Too Hot Exhaust

Not running AV fuel are you? For that type of heat generation you've got to have too much unburned fuel getting through. You've described no other "drivability" problems ...... that is, misses at idle, surges, exhaust smells funny ...... really poor fuel economy ....... you have no emission controls ......hell .....do you even have a PCV valve?
Q: When you say "plugs that match the ignition" what do you mean? I would think that you would put the heat range in that belongs to the "Dauntless".
It's hard to imagine this is happening just because of the HEI swap. It will jump a wider gap .....even in lean or cold conditions ...heck it'll even fire a fouled plug..... but it shouldn't modify your flame duration any ........if anything I'd think that it would give you cleaner combustion ......not the "after burner" effect that you're describing (unless you're running AV fuel)
Are you sure that you don't just have a leaky "fuel enrichment" circuit if not just a plain leaky carb. The last Holley that I worked on was really simple and had external float adjustment ...... have you checked this out?

GeeAea

/wwwthreads_images/icons/tongue.gif Sometimes a lean mixture can cause delayed burning and the exhaust gas temps go up./wwwthreads_images/icons/frown.gif

CJDave

Yes Dave, I agree ........ a too lean condition can create an incomplete flash in the combustion chamber .....or even a miss ...... both of which would send unburned fuel into the exhaust manifold where it would be ripe for ignition. I've just never have heard of this problem in a non-smog motor....... Oh I've blow several mufflers off by turning off the ignition to cause a back fire when I was a juvinile..... heck .. I once did a tune on a 307 chevy with an AIR pump ......accidentally pulled the vacuum line off the diverter valve ...... which vents the air instead of sending it to the exhaust manifold when you let off the gas ..... I did a road test and pulled some higher rpms in second gear and let off the gas ....... blew the muffler out at the seams ...... I did that tune for nothing that day ...... all my labor went to the new muffler....... I NEVER made that mistake again with an air pump motor.

Heck ........ with a 68 motor ...... without all the restrictions of later motors........ this should be a trouble free swap.

Although I think this has to be a fuel related anomoly (leaking carb, etc.) since the condition didn't evidence itself before the distributor swap ....... why not try advancing the timing to start the combustion process sooner.

......I wonder ....... if he got an even firing ditributor by accident ....... would the rotor be in the right position to just catch the cylinder late in the combustoin stroke ...... ........ Naah ......(just thinking aloud)

/wwwthreads_images/icons/smile.gifGeeAea/wwwthreads_images/icons/smile.gif

Re: Too Hot Exhaust- dorfs!!!!

That was 6000 feet elevation .....not 6000 rpm. Now that you made me take note of that ......... wouldn't 6000 feet simulate a "wider throttle opening" that is IT WOULD ENGAGE THE FUEL ENRICHMENT CIRCUIT ( the additional fuel induced into the intake stream to compensate for lower vacuum at wider throttle opening at road speed ) since it has less vacuum. I know that at higher elevations an auto trans shift points change due to the "simulation" of a wider throttle ...... at least on those using vacuum modulators for shifting - Chrysler used a throttle position valve in its models.
I don't know how this is adjusted on your Holley ........but I'm sure that there is a remedy that shouldn't be too complicated. I believe that the fuel enrichment circut was a spring thingie which was held back by one of the vacuum sources ( either ported, venturee, or manifold ) .....as the vacuum decreased ......the valve induced more fuel. Perhaps rejetting (smaller)

dorfs operates in the upper stratosphere ......... he'll know what's up.

Re: Too Hot Exhaust- dorfs!!!!

I too did the HEI conversion on my 225. Both the mechanical and vacuum advance distributor curves for the 231 odd-fire motors is different than the specs for the 225. I found this out when I took the rig to a tune-up guru. The distributor had a bad shaft, (luck of the draw from the wrecking yard), so that was replaced with another used shaft and the curve was re-tailored to match the original 225 specs. Also a new vacuum can was installed to match the 225's original that had less advance to avoid engine damage in time. These specs can be found in better libraries' reference section in the Mitchell's Manuals. Then with the correct info, someone that knows how to work with a distributor machine can set it up correctly. I guarantee you that if you get rid of the headers and go back to stock cast manifolds, you'll lower the under hood temp a bunch and only lose power above 3500 rpm, probably not an area you exceed very much. I also had the Holley 390 and Offenhaeuser Dual Port intake manifold. Ran real good with stock cast exhaust manifolds. I've now crossed over to the even-fire side with a '80 Buick 252/4.1L V-6. More power yet.