Car Surges at Low Speeds
 

Well after months (and I do mean months) of trying to get a GT40 5.0 crate motor to run right in my '68, I think I've got it going pretty good. My only problem now is that when driving at low RPMs the car seems to run rough or surge a bit. This all goes away when you step on the gas and what a rush that is.

I've messed with the timing and carb quite a bit and everything seems right there. Any other options?

How much intial timing are you running?? How about total??

Is it a Holley?? Check the float level first. Then also see if you have Vacumn and how much.

Which power valve is in it??

Bump the primary jets two numbers and see if it helps.

What do the plugs look like??

There is a good start for you.

Vacuum leak?
 

Any possibility of a vacuum leak?

Rev

I'm back at trying to solve this and I still need some help. Following is what I've done so far:

o Timing - 6 degrees initial, 35 degrees total

o Vacuum - I did 2 tests for vacuum:
1. Cranking Vacuum - Very erratic going from 0 to 4 in.
2. Running Vacuum - Still erratic, at 2K RPMs the sweep was
shorter and faster.

According to my book, there are 3 possibilities:

1. Carburetor or intake manifold leak
2. Burned or stuck valve
3. Broken piston or piston rings

Anything else I should look at before a tear the motor apart again? Thanks for your help.

With an erratic idle at vacumn i would check for vacumn leaks as rev as suggested first

A little more info on this. I pulled all the plugs and did a compression test. All cylinders are within 10 lbs. High was 180, low was 170. All the plugs looked good except #8 which was black. Not oily, but what looks like carbon.

Is my next step to pull the intake manifold? Or is there a way to test of a leak without doing this?

Spray wd-40 or carb cleaner all around where the intake meets the head and the baseplate off the carb and see if cahnges the idle at all.

With the compression the way it is you can rule out a burnt valve. Try the WD-40 stuff for an external vacumn leak. But, it can leak on inside too.

I'd just pull the intake, it's not that hard, and eyeball those gaskets good. Then before you reinstall dry fit the intake and check the gasket fit. Incase the heads have been milled excessive, etc.

Buy, GOOD gaskets and leave the end gaskets out. Use RTV. When done properly it is a MUCH better seal and allows the manifold to settle into place easier.

Thanks for the advice Gearhead. I pulled the intake and found my problem. The gasket was blown between the rear water galley on the head and #8 intake runner.

This brings up another question. I'm running an Edlebrock Performer RMP intake. This manifold only has water galleys in the front. I'm thinking that the water pressure at the rear is what is wiping out my gaskets. This is the 2nd time this has happened.

Does anyone else use a Performer RPM intake? And if so, what do you do about this problem?

Glad to hear you found your problem. I have used those intakes before without any problems. \

I would dry fit without gaskets to see how the intake surfaces meet the head surfaces.

Also, when you reinstall leave the end gaskets out, use RTV, and use some RTV around the water passages, front and rear. Don't use alot of RTV around the water outlets, just a light coat.

On the end gaskets, don't use them and put a bead of RTV, around 1/4 in dia. Let it dry for 10 minutes or so. It should just start to skim. Lower the intake, without carb, straight down and start bolts and tightning from the center out.

Good luck

To add a little i put just a smear of rtv on the front and rear water passages as well on mine and when i say a smear it should be so thin that you can still easily see the gasket material behind the rtv because when it sweezed down there is little to no room so the slightest amount works.

Interesting sideline to all of this. I sent an e-mail to Edelbrock to see if this is a common problem with the Performer RPM intake. Their response was to not use RTV instead of the front and rear gaskets.

This contradicts the common wisdom on this including Edelbrock's own web site, so I think I will not go this approach. Also, this was not my problem area. They also recommended Fel-Pro gaskets instead of the compressed paper material. I do think I will go that route.

I'll let you know how it all comes out.

on my first motor i used the front and back gaskets and to make a long story short it caused me to blow my motor. hydrolocked the 3rd cylinder... anyway on my second motor i usded rtv on the front and back and had no problems. i think edelbrock says it because they have to otherwise people would say then why do they have it in the set. or if someone didnt use then and not enough rtv and caused another problem... they would just say edelbrock told me not to use it and then they would be liable. so who knows. just do whatever you think works best. ask more people who have installed your intake and get there opinion.

This is a problem that I thought I fixed several months ago, but now seems to be back. My car has been running great for months until last week. I started to notice a rough idle and a bit of surging at low RPMs. I hooked up a vacuum gauge and found that I have a vacuum leak.

I'm pretty sure that it is the intake manifold again. To confirm this,
I checked the compression to rule out a burnt valve. All cylinders are right around 155 lbs. The plugs look fine except for #8 which is a bit on the gray side. I checked the torque on the intake bolts and they are all fine.

I think what I'm left with is the heads and intake are not fitting right. How can I confirm this? And, what can I do about it if this is the case?

Sequence and steps?
 

Are you torqueing down the intake in the correct sequence and in 3 separate steps? Doing the torque down a 1/3 at a time and in the correct sequence lets the intake settle down to the heads a little at a time and with an even pressure on the gaskets. If my memory is correct, it's 17 lb/ft total for the intake bolts but be sure to double check that. I do 6 /12/17-18 for the 3 steps.

Rev

I am doing it in 3 steps:

1. 6lbs
2. 15lbs
3. 22lbs

Do you think 22 lbs. is too much?

Didn't remember?
 

I was just going from memory. If 22 is what it calls for, then use that torque. I was just trying to think of something to account for the leaks. Sounds like you're doing it correctly though.

Rev

I checked with Ford Racing on my intake gasket problem. According to them, you must use a specail Ford gasket on the GT40 aluminum heads. I've been using Fel-Pro Printoseal gaskets which, according to Ford Racing, will not seal to the heads.

Anyone else heard of this? It doesn't sound right, but I'm willing to try anything at this point.

Fel-Pro printoseal
 

I did use Fel-Pro Printoseal gaskets with my TFTW heads and Edelbrock Performer with no problems. Seems like any good gasket should work. The Ford gaskets are worth a try though, especially if Ford Racing says they are mandatory. Does seem strange that nothing else would work.

Rev

I have sealing issues with my 351w's TWTF heads and edelb. performer intake. I figure that the car does so much temp fluxing that the parts are moving, growing/shrinkng, at different rates effecting my seal. After trying almost every "soft' gasket on the market, even the fel-pro printoseal, I found one that I believe is actually working.

Everytime I'd remove the intake, the gaskets looked completely demolished. and I used a bead of RTV front and back everytime. So I started looking for a solid, metal gasket which i found, made by felpro. It has a blue coating all around it and is very firm. But I've noticed lately that I'm getting a drip of coolant here and there from the heads. i'd really like to find a set of deadsoft alluminum gaskets for the intake. Is this a bad idea? Has anyone seen em?