.8 would win. Rb30 would kill either

[NerdJuice]

*eyeroll*

I'd definately love a V cam but I don't know if it's worth the $4k +. I'm all for buying quality parts but about a months income for just an intake cam is a bit much.