Gun Jam

This possible vac leak could somehow occur from inside the valley under the manifold (internal vac leak) making its detection much more difficult.

67mustang302

What intake gaskets are you using?

piperdriver

I do have a PCV, doesn't appear to be leaking.

The intake has Felpro gaskets, I'm not sure which ones as the builder installed them.

Is there a way to tell in the vacuum leaking is coming from under the intake?

Gun Jam

The only real way to know is if you had a baseline vac reading before the problem started

example was 14.5 at idle 850rpm hot now its 12.0 at idle same temp and engine rpm.

However!!! if the issue is sever enough you would be able to positive ID a vac leak the same way.

Engine at run temp rpm at reasonable idle say 850 to 900

Hook vac gauge into full manifold vac line off carb the lowest one typically not the one the distributor plugs into.

if the gauge reads 12s or lower at 850 hot then you almost certainly have a vac leak (assuming non radical cam)

if its in the 14 to 13s thats debatable depending on cam.


I love felpro gaskets with the exception of the soft intake gaskets they make I cant remember but it might have been the 1250??? This is a soft rubber like gasket with a blue outline that seals extremely well but has no crush resistance. Some people think they are awesome but I think they suck bad and thats because literally the weight of the intake manifold + 5 foot pounds on intake bolts over about 6 months crushes these gaskets to the point where they split and leak particularly at the water jackets. I have tried multiple times and came to the conclusion that maybe if you only hand tighten the bolts using fingers only or just left the bolts out it would work for a while. What a waste of time these were.

I switched to the edelbrock fiber like gaskets with the black outline torqued the bolts to 20ftlbs and they dominate! I got to inspect one after about 8months of service life when it failed due to that exhaust gas leak the water jacket ports and intake ports looked perfect 100/100.





you can see the deformation of the gasket around water jacket. Looks like I might have used about 40ftlbs.....actually it was about 12 or about half of the standard tq rating attempting to use less gave the same results its almost like they melt and then split over about a 6 month period.

67mustang302

I asked specifically because of the 1250's. Tons of people have issues with them tearing.

I've never been able to get a pair to last longer than about 12-18 months.

The 1250-S3 is more like an OEM type gasket though, same as the 1250 but with a steel laminate core so it doesn't distort like that.

If you can find a shop with a smoke machine, they can check to see if you have a leak, and where it is.

barnett468

OMG...ok, i have a headache now. i said ALL vacuum ports. a pcv is connected to the intake and is nothing more than a HUGE vacuum leak.

plug the thing on the intake or carb or wherever it is connected to. CAREFULLY and THOROUGHLY redo your leak test with FLAMMABLE brake cleaner only. do NOT use carb cleaner or wd40 etc. spray it at the pcv hose where it connects to the intake or carb also.

leave it plugged and do your plug color test and maybe also tell us where it is plugged into the intake or carb as i previously asked.


well are tge the hard metal gaskets or the soft flexible ones?


yes, take it off and replace the gasket.

barnett468

hello gun and poiperdriver

i tourque the intake bolts in stages and use the factory tprque pattern.

after i have torqued the last bolt to the required spec.

i start at the first bolt and torque them again. the bolts are always loos after the first final torque.

i do this a total of 3 times.

after this, i run the car for maybe 30 minutes then torque rhem again and will then run it for a few days and torque them again. they are rarely loose at this point.

if the bolts are "stretched" they need to be replaced.

grade 8 bolts can be torqued higher.
.

Gun Jam

That's an excellent method Barnett....unless its a 1250.

If you used factory tq spec on at 1250 you would probably experience almost instantaneous failure especially if you re-torqued them.

I know it looks like hell but that photo is of a brand new 1250 with less than 6mo time and about 12ftlbs using the recommended tq pattern. Recomended tq is 18 to 20.

-Gun

barnett468

hello gun jam.

i'm not quite sure how to say this because i like you, lol, but i have actually installed around 10 zillion 1250 fel pros and never had a leak ever...never

your prob must have beem from irregular gasket surfaces?

fel pros just don't like you?

at just 12 ft lbs, the bolts are definitely going to loosen up.

this is not to say that there are not better gakets out there by any means.
.

Gun Jam

I gave it a really good shot...Apparently Im not the only one.

I would have to based on my experience not recommend them to anyone for any reason.

Did you see the above photo I posted? What is your analysis of the failure?

-Gun