Since I got my car, I have tried to find the differences between the LT1 and the modern chevy small block.

I know the differences now. But my question is, why did GM goto the Reverse Cooling? Did it really make a difference or was it a failure? I know I may not be able to get my answer . But from what I have looked at , I dont think GM used the reverse cooling on any other motor after the LT1. And I know they didnt use it on the LS1. So does it even have an advantage?

Mike

 

I beleive the reverse cooling sent the coolant through the heads first and block second as opposed to the block being cooled first in the traditional SBC platform. The advantage to the heads being cooled first is that is where the power is made and keeping those cool provides optimal burn......

Brad

 

From: http://www.idavette.net/hib/ls1c.html

Cooling the Traditional Way

Remember 1992, when Chevy raved about the Gen II’s reverse-flow cooling? Well, reverse is, apparently, out. The new engine uses conventional pushrod V8 cooling. Coolant is pumped into the block, around the cylinders, up into the heads, then out to the radiator. The reason Gen II went reverse was that, to make the power Corvette Development wanted; it had to have a higher compression ratio (LT1, 10.2:1; LT4, 10.8:1). Higher compression made for detonation. The cooling system was revised to run the cylinder heads cooler as an antidetonant strategy, and to run the cylinder bores hotter for higher oil temperature and less friction. Clearly, reverse-flow cooling, the publicity darling of the Gen II engine, was really nothing more than a fix that allowed the limited cooling of the old Small-Block head to work with the higher compression necessary to reach the 300 horsepower level.

Air in the cooling system becomes problematic if it gets into the water passages surrounding the combustion chambers. This often causes localized boiling and that, in turn, allows hot spots to develop on chamber walls and they cause detonation. The problem with reverse flow is that with coolant flowing downward and air bubbles flowing upward; keeping air out of the Gen II cooling system was difficult.

Though the LS1 has a lower static compression ratio; its cylinder heads have improved combustion chamber design and intake ports that breathe better. Those features allow them to make more power. The clean-sheet-of-paper approach also allowed design of the cooling passages around the chambers to be more efficient such that the engine can put out more power than the Gen II but yet have coolant flow in the conventional direction to eliminate problems with aeration. With a better combustion chamber and water jacket design and improved antifriction technology in the block, pistons and rings; it made sense to go back to the normal-flow cooling system.

 

Reverse Cooling

...what stops us from dropping in a ZZ4 crate...

 

and severly limites head choices.

Don't let wings post make you feel like we have flawed technology though. If your running a 160 or 180 degree stat and have the fans programmed to come on earlier like most of us here do then you aren't likely to have any problems with localized boiling causing hot spots and detonation.

 

That's probably all true.


The LS1 also is all aluminum and would probably benefit with std cooling since the al block expands at a different rate than the steel cly sleeves which can lead to piston slap.

Hey...it sounds right to me

 

ty folks. I wonder if they will try it again on any other GM motors? I doubt it though.

 

I'm not saying anything bad about the LT1. As far as I'm concern, I love it. I was just trying to show why GM did the reverse cooling and why they switched back. That's all.

 

I know you were just posting the facts Wing wasn't trying to make it sound like you were bashing our beloved LTX's

-brent

 

 

Basically, it was the last gasp effort to get more power out of a production SBC before they changed to a complete, brand new design (LS1).

 

Ok so GM decides to reverse cool this thing, but then why do they design the motor to run at such a high temp? I mean the fans don't kick until like 240 or some obsurd temp. They seemed to have the right idea but couldn't cully finish it, cool the top end for better performance, but let the motor et hot for better emissions?

 

As far as I know the only reason that GM stopped using reverse flow cooling was that they were facing legal action. Someone else had the patent rights to reverse flow cooling.
Also what AsianSensation said is true, it allows for higher compression with out detonation. Look at the LS1 it runs at 10 to 1 compression were the LT1 runs at about 10.5 to 1. Also you can run lower grade gas in it without adverse effects not that you would want to.

 

Fans come on at 225. Dont remember the specifics but it doesnt matter. I never really get over 180 unless the car sits and idles for 10 minutes, it doesnt reach that high of a temp.
Also, I doubt someone has a patent on reverse flow cooling. I dont see how that can legally work. It would be interesting to know if its true, but I highly doubt it. Most likely they didnt stick with it because it was not needed and standard cooling has more advantages over reverse flow at least component-wise. Reverse flow is slightly problematic, at least when we want to run better 15 or 18 degree heads and/or get a new radiator but I agree that its nice we can run over 11:1 compression with ease on pump gas.

LT1- 10.4:1
LT4- 10.8:1
LS1- 10.2:1

 

Actually, the thermostat is a 180º when most other emission friendly engines were using 195º, so it is not really designed to run at a high temp, but lower. All engines with electric fans are going to heat up when there is no air moving across the radiator. If you want it to not get to 226º when the fans are supposed to come on, you can easily change it with a fan switch or programming.