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cams/cam gears help please

fatz
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Mik Experienced

Mik

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I am running GT-RS turbines on my stock RB26. My turbos would be a fair bit bigger than a single GT3540.

I was originally running standard cams with vernier cam gears. I found that the best response was acheived with 0 degree timing for both inlet and exhaust. With this setup, the best I could achieve was 1.3 bar at about 5500-5600RPM.

I then dropped in a set of PONCAM type B cams (still running at 0 degrees in and ex). I now have 1.4 bar at about 5200RPM.

With the cams, I have definately lost a bit of power under about 3500RPM, but 4500-5000RPM, seems to be a bit better and MUCH better from 5000-8000RPM.

I reckon just spend the money on the cams and don't bother with the gears.

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fatz Grand Master

fatz

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  • Author
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cams as boost response

engine/turbo: rb26/ gt3540 (xr6t turbo)

response: comes on about 4000rpm and relly nails you at 5000rpm

basically ive spoken to a few peopl and heard a few things in regards to cams and cam gears

lots of people have said cam gears to bring it on earlier ($500)

but with cams there has been mixed oppinion ($990)

basically im looking at a set of tomie poncams spec b( say they bring one large turbos earlier)

so basically anyone willing to confuse me more please do

should i just get the pon cams

or should i just get the cam gears

or should i get both

help please

car currently makes 270rwkw at 1 bar(stock computer stock injectors)

note: there is a power fc and injectors inthe wings as well to tkae ful advantage of the cams

pete

Amaru Veteran

Amaru

Posted
Posted

Get both... im only running 2530's but the difference the cams made was amazing. Power seemed alot stronger through the whole rev range, and response was increased quite alot too. Definately the best bang for your buck mod I have ever made to the car. I got Tomei Poncam B's (260 in/ex) and Tomei cam gears.

Mik Experienced

Mik

Posted
Posted
freaky i start the thread and im the third post

so sound like tomi brings it on abit more

a proper tune would probably help to

got a mines standard computer tune now so ill see if that make a diffrence tonight

yea baby

The cams definately bring it on a bit quicker...just don't expect a miracle.

A stroker kit or even 87mm bore and higher comp would make a difference too.

Freebaggin Proficient

Freebaggin

Posted
Posted
I am running GT-RS turbines on my stock RB26. My turbos would be a fair bit bigger than a single GT3540.  

I was originally running standard cams with vernier cam gears. I found that the best response was acheived with 0 degree timing for both inlet and exhaust. With this setup, the best I could achieve was 1.3 bar at about 5500-5600RPM.

I then dropped in a set of PONCAM type B cams (still running at 0 degrees in and ex). I now have 1.4 bar at about 5200RPM.

With the cams, I have definately lost a bit of power under about 3500RPM, but 4500-5000RPM, seems to be a bit better and MUCH better from 5000-8000RPM.

I reckon just spend the money on the cams and don't bother with the gears.

Great info Mik, there is a distinct lack of info on cam upgrades on this forum so thanks.

Do you have dyno charts showing the difference between the stock and Tomei cams? If not do you know the numbers.

The Tomei website say themselves that with Poncams there is no need for cam gears with Poncams as they optimised them at 0°/0° timing.

fatz, the fact is, you've got a big mother of a turbo with a 1.06 A/R exhaust housing and there is bugger all you can do to bring the turbo on earlier.

You'd be better off focusing on spreading power across the top end to give as broad a power band as possible, much easier to do than trying to beat the laws of physics. Cams would prob be the best way as the other guys have said, and just keep the revs up.

I currently have stock cams with exhaust only adjustable cam gear but I wanted to get more top end and a broader spread of power. It worked with 10rwkW more but a far better feel up top with more power overall.

I now have a set of Tomei Poncams for my RB25DET that I haven't installed and I am looking to get more grunt but more importantly get a broader spread of power. The website says it will help spool up a bigger bolt on turbo but I'm not sure the effect is gonna be that signifincant, I think from maybe 3200rpm there will be a difference up to I hope 7500rpm.

Amaru Veteran

Amaru

Posted
Posted
The Tomei website say themselves that with Poncams there is no need for cam gears with Poncams as they optimised them at 0°/0° timing.

From my limited understanding, thats true for GTST but the RB26 cams benefit from adjustable cam gears.

Mik Experienced

Mik

Posted
Posted

Unfortunately, I don't have before and after dyno plots, because most of my tuning has been done on the road.

The only reason we did the final tune (after the cams) on the road was because it was getting very hard to tune the top end on the street!

The dyno we used is pretty pessamistic (260kw@4 wheels) was good enough for a 120mph trap speed in a series 3 R33 GTR.

With a bit more tuning, the car now makes 290kw on this dyno. I haven't had a chance to run it at the drags yet.

Here are a few numbers:

RPM BOOST(PSI) POWER(kw) TORQUE(nm)

4200 10 114 374

4500 11.4 132 410

4700 13.8 158 470

4900 16.1 185 527

5200 19.3 230 614

5300 20 242 628

5800 19.7 253 608

6500 19.6 281 600

I have a reasonable spread of torque now. Above 595nm between 5100 and 7500RPM

Yorik Community Regular

Yorik

Posted
Posted

I am hoping to fix the lack of Cam info on these forums over the next few months. Wiht my previous engine (SR20) I ran PONACAM's and I measured a nice imporvement over the whole rnage with GTech Pro Comp.. I will be doing the saema long with Desktop Dyno simulations.. but I will be going with a set of low duration high lift PROCAM's on my RB26. Hopefully I can prove that the extra dollars you pay for Tomei equipment is worth it in the mid range..

I don't know how mnay people will benefit from it, but I know that my work on the SR20, made a lot of interest in the SilviaWA forums.. I enjoyed the PONCAM's, but I will be going more 'insane' with the RB26 as I live on strange roads and I believe that mid range torque hold the key to fun up heere, so I am lookinf gor as much lift as I can get..

Hoping to help......

lwells Grand Master

lwells

Posted
Posted
From my limited understanding, thats true for GTST but the RB26 cams benefit from adjustable cam gears.

From reading SydneyKid's posts about Tomei Poncams, that's my understanding too. RB25DET Poncams are usually spot on, whereas RB26 Poncams definately require adjustment. IIRC SydneyKid recommends camgears for both regardless (because no two engines are alike).

LW.

Yorik Community Regular

Yorik

Posted
Posted

Well I am more keen on lift then duration, so I am more inclined to take the 260 deg in/ex with 10.85mm lift, of course this also means that I ahve to change to solid lifter, valve springs, retainers as well as my base diameter changing.. I will also be fitting a metal head gasket, Kevlar timing belt, oil restricter and other associated guff at the same time.

Uncomplicated, simplistic view on cams..

An increase in Lift will give mid range and good strong torque, where as increase in duration will create more power but higher in the rev range, generally at the sacrifice of low rpm power and stability..

If you want to know more, I suggest research, and also the program Desktop Dyno.. Create an RB engine block from details widely available and then swap different cam profiles in and see what happens, I did this for my SR20 and I put around 40 or so different cam profiles into the program so that I could tell what sort of Torque and Power curves I coule expect.. From this, along with financial constraints and nto wanting to remove the head, I chose the Tomei PONCAM...

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