LT1 stock exhaust questions

[stearnman]

LT1 stock exhaust questions:

Ok, I’ve had these questions regarding the stock LT1 exhaust system plaguing my mind for awhile and need some clarification.

1) Where is(are) the main point(s) of restriction? (As I look at my car, the diameter of the exiting pipes(tips) from the mufflers are smaller than the main pipes…I would think this to be the main restriction, but am obviously not certain.)
2) What is the pipe diameter of the stock exhaust? (The “outer” diameter that I measured before the mufflers is approx. 2.75 inches. Not sure as to what the gauge of the pipes are, so I unsure what the “inner” diameter is.)
3) I’m assuming that the stock exhaust does not have mandrel bends. If this is true, how much restriction are we talking about here? More restriction before the resonator or after the resonator? (I think the bends in the pipe are more acute after the resonator.)
4) How much restriction is in the resonator?

I’m looking forward to learning more on this!!

 

[Toms007]

Chris, I have no basis on what I am going to say other than what I have heard/read on the different forums, so here goes. The LT1 exhaust is a fairly efficient system. It is surprisingly free-flowing. With that being said, I just wanted my corvette to have more of a muscle sound to it, so I put on the Corsa system. A very well engineered, high quality exhaust. Pricey? Yes, but I wouldn't change back to the stock system

 

[96corvetteLT4]

I agree with 'toms94' on the stock exhaust system.

This brings up another question for me, how much can you modify the engine before the stock exhaust becomes too restrictive? This will probably generate several replies due to the fact that 'too restrictive' is a relative term determined differently by everyone. I have an LT4, and have seen where people have added headers and other exhaust work to a stock, or slightly modified engine, with 20hp or so increase. For the money spent on headers, cats, etc, I would like to see a better improvement.

Can I get the same 20hp or so increase from the installation of a cam, like the LT4 'hotcam'?

 

[John Robinson]

Exhaust

On my stock 93 LT1 the pipes ID is 2 1/2", The resonator is two open tubes with perferations that are the same size as the pipe. I did have the resonator removed and straight pipe welded in it's place. The sound is deeper. As for resonance it has not been a problem with my coupe. Steady crusing is as quite as it was with the resonator. I believe if you have a manual transmission the results would be more dramatic because of downshifting and compression breaking. It only cost me $80.00 for a muffler shop to do this so it was cheap for experimenting purposes. If money were no object I would have the Corsa in a heartbeat. But what I have is very pleasing to me.

 

[Aurora40]

LT1 stock exhaust questions:

Ok, I’ve had these questions regarding the stock LT1 exhaust system plaguing my mind for awhile and need some clarification.

1) Where is(are) the main point(s) of restriction? (As I look at my car, the diameter of the exiting pipes(tips) from the mufflers are smaller than the main pipes…I would think this to be the main restriction, but am obviously not certain.)

Here's an interesting article on the ZR-1 exhaust. This is the '93 that had less taper into the resonator. On the earlier exhaust it tapered down to like 1 7/8" OD into the resonator...

http://www.zr1specialist.com/HAT Web/articles/backpressure.htm

 

[John Robinson]

Confused

This is the '93 that had less taper into the resonator. On the earlier exhaust it tapered down to like 1 7/8" OD into the resonator...

Aurora40

Are you saying on earlier C4's the resonator was 1 7/8 inches and at some time it was changed to 2 1/2?

I ask this because when I went to the muffler shop to have mine removed they told me it was 1 7/8 so I had it removed only to find out it was 2 1/2. I did not get the backpressure relief I was looking for but did get a better sound. Any information you can give on this subject would be most appreciated.:confused

 

[stearnman]

Here's an interesting article on the ZR-1 exhaust. This is the '93 that had less taper into the resonator. On the earlier exhaust it tapered down to like 1 7/8" OD into the resonator...

http://www.zr1specialist.com/HAT%20Web/articles/backpressure.htm

That article was on the money for info I was seeking! Thanks Aurora.

As I look at my car, the muffler exit does seem very restrictive...not even knowing what's inside the muffler itself. I think I will go for muffler removal in favor of heavier sounds for now. For looks, I'll keep consistant with the twin tips on most our after market exhausts.

Whether it adds performance to a stock engine or not won't concern be too much for now. Eventually I do want to explore the points that 96corvetteLT4 have made above regarding how much engine modification can a stock LT1 exhaust handle before parts/sections of it become restrictive to the point of HP and torque losses.

Thanks again for the input guys!!

 

[Aurora40]

Aurora40

Are you saying on earlier C4's the resonator was 1 7/8 inches and at some time it was changed to 2 1/2?

