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Timing 2 Exhaust Cams

Jokkeri

By Jokkeri,
in Engines & Forced Induction

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Jokkeri Rookie

Jokkeri

Posted
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I had my RB25DET head checked and I bought another exhaust cam to replace the inlet cam so I can put adjustable camgears to my car. The cams need timing so I was wondering do I just time both cams to "stock" exhaust cam timing?

I got some specs from the tomei website and it seems inlet should be 120degrees and exhaust should be 117degrees. So should I just time both exhaust cams to 117degrees? Later I'm gonna go to a dyno to get them adjusted properly but for now I just want to get the car running safely because I'm putting in a bigger turbo and lot of other things.

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https://www.sau.com.au/forums/topic/411856-timing-2-exhaust-cams/
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_x_FiReStOrM_x_ Community Regular

_x_FiReStOrM_x_

Posted
Posted

The difference between 117 or 120 shouldnt matter, if its just to get the car running. Just be careful; always turn engine over by hand, with no compression, SLOWLY to make sure there's piston-to-valve clearance before running it. If you feel excessive resistance, stop. lol.

  • 3 weeks later...
Jokkeri Rookie

Jokkeri

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A bit late reply but... I have a Holset hx40/35 hybrid coming to the car and I know a guy who did that and the turbo reached max power way earlier with the adjustable camgears.

Are you saying VCT is better compared to adjustable camgears that have been set up properly?

The Dan Grand Master

The Dan

Posted
Posted

No.

VCT cannot ALWAYS compare to proper cam profiling and cam selection. But 90% of the time yes it will be better.

The engine with adjustable cam gears may have been set up for response rather than peak power though. VCT is a combination of both - response and the ability to maintain peak power due to the lobe seperation and its variable nature

Jokkeri Rookie

Jokkeri

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Well with the camgears I was kinda hoping to sacrifice some peak power to get more response and get the max power sooner because I wanna drift the car and with the stock cams and motor the turbo probably isn't gonna start making power untill near 4000rpm

The Dan Grand Master

The Dan

Posted
Posted

Well with the camgears I was kinda hoping to sacrifice some peak power to get more response and get the max power sooner because I wanna drift the car and with the stock cams and motor the turbo probably isn't gonna start making power untill near 4000rpm

With stock cams you are wasting your time thinking about advantages and disadvantages. You are only going to get so far and VCT will be better than anything you can time on a dual adjustable setup.

Custom cams that are profiled specfically for an exact seperation etc are going to benefit from that.

HYPED6 Collaborator

HYPED6

Posted
Posted

I did a ca18 once. Had 2 NA exhaust cams.

It was rubbish........ Has any one thought about the cam profiling of an exhaust cam.

Are the lobes in the correct position on the camshaft to actually work effectively as an intake cam with everything set at 0?

PS........ I <3 VCT

Jokkeri Rookie

Jokkeri

Posted
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Posted

Well damn... I'm just about to now put the engine back together so right now it would still be pretty easy to put the intake cam back to the head because the head isn't on the car yet. Well a bit annoying because I bought the cam and camgear for nothing then... haha

The Dan Grand Master

The Dan

Posted
Posted

Well damn... I'm just about to now put the engine back together so right now it would still be pretty easy to put the intake cam back to the head because the head isn't on the car yet. Well a bit annoying because I bought the cam and camgear for nothing then... haha

You bought a standard cam?

R31Nismoid Grand Master

R31Nismoid

Posted
Posted

Well with the camgears I was kinda hoping to sacrifice some peak power to get more response and get the max power sooner because I wanna drift the car and with the stock cams and motor the turbo probably isn't gonna start making power untill near 4000rpm

You have a Holset HX40... You will never have response with a truck turbo, so forget trying to get response by playing with things.

Go with VCT and just hope for the best IMO.

Jokkeri Rookie

Jokkeri

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This is a holset hx40/35 hybrid made from parts from the super series and Fullrace model. I'm from Finland and around here Holset are one of the most popular turbos in here because they outspool and outpower some garrett turbos and they are cheap and reliable.

And yes I bought a standard exhaust cam used because I got it for cheap.

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