How Big Can I Go?

[StockyMcStock]

So i have an R33 RB25DE series 1 head on my 25/30 right, and i want to stick a big exhaust cam in it. I understand that above a certain amount of lift, you need to grind off a bit of the head so that the lobe tip clears as it swings around. i really don't want to disassemble the engine, so i was hoping to avoid modifying the tunnel if i could help it.

Question is, how big can i go on the cam before i require grinding? I want either the HKS 256 duration, 8.8mm lift or the HKS 264 duration, 9mm lift.

Cheers,

Stocky

[saliya]

You can get cams that have more lift but require no extra head clearance by using a smaller base circle...

Regards,

Saliya

[BHDave]

The 264 exhaust will fit a 25det head. If you can confirm no difference between the top side of the 2 heads then you're sweet.

[StockyMcStock]

okay so the 264 with 9mm of lift will go straight in without grinding the cam tunnel edges? the rest of the head is identicle to a DET head.

[BHDave]

mine did. I've yet to have a problem with about 5k on the clock since install. I run the 256 8.8 inlet to maintain VCT and the 264 on the exhaust side.

[StockyMcStock]

excellent, i'll go the 264 then. cheers mate!

[Cubes]

Nice.. Be sure to throw a dyno sheet up showing us the after affect.

These DOHC's really need cams to get them reving hard when sitting on the 3ltr bottom end.

[Sydneykid]

Clearancing for high lift cams is great exaggerated. Around 30 minutes with a die grinder will fit the highest lift exhaust cam you can buy. No need to remove anything other than the camshaft. Shield the swarf spray with a rag and then clean up with a vacuum cleaner when finished.

cheers

[StockyMcStock]

interesting - lucky i won't have to bother grinding with the 264 though. going to get an adjustable wheel at the same time and try and dial them in with a degree plate/dial guage properly. throw it back on the same dyno and see what it does.

don't worry cubes i'll post dyno sheets. my guess is 410rwhp on 15psi, but that's just a guess.