What to expect out of 383 hotcam and boost rpm wise - LS1TECH - Camaro and Firebird Forum Discussion



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What to expect out of 383 hotcam and boost rpm wise

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Old 12-03-2017, 07:09 PM   #1
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Default What to expect out of 383 hotcam and boost rpm wise

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?
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Old 12-04-2017, 03:08 PM   #2
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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.
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Old 12-04-2017, 03:51 PM   #3
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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!
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Old 12-04-2017, 09:21 PM   #4
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Why not just get a decent cam in there?

Does not make sense to me to have a Ysi and a hotcam.
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Old 12-04-2017, 09:39 PM   #5
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Why not just get a decent cam in there?

Does not make sense to me to have a Ysi and a hotcam.
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.
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Old 12-04-2017, 09:52 PM   #6
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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.
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Old 12-05-2017, 12:08 AM   #7
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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.
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?
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Old 12-05-2017, 09:20 AM   #8
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Set your budget, cause lifters and springs are gonna vary from cheap to pricey.
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Old 12-07-2017, 07:03 PM   #9
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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...
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Old 12-07-2017, 11:14 PM   #10
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Good point. If you have a crappy rubber inlet you could be sucking it closed.
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Old Yesterday, 10:49 AM   #11
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Would a PAC 1218x be a decent upgrade? Should I change anything else while I'm in there like add a rev kit?
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