Big Block Heat

[Joel T.]

Re: Big Block Heat

It's my understanding that L-78 has full time vacuum advance but the OE 201 VAC is not a good choice because it requires about 15.5" to pull to the limit and the engine will only produce about 14" at 900.

A 12" B20 VAC is a much better choice.

So what VAC does your L-78 have, and does it perform to spec?

Duke

Hi Duke;

Thanks for weighing in... I need to check all that.... and will post some results by the AM...

I'm a convert to your 2" rule.. and have applied it to my '63 with good results... Now I need to check into this puppy.

Regards,

Joel

[Ridge K.]

Re: Big Block Heat

I've been driving (not trailering) big block Chevrolets for just over 40 years now, and presently have two sitting in my garage ('66 and '67).

Living in Oklahoma summer heat with frequent 100 degree temperatires, every big block I've driven over these past forty years have ...ran hot. It's only a problem to the boil-over point, during the hottest part of the summer.

I've tried everything over this lenghty period of time (timing, NOS radiators, aftermarket radiators, aftermarket fans, etc.).
The only 100% effective fix I've found for our 100+ degree days, is a high volume water pump. That seems to me to be the factory "flaw" or at least the one that "is the straw that breaks the camel's back".

With a high volume, aluminum water pump purchased right out of the GM Performance Parts catalog,...... my problems have been solved.

The pump won't judge well,....... but on a driver, will help keep the engine cool.

[Kenneth B.]

Re: Big Block Heat

[quote=Ridge Kayser (45955);500728]I've been driving (not trailering) big block Chevrolets for just over 40 years now, and presently have two sitting in my garage ('66 and '67).

Living in Oklahoma summer heat with frequent 100 degree temperatires, every big block I've driven over these past forty years have ...ran hot. It's only a problem to the boil-over point, during the hottest part of the summer.

I've tried everything over this lenghty period of time (timing, NOS radiators, aftermarket radiators, aftermarket fans, etc.).
The only 100% effective fix I've found for our 100+ degree days, is a high volume water pump. That seems to me to be the factory "flaw" or at least the one that "is the straw that breaks the camel's back".

I cant argue with success but wouldn't a high volume pump move coolant through the radiator faster which would give it less time to cool before returning to the block? I have found that the new fan clutches are 190 degree & that is too high. I have four 67 big blocks. Two 435'S. one 400/air & one 390/air all will run no hoter than 190/200 in 90 degree heat. I he 435's are 4:11 rears.
KEN

[Ridge K.]

Re: Big Block Heat

Ken, your thought makes perfect sense to me. Maybe one of our resident engineers will comment.

I described my results in either three or four cases. The possibility always exists that it was simply shear luck that my cars seemed to be responding.

Another factor is that I have much more experience with 396 Chevelles. You clearly have more experience with 427 Corvettes.
Interesting thoughts.......

[Jack H.]

Re: Big Block Heat

Quite true! Plus, with the altitude here, most cars run leaner when the carbie is 'tweaked' for the altitude.

BUT, in order to get all those awards, this car literally went everywhere (Florida for PV, Los Angeles, Chicago, Detroit, Scottsdale, Joplin, Bloomington). So, while cumulative drive time WAS somewhat restricted, the car DID spend time at/near sea level, eh?

[Jim T.]

Re: Big Block Heat

Jim;

I'm pulling vacuum from the side of the front metering block.. I do not even see a vacuum port at the base.... I can probably tap into manifold vacuum from the power brake port....

Am I correct in assuming that what I have is ported vacuum versus full time? Is this an original design issue?

Thanks,

joel

The vacuum port according to the Holley information I have coming from the metering block is ported.
Do you have a vacuum hose from the base of the Holley going to the choke pull off? You can tee into this vacuum hose for full time vacuum.

[Joe L.]

Re: Big Block Heat

I've been driving (not trailering) big block Chevrolets for just over 40 years now, and presently have two sitting in my garage ('66 and '67).

Living in Oklahoma summer heat with frequent 100 degree temperatires, every big block I've driven over these past forty years have ...ran hot. It's only a problem to the boil-over point, during the hottest part of the summer.

I've tried everything over this lenghty period of time (timing, NOS radiators, aftermarket radiators, aftermarket fans, etc.).
The only 100% effective fix I've found for our 100+ degree days, is a high volume water pump. That seems to me to be the factory "flaw" or at least the one that "is the straw that breaks the camel's back".

With a high volume, aluminum water pump purchased right out of the GM Performance Parts catalog,...... my problems have been solved.

The pump won't judge well,....... but on a driver, will help keep the engine cool.

Ridge-----

If the pump you used was a GM #14058915, that really isn't a high volume pump. It's a very good waterpump (never actually used on a PRODUCTION engine, though) but it's just a standard volume pump, pretty much the same as any of the cast iron big block pumps except for the casting material.

[Ronald L.]

