Rb30/26 Cam Selection

[danny14]

If you are using a GT35R with the 0.8 (ish) housing and a 3.5" exhaust then you are wasting $6k... sorry. Exhaust back pressure will be too high to take advantage of cams with overlap. I would also forget about any cams that have increased duration over stock with what ever you get done.

I would have bought a gearbox with an OS Giken gearset for that money.

So are you saying exhaust is to small ?

[danny14]

Who else agrees with above ? ..........

[bigmikespec]

Yes, but that is not the overall issue... the whole exhaust side including turbocharger will be too small.

The problem is you will have way too much engine for the turbocharger you have selected, you will end up having high exhaust back pressure relative to boost pressure and with the duration camshafts you are thinking about you will end up having reversion.

To take advantage of the 'blow down' effect (i.e. 1:1 ratio of exhaust manifold pressure to boost pressure) you need bigger turbo, bigger exhaust housing, an engine built to rev high (as most of its life will be above 5000-6000rpm if it is an RB).... then you can spec some longer duration camshafts with some overlap.

If it was me, RB26/30 with the turbocharger you have, E85 so you can screw as much into the turbocharger as possible with a stock RB26 head (just get rid of sharp edges and unshroud valves in combustion chamber) and spend $6k on your driveline!

[Piggaz]

^^^ because you'll need it. Driveline's ain't cheap...

[bigmikespec]

Who else agrees with above ? ..........

Lol, it is not a matter if how many agree... It is a fact that it will be the case. Some reading on subject would help.

[Piggaz]

As above, with big Micky. No need for a cam that will spin to a million.

A - you're limited in revs (7250 RPM)

B - it's a street car/circuit car. Area under the curve wins.

Micks RB30 with 250 poncams does NOT fall over on an RB 30, what's the point on going more duration when they will let you make more power higher in the rev range.... You'll never get there (with your rev limit) and will only hurt bottom end.

[danny14]

Yes, but that is not the overall issue... the whole exhaust side including turbocharger will be too small.

The problem is you will have way too much engine for the turbocharger you have selected, you will end up having high exhaust back pressure relative to boost pressure and with the duration camshafts you are thinking about you will end up having reversion.

To take advantage of the 'blow down' effect (i.e. 1:1 ratio of exhaust manifold pressure to boost pressure) you need bigger turbo, bigger exhaust housing, an engine built to rev high (as most of its life will be above 5000-6000rpm if it is an RB).... then you can spec some longer duration camshafts with some overlap.

If it was me, RB26/30 with the turbocharger you have, E85 so you can screw as much into the turbocharger as possible with a stock RB26 head (just get rid of sharp edges and unshroud valves in combustion chamber) and spend $6k on your driveline!

I am running e85.

[bigmikespec]

Good one, if it is not too late get your head back! Or just get them to do as I suggested and forgot all the porting.

[danny14]

Good one, if it is not too late get your head back! Or just get them to do as I suggested and forgot all the porting.

Wouldnt it be better if I got it ported and just went smaller cams ?

[bigmikespec]

Wouldnt it be better if I got it ported and just went smaller cams ?

No, by what reasoning? You are enlarging the ports slowing the velocity of exhaust gases. You would not see any benefit for the power you want to make. Or you can give me the money and do what I said if it makes you feel better jks

[danny14]

No, by what reasoning? You are enlarging the ports slowing the velocity of exhaust gases. You would not see any benefit for the power you want to make. Or you can give me the money and do what I said if it makes you feel better jks

Can someone else share some light into this I want to know what everyone else thinks

[bigmikespec]

Can someone else share some light into this I want to know what everyone else thinks

I didn't get opinions from a bunch or forum members (the majority have no idea), I went out did some research, bought some books and talked to the right people. You need to do the same and come to your own decision.

[monty_r33]

guys, i'm doing the rb30/26 conversion with the following specs:

forged bottom end

GT35/40

RB26 ported head

Greddy Plenum

I'd like to run some decent boost through it.

I'm looking at the Tomei cams. I want good responsive power across the range, not just top end, so nothing too laggy.

Am I better off going for low lift like a 9.15mm with 260 duration, or should I go for something with a little more lift?

Appreciate any recommendations

thanks

I was using hks 272 with 8.somthing lift and they gave me crazzy mid to top end power. But had nothing down low caused by the 6:1 comp. Now have camtech cams that are 2 different sizes but both are massive compared to the hks cams I was using. Cant comment on how they work as the car isnt finished. Waiting on a haltech

[monty_r33]

Camtech cams in sydney are great to deal with and some of the guys there have skylines with there cams in them. So they can advise you from there experience and not from theory.

[XKLABA]

I got absolutely nothing useful from that, other then the fact they have a cam grinder which must mean they must have real world experience of what effect different cams do in different cars at different settings etc etc, sarcasm, just in case you missed it

If they know so much and are so good why doesn't every one use their cams

The info this guy needs is already in this thread from people that have been there and done it in these particular cars but for some reason he want to overlook it, seems to me he has already made up his mind and is looking for validation of his decision

[Piggaz]

I was using hks 272 with 8.somthing lift and they gave me crazzy mid to top end power. But had nothing down low caused by the 6:1 comp. Now have camtech cams that are 2 different sizes but both are massive compared to the hks cams I was using. Cant comment on how they work as the car isnt finished. Waiting on a haltech

Why on earth did you have 6:1 comp?

[XKLABA]

Why on earth did you have 6:1 comp?

Probably the same reason he had 272 with 8 something lift

[bigmikespec]

I got absolutely nothing useful from that, other then the fact they have a cam grinder which must mean they must have real world experience of what effect different cams do in different cars at different settings etc etc, sarcasm, just in case you missed it

I didn't miss it... in case anyone else did, they have a cam grinder, they sell cams, make money from them. The more cams they sell the more money they make.

Danny, listen to the advice instead of trying to find information to justify your decision. Tell Kelford you made a mistake, get them to unshroud the valves and knock of the sharp edges in the combustion chambers and thats it. Get some stock duration cams made by them with as much lift as you can with the springs you have.

[danny14]

I didn't miss it... in case anyone else did, they have a cam grinder, they sell cams, make money from them. The more cams they sell the more money they make.

Danny, listen to the advice instead of trying to find information to justify your decision. Tell Kelford you made a mistake, get them to unshroud the valves and knock of the sharp edges in the combustion chambers and thats it. Get some stock duration cams made by them with as much lift as you can with the springs you have.

Ok its not to late . I just dont know if your one of those guys out of the majority of people that dont know what they are talking about .I dont know who you are you get what im talking about .

How small in duration and would a 10.8 lift be the go . And heavier springs ve a good option to guys . Its hard to know who to trust these days I have been burnt alot as you know from my original 32 build in my build thread .

[bigmikespec]

Ok its not to late . I just dont know if your one of those guys out of the majority of people that dont know what they are talking about .I dont know who you are you get what im talking about .

How small in duration and would a 10.8 lift be the go . And heavier springs ve a good option to guys . Its hard to know who to trust these days I have been burnt alot as you know from my original 32 build in my build thread .

I actually think the Mines cams would work well as an 'off the shelf'... I think they are around 250° duration and over 10mm lift; might be stock base circle too which would save you some more hassle, can anyone confirm?

You need to choose a cam then select a suitable spring, talk to someone from Ferrea they are a top quality product in terms of head components.