qwiketz

Hi guys. I have a low compression 383, cnc'd lt4 heads, ported matching intake, and a vortech ysi. The car has pretty much all the supporting mods too (long tubes, dual 3" exhaust and more). In the past, even with the t trim, the power dropped off after 5000 rpm which is very unlike most centri blown cars. It wasn't detonation; power just dropped off.

My guess is that they put the springs that came with the hot cam in there and they just aren't enough for boost.

I read the thread on here a few weeks ago about what springs for boost so I'm guessing that I need something with around 150lbs of seat pressure.

My question is with the hotcam and the right springs and my displacement, what is a realistic operating range on this thing? Power being limited to just over 5000 rpm sucks because I can't spin the blower fast enough even with a small pulley. With the right springs, how high should I be able to spin this thing?

Purple Poncho

iTrader: (1)

With the proper dual spring in there 6000-6100 shouldn't be a problem. Spin the blower to max plus 5% at your cam's max rpm. How does your boost curve look? It can be a sign of belt slip.

qwiketz

Thanks. Belt slip isn't an issue (at least not the main issue). The setup really is limited by how fast I can spin the motor due to the crank only being a 7.35". At 6000 rpm, that puts me at 55000 and the blower is capable of 65,000. With 5000 rpm, I'm only spinning it 46k.

The power falling off was consistent with the t trim and the ysi. The blower is making boost (about 14 psi) but it isn't translating into power.

I know that the stock hot cam springs are weak even for naturally aspirated motors. I'm hoping that maybe swapping these out will help bring car back to what a centri car dyno should look like. If I could get 6k, that would be good enough for now!

Shownomercy

iTrader: (1)

Why not just get a decent cam in there?

Does not make sense to me to have a Ysi and a hotcam.

qwiketz

The car originally had a T trim when I got it. Found a deal on the YSI that I could not pass up . Eventually I'm gonna pull the motor out freshen up and then put a real cam in it. For now I'm just trying to do something to get it working somewhat propenly and without much downtime . I literally just got the car running correctly after five years this past week . I'm working more towards racking up miles rather than maxing out the performance . That something that could go on for almost ever.

Shownomercy

iTrader: (1)

Fair enough.

Def get some good springs and lifters in there.

I am not sure where the limit is on cast cams and spring loads, may want to look into that before going crazy on spring choice.

qwiketz

saw your post on springs:

You really want 155-160lb of seat pressure.

~2inch valve, with 10-15psi on it, is gonna take 20-30lb off your rated spring rate.

any idea what model will fit my lt4's? What lifters should I check out?

Shownomercy

iTrader: (1)

Set your budget, cause lifters and springs are gonna vary from cheap to pricey.

pro94lt

What are your plugs and what are they gapped at? What is on the blower inlet? Rubber? I had 2 different issues with my car that is similar to yours it's just a 350...

Purple Poncho

iTrader: (1)

Good point. If you have a crappy rubber inlet you could be sucking it closed.

qwiketz

Would a PAC 1218x be a decent upgrade? Should I change anything else while I'm in there like add a rev kit?

moehorsepower

iTrader: (3)

Yup, had an issue like that where at a certain RPM it would just not rev any higher, Put it on the dyno and saw the rubber boot sucking down.