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Discussion Starter #1
My GTO is my daily driver. I know that any mods increase the risk of failure, but how far can the engine be pushed with a reasonable expectation of reliability from the stock short block, T56, and remaining drivetrain? I am hoping 450-500 motor net (100-150 over stock).

I won't be side stepping the clutch, power shifting, or otherwise "race" stressing the car (that will be the GN's burden). I do generally like to "use" it (lots of 75% throttle), just not abuse it. I might run KD's, Pilots, or other summer tire.

I know that the clutch is a weak link, but under the above criteria, would it be OK or would I need an upgrade to Z06, aftermarket single disk, or two disk?

tyvm,
Tom
 

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Well, the rear from what I'm hearing will be the first concern. The half shafts aren't good for hard launches. I think they'll start snapping in the 1.5-.6 60 ft range. The T56 can take amazing abuse. As for the LS1 itself they can take quite a bit of torture. Our own '00 Z28 went down the 1/4 mile over 200 times with 10.4-11.2 quarter mile times with a 175 shot, LS1 Hot Cam, 5.3 liter heads and other significant bolt ons. So there's your answer. LS1s love nitrous as long as you set it up right. I will admit that we did on one occasion crack a valve when we were nearing a 200 shot of nitrous. That motor was horribly abused and eventually we cracked the block but in certain areas of that motor's life it was making 550+ hp and nearly 600 ft/lbs. of torque.....not recommended for longevity but we wanted to see just how bad we could abuse one.
 

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Discussion Starter #3
What's the point of the 5.3 liter heads, CR change?

Tom
 

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Our head porter gets better flow numbers out of those heads and yeah, suddenly you've got a 9:1 comp ratio if that's what you want. I believe he actually just used them because of their flow properties and decked them or used different gaskets to put some more comp into them
 

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The 5.3L heads have a smaller combustion chamber bowl. Smaller combustion chamber = higher compression ratio. THe higher the compression ratio, the bigger the bang when ignited, the bigger the bang, the harder it pushes the piston back down, the harder the/faster the piston goes down, the harder/faster it twists the crankshaft...........

Your engine itself if modded correctly and keeping detonation (pre-detonation that is) under control will be as reliable as stock. It's everything else behind it that'll start giving way like the clutch and the rear end. The stock clutch is woefully inadequate for the stock levels of power as is. The rear end on these cars is better because it's a Dana and more stout than the 7 & 5/8ths rear on the F-Body's, but being an IRS setup, I can see it spitting rear halfshafts before chunking the rear gears.
 

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Mixer, you might be right about the comp ratio, I'll have to check w/ him. He handles the LS1 specs while I usually stick to the LTs. I thought he told me the 5.3s lowered comp....perhaps I was mistaken and he used 6.0 heads?
 

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The only way you'd benefit from a lower compression ratio on one of these motors would be if you were planning on running a forced induction route.

Stock compression is 10.25:1. Dropping it to 9:1 is a huge decrease and would kill power running N/A.

Most aftermarket heads have filled in combustion chambers which in turn increases the compression ratio.
 

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6.0 Heads(71.06cc) are just like LS6 heads(64.45cc) but with a larger cc combustion chamber. The 5.3's (61.15cc) have a smaller cc combusion chamber. LS1 5.7 heads are 66.67cc. On a stock short block you can control the static CR by changing around the heads. Be carefull, some head gaskets have a shorter installed height....means a tiny bit more comp.

The new AFR heads are available from 64-76 cc chambers.
 

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CMNTMXR57 said:
The 5.3L heads have a smaller combustion chamber bowl. Smaller combustion chamber = higher compression ratio. THe higher the compression ratio, the bigger the bang when ignited, the bigger the bang, the harder it pushes the piston back down, the harder the/faster the piston goes down, the harder/faster it twists the crankshaft...........

Your engine itself if modded correctly and keeping detonation (pre-detonation that is) under control will be as reliable as stock. It's everything else behind it that'll start giving way like the clutch and the rear end. The stock clutch is woefully inadequate for the stock levels of power as is. The rear end on these cars is better because it's a Dana and more stout than the 7 & 5/8ths rear on the F-Body's, but being an IRS setup, I can see it spitting rear halfshafts before chunking the rear gears.
Yeah I'm wondering how the rear shafts are going to hold up too!! But I'll take a ripped up shaft over chewed up gears anytime. Hopefully the inner joints and splines can take the abuse.
 

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Discussion Starter #10
Thanks.

My first choice would be to keep the factory airbox, filter, MAF and exhaust. I'd like the biggest gains to be in the midrange and not give up too much low end (or better yet see some gains). Have I now limited myself so much as to not get 100 hp from a head/cam swap with appropriate tuning?

tyvm,
Tom
 

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I can understand why you’d want to keep the stock exhaust as it also functions as an auditory mechanism too. However, I would yank the stock airbox regardless. It is flat out restrictive. I never messed with the MAF or TB on mine as both are well sufficient for that level of power. As a matter of fact, if you want an extra 100rwhp and you do heads and cam, I’d recommend going back to the stock TB and MAF for tuning purposes anyway.

In a way, you are limiting yourself if you don’t want to do too many “bolt-on” style mods. But if you go with a more aggressive cam and head setup, you can compensate and it can be achieved. However, you still won’t see 100% gain from the heads and cam as they rely on everything else to be free flowing too! It’s a whole system that works in unison.
 

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I'm not so sure the IRS componentry is a "weak" as it is suggested.

The only reference I can find re the half shafts is as follows:

"... are thinking slicks I have a half shaft with lots of big ball bearings that says GM can't build axles that hold 900 nm."
Mike
 

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CMNTMXR57 said:
The rear end on these cars is better because it's a Dana and more stout than the 7 & 5/8ths rear on the F-Body's, but being an IRS setup, I can see it spitting rear halfshafts before chunking the rear gears.
Nice article on Dana http://biz.yahoo.com/prnews/040107/clw069_1.html
:drink: :drink:
 

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I'm not so much worried about the half shafts themselves, rather the u-joints where they'll twist like pretzels.
 

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Hi Guys,

At an educated guess, and going by experience on LS1.com.au Forum. The propshaft (or tailshaft) is the weak link.
From MY2001-on they changed to a rubber doughnut coupling at each end and quite a few let go right at the diff-end.
The earlier (pre-2001) shaft used a good old u-jay at each end and is quite a bit stronger.

--- Sid447 ---
 

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Fitting a good twin 2.5" exhaust with 1-5/8" 4>1 or Tri-Y headers and a maf-pipe, along with a good LS1edit tune is worth on average about 60-80rwhp.
And better torque all through the rpm range.
The Tri-Y's make better torque lower down and not much in it at the top.

--- Sid447 ---
 
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