I ask this because when I went to the muffler shop to have mine removed they told me it was 1 7/8 so I had it removed only to find out it was 2 1/2. I did not get the backpressure relief I was looking for but did get a better sound. Any information you can give on this subject would be most appreciated.:confused

It's my understanding this was just on the ZR-1. When the LT1 came out in 1992, it used the same design of exhaust system (vs the L98's single pipe most of the way), but had a better resonator. So in 1992, the LT1 had a better exhaust system than the LT5. I think Chevy realized this and for 1993 the ZR-1 got a better resonator along with a few other improvements that bumped the power up 30hp.

 

[stearnman]

It's my understanding this was just on the ZR-1. When the LT1 came out in 1992, it used the same design of exhaust system (vs the L98's single pipe most of the way), but had a better resonator. So in 1992, the LT1 had a better exhaust system than the LT5. I think Chevy realized this and for 1993 the ZR-1 got a better resonator along with a few other improvements that bumped the power up 30hp.

Here's another question...

All LT1s from '92 to '96 made (were rated at) 300HP, but only the '92 had 330 ft-lb torque while '93 to '96 generated 340 ft-lb of torque.

How did GM add 10 ft-lb of torque? What's the difference between the car years? Was it in the exhaust system or in the engine?

 

[Aurora40]

Here's another question...

All LT1s from '92 to '96 made (were rated at) 300HP, but only the '92 had 330 ft-lb torque while '93 to '96 generated 340 ft-lb of torque.

How did GM add 10 ft-lb of torque? What's the difference between the car years? Was it in the exhaust system or in the engine?

There were numerous detail changes between the 1992 and 1993 engine. I can't recall offhand what they were, though, just remember that there were many small changes after the first year of the LT1.

 

[LT4man]

Chevy went from strictly a speed density system for A/F management to a speed density AND mass air flow sensor system.

They also went from a batch type injector firing to sequential fuel injection.


Save The Wave!

 

[stearnman]

Chevy went from strictly a speed density system for A/F management to a speed density AND mass air flow sensor system.

They also went from a batch type injector firing to sequential fuel injection.

Ok then, can one easily upgrade a '92 to what you just stated?

I'm assuming some form of computer upgrade would be needed to accommodate the speed density sensor and the sequential firing.

 

[LT4man]

I believe you could upgrade the system. You would need to install wiring for the MAF. The chip in the ECM would have to be upgraded, also.

Al at PCMforless could shed some lite on this.

Save The Wave!

 

[LT4man]

Instead of doing the MAF and ECM work, you could............

Have your Lt1 heads ported and stick a different cam into the engine.

You would probably pick up 40-50 real rear wheel horsepower!!!

Save The Wave!

 

[stearnman]

Instead of doing the MAF and ECM work, you could............

Have your Lt1 heads ported and stick a different cam into the engine.

You would probably pick up 40-50 real rear wheel horsepower!!!

Ah...believe me, once I get the money I'm going straight for a 383 or 396 stroker long block or turn-key engine!

Thanks again for the input LT4man!!

 

[John Robinson]

more horsepower

Here's another question...

All LT1s from '92 to '96 made (were rated at) 300HP, but only the '92 had 330 ft-lb torque while '93 to '96 generated 340 ft-lb of torque.

How did GM add 10 ft-lb of torque? What's the difference between the car years? Was it in the exhaust system or in the engine?

Aurora40 has a post in general discussion for owners manuals for 93 thru 96.
On page 319 there is a power curve chart that shows the horsepower at 315 and the torque at 340. I have also checked the manual in my car and it shows the same thing. GM obviously tweeked another 15 HP and 10 FT #'s of torque out in the 93. Every where else I look says they only had 300 HP for 93 since I had eye surgery in Dec. I may not be seeing it right. So if any of you eagle eyes out there could look at the power curve chart in your manual and let me know what you see it would be appreciated as I may be wrong about the HP.:crazy

 

[Aurora40]

It looks to me like the horsepower line comes up about 2/3 to 3/4 of the way between the 280hp mark and the 315hp mark. You can blow the .pdf file up to about 200% or more to see it better.

I'm sure the graph shows a 300hp peak. That graph isn't a real dyno run, rather it's a marketing type tool to show the general power of the engine, not of any one specific engine. I'm sure it's smoothed over and tweaked to make it more general and pretty. Though I don't doubt that the shapes of the curves represent the way the engine performs.

 

[stearnman]

Think I found the torque gain from '92 to '93

Here's another question...

All LT1s from '92 to '96 made (were rated at) 300HP, but only the '92 had 330 ft-lb torque while '93 to '96 generated 340 ft-lb of torque.

How did GM add 10 ft-lb of torque? What's the difference between the car years? Was it in the exhaust system or in the engine?

There were numerous detail changes between the 1992 and 1993 engine. I can't recall offhand what they were, though, just remember that there were many small changes after the first year of the LT1.

Ok, I think I found where GM gained the 10 ft-lbs of torque...most-likely.

While I was doing research for my water pump change for the weekend, I came accross this:

Apparently there was a change in CAM specs from '92 to '93( thru '96). I'm thinking this is the most-likely reason for torque gain.