Right now I have a 92 SD TPI 350 with Vortec heads set up for .600 lift, and a zz4 cam. Nothing is ported and I currently have 1.5 rockers.


I was wondering if I would benefit from an LT4 hotcam with 1.6 rockers, and under drive pulleys. I know the vortecs seem to lose intake flow between .500-.600 of lift. The hotcam would put me at .525/.525 with the 1.6 rockers.


Would these upgrades be worth the money and would I feel the HP gain from the upgrades?


thanks

 

Many will say the added lift will give u more duration with full flow in the runner even though the runner flow stops increasing. I dont know anyone that has that much dyno and flow bench time to say that for sure. My thinking is the added lift only strains the vlv train more for no benefit and its possible the flow pattern/swirl of the intake is disturbed. But again im guessing here though street motors perform better with better swirl - something all stock heads since the 90's have improved on. The real test would be to flow-bench your heads to see at what lift flow starts to turn down. But again whos got that time and money?

Ive come across some magazine-dyno articles and the TPI seems to do better on the wider lobe separation angle like a 114 (or larger). I recall Crower has some nice cams on a wide LSA u might look at. Lift is your call but again i dont see the need to stress the vlv springs more than needed. But the difference between 0.500" and 0.525" lift cam maybe cost more than anything else. If it saves u from roller rockers it would be a large savings. I know everyone loves the price of a Hot Cam and the Crower will be a quality part u have to pay more for. But Crower also has some cams on cast cores that are fairly cheap and they custom grind for only like 30 bucks more. They can also regrind your core too.

Hope this helps.

 

I think the dyno would probably see a few HP gain, but not sure what you'd feel on the "butt dyno". You said "nothing ported". Does that mean stock TPI? I had a zz4 cam with stock heads and stock TPI, but really felt the difference when adding a heavily ported plenum and runners. Meaning a stock TPI is your current restriction, not the heads or cam.

 

So lets say I port the tpi intake to match the vortec ports, port runners and plenum, add 1.6 rockers and underdrive pulleys. Would this be the way to go or just do the porting?

 

As for the under drive pulleys, I mean, you'll always gain SOME....you'll never gain much. I suppose every bit helps, but you could take out the back seat too, if it's THAT important. I dunno. I'm happy without 'em on mine.

..as for everything else, I think if you port the manifold, really open it up, and match it to a set of high flow runners and ported plenum, you'll REALLY be up there in the Vortec Head/zz4 cam wheel house! ....AFTER you tune it and get her all ironed out and running well, you could try the 1.6rr's. Honestly not sure if you'll see much. Maybe you will. I don't feel comfortable offering an opinion on that level lift 509/544 (IIRC) with vortecs heads and TPI manifold.