If it moves freely you can wire it open.
CK5
Register an account today to become a member! Once signed in, you'll be able to participate on this site by adding your own topics and posts, as well as connect with other members.
76’ 400ci overheating bad
- Thread starter CraigFulton
- Start date
CraigFulton
1/2 ton status
Holy shit you guys won’t even believe it. I got home and checked the heat riser valve and sure enough it was stuck CLOSED. Forcing exhaust and heat back. I can’t even believe it. All of this work and effort and $100’s. That stupid valve.
Yeah, I have wired a couple open over the years. Nice find, hope it solves some issues for you. Now you can move on to fuel injection which is so sweet, carbs are fully obsolete in my opinion.
You asked earlier, I didn't respond. No, you can't just remove the EFE. As I recall the manifold is different on that side to accommodate it, I want to think the manifold to EFE mating surfaces are flat, and the EFE "outlet" is tapered to accept the flared end of the exhaust pipe. I'm pretty sure it was OEM on Corvette's for a bit, as I've seen them in the Corvette-only aftermarket parts catalogs...there is a spacer made that replaces the EFE.
CraigFulton
1/2 ton status
Found a spacer for $35 to replace the valve. I think I’ll still block the crossover on the intake. Bad idea?
In Florida you wont likely need any pre-heating of the air fuel mixture,if you lived in a colder climate where it drops below freezing you could run into carb icing issues or poor driveability issues during the warm up period after a cold start without an operational EFE valve..
GM used block off gaskets on intakes on heavy duty truck applications often,and most intake gasket sets came with them,it was your choice whether to install them or not..
The EFE valves that are vacuum operated had a spring in the vacuum can to open the EFE valve when the engine was off,or if it lost the vacuum supply,(It closes by vacuum and opens when the ported vacuum switch denies vacuum to it after it warms up)--so you wouldn't overheat the area under the carb where the heat passages are in the intake and cause vapor lock or fuel boiling issues..its not often one of that style will fail in the closed position,but it did happen often on the older heat risers that used a thermostatic coil spring to open and close it..
I have cut out the butterfly valve on the EFE in more than one vehicle and just put short bolts in the holes the shaft rode on after tapping threads in it..as noted by Dygear,its incorperated in the design of the y-pipe and manifold ,you kind of need it if your going to run stock exhaust pipes..a muffler shop might be able to make a spacer for less than $35,all it consists of is about 2" of pipe with a flare on one end and a flat shoulder on the other..I'd just "delete" the flap on the original for $0...
GM used block off gaskets on intakes on heavy duty truck applications often,and most intake gasket sets came with them,it was your choice whether to install them or not..
The EFE valves that are vacuum operated had a spring in the vacuum can to open the EFE valve when the engine was off,or if it lost the vacuum supply,(It closes by vacuum and opens when the ported vacuum switch denies vacuum to it after it warms up)--so you wouldn't overheat the area under the carb where the heat passages are in the intake and cause vapor lock or fuel boiling issues..its not often one of that style will fail in the closed position,but it did happen often on the older heat risers that used a thermostatic coil spring to open and close it..
I have cut out the butterfly valve on the EFE in more than one vehicle and just put short bolts in the holes the shaft rode on after tapping threads in it..as noted by Dygear,its incorperated in the design of the y-pipe and manifold ,you kind of need it if your going to run stock exhaust pipes..a muffler shop might be able to make a spacer for less than $35,all it consists of is about 2" of pipe with a flare on one end and a flat shoulder on the other..I'd just "delete" the flap on the original for $0...
CraigFulton
1/2 ton status
So by deleting the EFE valve plate I wouldn’t really need to worry about the crossover any longer?
Great advice and info everywhere. I really appreciate your knowledge sharing.
Great advice and info everywhere. I really appreciate your knowledge sharing.
