Rb26 Cam Choice

[Brezza]

Hi guys,

Basically my current setup i'm pushing around the 360rwkw at 24psi on E85

Mods are:

forged pistons

std conrods

race bearings (main & conrod)

R33 GTR crank

recond head

STD cams

2860-5's

MINES dump pipes

aftermarket front pipe

3in decat & cat back with a 3.5in muffler

1000cc injectors

2x 500hp walbro fuel pumps intank

upgraded fuel lines running to a larger fuel feed to supply the extra volume needed for e85

Nistune ECU

Nismo AFM's

ARC 70mm intercooler

K&N air filter in STD airbox

the car has great response, pulls very hard when on boost, but the dyno graph seems to flatline up high in the RPM

the tuner has tried opening up the airbox but that makes no difference.

the boost doesnt seem to hold at 24psi right through the rev range, it trails off to 20psi

the tuner originally thought it may have been the STD intercooler i had which was limiting power, but when i changed to the slightly larger ARC one it made no difference.

the tuner suspects that it may just be at the limit of the STD cams, people have said its the 3in exhaust but the tuner is certain that the 3in isnt the issue, as he's had cars with a 3in exhaust push 450kw

so now i've been looking at drop in cams and have come accross the following:

Tomei Poncams type B 260degree, 9.15mm lift

HKS stage 1 272degree, 8.7mm lift

camtech cams 272degree, 9.7mm lift

kelford cams 272 degree, 8.95mm lift

they're all roughly the same price for 272 cams, all about 800-900 bucks.

I know the tomei ones are drop in and require no spring changes.

but the others being longer duration and different lift some places are saying that you need titanium springs and retainers, which is adding another 500 to the price.

i am just wondering whether from people's experience what duration and lift is the maximum you can go on std springs and retainers, so basically i am saying a true drop in cam.

my tuner says that as long as you stay under 10mm lift you'll be fine with std springs, but the ramp rate does play a part because it can put more pressure on the spring and some say that the harmonics of the springs can cause power loss at certain points??

i know 272 is very different to a 260 or a 264, but i do want that lump in the cam and i do also want the added performance of a better breathing cam.

[dorifticon]

Leaving aside the issue of spings etc, remember that you need enough physical room in the cylinder head casting to swing the cam lobes.

I think 10mm lift is getting close to the limit, if not over already. Mine are 10.5 mm and need to modify the cam tunnels (ie remove the lip on the edge of the cylinder head where the cams sit).

I don't think it's feasible to swing a die grinder around with the head still attached to the motor so might be something to think about.

[R31Nismoid]

I'll say this first before the rest, cams will not fix your problem.

Read on if you want to know why, as it has nothing to do with cams, otherwise go with what you've been told.

E85 is masking the exhaust restriction just like race fuel does.

I have the same setup as you, but make more power on 5psi less and on PULP.

Difference? 3.5" exhaust.

I'm even using the stock cooler as are most other people making 360-380, no problems at all. To say it was the cooler is poor advice, which you've now seen first hand was plain wrong.

IMO that's two strikes for that tuner (cooler/exhaust), go somewhere else.

You also didn't need upgraded fuel lines so i hope that wasn't more bad advice and the 3rd strike...

[choyda]

If or when you look at cams, Jun make them too.

[Brezza]

I'll say this first before the rest, cams will not fix your problem.

Read on if you want to know why, as it has nothing to do with cams, otherwise go with what you've been told.

E85 is masking the exhaust restriction just like race fuel does.

I have the same setup as you, but make more power on 5psi less and on PULP.

Difference? 3.5" exhaust.

I'm even using the stock cooler as are most other people making 360-380, no problems at all. To say it was the cooler is poor advice, which you've now seen first hand was plain wrong.

IMO that's two strikes for that tuner (cooler/exhaust), go somewhere else.

You also didn't need upgraded fuel lines so i hope that wasn't more bad advice and the 3rd strike...

to do the 3.5" exhaust, did you do it from the merge of the front pipes of just cat and cat back?

i've been quoted up for a 3.5in piping cat back which is $600, this still uses my 3.5in muffler.

the fuel lines weren't upgraded, just a second feed to the engine from the tank. most cars on e85 here have the surge tanks and twin 044's running 2 lines to the fuel rail.

the second feed is the same thickness as the std line and runs next to it.

i've probably gotta look at doing the exhaust before i spend money on cams and find i've just wasted more money.

