Small Cams = Rising Inlet Temps?

[Scooby]

However, I'm at 280rwkw rather than 300-330 (I know we're not racing dynos) and there is a curious hike in temp at 15 psi which I'd like to discover the reason for since I should have 7 psi or so before temp becomes a prob. Unless of course it is cam or turbo related as suggested.

[Scooby]

dyno'd today locally, 272 rwkw which is close enough to the 279 recorded in Sydney. pressure drop across the cooler remained at 3 psi up to 19 psi so far. no rise in inlet temp above 45 deg noticed, even at engine temp of 100 deg.

only difference has been putting the stock manifold heat shields back.

[rob82]

dyno'd today locally, 272 rwkw which is close enough to the 279 recorded in Sydney. pressure drop across the cooler remained at 3 psi up to 19 psi so far. no rise in inlet temp above 45 deg noticed, even at engine temp of 100 deg.

only difference has been putting the stock manifold heat shields back.

I noticed earlier that you have the cams on the std centres - is this on the std cam gear centre lines??? I can tell you that the cam timing on my Rb30/26 took alot to get correct and thats with the std cams. I'm at 4ret on the exh and 16ad on the inlet in crank degrees. Remember that this will be dependant upon where the idler pulley is placed along with deck height. My -5 are making 12psi by 3300rpm - time to check the cam timing.

[Scooby]

I noticed earlier that you have the cams on the std centres - is this on the std cam gear centre lines??? I can tell you that the cam timing on my Rb30/26 took alot to get correct and thats with the std cams. I'm at 4ret on the exh and 16ad on the inlet in crank degrees. Remember that this will be dependant upon where the idler pulley is placed along with deck height. My -5 are making 12psi by 3300rpm - time to check the cam timing.

I often wondered about cam timing with a 38mm higher block and posted here about it but never got much of a response. 16ad on the inlet is al ot how much before you bang valves.

Why does the idler pulley location matter?

[SLAPS]

Recently had my 26/30 tuned. Running R34N1s, Trust dumps, nismo pump and 600 inj, Vipec plug and play. Stock FMIC. Produced 370 rwhp at 15 psi and 11.2 afr. Power drops after 6250. A brief run at 17 psi produced 390 rwhp

Increasing boost above 15 psi makes intake temps rise dramatically. The tuner (a good one) claims this is due to the stock cams that are choking the inlet (cooling gas) and outlet (restricting hotside gas escape).

The tuner is right but maybe he's describing the problem poorly.

The turbo's are near their limit so they will be running in to choke and unnecessarily heating the air... BUT....

More boost = increased inlet temps regardless if its 390rwhp or 490rwhp.

As you are starting to push near 300rwkw you may wish to consider a 100mm thick bar/plate if you haven't already. The stock gtr or cheap ebay 76mm coolers start to struggle as they approach 300rwkw (400rwhp).

When I say struggle I mean internal flow restricts airflow creating a pressure drop.

If the FMIC is creating up to a 5psi pressure drop at 500hp worth of air the turbo will be pushing 20psi if your running 15psi at the plenum.

Its a vicious circle. With the heat of 20psi comes greatly increased inlet temps so not only does the ol' fmic have to deal with trying to pass the air it also has to try and cool a much greater temp.

If you were to drop in a set of cams the restriction would be less as such the demand on your FMIC would be less.

But do consider the 'whole package' (FMIC and Cams to make the most out of your setup) it may not be as simple as dropping in a set of cams as the turbos will be running slightly in to choke and pushing out some fairly hot air as a result.

I personally wouldn't do both at once as I haven't had experience with your particular setup.

I would look at a decent 100mm FMIC before I would consider cams as 15psi is bugger all.

EDIT: Well... That will 'learn' me from having a few too many JD's and jumping straight on to SAU not reading a full thread. 45degree's inlet temp are fine, 3psi pressure drop 'ok'.

As others have now suggested. Look at cam timing due to the additional block height it may be out pushing up the mid range and un-necessarily killing top end or it may be completely out of whack unnecessarily killing power everywhere.

I've always dialed my cams in so no issues. I can't say I've seen anywhere near 16degree's AD though. Its only ever been a 2-3 degree's out.

Edited May 1, 2009 by TheRogue

[Scooby]

Just had the thing retuned here in Canberra, 336rwkw @20psi 7Krpm inlet temps not over 48deg C. Same convex power curve as before (previous post with dyno chart) but bigger numbers. As said before only thing I chnaged was the stock exh mani heat shileds. So buggered if I know, but it works well now. I'll try and scan the dyno pull.

Cheers

[rob82]

I often wondered about cam timing with a 38mm higher block and posted here about it but never got much of a response. 16ad on the inlet is al ot how much before you bang valves.

Why does the idler pulley location matter?

Becuase some people put on two tensioner pulleys, if every body only used the left idler as the tesnioner than it wouldn't matter. Remember I'm talking crank degrees so only 8 camshaft degrees. I can tell you that your cam timing is massively out if your on std centres. I could give you my lift at TDC figures or you could just do want any good eng builder should do and dial the cams in properly!

What makes you think that your not closer to banging the valves with std centres and increase deck height??? Take it back to the dyno and dial in 5deg inlet advance and watch the torque and top end come back!!

Whats even more scary is that no one else has piped up and said anything about cam timing!!!

[unique1]

Becuase some people put on two tensioner pulleys, if every body only used the left idler as the tesnioner than it wouldn't matter. Remember I'm talking crank degrees so only 8 camshaft degrees. I can tell you that your cam timing is massively out if your on std centres. I could give you my lift at TDC figures or you could just do want any good eng builder should do and dial the cams in properly!

What makes you think that your not closer to banging the valves with std centres and increase deck height??? Take it back to the dyno and dial in 5deg inlet advance and watch the torque and top end come back!!

Whats even more scary is that no one else has piped up and said anything about cam timing!!!

very very interesting info rob, definately good to bring that up i also cant beleive its not been mentioned! My rb26/30 with 3076r is also struggling to make any decent power though im blaming other problems and yet to see if it solves it but cam timing is something i havent even thought of with this motor considering it was a throw together motor combo at the time and on the cheap. So could u possibly measure the lift at TDC and post it so i can check if mine is out? Im gonna go out and buy a degree wheel etc in the next few days anyway but if you could measure yours up i can check it asap.

[Scooby]

What makes you think that your not closer to banging the valves with std centres and increase deck height??? Take it back to the dyno and dial in 5deg inlet advance and watch the torque and top end come back!!

Good point. The guy who tuned it here said a 2.8 stroker he did - albeit without the deck height - had 12 deg and loved it. Presumably the 3.0 will want more.