I don't understand the thinking , can someone explain the advantage.
thanks
greg

 

Gen II engines, the LTx's, have a reverse flow cooling system. The coolant flows in the opposite direction that it "always did" before this series engine. This is not a change easily made to the Gen I engines.

The above is NOT to be confused with the reverse rotation water pump used in all Gen I, C4s. The serpintine belt turns the water pump pulley in the opposite direction a "V" belt does. Therefore, a reverse rotation pump is required to make it function properly.

RACE ON!!!

 

The design advantage with the "Reverse Flow" heads on the LT's is that it cools the cylinder head first thus keeping the running temps in the cylinders down so that a higher compression ratio could be used without the adverse effects of detonation (pinging). By introducing the "cold" water to the cylinder head first (basics of thermodynamics says faster heat transfer at larger delta temp) the majority of the heat generated in the cylinder heads is transfered to the "cold" coolant first and thus reduces combustion chamber temps therefore reducing the chance of detonation due to "hot spots" in the combustion chambers from poor cylinder head cooling.


Obviously the cats meow seeing as how the LS motors went right back to the "conventional" flow cooling. Not that the design didn't work, just looks like it wasn't as big of a deal as the General made it out to be seeing how they went back to the "older" technology to cool the new LS1/6 platforms

 

heat is HP and they found out that even if it prevented detonation it killed HP because the chambers in the head were cooler.

 

The LT1 head desing made gobs of HP. A simple cam swap with a set of headers and you are at 350+RWHP with an LT4 (Same HP killing reverse flow heads). Where a normal set of GM heads would cause a motor to detinate at 10.5/1 the reverse cooling heads enable the same motor to run on 87 octane.


Here is the real reason the LS1 went back to traditional cooling not because it made more power. The real reason was because traped air was PITA for the engineers to deal with and the LS1 heads where so good they did not need the extra compresion.


"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.

Like most engines of the last 20 years or so, the LS1 uses a 195 degree thermostat. Nominal coolant temperatures are similar to what we see in LT1/4 engines. The new engine will use "Dex-Cool" coolant introduced last year in many GM vehicles. Dex-Cool has entirely new anticorrosive chemistry that is longer lasting and more friendly to cooling system parts, especially seals."

 

if the reverse flow heads made more HP the NASCAR engines would use them. the hotter the combustion chamber the more HP as long as you can control detonation. the reason that a aluminum headed engine needs more CR to make the same HP is because the aluminum heads pulls more heat from the combustion chamber.the new LS-2 6 liter engine uses 10.9:1 CR and does not use reverse flow. it was a crutch till they got the new LS engines out. air bubbles in the head water jackets are always a problem as we had to run external plumbing on our BBC aluminum headed drag engines to get rid of the hot spots,localize boiling, in the combustion chambers with the 14:1 CR.

 

NASCAR is not a relevant statement we are talking about stock GM heads.The LS1 makes its power form the 15 deg angle and better flow so there is no need for the higher compression. The LT was a huge improvement over any stock SBC head GM had ever mass produced and that is why the LT's make more power then all previous Gen I SBC's. You can bash the LT heads and reverse cooling if you want but the concept worked and made better HP then non RV motors and if the LS x would have used it and ran higher compression they would be making more HP, but they would have the same inherent problems with cooling due to reverse cooling propensity to create air pockets. By no means was reverse cooling a gimmick. Is the LS1 better then the LT, yes but the LT is better then the previos Gen. If you want to talk about a bad idea with the LT1 then you need to look at the opti. Placing a distributor with moisture problem under a water pump and at the bottom of the motor is a problem.

 

i am referring to the concept of reverse flow,if it was better they would still be using it and if it made more HP you can bet it would be on the NASCAR engines

 

I am also refering to the concept but as it aplyes to a normal SBC. What the limitations are of RC I can not tell you, why it was scraped is because they came up with a better mouse trap, 15 deg heads and reverse cooling has its problems, mostly cooling.

 

GM could have very well stopped using the reverse flow cooling due to legal issues: http://www.evansvsgm.com/

 

And now ur gonna get my 2 cents here. Since i just picked up a used '94 Z28 for a daily driver i have to say something about the RC LT1 - i'm very impressed. It is only rated as 270 hp but getting on that throttle is just fast fun. I don't why it feels so fast (maybe my previous DD ricer was such a dog) and yet it doesn't smoke the tires. Man i'm passing everything at the on-ramps but no tire noise. Kinda thought the roller cam would be a hi-rever but redline is 5250 rpm and the trans shifts by 5500. It really gets up and runs above 2250 rpm for a 4 seat car and i'm very happy with it. Forgot and left the emergency brake on for a freeway drive and didn't even feel/notice the drag - plenty of torque. Had to replace rear rotors already though ($450).
The owners manual says 91 octane but that lower octane can be used if throttle use is controlled - no WOT. I had the brake mechanic look for my rear diff tag but he said it was missing. I suspect fwy gearing as it hasn't broke the tires loose yet - but i haven't tried from a dead stop yet either.
With a factory rating of 270 hp i feel this engine/car has great potential. It does seems as fast or faster than the '92 LT1 vette i road in not long ago. Once i get my C3 back on the road (and out of the garage) i would like to try pocket porting the heads with a new camshaft and Edelbrock headers (full exh sys - hi flow cats and mufflers too). This should let that LT1 short runner intake breath at hi rpm. The FI is multi rather than sequential but seems fine with no complaints here.
I know i don't have much input about the reverse cooling right now but i want to report this RC LT1 is a lot of fun for the money as is.
cardo0

 

That makes things a bit more clear and looks to be the little secret GM didn't tell about why the ditched RC.

 

That web page gives one side of the story. However court proceedings in CT are public
(not secret) events, and the second case was covered here in the local papers.

A google search turns up a little more balanced report of the story here:

http://www.zwire.com/site/news.cfm?n...76&amp%3Brfi=6

And a sympathetic magazine article here:

http://www.fortune.com/fortune/small...7977-2,00.html


The newspaper story (Litchfield County Times, 11/28/03) concludes with some interesting
paragraphs.