Intake manifold choices

[canyncarvr]

I have been running an Edlebrock Performer RPM for some time, always with the same problem. This area does a 'fuel change' twice a year with a change to 'summer blend' around Memorial Day. That causes a problem when an 'unseasonably' warm day comes around in April or early May. The vapor pressure is SO low for the winter fuel blend, a warm day gives me hot-soak problems and sometimes boiling fuel.

Headers are ceramic coated to reduce heat. I have a cool-can...but keeping ice in it is a PITA.

Does anyone have experience with Edlebrock's 'air gap' intakes enough to say they definitely work better than a 'plain' manifold? Seems a given, but input from some that have tried them would be good to hear. It would be about $1000 to change to an air-gap, so it's not a pocket-change situation. IF I had a pretty good idea that an air gap would make a definite difference, I'd give it a shot.

Got stuck yesterday with a 'no start' flooding issue after my third 'hot soak' stop of the day. It's a bother.

Thanks.

 

[Mike69cuda]

Have you considered an insulating plate under the carb? I think I bought a 1/2 inch one that has worked well.

 

[toolmanmike]

Edelbrock carb? Typical

 

[gzig5]

Sounds like the problem is hot fuel in the carb, not the intake. Doubt the air gap helps. Carb insulator and insulated fuel lines might help keep heat out of the carb.

 

[rumblefish360]

Also! Edelbrock sells a .333-ish thick fiber gasket that helps with the heat issues.

Are you running stock or aluminum heads?

 

[Topless69]

Try a 1/2 inch or 1 inch phenolic carb spacer.

 

[canyncarvr]

Stock 'X' heads. 4779 Holley. Insulated fuel lines. This last stoppage, the fuel bowls were easy enough to touch...nowhere near the temps bubbling fuel bowls have been up to in the past.

Fuel lines come into the Holley from the front, are well away from header heat...as far away as I can get it, anyway.

Yes, I have a phenol spacer. It's just not on, yet. Yeah...helpful. I haven't sussed out the change in throttle cable holder/angle I'll need.

I did replace the needle/seat assys today. The sealing o-ring was barely larger (.001") than the barrel of the needle assy... .304". I didn't see any leakage from the fuel level holes, but the car wasn't hot, either. I turned the float level down a turn just for fun.

Sounds like the problem is hot fuel in the carb, not the intake. Doubt the air gap helps.

Isn't that the point of the air gap? ...to keep fuel in the carb from getting hot?

 

[Ironracer]

Stock 'X' heads. 4779 Holley. Insulated fuel lines. This last stoppage, the fuel bowls were easy enough to touch...nowhere near the temps bubbling fuel bowls have been up to in the past.

Fuel lines come into the Holley from the front, are well away from header heat...as far away as I can get it, anyway.

Yes, I have a phenol spacer. It's just not on, yet. Yeah...helpful. I did replace the needle/seat assys today. The sealing o-ring was barely larger (.001") than the barrel of the needle assy... .304". I didn't see any leakage from the fuel level holes, but the car wasn't hot, either. I turned the float level down a turn just for fun.



Isn't that the point of the air gap? ...to keep fuel in the carb from getting hot?

It helps w/ heat soak, some... but mainly helps a denser cooler charge

 

[Oldmanmopar]

The air gap will do little to help your problem. You need to stop the fuel from vaporizing in the fuel line. In the mid 80's not sure of what year they made a fuel filter with a return line built in for this reason.

I had the same issue with my Duster. Everytime I would go to start it after stopping for a while it would flood. I began turning the electric pump on and off until cool fuel reached the carburetor .

Tony Hershman. a Troyer Race car shop owner told me to put a return on my car. This was not cheap having to buy the line, fittings and the new regulator. But Tony and his son are well known in racing. His son is Kyle Bush's spotter .

Being it had an electric pump I had to get a different pressure regulator to use on the return line .

So I replaced the regulator on the feed line and used it as a return . Then ran a new feed line directly to the carburetor. $200 for line alone . But I trusted Tony and the Nascar guys. I never had that problem again. In fact the time slips were more consistent going back to back rounds.

Big difference that you all could not imagine. You need to keep the fuel moving in a circle back to the tank so it stays cool.

Its the fuel in the line that when it is boiling will not let the floats shut off the needle and seat until it gets solid fuel. It has nothing to do with the intake or carb. Fuel injection would be the ultimate fix. We are now going with a holley 4500 sniper on the new car.