I wouldn't lose sleep over deleting it in a warm climate --GM did not use EFE valves and blocked off the ports in the heads to intake with steel/asbestos sandwiched gaskets on their bigger trucks like C-60's factory,figuring they would be plenty warm even without them..
Many aftermarket aluminum intakes have no "hot spot" in them,there are no heat passages at all..their theory was a cooler fuel air mixture was more dense and richer and would give more power..either that or they saved $2 by not bothering to cast them ..
Many aftermarket aluminum intakes have no "hot spot" in them,there are no heat passages at all..their theory was a cooler fuel air mixture was more dense and richer and would give more power..either that or they saved $2 by not bothering to cast them ..
CraigFulton
1/2 ton status
But should I bother blocking off the exhaust crossover in the intake after I delete the EFE? Just trying to save steps in this conversion work if I can.
Again something I'd ask Holley. In your present climate probably not needed at all, but I know GM ran heaters on the throttle bodies (even TPI, which sees no fuel) and under certain circumstances, maybe it's needed. Icing is the sole concern AFAIK, and I've not seen that issue up here in the NW with the TB heaters/crossovers deleted.
Probably thinking about it too much, delete it and call it good is probably a safe bet. But the TB's have a lot less issue with heat than carb in the first place. Pressure, flow, capacity, all different than having a float bowl.
Probably thinking about it too much, delete it and call it good is probably a safe bet. But the TB's have a lot less issue with heat than carb in the first place. Pressure, flow, capacity, all different than having a float bowl.
Well I am late to read this, but I don't see where anyone said anything about the base timing.
I do see that you found the heat riser valve stuck, but I think that you can help it a little more by advancing the timing. What I read was that it's at 6* now? You should try it at 10 to 12 and see how it responds. Listen for pinging when up to operating temperatures. Then back it down if needed. This is assuming that the fuel mixture is correct.
I have had a couple of 400s and usually end up with 11 or 12 degrees BTC. My '72 has a 406 and it is at 12* initial and 32* total, all in by 2800 rpm. (If I remember correctly)
I do see that you found the heat riser valve stuck, but I think that you can help it a little more by advancing the timing. What I read was that it's at 6* now? You should try it at 10 to 12 and see how it responds. Listen for pinging when up to operating temperatures. Then back it down if needed. This is assuming that the fuel mixture is correct.
I have had a couple of 400s and usually end up with 11 or 12 degrees BTC. My '72 has a 406 and it is at 12* initial and 32* total, all in by 2800 rpm. (If I remember correctly)
CraigFulton
1/2 ton status
Ok. I was thinking of advancing it to 10 for the EFI conversion this weekend.
Subscribed! I am tempted to pull the trigger on the Q-jet style Sniper EFI system too! I mean, my Qjet is dialed in and I have no issues with it, but i can't help but think how much nicer EFI would be. The only thing that held me back before was that they didn't have a unit that would allow us GM owners to retain our stock air cleaners with cold air intake ducts. Have you checked to see if the factory air cleaner fits on top of that unit yet?
CraigFulton
1/2 ton status
I posted on another thread but I’ll updated here too. I removed the valve plate from the heat riser and blocked off the exhaust crossover on the intake. Holley recommended it. You guys will love this too: the intake bolts were mostly hand tight along with the exhaust manifold on passenger side. Last guy that assembled this is a hack.
I got the EFI tank installed today too. I just need to wire it up and hope it starts rights up.
Stock air cleaner fits right up. Can’t even see the unit once it’s on. Most people would want to show it up but I’m pumped it will still look somewhat stock.
I got the EFI tank installed today too. I just need to wire it up and hope it starts rights up.
Stock air cleaner fits right up. Can’t even see the unit once it’s on. Most people would want to show it up but I’m pumped it will still look somewhat stock.
CraigFulton
1/2 ton status
CraigFulton
1/2 ton status
She’s alive and kickin on fuel injection. Only drove a few miles. It’s still in learning mode but the wife was ready for me to stop.
