Lack of maintenance and/or the engine has some blow by i.e. oil consumption and/or PCV system is not functioning properly would be my guesses. I would reuse the valve cover gasket but that is why I get the blue ones so I can reuse them.
Went back and read the entire thread. You are going to a lot of trouble to install the GT40 heads and Explorer/Cobra upper and lower not to have TMoss port the lower intake. He ported the Cobra lower on my old 302 and it made a difference. Best way is to email him and ask him what he would charge to port it (moss tpsa@ sbc global. net - remove the spaces). You should also be able to run a set of 1.7 pedestal mount roller rockers and not have piston to valve clearance issues which will pick up a little more hp. Read I said should not have PTV clearance issues but you should always clay the motor. Go hear and start at Post #946:
Progress Thread - Hoopty v2.0 - Back in action!
There is actually a tool made for that.stangnet.com
You can keep the 65 mm throttle body as there will not be a lot of performance increase jumping to a 70mm with your combo.
If you really want to move up to 24lb/hr injectors I would say use the throttle body money to get a Pro-M 75mm Bullet MAF for 24/lb/hr injectors.
75MM Bullet Unflanged
The Pro-M 75mm unflanged Bullet is a direct replacement for the 88-93 5.0 Mustang (Fox Body / Third Generation), as well as any other Ford vehicles originally equipped with a 55 or 70mm unflanged Mass Air Meter housing.www.promracing.com
Do not get fleabay or Amazon injectors...cannot stress this enough.
8 x Fuel Injectors fit Bosch OEM 0280150947 For Ford E-250 350 Econoline Mustang
8 x Fuel Injectors fit Bosch OEM 0280150947 For Ford E-250 350 Econoline Mustang Details Manufacturer Part Number: 0280150947 Compatible part number: M-9593-LU24,M-9593-LU24A,0280150965, 0280155715, Ford F1TE-D1A / F1TZ9F593C / F1TE9F593D5A / 0280150759 / 0280150728, 4G1259, 16-168, AUS...ksm-motorsports.com
With the calibrated MAF from Pro-M you do not need to get a tune as it compensates for the larger injectors. I am only suggesting Pro-M as I ran one for years on my old 302 combo which made right at 275 rwhp on the 24 lb/hr injectors. There are other calibrated MAF's out there I just like the Pro-M's.
Do this outside if you can. Flip the GT40 heads over so the combustion chambers are facing up. Fill each combustion chamber with gasoline so the valves are covered. If gasoline drips down the valve stem then that valve leaks. Mark which ones leak with a paint pen. Take the GT40 heads to a machine shop and have them fix any of the leaking valves (if its more than one or two just have them do all of them) and install these springs:
This is all cheap insurance so you don't have to pull the heads back off in a few weeks or months. The springs will be fine on the stock cam and are good up to 0.540" lift which is way more than the stock cam and leaves you room to put a cam in later down the road because you will if you are any kind of gear head. If the springs that are on it are the stock springs they are gonna be weak due to run time and just being old. Springs cyclically fatigue due to being used, this is called metallurgy.
If you have not already you will need to drill the lower intake to accept the Air Charge Temperature (ACT) sensor in the #5 runner. If you send it to TMoss you can ask and see if he will do it for you or watch this video (pretty decent):
View: https://www.youtube.com/watch?v=QSO_3Zwrrc8
If you have not already ditch the lower intake to cylinder head bolts and run studs. See here, Post #7:
I would also suggest that on aluminum heads you heli-coil the threaded holes where the intake attaches if you do use bolts as they have a tendency to pull the threads. I did it on my Edelbrocks and my AFR's and I am using studs on both as it only took stripping one to teach me a lesson.
You can make a TDC tool which takes all the guessing out of finding TDC. Some like this approach and others complain its overkill but when you do it this way there is no doubt where TDC is (Post #27):
Engine - Can't get the motor to fire.
Pretty much anytime someone has the distributor out, does internal engine work that involves rotating the engine, and then it won’t start when all back together is because the distributor is 180* out. Ask me how I know lol.stangnet.com
Probably late on all of this but figured if anything maybe its a good read and will spark some discussion.
Great questionWhy didn't you unbolt the headers from the h-pipe?
Excellent point. Pretty much what I was expecting.I suggested how to check the valve to seat with gasoline. Other than that you will need a machine shop quality straight edge to check how flat the heads are and a tool to check closed and open pressures on the springs. Again, you are going this far so why not just take them to a reputable shop and have them look them over?
Just soak them down real good with some penetrating lubricant. Try and heat them with some heat too,a MAP gas torch works great and is cheap.Great question
They were pretty rusty. I was worried I would strip the bolts and muck it all up. I may do this anyway now …
Thanks. Got one of those and will do this.Just soak them down real good with some penetrating lubricant. Try and heat them with some heat too,a MAP gas torch works great and is cheap.
Also,and impact driver will be your friend here. Since you already removed the heads,the headers are probably going to fight you if you try a regular socket wrench setup. The "impact" motion should knock those nuts right off.Thanks. Got one of those and will do this.
Thanks. Best purchase I ever made was my 1/2 Dewalt impact. I wouldn’t even be trying this in New England without it.Also,and impact driver will be your friend here. Since you already removed the heads,the headers are probably going to fight you if you try a regular socket wrench setup. The "impact" motion should knock those nuts right off.