3071r, Cams, Cam Gears - Results Now Posted

[Simon-S14]

hey guys, ive installed some cams in my rb25 in the hope to bring on a stronger midrange, however once dyno'ed and tuned up the results were the opposite to what i was after, Peak power went up by 20 rwkw, and midranged suffered... however with a bit of tuning we were able to get the midrange back up to where i was before with the stock cams, so i hadnt lost anything.

It was then decided to get cam gears and chuck them on and retune it, was waiting for the weather to cool down a bit before we retune but should be tomorrow night. I want some insight as to where we should be looking to go with the cam timing to get the results i wanted. As my car is used for drift, a broad midrange powerband is much preferred over a dyno queen style set up. VCT has gone also.

Now im no expert, but it looks like according to this sheet that the cams have a different base circle to stock RB25 cams, so as they sit, the intake is currently 10degrees retarded anyway and the exhaust 4 degrees advanced.

stock cam specs

http://www.tomei-p.co.jp/_2003web-catalogu...haft-specs.html

So anyway, any thoughts on which was we should go with the cam gears?

Edited March 10, 2008 by Simon-R32

[rev210]

My tip is to tune for the 3000 - 5500 rpm range first and disregard any power drop off up top initially.

Most people seem to go and tune cams and shoot right away for top end and work down.

The first cam to play with is the intake cam. The advancing of the cam timing increases the cranking compression, this increase is the reason (part of) why you can gain more mid range/earlier boost response.

Really try to nail the turbo's full boost rpm.

the basics I work off;

* Advancing the intake cam moves the valve closer to the piston (be careful- not too far) and as a result you get increased cranking compression. You end up with better bottom end power. The peak magnitude of power changes is centred around really the peak of the hill (one spot) but, kind of moves the whole hill under it. You advance and generally the power peak moves down the rpm range, to a point. I think you find due to the relation to cranking compression , things like turbos airflow/boost characteristics make it slightly more tricky and effect which way you go from 0 -or+ and how far.

* Retarding the exhaust cam moves the valve closer to the piston (be careful not too far) it tends to effect power more generally over the entire curve. But to less magnitude than the intake changes do. The exhaust cam setting is more of a mystery to me (someone may be clever enough to help here) sometimes advanced sometimes retard.

* Tune at an initial boost a little lower than you want to end up at. Tune for increased boost later.

* Dial in and advance/ retard intake cam first , then the exhaust cam.

* I think the idea with the bigger cams , is 'not' to assume they need more overlap like the stockers 2+adv and -4/-6 exh, they have bigger overlap out of the box anyway. Thats why I think the stock cams need help and they are too small. being designed with some sort of emissions in mind compromises them in this way.

[blind_elk]

Isn't VCT so you get the best of both worlds - good mid-range AND top end? So if you disable VCT, you lose mid-range?

Standard spec cams (R33 RB25DET):

Inlet: Duration 240 : Centreline 120 : Open TDC : Close 60 ATBC

Ex: Duration 240 : Centreline 117 : Open 57 BBDC : Close 3 ATDC

Overlap 3

LSA 118.5

[Simon-S14]

thanks for that mate, has given me something to work with, I have set the intake 4 degrees advanced and exhaust 4 degrees retarded, rather then setting them both at zero then having my tuner spend time pulling them apart and setting it up anyway.

So taking note of what you have said, i'll go set the exhaust back to zero and go from there.

[rev210]

yep. set exhaust at 0. The muck around you have is really with the ignition timing for each setting of the intake cam. I think this is related to the compression changes the intake cam effects. You want more timing to bring the turbo action in earlier but, it's striking the balance between what you are safely able to run at different cam positions.

It's a good idea to really focus the tune on the 'bottom end/mid' and even go as far as to say to the tuner you don't give a rats behind about the top end, even if it decides to take a big drop. Fix that later, it's pretty easy to do. You need to make it crystal clear as most of the guys who walk in are chasing a bigger number. These are the guys I find make up the back of the field on race days.

Edited March 9, 2008 by rev210

[rev210]

oh and be prepared to advance the exhaust cam, it's not always retarding that works best.

[Simon-S14]

thanks mate, yeah my tuner knows what i want, but the fact is it still makes plenty of peak power, while we havent even really pushed for big numbers.

I'll post results when i get them anyway, but thanks for your help mate.

[rev210]

No worries dude. Best of luck with the tune

[Simon-S14]

Just got back from a late night dyno session, massive thanks to Jeff from the Speed Lab for going out of his way to do it all for me!!! anyway after some stuffing around, debating and theory... and some backwards runs. we finally got some results.

intake was set to 5degrees advanced (5 degrees on the cam is 10 on the crank) and the exhaust cam was retarded by 2 degrees. the difference was then huge, made more power everywhere in the revrange but drop a small amount in the peak power. which is just fine by me as thats what i was after,

lo and behold... the results!

not bad for 600 bucks all up spent on cams + gears and other things.

This graph is with stock cams, 20 psi its vrs the stock turbo also.

Edited March 11, 2008 by Simon-R32

[NYTSKY]

Wow thats a nice improvment.Name brand cam gears?

What cams are in there?

[rev210]

Thats a great gain there.

[wolverine]

looks like 15-18% down low gain. that should feel better using the seat-of-the-pants dyno.

[Simon-S14]

you bet! it spools earlier and just hauls now... then around 4500 rpm it starts pulling even harder.

previously i had no wheel spin (due to a very well set up car and sticky tyres) but now its starting to turn the tyres!

[Dale FZ1]

Very creditable results; that shows as +20kW through a large part of the range.

Does it show itself as extra response driving into full load (ie boost), or mainly once you're there?

edit: bit slow to post, looks like question answered.

Edited March 10, 2008 by Dale FZ1

[BHDave]

Nice result.

Out of interest, was it the inlet or exhaust that had the biggest effect on the curve? And what did adjusting the exhaust side do to the overall shape (seeing as i only have an adjustable exhaust wheel and retain vct)?

[PHaT MR30]

Good work simon! ive been waiting for these results!

This was still with the 25 bottom end? and standard exhaust manifold?

What type of cams are they?

[toffy]

nice mate, have you got graphs of before cams and gears ? would be interesting to see the difference between the three

[BOZ22N]

Nice result

[joeyjoejoejuniorshabadoo]

so the 3lt bottom end is a no no and this is the answer now?

[Simon-S14]

hey guys, i'll post up a graph from a run when i first had the 3071R fitted, we ran 20 psi through it and it made 283 rwkw, but you can see how slow it is to build boost and how little midrange there is. Scroll up ive posted it in with the other dyno graph. BTW the dyno last night was done in a 39 degree dyno room... due to our crappy heat wave adelaide is having atm...

JoeyJJJJ: 3L bottom end still being built on the side, if the 25 pops i'll chuck the 3L in... but not a moment sooner haha.

Just to clarify, the turbo is the cropped version, rb25 is a 100K km stock motor which has had plenty of thrashing from me with it, perfect health so far, stock intake manifold stock exhaust manifold also. Running a RB20 ecu remapped by what i can only call a nissan ecu GURU here in Adelaide.

Cheers for the comments, the difference is certainly noticeable!

Edited March 11, 2008 by Simon-R32