Cam questions?

[skyla]

I'm in the market for some new cams, I have been slowly getting parts for my engine, and have started looking for cams. I believe the standards cams for a RB25DE are 240 duration and 7.9mm lift. What sort of profile would be good for a car that is slowly been modified and will be mainly a road car but will be raced on the track every now and then.

The local performance shop has suggested I get some 270 duration cams, but I haven't managed to find much info on the subject. Another potential problem is that with the standard hydraulic lifters will only alow an extra 1/2 to 1mm lift before the head has to be modified.

Does anyone know much about adding a set of more agressive cams, the pros and cons, what sort of power gains can be achieved?

What cam profile would be the best for use on road and track?

I have already replaced the standard ecu with a GTS link, so I won't have any problems in that department.

Any info greatly appreciated.

[dondesoto]

I'm in the market for some new cams, I have been slowly getting parts for my engine, and have started looking for cams. I believe the standards cams for a RB25DE are 240 duration and 7.9mm lift. What sort of profile would be good for a car that is slowly been modified and will be mainly a road car but will be raced on the track every now and then.  

The local performance shop has suggested I get some 270 duration cams, but I haven't managed to find much info on the subject. Another potential problem is that with the standard hydraulic lifters will only alow an extra 1/2 to 1mm lift before the head has to be modified.

Does anyone know much about adding a set of more agressive cams, the pros and cons, what sort of power gains can be achieved?  

What cam profile would be the best for use on road and track?

I have already replaced the standard ecu with a GTS link, so I won't have any problems in that department.

Any info greatly appreciated.

well as you can see , theres not too much knowledge about cams for the rb25 s . like you said the limiting factor seems to be the hydraulic lifters . maybe you have to go to solid lifters , seems to be plenty cams available for the rb26 with big lifts and durations , and they,ve got solid lifters . i,ve got a spare rb25de head lying around so must check it it out and see what can be done .

[NA_R33]

u can modify hydraulic lifters to solids by changing the cores, some people are against it, but i recently asked an engineer that builds alot of race cars about it and he said he does it all the time. If u have access to a good machinest it shouldnt cost u much at all. Our workshop does odds and ends for some of the local auto shops and this comes up quite regularly, as well as lightening valvles, lifters and things.

[hrd-hr30]

how do you lighten a valve???

[NA_R33]

stick it in the lathe sp* and machine bits off them...

[tikki169]

As far as I know you should be able to go as far as 276 with hydrolic lifters, it's when you start appraochinig 288 that you get the problems. It's the same in most cars, but with 288 you're gonna get a very lumpy ride.

[skyla]

thanks for the replies, much appreciated. My next question is, would it be better to keep the vct or get rid of it and get a set of adjustable cam gears? Which would give the better results?

[hrd-hr30]

stick it in the lathe sp* and machine bits off them...

spelling looks OK to me!

what bits don't you need? I mean, you can't shorten them, you can't reduce the diametre of the stem or the head, and any changes to the combustion chamber side of the head would loose compression, changes to the back of the valve head would affect flow (maybe for the better I guess). You might be able to tulip the valve stem below where it meets the guide, but only if its a one piece valve. I just don't see much room for lightening a valve, and it certainly isn't a normal tuning mod.

[NA_R33]

No its not normal.. we've done it for a guy that races VW?? i think from memory. As the stem curves down to the base of the valve we make that radius tighter.. the guy was after 100th's of gram.. but with lightened lifters and the like, fewer or smaller valve springs could be used (he said that in the past when he had, had it done they were using double valve springs and could go back to singles) to do the same revs reliably...

[tikki169]

AsJon said on VW's you are able to machine them a little. I know guys that use to do this but also take a nissan STI (think it's a SR20 NA) valves, reseat them into the head ans they are larger and then cut the stems down and have the grooves cut back into them. Though they were doing this mainly on Rally car heads

[hrd-hr30]

AsJon said on VW's you are able to machine them a little. I know guys that use to do this but also take a nissan STI (think it's a SR20 NA) valves, reseat them into the head ans they are larger and then cut the stems down and have the grooves cut back into them. Though they were doing this mainly on Rally car heads

but none of that was done to lighten the valves, just to make it fit....