[R31Nismoid]

Needs to be 3.5" from the merge of the front pipes, after the cat isn't enough. Gotta be 3.5 the entire way.

How big are the front pipes?

[Brezza]

I'm not 100% sure?

it was on the car when i bought it, and i've never gotten around the measure them.

I'm trying to tee up with the exhaust bloke to maybe enlarge the merge if needed?

i think from memory it merges larger than 3in and tapers down to 3in at the flange to the cat.

I'll have to measure the front pipes when i get a chance.

what would the front pipes need to be diameter wise? 2.25 or 2.5in

[Brezza]

Update on this:

have bought some Tomei Poncams type 'B'

and also have the caar booked in next week for a 4inch cat back system.

the front pipes are decent, 2.75in twins to a 4in merge.

currently the front pipe exits at 3in and its 3in cat back.

so it'll be 2.75in off the turbo's and 4in from the merge back!

i'll be getting the car dynoed before the cams go in, just to see if it really made any difference. as i havent changed anything else.

then the cams will go in and hopefully the car will pull 500+hp

[Piggaz]

I'm going with the exhaust too small aswell. 3 inch is nothing and it seems to be one of the biggest factors in poor results with these things. Make sure the mufflers don't 'taper down' to something silly like 2.5 inch inside!

[GTR_JOEY]

Agree on the exhaust as well... I'd be willing to bet that the 3 inch diameter was ur problem

3.5 would just be a pass mark

[Piggaz]

Going from 3.0 3.5 is almost 36% more area inside the pipe. Going to a 4 inch is close to 80%.

[Brezza]

The muffler that is going on will be 4in internal diameter.

its going to be made up, not some off the shelf item.

i'm really curious to how it will sound with a bigger exhaust too.

the 3in sounds like its full when at WOT.

fingers crossed for some good gains!

[luke gtr]

Quick question, how good are the standard valve springs?

Little parrallel to topic, and I'm looking to make some decent power soon, which will entail more boost.

If anyone can help, cheers.

[TiTAN]

if they are crap you will see valve float. if you are getting valve float turn the boost down or change the springs.

[Brezza]

i think most of the time, the std springs are fine for poncams.

they're usually needed for high lift cams. 10mm or more?

correct me if i'm wrong.

[livewire]

Very interested to see how this turns out

[luke gtr]

if they are crap you will see valve float. if you are getting valve float turn the boost down or change the springs.

That's what I was wondering....

How crap are they?

What boost and/or power level are the standard cams and valve springs good for?

[GTR_JOEY]

That's what I was wondering....

How crap are they?

What boost and/or power level are the standard cams and valve springs good for?

correct me if im wrong but the standard valve springs are pretty good, they get a bit tired after a while as all engine components do

there are alot of stock heads pushing 350rwkw and reving to 8 and past that even.

Like whats already been stated ur goin to know if theyre not working properly as valve float will show up at the top end of ur power curve on a dyno graph

as for standard cams, they too do a pretty good job up to and past 350rwkw... gains are to be had by changing them out at this stage of tuning though some people are content with just some aftermarket cam gears with a bit of adjustment

[luke gtr]

correct me if im wrong but the standard valve springs are pretty good, they get a bit tired after a while as all engine components do

there are alot of stock heads pushing 350rwkw and reving to 8 and past that even.

Like whats already been stated ur goin to know if theyre not working properly as valve float will show up at the top end of ur power curve on a dyno graph

as for standard cams, they too do a pretty good job up to and past 350rwkw... gains are to be had by changing them out at this stage of tuning though some people are content with just some aftermarket cam gears with a bit of adjustment

Cheers, thats the kind of info I was after.

Will help heaps.

[KiwiRS4T]

Update on this:

have bought some Tomei Poncams type 'B'

and also have the caar booked in next week for a 4inch cat back system.

the front pipes are decent, 2.75in twins to a 4in merge.

currently the front pipe exits at 3in and its 3in cat back.

so it'll be 2.75in off the turbo's and 4in from the merge back!

i'll be getting the car dynoed before the cams go in, just to see if it really made any difference. as i havent changed anything else.

then the cams will go in and hopefully the car will pull 500+hp

That will be great - you will be doing a lot of people a favour if you make one mod at a time and dyno after each - you may need to touch up your tune after doing just the exhaust to account for the extra flow. Looking forward to seeing the results - my money's also on the exhaust doing the most but always ready to be proved wrong by hard evidence!