Two questions

[John L.]

I spent most of my time with Pontiacs, so I am more familiar with 389's than 327's. I have two questions regarding the 327 shp engine setup.
1) What purpose does the idler pulley and second belt serve?
2) What purpose does the water pump by pass serve?
I have a '65 350hp 327 and neither of these items are present. I will be doing some engine work and I am wondering if I need to add these back on.
Thanks in advance.

[Stuart F.]

Re: Two questions

John;

Having spent time with both (389 Ponchos and 327 chevies) I can offer the following;

1) If you lose a "long" alternator belt (common w/389's), you still have the short water pump drive belt w/idler pully to keep the cooling system going. You should know the lessons learned w/389 reverse cooling systems wherein they found out the hard way that a performance engine at high rpm's needs to keep it's cooling system in operation. Early 389 ponchos often threw their alternator belts and the engine temp needle would bury immediately as with the reverse cooling you MUST have an operable water pump. You have no natural flow of coolant due to heated coolant rising to the top in the radiator.

The by-pass noted in your #2 question is for a similar purpose. Though I have not read any engineering papers on it, I can speak from experience. Last year I drove my 63 L-76 nearly 30 miles on the highway with a thermostat that was frozen closed. The engine seemed to be running normal until I jumped on it up to +100mph for a short period of traffic passing before an exit. On the exit my surge (expansion) tank began puking out coolant like crazy through the overflow (pressure relief cap). I proceeded on home about another 2 to 3 miles at side road speeds and arrived ok. I had lost a lot of coolant, but all tests proved every thing was ok and pointed to the stuck thermostat. Had I not had that by-pass I think it fair to say I may have lost an engine. Even with the stuck thermostat, my cooling system was still able to provide limited function under normal driving conditions as it continued to ciculate through the engine.

Let's see what others more familiar with the engineering aspects of the design have to say.

Stu Fox

[Terry M.]

Re: Two questions

John;

Having spent time with both (389 Ponchos and 327 chevies) I can offer the following;

1) If you lose a "long" alternator belt (common w/389's), you still have the short water pump drive belt w/idler pully to keep the cooling system going. You should know the lessons learned w/389 reverse cooling systems wherein they found out the hard way that a performance engine at high rpm's needs to keep it's cooling system in operation. Early 389 ponchos often threw their alternator belts and the engine temp needle would bury immediately as with the reverse cooling you MUST have an operable water pump. You have no natural flow of coolant due to heated coolant rising to the top in the radiator.

The by-pass noted in your #2 question is for a similar purpose. Though I have not read any engineering papers on it, I can speak from experience. Last year I drove my 63 L-76 nearly 30 miles on the highway with a thermostat that was frozen closed. The engine seemed to be running normal until I jumped on it up to +100mph for a short period of traffic passing before an exit. On the exit my surge (expansion) tank began puking out coolant like crazy through the overflow (pressure relief cap). I proceeded on home about another 2 to 3 miles at side road speeds and arrived ok. I had lost a lot of coolant, but all tests proved every thing was ok and pointed to the stuck thermostat. Had I not had that by-pass I think it fair to say I may have lost an engine. Even with the stuck thermostat, my cooling system was still able to provide limited function under normal driving conditions as it continued to ciculate through the engine.

Let's see what others more familiar with the engineering aspects of the design have to say.

Stu Fox

Stu,

I think you captured (pun intended) the reason for the captured belt correctly.

I always thought the water pump to intake by-pass hose had to do with a more rapid climb to normal operating temperatures -- or put another way more rapid engine warm up. I will watch for more discussions on these topics. They are much more interesting than NCRS and clones.

[Kenneth B.]

Re: Two questions

Stu,

I think you captured (pun intended) the reason for the captured belt correctly.

I always thought the water pump to intake by-pass hose had to do with a more rapid climb to normal operating temperatures -- or put another way more rapid engine warm up. I will watch for more discussions on these topics. They are much more interesting than NCRS and clones.

That is what I was also told that it got hot water to the intake faster. Also I would like to give a big AMEN to your last statment.

[John L.]

Re: Two questions

Thanks everyone for the information. I will add these features back to the engine.

[Duke W.]

Re: Two questions

Corvette engines have up to three bypass circuits, internal (the third hole in the water pump legs), the heater core circuit, and the extenal bypass.

The latter was usually only on SHP engines, not base engines. It's never been clear to me why it was needed unless the car had no heater system, however, it could be a "safety system" to preclude excess pressure and/or pump cavitation if a SHP engine is revved very high when cold, prior to thermostat opening.

Duke