Before

After

\

https://www.holley.com/products/fue...sniper_efi/sniper_stealth_4500/parts/550-841y


What I wanted to add is that if you are pulling fuel from the tank your symptom may be lack of pump pressure also. because its boiling before the pump. You'll lose power then when you go to start it it floods . Double whammy.

My car was pushing fuel. But I have seen the pulling problem.

Then I installed the 80's three nipple filter on a manual pump on the car with a factory style return . Most cars after 70 have a return line you can plumb in.

 

[rumblefish360]

@Oldmanmopar , @canyncarvr

The return line is an excellent idea. I don’t know when the return line fuel filters came into play by my ‘79 Magnum has one. I have an Edelbrock electric pump. The car has a return line from the factory. (Lucky there) I made use of it and haven’t had an issue since. I also use the thick gasket from Edelbrock. That alone stopped the fuel from boiling. The return line was icing on the cake.

 

[doogievlg]

@Oldmanmopar , @canyncarvr

The return line is an excellent idea. I don’t know when the return line fuel filters came into play by my ‘79 Magnum has one. I have an Edelbrock electric pump. The car has a return line from the factory. (Lucky there) I made use of it and haven’t had an issue since. I also use the thick gasket from Edelbrock. That alone stopped the fuel from boiling. The return line was icing on the cake.

Ill throw another vote on the return line set up. When I was younger I was around a handful of guys that had always ran return lines so I just assumed it was normal and everyone did it.

 

[12many]

What you also need is this (if you can find ):

I run that under a 750DP on an Air Gap. Also, all fuel line is covered with DEI Fire Sleeve:

My engine “bay” is much more oppressive than any A,B,C alphabet car will ever be. I don’t have the issues you describe using the two items above. Using a Carter electric fuel pump with no return line atm.

 

[Mattax]

Had something similar when picking up my jeep's axles from the parts store (new bearings pressed on). Warm enough day and being parked just the right amount of time. A one off situation. Otherwise I usually add a half tank of low rvp gasoline. That's not a realistic answer for a daily use for two months.

All answers are good.
It all depends on the specifics. You can cross into another fuel area with lower RVP allowance and might be fine.

Issues with winter fuel on warm days can show up different ways depending on the driving and the layout.
It absolutely can be showing up in the carb, even if that's not where the bulk of the vaporization is occuring.
I've posted an AFR graph showing what happened when the top of the air cleaner was removed on a hot day after driving locally with winter fuel.
Hot Fuel Lines
Not moving or moving slow has always been a heat soak challenge. Hence the change in fuel filter mounting in 1963
Carburetion and Performance Diagnosis (Session 188) - Master Technician's Service Conference

racingfuelsystems-What to do about Winter Fuel in hot temperatures?

1973 Getting Them Started - Technician's Service Conference (Session 307)

 

[canyncarvr]

What I wanted to add is that if you are pulling fuel from the tank your symptom may be lack of pump pressure also. because its boiling before the pump.

NOT pulling. I have an electric pump mounted at the tank.

A question on the return line idea: Eventually all the fuel will become the same temperature. The fuel in the tank will not always be cooler due to the constant recirculation. What makes the idea useful is that the engine is not run long enough under 'normal' circumstances to get to that equilibrium? The large surface area of the tank continually cools the fuel to some extent...even though it is mostly exposed to hot asphalt all the time? The recirc idea will work for 'some' time but eventually the process will become insufficient? Yes, I am picking at a bit of a nit, but am curious about the technical aspects of the matter. ...just ruminating.

All answers are good.
It all depends on the specifics. You can cross into another fuel area with lower RVP allowance and might be fine.

THANKS for the input!

Damn the specifics! Full speed ahead!! Or...Full Stop if'n the dang thing won't even start. While fussing with it in the parking lot the other day, a driver driving by said, 'Nice car!'. I replied: 'It would be NICE if you got it started!'

She said, 'No thanks.'

Yes. A different Reid index fuel would work, I'm sure. I'm too cheap for that. Just making the 25 mile trip to buy non-alcoholick fuel at $6.00/gal. is enough for me.

I do appreciate the input(s). I've GOT to get my phenol spacer put on. Maybe a couple of simple spacers under the MoPar high bracket will do the trick. ....more ruminating....

