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Cooling system flow direction

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When the Lt1 first came out, a big deal was made about the flow direction of the coolant, from the top, or heads on down, as an improvement in engine cooling system technology, and adding to the longevity of an engine. Now, I recently read that the LS1 & LS2 were reverted back to the old system, of coolant flow from the bottom of the engine up and out thru the heads. My question is, is this correct, and if so, why? What was the technical reasons for reverting back? The explanations for going to the heads first system made a lot of sense, and I have not heard anything about why this methodology was dropped, if in fact it was dropped. If it wasn't, then why is this significant difference not publicized as superior to the life of the new small-block engines, when compared to the competition?

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O.K. Dave, I went back to my resources and found the magazine article that started me wondering. It was in the July,1997 issue of "Car Craft" magazine, in an article called,"Shoe-In", starting on page 41. It was written by Marlan Davis, a man who knows cars. This article is about transplanting a '97 Corvette LS1 V-8 into a '55 Chevy Del Ray 2 dr. shoebox. The transplant was being done as an experimental exercise by Scott Leon of the Chevy Raceshop at their Desert Proving grounds, to see what would be necessary to make this a successful transplant. On page 42 of the article,Davis quotes from Leon, "Unlike the late LT1 and its reverse-flow cooling system, LS1's use bottom-up cooling, albeit modified from conventional systems with a suction-side thermostat and weep lines coming off the rear of the heads."............. The article also has a list of the 24 stock Chevy parts that were used from other applications to make this transplant a success. I guess all things are possible when you have the entire GM parts bin to pick from! But nowhere in this or any other article is an explanation of why the cooling system was reversed -- again! As an aside to this is a comment that was made in another thread about the new Impala 9C1 & 9C3 police cars, not using the new V-8 because of idling cooling problems! Hm-m-m-m???

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Now I went a-diggin' again from an inquiry made by one of our correspondents on another thread asking about LT1 specs. So this is straight from the General's archives. on the 1996 Caprice/Impala- Engines page on the Product Information Guide. "A reverse-flow cooling system circulates coolant through the cylinder heads before the engine block, improving heat transfer in the engine and radiator, and allowing a higher compression ratio for increased power" If it was so good in '96 that this feature was one of six features that was highlighted about the technical features of these cars............. WHY ARE THEY NOT STILL USING IT ? I'M still waiting for a responsible answer!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

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Well Dave, I finally got the answer to my question....... but not from any of the "experts" on this forum! I just got the Dec.2005 issue of GMHIGHTECHPERFORMANCE magazine. They had a feature article on the LT1 vs the LS1 engines. In this article, on p.62 they quote GM engine-builder Ray Bohacz, when asked why the switch. He said," There seem to have been several reasons behind it. Apparently there were some problems with air pockets developing in the systems themselves. I'm also not sure that reverse-cooling reaped the benefits that GM thought it would. It allowed them to run a high compression ratio in the LT1(10.4:1), but high compression means a high output of oxides of nitrogen, and that raises emissions questions. As for the LS1, its' heads are so much better that they make more power without the emissions penalty." Now that's his quote, but I don't agree with some of the statements that he made as fact, i.e., high compression raises NO2 output. Other studies have concluded otherwise, but somebody got convinced at GM! <_<

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The stuff that shows up on the right side of the C&G page!  Wow.  Of 2005 vintage. 

The 5.7 V8s and 4.3 V8s put into the RWD Caprices of the mid 90s touted the reverse coolant flow for keeping the top of the engine cooler and it sort of made sense to me, at least reading what they had to say.  So many of these are on the road and I don't believe that people took their stock/base back to the dealerships to have their water pumps changed so the vanes pushed the coolant in the other direction.  And so many of them have successfully racked up 200,000 + miles.

The other thing that was said of these reconfigured engines was that the spark control (sounds like the equivalent of a distributor and rotor) now had an optic feature.  I've read that some people had to replace these along the way.  I'm not exactly sure how this system would work.

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18 hours ago, trinacriabob said:

The stuff that shows up on the right side of the C&G page!  Wow.  Of 2005 vintage. 

The 5.7 V8s and 4.3 V8s put into the RWD Caprices of the mid 90s touted the reverse coolant flow for keeping the top of the engine cooler and it sort of made sense to me, at least reading what they had to say.  So many of these are on the road and I don't believe that people took their stock/base back to the dealerships to have their water pumps changed so the vanes pushed the coolant in the other direction.  And so many of them have successfully racked up 200,000 + miles.

The other thing that was said of these reconfigured engines was that the spark control (sounds like the equivalent of a distributor and rotor) now had an optic feature.  I've read that some people had to replace these along the way.  I'm not exactly sure how this system would work.

The name wasn't Opticspark it was OptiSpark.It was exactly a distributor and once they got it right, they are fantastic. The original ones could get moisture into them that couldn't get out.  The later ones and aftermarket ones get vents so the moisture can evaporate out.   The optispark is situated behind the water pump and connected directly to the crankshaft. It has a disk with 360 slots in it (one for each degree of turn) and an optical sensor could detect the exact position of the crank with high accuracy. This allowed for very precise control of the spark in a time before true electronically timed ignition.

Replacing a bad optispark is a pain in the butt... doubly so on cars with the towing packages. To get to it, the water pump must come off. On towing package optioned cars, this means the mechanical fan and the entire secondary belt system that drives it must also come off.   For added fun and excitement, if you have a water pump go bad, not only can you count on it take the optispark with it, but you can also lose power steering as the spot where the water pump fails causes coolant to leak right onto the ribbed side of the serpentine belt making it too slippery to run the power steering pump under load.

The whole system gets a bad rap even among guys who love the LT-1.... but when you have one running well, they run really really well.

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4 hours ago, Drew Dowdell said:

The name wasn't Opticspark it was OptiSpark.It was exactly a distributor and once they got it right, they are fantastic. The original ones could get moisture into them that couldn't get out.  The later ones and aftermarket ones get vents so the moisture can evaporate out.   The optispark is situated behind the water pump and connected directly to the crankshaft. It has a disk with 360 slots in it (one for each degree of turn) and an optical sensor could detect the exact position of the crank with high accuracy. This allowed for very precise control of the spark in a time before true electronically timed ignition.

Replacing a bad optispark is a pain in the butt... doubly so on cars with the towing packages. To get to it, the water pump must come off. On towing package optioned cars, this means the mechanical fan and the entire secondary belt system that drives it must also come off.   For added fun and excitement, if you have a water pump go bad, not only can you count on it take the optispark with it, but you can also lose power steering as the spot where the water pump fails causes coolant to leak right onto the ribbed side of the serpentine belt making it too slippery to run the power steering pump under load.

The whole system gets a bad rap even among guys who love the LT-1.... but when you have one running well, they run really really well.

That's a wealth of information.  I didn't know about the 360 increments.

In RWD form and with such an engine bay, these engines look like a beauty.  Certainly like nothing we see today.  I don't know how much the Optispark fix would cost (I'll look) but if the water pump had to come off and the car had some miles on it, they might as well do the water pump at the same time.  Now if the water pump goes, that sounds like a bad domino effect.

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