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Hi Lift Camshafts And Base Circles And Lifters..

R32 TT

By R32 TT,
in Engines & Forced Induction

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R32 TT Mentor

R32 TT

Posted
Posted

Hi guys,

I am in the process of an RB26 rebuild.

I am looking to buy some Tomei Procams with 260degree duration and 10.8mm lift on both inlet and exhaust.

A couple of questions:

1. I know I need valve springs to suit. Tomei have "Type A" valve springs which are said to be good for up to 10.85mm lift. Does this mean they are "right at their limit" if using a 10.8mm lift cam? OR are they exactly what I need? ie do they have appropriate clearance - I don't want them coil binding obviously. Has anyone had any experience with these? Can you run that "Type B" 11.5mm lift springs with a 10.8mm lift cam for some 'extra piece of mind' or is this unnecessary...?

2. Tomei seem to suggest that they reduce the base circle of their cams to get this lift. And they have lifters made for the job to most of this up. But of course this adds a further $500 minimum to the job. Has anyone successfully shimmed the stock lifters for these type of cam?

3. Lastly, if I DO need new lifters etc, then it may be better to back off the lift a little and go to say HKS 264 degree cams with only 10.0mm lift... (but I'd prefer as much lift as I can get).

Can anyone comment if HKS/Tomei have reduced base circles and how they go about resolving these problems?

Cheers!

M

CruiseLiner Mentor

CruiseLiner

Posted
Posted
Hi guys,

I am in the process of an RB26 rebuild.

I am looking to buy some Tomei Procams with 260degree duration and 10.8mm lift on both inlet and exhaust.

A couple of questions:

1. I know I need valve springs to suit. Tomei have "Type A" valve springs which are said to be good for up to 10.85mm lift. Does this mean they are "right at their limit" if using a 10.8mm lift cam? OR are they exactly what I need? ie do they have appropriate clearance - I don't want them coil binding obviously. Has anyone had any experience with these? Can you run that "Type B" 11.5mm lift springs with a 10.8mm lift cam for some 'extra piece of mind' or is this unnecessary...?

2. Tomei seem to suggest that they reduce the base circle of their cams to get this lift. And they have lifters made for the job to most of this up. But of course this adds a further $500 minimum to the job. Has anyone successfully shimmed the stock lifters for these type of cam?

3. Lastly, if I DO need new lifters etc, then it may be better to back off the lift a little and go to say HKS 264 degree cams with only 10.0mm lift... (but I'd prefer as much lift as I can get).

Can anyone comment if HKS/Tomei have reduced base circles and how they go about resolving these problems?

Cheers!

M

my jun cams, 272/11.35mm lift, have smaller base circle and use thicker shims under the stock buckets to get the correct clearances (plus hd valve springs, titanium retainers). not sure about the other info sorry.

N I B Grand Master

N I B

Posted
Posted

Large cams on RB26 needs machining of the head to clear the cam lobe,the springs are correct but need to be setup right mostl needing shims under the springs to get the correct seat pressure.You could get a custom made set of shims but at about 13mm you would have trouble.

Valve guides also become an issue.

GTR heads must be setup by a machine shop that knows what their doing.If you are not going for 700hp+ look to Pon cams.

R32 TT Mentor

R32 TT

Posted
  • Author
Posted
my jun cams, 272/11.35mm lift, have smaller base circle and use thicker shims under the stock buckets to get the correct clearances (plus hd valve springs, titanium retainers). not sure about the other info sorry.

Cheers! Sounds from what you're saying then that I shouldn't have too much trouble shimming them.

mmm... big cams you have there!

CruiseLiner Mentor

CruiseLiner

Posted
Posted
Cheers! Sounds from what you're saying then that I shouldn't have too much trouble shimming them.

mmm... big cams you have there!

also requires the machining of head for large lift (over 10.8mm i think) and shims were around 5mm thick compared to stock 3.5mm ones i think (all set up by a head specialist for exact clearances on all buckets)

yes cams are big and they sound nice too :thumbsup: a little annoying in traffic with the shacking of the car at lights, vrmm vrmm vrmm at idle but they sound sooo tough, and will be worth it when i can put some boost into the motor after run in. almost sounds like a rotary when idling, but alot deeper.

R32 TT Mentor

R32 TT

Posted
  • Author
Posted
Large cams on RB26 needs machining of the head to clear the cam lobe,the springs are correct but need to be setup right mostl needing shims under the springs to get the correct seat pressure.You could get a custom made set of shims but at about 13mm you would have trouble.

Valve guides also become an issue.

GTR heads must be setup by a machine shop that knows what their doing.If you are not going for 700hp+ look to Pon cams.

Hi mate,

Yup - I knew about the machining to clear the cam lobe - but thanks for pointing it out nonetheless.

Wow - are you saying I need 13mm shims??

Don't you think getting as much lift as possible is going to help with engine efficiency and spool up even at 500-550hp? (my target)

Its been recommended to me to go as higher lift as I can get in the duration I want and I thought it made good sense - I thought Poncams (as good as they are) were easier because you didn't have to worry about other valve train components. I don't mind mucking around a bit though to get the result I want... If its only shims and valve springs I am prepared to do it.

If its special lifters, modifications to valves guides and more hoo-hah, then I might not go that far.

What do you think?

proengines Rising Star

proengines

Posted
Posted

Personally, I would go for hks cams, you do need to machine the head to fit them with the higher lifts but they use the standard base circle which means you can use shims in the standard range. The cams with the smaller base circle are made so you can fit them without having to remove the head from the engine as they can give the same lift without having to make the top of the lobe sit higher and hit the head. It will cost you to have the head milled to clear the cams but means you can use the standard buckets and shims. We assemble the head with the standard shims, check the clearance and tip the ends of the valves to set the clearance. Usually by the time the seats are cut and the valves faced the clearance will close up by .005-6" which isn't much to remove from the end of the valve.

R32 TT Mentor

R32 TT

Posted
  • Author
Posted
Personally, I would go for hks cams, you do need to machine the head to fit them with the higher lifts but they use the standard base circle which means you can use shims in the standard range. The cams with the smaller base circle are made so you can fit them without having to remove the head from the engine as they can give the same lift without having to make the top of the lobe sit higher and hit the head. It will cost you to have the head milled to clear the cams but means you can use the standard buckets and shims. We assemble the head with the standard shims, check the clearance and tip the ends of the valves to set the clearance. Usually by the time the seats are cut and the valves faced the clearance will close up by .005-6" which isn't much to remove from the end of the valve.

Hi Greg, glad you stopped by on this one!

Tell me, is there a 'disadvantage' to running smaller base circles (other than the cost for new buckets?).

ie the HKS do a 264 duration cam up to 10.0mm lift. But Tomei do a 260 duration cam up to 10.8mm.

I am trying to get as much lift as possible. Would the extra 0.8mm lift of Tomei still be worth while?

Or would you go the 10.0mm lift HKS cams and save the money and extra hassle...

ylwgtr2 Grand Master

ylwgtr2

Posted
Posted
Personally, I would go for hks cams, you do need to machine the head to fit them with the higher lifts but they use the standard base circle which means you can use shims in the standard range. The cams with the smaller base circle are made so you can fit them without having to remove the head from the engine as they can give the same lift without having to make the top of the lobe sit higher and hit the head. It will cost you to have the head milled to clear the cams but means you can use the standard buckets and shims. We assemble the head with the standard shims, check the clearance and tip the ends of the valves to set the clearance. Usually by the time the seats are cut and the valves faced the clearance will close up by .005-6" which isn't much to remove from the end of the valve.

here here....thats what i did and thats what i would be doing....

  • 2 months later...

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