 

[canyncarvr]

I run that under a 750DP on an Air Gap.

You probably would have said if it applied: Did you have any too-volatile issues without the Air Gap to the extent you could say the Air Gap made a difference?

 

[12many]

You probably would have said if it applied: Did you have any too-volatile issues without the Air Gap to the extent you could say the Air Gap made a difference?

My engine (410) is in an A100 van under a doghouse cover. I initially ran a mildly ported Weiand Action+ with exhaust crossover blocked and a Street Demon with composite body. No insulator under carb, all fuel line covered with Fire Sleeve. No boiling or vapor lock. Then installed the 750DP on that intake with the insulator shown in previous post. Still no boiling or vapor lock, or any hard starting. Installed the Air Gap with the insulator and the DP, no change. All I can safely say is the AG as designed can make some difference with heat soak and related symptoms, how much? No idea. I just did all I could to protect all else from heat as best possible. The AG improved things performance wise obviously.

 

[rumblefish360]

@canyncarvr The main idea of the return line is not cool fuel though it will stay cooler for a long time. While I don’t know for sure, IMO, I don’t think the fuel in the tank will rise to any harmful or ill acting temp. I honestly don’t think it would reach the evening out temp of any issue or note. Ether the gas tank is to small and you’ll run out of fuel before you spend hours on the road or the tank is large where the evening out just doesn’t come to that equilibrium state. Thanks also don’t see the asphalt as a temperature hinderance while driving.

What do you mean about the recirculating becoming insufficient?

I do think the return line is more in step of not taxing the fuel pump.

Do so use that spacer. I suggest (*I Think*) the thick gasket from Edelbrock. That help me out a good bit for sure.

I went from A TorkerII-340 to a RPM- AG with very noticeable differences in the engines constant performance. The TorkerII-340 was heated, and performance would flatten out after a while. The RPM-AG never lost a step. This was an old combo, way back, 10-1-360, J heads and a Purple 292/.508 etc…. MP’s 12.5 second package. IIRC…

 

[Rat Bastid]

NOT pulling. I have an electric pump mounted at the tank.

A question on the return line idea: Eventually all the fuel will become the same temperature. The fuel in the tank will not always be cooler due to the constant recirculation. What makes the idea useful is that the engine is not run long enough under 'normal' circumstances to get to that equilibrium? The large surface area of the tank continually cools the fuel to some extent...even though it is mostly exposed to hot asphalt all the time? The recirc idea will work for 'some' time but eventually the process will become insufficient? Yes, I am picking at a bit of a nit, but am curious about the technical aspects of the matter. ...just ruminating.



THANKS for the input!

Damn the specifics! Full speed ahead!! Or...Full Stop if'n the dang thing won't even start. While fussing with it in the parking lot the other day, a driver driving by said, 'Nice car!'. I replied: 'It would be NICE if you got it started!'

She said, 'No thanks.'

Yes. A different Reid index fuel would work, I'm sure. I'm too cheap for that. Just making the 25 mile trip to buy non-alcoholick fuel at $6.00/gal. is enough for me.

I do appreciate the input(s). I've GOT to get my phenol spacer put on. Maybe a couple of simple spacers under the MoPar high bracket will do the trick. ....more ruminating....[/QUOTE

If the fuel is not sitting in the hot engine bay in hot fuel lines just sitting there the temperature doesn’t go up.

 

[canyncarvr]

What do you mean about the recirculating becoming insufficient?

Meaning the process of recirculation will no longer act as a cooling process: It will be INsufficient in that regard.

Granted, that would take awhile...and maybe never happen. ...was just a question.

 

[rumblefish360]

Thanks, gotcha. I’d imagine it could happen in traffic conditions… IDK for sure ether. But the shear amount of fuel is a lot of liquid to heat up.

 

[Bewy]

Returning fuel to the tank will cool the fuel for two reasons:
- the metal return line will dissipate heat in the fuel
- the fuel tank has a large amount of steel exposed to the atmosphere which will dissipate heat. Acts like a heat sink.

 

[canyncarvr]

Just recalled having a charcoal canister on the car years ago. That's where my cool-can sits now.

Having had that canister means I have a return line fitting on my fuel tank hardware. That would make running a return line a whole lot easier. From 'inline', a pre-fit line is $65 or so. Get a Holley regulator with a return line port and I'd be all set.

