Big Block Heat

[Duke W.]

Re: Big Block Heat

What's the number on the VAC?

When testing you should also measure the total advance when it is pulled to the max. Then hook it back up and verify that total idle timing is the sume of full vacuum and initial.

Duke

[Ridge K.]

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.

That's interesting, Michael. And I see from your profile, you're in Texas, .......not exactly a colder state.
That baffles me.
I've had over a dozen run too warm, with two or three frequently wanting to boil over on 100+ degree days.
None were air conditioned cars (only sissy's had air or an automatic in the day). All had the correct collant mix. Most all had either NOS radiators, or the top-of-the-line reproduction radiators, or in two cases, restored original radiators.

I can't be alone ...as if one scans all the other classic car discussion websites (Chevelle, hot rodding, etc.), one will find hundreds of discussions about big block Chevys running hot, and very few discussions of small blocks with the same problem.

Your experience has thrown me......

[Roger O.]

Re: Big Block Heat

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

Hi Joel,
Sounds like you might already have the B20 which is 8* @ 11-13 so you could be right on the edge with your vacuum.
The B28 is around 8*@ 6-8 so it would have you all in but 8* degrees might not be enough to help you.
Why don't you try setting up your initial advance to see if increased timing will help to keep the engine cooler ? If it does help you could then tailor your timing using vac advance , cent and initial to obtain good all around performance.

[Paul H.]

Re: Big Block Heat

That's interesting, Michael. And I see from your profile, you're in Texas, .......not exactly a colder state.
That baffles me.
I've had over a dozen run too warm, with two or three frequently wanting to boil over on 100+ degree days.
None were air conditioned cars (only sissy's had air or an automatic in the day). All had the correct collant mix. Most all had either NOS radiators, or the top-of-the-line reproduction radiators, or in two cases, restored original radiators.

I can't be alone ...as if one scans all the other classic car discussion websites (Chevelle, hot rodding, etc.), one will find hundreds of discussions about big block Chevys running hot, and very few discussions of small blocks with the same problem.

Your experience has thrown me......

You're not alone Ridge. Every big block I have ever owned over the last 35 plus years has, on balance, run about 15 to 20 degrees warmer than my small blocks under similar conditions. Stop and go traffic, which I avoid, on warm days is when they heat up the most.

[Roger O.]

Re: Big Block Heat

I have a couple BB customers that like to run in parades and with some minor modifications they do real well.
One mod is a vac valve under the dash to bring in about 25* of vacuum advance while idling along.

[Duke W.]

Re: Big Block Heat

If you just convert all ported vacuum advance applications to full time you accomplish the same goal a lot easier. How to do it has been discussed many times here.

All 1966-67 L-72 and L-71 are ported vacuum advance and all big blocks from 1968-on.

Duke

[John H.]

Re: Big Block Heat

Hi Joel,
Sounds like you might already have the B20 which is 8* @ 11-13 so you could be right on the edge with your vacuum.
The B28 is around 8*@ 6-8 so it would have you all in but 8* degrees might not be enough to help you.

Roger -

Just to clarify for someone using a timing light, the 8* you noted is distributor degrees, not crankshaft degrees; the B20 and B28 cans provide 16* of advance at the crankshaft.

[Ridge K.]

Re: Big Block Heat

If you just convert all ported vacuum advance applications to full time you accomplish the same goal a lot easier. How to do it has been discussed many times here.

All 1966-67 L-72 and L-71 are ported vacuum advance and all big blocks from 1968-on.

Duke

Duke, should I take from this comment....... that a 390 or 400hp '67 is not ported vacuum advance.
or, were you simply making your point about L-72, and L-71s as examples.

Thanks in advance, Ridge.

[Joe L.]

Re: Big Block Heat

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......

Ridge-----


The number cast on the pump won't be 14058915. That's the part number for the pump assembly and, consequently, the number found on the box the pump is supplied in. The casting number on the pump should be 3975928. The original part number for the pump assembly was GM #3977630. That was discontinued in October, 1983 and replaced by 14058915. Both pumps used the 3975928 casting.

[Joe L.]

Re: Big Block Heat

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

Roger-----


I believe it's a myth. First of all, I don't think the aluminum waterpump was used on any PRODUCTION L-88 engines although it's possible it was used on some very late 1969 L-88's. I doubt it but I would not rule out the possibility. It was definitely not used for 1967-E69 L-88's.It may very well have been used on CRATE L-88's after 1969, though.

The aluminum waterpump uses the same size bearing as all other big block waterpumps and the same 3/4" shaft size. However, the aluminum pump uses the 5/8" pilot shaft diameter as used for all 65-70 big block pumps and not the 3/4" pilot shaft used for 71-74 big blocks.

[Roger O.]

Re: Big Block Heat

Roger-----


I believe it's a myth. First of all, I don't think the aluminum waterpump was used on any PRODUCTION L-88 engines although it's possible it was used on some very late 1969 L-88's. I doubt it but I would not rule out the possibility. It was definitely not used for 1967-E69 L-88's.It may very well have been used on CRATE L-88's after 1969, though.

The aluminum waterpump uses the same size bearing as all other big block waterpumps and the same 3/4" shaft size. However, the aluminum pump uses the 5/8" pilot shaft diameter as used for all 65-70 big block pumps and not the 3/4" pilot shaft used for 71-74 big blocks.

Thanks for the info Joe , when you sit around a bunch of guys bench-racing you can hear about anything , sometimes its best to wear pretty high boots.

Roger

[Roger O.]

Re: Big Block Heat

Roger -

Just to clarify for someone using a timing light, the 8* you noted is distributor degrees, not crankshaft degrees; the B20 and B28 cans provide 16* of advance at the crankshaft.

John,
Sorry I definitely should have noted that. I probably should have just doubled it to start with so as not to confuse anyone.

Roger

[Duke W.]

Re: Big Block Heat

Duke, should I take from this comment....... that a 390 or 400hp '67 is not ported vacuum advance.
or, were you simply making your point about L-72, and L-71s as examples.

Thanks in advance, Ridge.

I don't think the '66-'67 390 and 400 HP big blocks are ported, but I'm not sure.

It's easy to test to see if your particular engine is ported or full time.

Duke

[Ridge K.]

Re: Big Block Heat

I don't think the '66-'67 390 and 400 HP big blocks are ported, but I'm not sure.

It's easy to test to see if your particular engine is ported or full time.

Duke

Thanks, Duke.