VTC or BIG cams, which is better?

[baycityspeed]

I've been told that the largest cams you can run in an RB25 with out sacrificing the VTC is a 264. Is this true? Also, if it is, at what point do you make more power with larger cams and no VTC than with small cams with it hooked up? I would like to run 272's and adjustable cam gears, but if I can't do that and keep the VTC, would it be better to go with 264's and leave the stock cam gears and the VTC on it?

I care only about drag racing, no drifting or road racing

[BrianV8]

I have played lots with the vct and daily driving i find it really gives the bottom end a lot more pep, if all your doing is racing i would not bother.

If your just bolting in cams to a stock head i would not go over a 258 and still rev the motor, I'm sure u can run a 272 with hydraulic lifters just don't plan to rev the motor over 5 grand. Solid lifter conversion to run a big cam and still make power!!

[baycityspeed]

Yea, I talked to a couple shops today and the general consensus was to only run the VCT on stock cams. If you get big cams, delete it. I want to run 272's. If I do, I will buy a dual spring / Ti retainer kit. I don't think it's really the hydraulic lifters that kill it. DSM's have hydraulic lifters and can be revved to 9,500 with them. KA24's have the same type valve train (hydraulic & shim over bucket) as the 25, and with the right valve train, they can be revved to 8,000 even with their long strokes. Seems like the only thing keeping a stock block 25 from revving too high would be the crappy rod bolts. My block is stock, so I won't rev it past 7,200 anyway. I don't want to sling any rods out the block.

[BrianV8]

ahh ya, Let me know how that head build works out and what parts you go with. One day want to do some sort of build on my motor, I have my rb25 making 400whp on a stock motor, I know it can handle it, but eventually want to do a build to keep it a bit safer

[baycityspeed]

I know this is hard to believe, but a buddy of mine makes over 650whp through a Chevy turbo 350 transmission on a STOCK RB25DET head and block. That would be well over 700whp through a 5-spd. I have seen him dyno several times. He runs a stock head gasket and head studs with stock cams. The turbo is a 67mm T4. I think 25psi boost and a 75 shot. The motor is in a 280zx. I have seen him run a 9.6@144mph in the 1/4. The motor held up for 2 years. He finally slung two rods through the block. The only thing he changed was the rev limiter. He used to shift @ 7,200. He bumped it up to 8k, and the rod bolts let go. I think these motors are a lot tuffer than most people think. Of coarse, tuning is the key.

[TheyKilledKenny]

A Chev tranny bell housing bolts to a rb engine =s ????

[baycityspeed]

If I remember correctly, he made his from plate aluminum, but I found a place online that makes them a while back.

[BrianV8]

ya the weak point is not so much the rod bolts as it is the ring lands, if you don't rev past 7200 the bottom end is good for a decent amount of power. The big weak point is the piston ring lands. Those are the first things to go when cylinder pressures get too high. From what i understand if you want your pistons to be safe keep it under 20 psi, i've had my motor to 23 a couple times see how it feels but never kept it there.