...except for actually putting it in. Hhhmmm....I've had that phenolic spacer for how many months? Yeah. I'll get right on it! ;)

 

[Bewy]

If you are going to a return line set up, you should ensure you use a bypass reg, & not try & use a dead head reg, which might cause pressure fluctuations &/or restrict flow.
The Mallory 6309 is a good reg.

 

[canyncarvr]

If you are going to a return line set up, you should ensure you use a bypass reg...

Yes. The Mallory is noted as being no longer available from the two retailers I found that had it listed. I have a
Holley 12-887 on my 'list-of-stuff' for a return line if that ends up being the direction this is headed. That part would fit my real estate situation better.

All of this has got me thinking about the Holley fuel pump I use. Rated at 7psi and installation said to not require a regulator, I wonder if the latter of that is not the best choice. 7psi is a bit much for a Holley carb I think. I would prefer 4-5psi. I had a regulator installed years ago when I took this car to the track, but removed it for the current build in the car. All of this having to do with a reasonable installation in the first place, NOT an RVP problem when using winter-blended fuel on a warm Spring day.

I did order a Trick Flow style (carb mounted) throttle cable holder that is built to accept a Mopar style cable. That will get me away from the angle problems of a raised/spaced DC style 'high' bracket I have now AND away from the in-the-way style (imo) of the Mancini bracket. Foremost, it will get my 1/2" phenolic spacer in place.

I have yet to determine if replacing the carb seats helped at all. This last flood was different from every previous situation in that the fuel was NOT percolating in the bowls, it was not that hot a day, but I do know that heat-soaks do 'stack' in this car. A .001" diameter difference between the brass and the o-ring in the original pieces has to be less-than-good. I have not touched my 4779 except for idle adjustments since it was new and just back from a local builder's set-up. That's been 20 years.

Thanks to all for good points and input. I appreciate it.

 

[Rat Bastid]

Yes. The Mallory is noted as being no longer available from the two retailers I found that had it listed. I have a
Holley 12-887 on my 'list-of-stuff' for a return line if that ends up being the direction this is headed. That part would fit my real estate situation better.

All of this has got me thinking about the Holley fuel pump I use. Rated at 7psi and installation said to not require a regulator, I wonder if the latter of that is not the best choice. 7psi is a bit much for a Holley carb I think. I would prefer 4-5psi. I had a regulator installed years ago when I took this car to the track, but removed it for the current build in the car.

I did order a Trick Flow style (carb mounted) throttle cable holder that is built to accept a Mopar style cable. That will get me away from the angle problems of a raised/spaced DC style 'high' bracket I have now AND away from the in-the-way style (imo) of the Mancini bracket. Foremost, it will get my 1/2" phenolic spacer in place.

I have yet to determine if replacing the carb seats helped at all. This last flood was different from every previous situation in that the fuel was NOT percolating in the bowls, it was not that hot a day, but I do know that heat-soaks do 'stack' in this car. A .001" diameter difference between the brass and the o-ring in the original pieces has to be less-than-good. I have not touched my 4779 except for idle adjustments since it was new and just back from a local builder's set-up. That's been 20 years.

Thanks to all for good points and input. I appreciate it.

The Mallory part number is 29388. Far better than that holley regulator. Any time you see a bypass regulator that has the fuel enter the regulator backwards from a dead head regulator know that that design was used because it was cheap to get to market.

Holley was way behind on bypass regulators and had to get something out there and that was what they did.

I actually saw one up close, in my hand about a month and a half ago. The ports were pretty small. Bypass area was at best enough to handle a Holley blue pump. Much more than that and the regulator doesn’t look like it can bypass enough fuel at low demand (like idle and cruise) and then you end up with pressure creep and the very real chance of pushing fuel past the needle and seat.

Also, return line size is pretty important. You want the line big enough that it’s not the restriction because if it is, it will do the same thing as a restrictive bypass.

Of course, there are exceptions to this. One I remember was a Barry Grant pump. On that one system the return line was what controlled fuel pressure. Between the return line and the regulator was how he designed that system to work. So if you had the return line too small you couldn’t get the regulator to drop the pressure enough. If the return line was too big you couldn’t get the fuel pressure up because it was all going to the tank.

I forget if that was a street/strip system or a drag only system. But if you didn’t plumb it exactly as the directions said, it wouldn’t work.