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What Is The Largest Spec Cams I Can Fit To My Gtr Head

Marko R1

By Marko R1,
in Engines & Forced Induction

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pure_methamphetamachine Collaborator

pure_methamphetamachine

Posted
Posted (edited)
not exactly...there is a way to keep everything friendly. Its doesn't involve pistons either.

A 1.8mm head gasket is not sufficient a-mod for clearance of lift of this nature. At high revs you also need DAMN strong valve springs for that lift.

People put universal blue on the crowns, put head on, cam belt etc and do a few rotations of the crank, remove the head and look for valve marks. This method, although indicative, can not account for valve expansion due to the heat transfered to it combined with the oscillary motion causing it to not only stretch in length, but also move sideways as it exits the guide. Upping the lift exposes more valve and the sway increases exponentially.

Even the Tomei website state that if you exceed 10.2mm in lift, you need to scallop them (and they do it for free when you buy pistons off them). Tomei pistons are also 0.4mm lower than std, allowing decompression for more boost but also higher lift.

End of the day, it's the owners choice. My question is, do you REALLY want to risk an entire engine?

Edited by pure_methamphetamachine
Swiper the Fox Grand Master

Swiper the Fox

Posted
Posted (edited)
A 1.8mm head gasket is not sufficient a-mod for clearance of lift of this nature. At high revs you also need DAMN strong valve springs for that lift.

People put universal blue on the crowns, put head on, cam belt etc and do a few rotations of the crank, remove the head and look for valve marks. This method, although indicative, can not account for valve expansion due to the heat transfered to it combined with the oscillary motion causing it to not only stretch in length, but also move sideways as it exits the guide. Upping the lift exposes more valve and the sway increases exponentially.

Even the Tomei website state that if you exceed 10.2mm in lift, you need to scallop them (and they do it for free when you buy pistons off them). Tomei pistons are also 0.4mm lower than std, allowing decompression for more boost but also higher lift.

End of the day, it's the owners choice. My question is, do you REALLY want to risk an entire engine?

my engine seems to live quite happily at 9500rpm+ using 11mm+ cams using my method. No piston mods whatsoever.

Edited by DiRTgarage
pure_methamphetamachine Collaborator

pure_methamphetamachine

Posted
Posted

I'm not saying it is not possible, there are just too many risks to not justify doing it. If you skim the head, if so how much, had it already been done, are you using REALLY good valve springs etc.

Just not a risk I'd be willing to take, that's all.

Swiper the Fox Grand Master

Swiper the Fox

Posted
Posted
I'm not saying it is not possible, there are just too many risks to not justify doing it. If you skim the head, if so how much, had it already been done, are you using REALLY good valve springs etc.

Just not a risk I'd be willing to take, that's all.

i see where you are coming from but you must understand im actually building these engines and putting them through more stress than joe average...not just some internet mechanic with an opinion. I always use top quality components and have recently changed spring brands as we have had excellent results with another brand we recently tested.

I have seen builds by 'pro' engine builders go pear shaped quickly due to some guys thinking building high horsepower/high revving RB's is an easy thing to do. There are quite a few pitfalls when building big engines that if you are unaware of can come back to bite you on the ass very hard.

pure_methamphetamachine Collaborator

pure_methamphetamachine

Posted
Posted
i see where you are coming from but you must understand im actually building these engines and putting them through more stress than joe average...not just some internet mechanic with an opinion. I always use top quality components and have recently changed spring brands as we have had excellent results with another brand we recently tested.

I have seen builds by 'pro' engine builders go pear shaped quickly due to some guys thinking building high horsepower/high revving RB's is an easy thing to do. There are quite a few pitfalls when building big engines that if you are unaware of can come back to bite you on the ass very hard.

I am neither bagging nor doubting you. It is just my opinion. And yes, I too have seen many "pro" build engines that fail instantly. Yet they never seem to learn...

Bugger about the cams dude. How the f did they manage to break?

  • 9 months later...
heller44 Mentor

heller44

Posted
Posted
paul - my cams are as follows:

A269IN (inlet) has 'U6' stamped on it

A252X (exhuast) has 'U7' stamped on it

lift are identical @ 9.15mm (as per my vernier)

My question refers to the information I have quoted above.

I have purchased a secondhand set of tomei 'b's for my 26. Correct boxes, looks the same as any photos, but absolutely no manufacturer markings or part numbers on the cams thamselves, other than u6 on the intake and u5 on the exhaust. Not really trusting myself with measurement off the callipers I have here, but definitely more lift than stock.

Does the 'u' number actually have any relevance?

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