Re: Big Block Heat

I agree on the comment above of ambient sensitivity.

Last weekend, Saturday was a 90+ and at idle for a long time (proving out the install of a new DeWitt's rad) the gauge pushed 240. out on the road the temperature dropped back quickly to, 200-210.

Sunday, about 80 degrees an a lot less sun load and the car was sitting near the 180 range driving the same streets.

Now I verified my gauge and sender before install. The sender (wired into the cars wiring) measured 210 in a beaker of continuously boiling water and water should be boiling at about 212 in Michigan.

These systems aren't linear, but that doesn't matter much either as long as it is close at the operating range.

Thermostat was verified as opening at 180 too by the same method. I returned one 180 deg unit that did not open at all until 195 even though it was marked 180...

[Ridge K.]

Re: Big Block Heat

Ridge-----

If the pump you used was a GM #14058915, that really isn't a high volume pump. It's a very good waterpump (never actually used on a PRODUCTION engine, though) but it's just a standard volume pump, pretty much the same as any of the cast iron big block pumps except for the casting material.

Thanks Joe, for that tip. I still have one on my SS Chevelle, so I'll check the number.

Perhaps I was believing the parts counter salesman's hype......

[Michael F.]

Re: Big Block Heat

all my big blocks back in the day and thru 84 NEVER ran hot, all were stock
67 427/435 cars except for a 70 454 ls5 also no heat issues.

[Roger O.]

Re: Big Block Heat

Ridge-----

If the pump you used was a GM #14058915, that really isn't a high volume pump. It's a very good waterpump (never actually used on a PRODUCTION engine, though) but it's just a standard volume pump, pretty much the same as any of the cast iron big block pumps except for the casting material.

Joe,
Just repeating what I have "heard" over the years but I was told that the 14058915 was the L88 pump and it was the closest thing to a blueprinted pump you could buy at the time. "Supposedly" was a higher volume pump than standard and far less prone to cavitation than standard and again "supposedly" had a larger bearing. Is there any documented truth to any of this ?

Roger

[Joel T.]

Re: Big Block Heat

It's my understanding that L-78 has full time vacuum advance but the OE 201 VAC is not a good choice because it requires about 15.5" to pull to the limit and the engine will only produce about 14" at 900.

A 12" B20 VAC is a much better choice.

So what VAC does your L-78 have, and does it perform to spec?

Duke

Hi Duke;

Ok, I did some checking.. I popped my Mighty Vac in the vacuum like via a "T"... Idle vacuum was 13" per that gauge... (a stand alone gauge read 9" at about 500 RPM and about the same 13" at 1000). Increasing the vacuum with the MV did not increase idle speed which tells me that we are getting full advance at idle already. Given this, I did not take the distributor apart..

I'm not sure what the difference is ported versus non-ported vacuum but from what I saw, the vacuum was there consistently.

I did come checking with my temp gun... after idling in the garage for a good while... The thermostat housing read 210.. the left side of the radiator registered about 200 and the right side top about 15 degrees less. Lower radiator hose was about 150.

Consistent with what other folks have posted, I do see a difference based upon ambient temp. We actually had a cool day a while back and the temp response was noticeably better.

Joel

[Roger O.]

Re: Big Block Heat

Hi Duke;

Ok, I did some checking.. I popped my Mighty Vac in the vacuum like via a "T"... Idle vacuum was 13" per that gauge... (a stand alone gauge read 9" at about 500 RPM and about the same 13" at 1000). Increasing the vacuum with the MV did not increase idle speed which tells me that we are getting full advance at idle already. Given this, I did not take the distributor apart..



Joel

Joel ,
You can't use the T for the test I referred to. You can use the T to monitor but you will not be able to increase the vacuum using the T.
First look at your tach with everything hooked up normally , then remove line from vac can nipple and plug , then attach hose from MV and pump it up to say 20" , if the idle increases over normal idle then your not pulling in all the way at idle.
(The most accurate way is to use your timing light to watch advance.)

[Roger O.]

Re: Big Block Heat

It might be best for you to check your vac advance by using a timing light and removing the vac line and watching your timing line.
I think with your low idle vacuum you might be a candidate for a B28 (VC1810 ).

[Joel T.]

Re: Big Block Heat

Joel ,
You can't use the T for the test I referred to. You can use the T to monitor but you will not be able to increase the vacuum using the T.
First look at your tach with everything hooked up normally , then remove line from vac can nipple and plug , then attach hose from MV and pump it up to say 20" , if the idle increases over normal idle then your not pulling in all the way at idle.
(The most accurate way is to use your timing light to watch advance.)

Hi Roger;

Sorry, I forgot to include in my post that I did that as well. Plugged the vacuum at the carb and connected the MV directly to the can. The can began to pull in at about 9" and was all the way by the 12-13" mark. I did take it up past 20" with no change. Also increased vacuum in small steps after 13" with no increase in RPM...

Regards,

Joel