Big Block Heat

[Joel T.]

Hi All;

I have been putting some miles on my 1965 BB to get things broken in.. there are probably 500 miles or so since the motor rebuild.

She runs hot, hotter than my small block. I've heard commentary that BB cars did run hot but I am trying to get a sense for what is normal here.

I have a repro temp sender in there so I know the readings are higher than actual.. She will certainly creep up at a stop light or after a higher speed run. An engine shut off and restart will result in a very high reading which will come down while driving. The car has never overheated, nor do I loose and coolant when I shut her down.

Timing is stock as is the distributor. I have a reproduction fan clutch in there as well. I'm not hearing any detonation. Is this just the nature of the beast or am I missing something?

Any thoughts or suggestions are welcome!

Joel

[Roger O.]

Re: Big Block Heat

A temp gun to confirm accurate temperature is a must. How much vacuum advance is built in your distributor ?

[Paul H.]

Re: Big Block Heat

My big block runs a little warmer than either of my small blocks. On a warm summer day in traffic it will creep up around 220. It cools right down to around 180 out on the open road. Prolonged highway on a warm day, it might get up around 220. My small blocks under the same conditions seem to stay around 180. All are stock cooling systems with clutch fans and I have confirmed the readings with an IR gun. On balance, it has been my experience that big blocks do run a bit warmer. It's alot of motor in a confined space after all.

[Joel T.]

Re: Big Block Heat

A temp gun to confirm accurate temperature is a must. How much vacuum advance is built in your distributor ?

Roger,

I have a temp gun so I will check out the actual numbers... On the distributor, I have not checked the can but I will. I got the TI system from Dave Feidler so I just assumed that it was correct, given that he knew what the application would be. I probably need to check vacuum at idle given that the cam in there is a bit hotter than stock. May be an issue there.

Joel

[Joel T.]

Re: Big Block Heat

My big block runs a little warmer than either of my small blocks. On a warm summer day in traffic it will creep up around 220. It cools right down to around 180 out on the open road. Prolonged highway on a warm day, it might get up around 220. My small blocks under the same conditions seem to stay around 180. All are stock cooling systems with clutch fans and I have confirmed the readings with an IR gun. On balance, it has been my experience that big blocks do run a bit warmer. It's alot of motor in a confined space after all.

Paul;

That's about what I am seeing... but as Roger pointed out, I need to get the exact numbers via a temp gun. I have that repro temp sender in there and I know they read high... I also agree that there is a lot of heat in there and a lot more mass to cool as well. When I got this car everything in that engine compartment was dried out. Today I make a point of opening the hood and leaving it open as soon as I put either car back in the garage after a run...

Thanks for the input!

Joel

[Terry D.]

Re: Big Block Heat

Joel
Check the archivies about timing and heat. This has been covered quite a bit. Timing can really cause problems in the heating department. Make sure distributor, vacuum advance and centrifical advance are all working properly. If you changed cams then it would be my guess that you don't have your timing curve set up properly for that camshaft. Just went thru this with a hopped up small block. Car was running hot and not a whole lot of power. John Hickley wrote a couple of great articles for Corvette Enthusiest about advance and timing. Also google "Lars Grimsrud, he did a great article along with Duke Williams about the different advance cans for GM distributors. Learned alot in the past few weeks about this problem. Now the car is a real pleasure to drive and quicker than I expected.
Hope this helps
Terry

[Joe R.]

Re: Big Block Heat

Joel,

Does your car have full time or ported vacuum advance? I can dig up a thread with some info from Duke about converting from ported to full time to make the engine run cooler, if you like.

Joe

[Roger O.]

Re: Big Block Heat

Joel
If you have a MightyVac gun put it on your advance can ,if it increases your idle speed from normal you might have to get a vac can more suited for your engine build.
Roger

[Jack H.]

Re: Big Block Heat

My L78 was bone stock (Duntov, B-Gold, Triple Crown) with a 'Last of the Mohicans' NOS Harrison BB aluminum radiator (MAN, did I have to look and 'bend over' to get that item!). The temp sender was a real McCoy AC part from the era. The fan was factory stock and fan clutch was a Fred Oliva restored item.

It ran quite consistently at 180-190F (verified with an IR gun)...

[Joel T.]

Re: Big Block Heat

All;

Great advice and food for thought!

The set up is stock, with a 4150 Holley on top so I have to believe it is full time vacuum...

I do have a mighty vac. I assume I will pop a "T" fitting in there to see if I can apply more vacuum and increase idle speed... slick idea (wish I thought of fit ).

Unfortunately there was very little original under the hood when I got the car so most of the key components are repops.. radiator (DeWitt), shroud (I forget), fan clutch (Paragon) and sender (ditto). However, to Jack's point, they will run cool(er) that what I am seeing so I need to start digging.
Joel

[Jim T.]

Re: Big Block Heat

If your vacuum soruce on the Holley for the vacuum advance is not coming from a port at the base of the Holley but from a port at the side of the Holley, you do not have the vacuum line connected to full time advance.

[Joel T.]

Re: Big Block Heat

If your vacuum soruce on the Holley for the vacuum advance is not coming from a port at the base of the Holley but from a port at the side of the Holley, you do not have the vacuum line connected to full time advance.

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

[Rich P.]

Re: Big Block Heat

Joel,

in my experiance working on these cars a big block is much more sensative to ambient temp than a small block. In other words Jacks car could run coller because he is in CO where the temp and humidity is generally better than NJ in the summer.

Rich

[Joel T.]

Re: Big Block Heat

Joel,

in my experiance working on these cars a big block is much more sensative to ambient temp than a small block. In other words Jacks car could run coller because he is in CO where the temp and humidity is generally better than NJ in the summer.

Rich

Hi Rich,

How you been? I understand what you are saying. We actually had a cool day, a few days back and she managed to hang in there.... In any event I will check these things out... I need something to tinker with!

Joel

[Duke W.]

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