C4 Tech/Performance L98 Corvette and LT1 Corvette Technical Info, Internal Engine, External Engine

Headers and a tune.

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Old Jun 11, 2023 | 09:37 PM
  #21  
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Assuming that my 80,000 mile car still had 330hp and 340tq at the crank. Then factoring in a %15 drivetrain loss.
I'm up 5hp and 15tq over stock
The real difference i feel is the torque comes in much sooner over stock.
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Old Jun 12, 2023 | 12:33 PM
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I'll be sending out my pcm today or tomorrow. Not sure when I'll be able to get it back to the dyno.
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Old Jun 12, 2023 | 09:22 PM
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Originally Posted by Brick330
Assuming that my 80,000 mile car still had 330hp and 340tq at the crank. Then factoring in a %15 drivetrain loss.
I'm up 5hp and 15tq over stock
The real difference i feel is the torque comes in much sooner over stock.
The 15% number is not right, IMO....IF your car is a stick. 10% is much more realistic for stick shift cars.

For reference, my LT1 stick is BOX stock, other than a K&N the PO put in it. At ~155,000 miles, that car did 278/312. Stock manifolds, exhaust, mufflers, everything. Stock.





Knowing that the car was rated 300 horse, flywheel from the factory, ^that's^ less than 10% drivetrain loss.

Last edited by Tom400CFI; Jun 12, 2023 at 09:34 PM.
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Old Jun 13, 2023 | 09:16 AM
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Originally Posted by Tom400CFI
The 15% number is not right, IMO....IF your car is a stick. 10% is much more realistic for stick shift cars.

For reference, my LT1 stick is BOX stock, other than a K&N the PO put in it. At ~155,000 miles, that car did 278/312. Stock manifolds, exhaust, mufflers, everything. Stock.





Knowing that the car was rated 300 horse, flywheel from the factory, ^that's^ less than 10% drivetrain loss.
from the sound of this, my lt4 is wounded then.
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Old Jun 13, 2023 | 10:12 AM
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Oh! That's an LT4! Somehow, I missed that.

Yeah, for an LT4, that doesn't seem great to me. I think my LT1 is strong, but I think LT4's should do about 300 RW, stock.
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Old Jun 13, 2023 | 10:30 AM
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Originally Posted by Tom400CFI
Oh! That's an LT4! Somehow, I missed that.

Yeah, for an LT4, that doesn't seem great to me. I think my LT1 is strong, but I think LT4's should do about 300 RW, stock.
Welp now I'm worried lol, PO left much to be desired and I have been cleaning up his mess for 2 years now.

It wouldn't start the the day after I got it home.
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Old Jun 13, 2023 | 11:14 AM
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That sucks....BUT, you're making headway! You went from a car that wouldn't start to one that's making 300+hp crank...so that's a good trend!
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Old Jun 13, 2023 | 01:33 PM
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I'll get it scanned for codes, I have had a check engine light on and figured it was from the lack of rear O2 sensors before the tune. Now I'm curious, ill also be running a compression test on it.

Any idea what I should be looking for psi wise?
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Old Jun 13, 2023 | 03:27 PM
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No idea. Mainly, you want to focus on seeing even numbers across all 8 cylinders. W/in 10-12% or so.

What part of Mass? I grew up in Bolton.
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Old Jun 13, 2023 | 04:54 PM
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Springfield area.
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Old Jun 13, 2023 | 05:47 PM
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Right on. Ski at Mount Snow!

Race at Epping!

Track days at Palmer!

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Old Jun 13, 2023 | 08:29 PM
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Every dyno is different. 278 on one dyno could be 290 on another.
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Old Jun 13, 2023 | 11:10 PM
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Yep. That's TRUE....but 290 would still be off the mark.
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Old Jun 15, 2023 | 03:23 PM
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Pcm went out today, I'll hopefully get it back next early next week.
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Old Jun 22, 2023 | 08:34 PM
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Not a great day, I spun a bearing on the dyno.

I'm looking into options to get this fixed. Any input would be greatly appreciated.

This might turn into a rebuild or 383 thread.
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Old Jun 22, 2023 | 10:27 PM
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Hey Brick, sorry to hear that. At least you know what went wrong so you're not in the dark!

Take it as an opportunity to build a motor!

Maybe start a build thread?

If either of my cars currently spun a bearing I would probably pull the motors and stroke em as part of the rebuilding!

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Old Jun 22, 2023 | 10:30 PM
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Damn. Shitty. Sorry to hear that.

I would go 383 if I had a damaged crank, that's for sure.
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Old Jun 23, 2023 | 10:11 AM
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Originally Posted by Tom400CFI
Damn. Shitty. Sorry to hear that.

I would go 383 if I had a damaged crank, that's for sure.
This is my though too, I have called around a few shops and it looks like the machine work on the block would be in the range of 1k.

Then I would need to source a 383 rotating assembly.
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Old Jun 23, 2023 | 01:32 PM
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Called around a few shops and got a very basic quote to get all the machine work done to the block. If turning it into a 383 and getting the heads checked and p&p its going to run me about $1600.

I found this kit in an older thread about 383s and its on sale soooo..... Around 4k if I do all the assembly myself. Not as bad as I figured

383 kit
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Old Jun 24, 2023 | 09:39 PM
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IME back in the 1980s, working on cars from the 1960s and 1970s headers, exhaust and a tune was the easiest and cheapest horsepower available, beating heads, cams and intakes by a wide margin for a lot less $$$.

IME 50hp is a lot to expect from just headers, but I would say 25 is probably a sure thing.

Then you had to just have deal with the headers leaking every 6 weeks ..... which is why I personally never put headers on a car any more.
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