As per this thread, I found the cause of my tbird being down on power a bit and bucking at low throttle were leaking intake valves:
Issue Solved - engine bucking/surging at partial throttle
The initial looksee from a recommended machinist is that I yes, all of my intake valves are leaking (I stopped testing after 3) which explains the loss of compression.
He's working up a full cost for me after he tears down the heads (tomorrow) but his initial reocmmendations are as follows:
1) Check each cylinder to makes ure the rings are still intact (should be OK since i didn't see any scoring but I'll double check by looking down at the top rings
2) I should consider upgrading to SS valves for at least the intake if not intake+exhaust. If these valves are indeed distorted and I go with stock valves, I'll probably need to relap the intake between races (not worth the effort + gasket costs). Other teams using 5.0s in lemons locally are getting 5+ races between teardowns with this same combination (GT40 heads + SS valves).
Since he seems cool with me buying them and having them shipped to his shop (alternative is buying them from him at $20/each -- he says yeah, he's marking them up), I wanted to see if you guys have any thoughts or a specific part suggestion.
Given how many parts are out there, I figured (IIRC, Madmikey pointed me to a specific flat top piston on summit that was half the price of what I was looking at before).
Here's what I know so far:
* GT40 heads from a 1996 Ford Explorer.
* Current valves are probably original w/ 180K mi.
* Valve seal reground when I first got the heads but then I cooked the heads pretty good (disclored oil so 300F+ very likely). This is probably why they leak
As per this FAQ (Five.Oh Info : The Ultimate Ford GT40 and GT40P Cylinder Head FAQ
- intake valves are 1.84"
- exhaust valves are 1.54"
Here's what I found so far for SS valves
Ferrera 5000 SS Exhaust 1.55" (?) - $85
Ford 5.0L 302 351W w/GT40 FERREA 5000 Stainless Exhaust Valves Set/8 1.550+5.075 | eBay
Ferrera 5000 SS Intake 1.85" (is this the right size?): $87
Ford 5.0L 302 351W w/GT40 FERREA 5000 Stainless Intake Valves Set/8 1.850+5.075 | eBay
Might be able to make a cheaper offer on these
Ferrea 5000 Series Valves FORD 351W & GT40 Mustang 1.55 EXH 1.85 INT | eBay
I've also read about people recommending valve springs from Alex's Parts but I don't know anything about their valves.
They are made by
1.845" Intake Valves - $64.50+ship
Precision Engine Parts: company is based in US and make valve guides domestically but no reference to where their valves are MFG. Anyone know this company? No ISO certification quoted for their factory (something I look for when trying to determine if a company I've never heard of is legit.
1.54" Exhaust Valves - $52.50+ship
Mfg: Qualcast. based in TN. As per their intro video, All factories have ISO9000 or TS16949 certification. I suspect it's a decent product.
"Long tip length applications such as GT40 and GT40P heads can be converted to use .393" tip lengths on both intake and exhaust. The conversion normally requires the same retainer and lock set up as the intake making all sixteen retainers and locks the same, not staggered."
Do the valves need to be slightly larger than stock (1.55" vs 1.54" and 1.85" vs 1.84") so the seals can be cut to fit?
Are there any others SS valves I should consider?