67 427/400 Fresh Rebuild Frustration Help

[Dereck S.]

Re: 67 427/400 Fresh Rebuild Frustration Help

Thanks Mike. That's good to know. Dereck

[Duke W.]

Re: 67 427/400 Fresh Rebuild Frustration Help

A dead VAC can cause high coolant temperatures. I don't recall you saying what is installed and if it meets spec. Also, if it's set up for ported vacuum advance, convert it to full time.

Duke

[Dereck S.]

Re: 67 427/400 Fresh Rebuild Frustration Help

I'm running a new NAPA B26 with actual measured start at 7.5" Hg and full advance at 12.5" Hg. Initially, I had an NOS 360 canister that I removed early on. Using a hand vacuum pump I noticed it started later. However, I didn't record the actual measurements. I put 100 miles on the car on Saturday with initial timing set at 7 degrees. It ran good aside from the coolant temp that rather quickly increases as the car idles. Even with ambient temps in the low 70's. I'm concerned how it will behave with ambient temps in the 80's.

[Leif A.]

Re: 67 427/400 Fresh Rebuild Frustration Help

I'm running a new NAPA B26 with actual measured start at 7.5" Hg and full advance at 12.5" Hg. Initially, I had an NOS 360 canister that I removed early on. Using a hand vacuum pump I noticed it started later. However, I didn't record the actual measurements. I put 100 miles on the car on Saturday with initial timing set at 7 degrees. It ran good aside from the coolant temp that rather quickly increases as the car idles. Even with ambient temps in the low 70's. I'm concerned how it will behave with ambient temps in the 80's.

Dereck,
Are you sure your fan clutch is functioning as designed? Air flow, especially at idle, is critical on the C2. If the temp is "normal" on the highway and only, suddenly, increases when you're at an idle, you have an air flow problem. I was chasing a similar sudden increase in temp on my L79 and replaced the fan clutch with one from K&B and it solved my problem.
The one listed below is a bit spendy but, they work very nicely. Best of luck with your car.

https://www.parts123.com/parts123/yb.dll?parta~dyndetail~Z5Z5Z50000370a~Z5Z5Z5AAIML~P140.00~~~~S5V90OS4RS64201117880i~Z5Z5Z5~Z5Z5Z50000370a

[Dereck S.]

[Stephen L.]

Re: 67 427/400 Fresh Rebuild Frustration Help

My rule of thumb for a fan clutch: After running engine to operating temp, shut engine off. Fan should only rotate about 1-2 revolutions before it stops.

[Timothy B.]

Re: 67 427/400 Fresh Rebuild Frustration Help

Dereck,

Just for a test increase the initial timing to approx 18* BTDC and see if the engine runs a little cooler at idle and low speed.

You can't leave it there unless you re-curve the distributor so don't go high rpm's. Low speed driving will be ok for the test, if the temperature gets better the total centrifugal advance can be reduced to allow for the additional initial advance.

[Dereck S.]

[Duke W.]

Re: 67 427/400 Fresh Rebuild Frustration Help

The OE max centrifugal is 32 @ 5000, so with 13 initial total WOT advance is 45, which is a bit high, at 5000-up. In order to verify the true total WOT advance you will have to rev the engine to over 5000, assuming it has the OE weights and springs.

Suggest you install lighter springs to get all the centrifugal in by 3000-3500, and go from there.

Duke

[Dereck S.]

[Duke W.]

Re: 67 427/400 Fresh Rebuild Frustration Help

Remember that the OE spark advance maps back then were VERY conservative. There were no detonation sensors back then and GM had to warrant the engine for up to 5/50.

Get a Mr Gasket 928G spring kit and install the black springs first, which should be the lightest and should bring max advance in by no more than 3500. Set total WOT advance at 40, which would be the full 32 centrifugal with 8 initial. Then test for detonation. Lug it up hills at low revs like off idle to 2500. If no detonation I say you're good to go. If it does detonate back off total WOT advance in 2 degree increments but don't go below 36. Keep it at 36 and install one silver spring in place of the black. Then silver/silver, silver/gold, and finally gold/gold if necessary.

The quicker centrifugal curve will yield greater low rev advance and improve low end torque without having to dial in excess total WOT advance.

Duke

[Dereck S.]

Re: 67 427/400 Fresh Rebuild Frustration Help

Quick update,
I decided to convert the vacuum advance from ported vacuum to manifold vacuum. The B26 can is all-in at 12.5" Hg. My distributor is all-in mechanically at 32 deg crank. This was tested on a SUN machine not on the running car. I set initial at 8 deg as a start point. I'm pulling 14.5" Hg manifold vacuum at idle after adjusting the idle mixture screws. I reset the idle screw to idle at 800rpm. High engine rpm all-in advance (initial + mechanical) is right around 40 deg. That's likely pushing the limit. I'll back off 2 deg if needed after further testing. So far, wow. I should have done this 35 years ago. It was only 60 deg F out today so I couldn't properly assess idle temp which tends to climb quickly from 180 deg to 210 deg when at a stop light. I'm confident idle temp will improve. Idle is rock steady. No detonation was detected at various driving conditions but it needs to be assessed on hot days. Even low speed cruise is greatly improved. So far I'm very impressed with this change.