Q: I am currently running a 12:4 compression 351W in a Pinto. The engine has World Products Windsor heads, 926 cfm double pumper carburetor on a Victor Jr. intake, 254-degree duration (at .050-inch lift)/.571-inch lift solid cam, and MSD ignition. The transmission is a C-4 with a 4,500 rpm stall converter. I am running 7 psi of fuel pressure through a Holley “blue” electric pump.
The problem is, I have no power past 5,000 rpm. I have tested the fuel pump through the regulator; it flows 90 gph (I run 1/2-inch fuel line). Total timing is set at 36 degrees. The seat pressure on the Crane valve springs is 115 pounds. I have replaced the coil and tested the MSD 6AL box via the “jump” method outlined in the instructions. I also did a compression test, and each cylinder registers 225 pounds.
Where am I losing power? Where do I go next? I’ve run a best of 12.12 at 104 miles-per-hour at the track. I ran 11.60 with a milder 302 in the same car.
A: There are a couple of things you can check. The first is the torque converter; are you sure it’s stalling at 4,500 rpm or is it just rated to that? We’ve seen converters that lock up too soon, and that can keep an engine from making high-rpm power.
The second thing to check for is a restriction in the induction system. Poorly matched intake manifold gaskets or heads that don’t line up with the intake ports on the manifold can cause your lack of high-rpm power.
id look for valve floating issues, sounds a little light on seat pressure for a solid cam. especially at higher rpm’s
check your plugs by shutting off engine in the lights and coasting to a stop, don’t let it idle even for a few seconds. Make sure your harmonic balancer lines up 0 at real TDC. Also run a fuel pressure gauge by the carb inlet to verify fuel pressure at high rpms. Are your carb floats set correctly? Have your plug gaps closed up? As above your springs are too light also.
A loose convertor will give you too many rpms,who you got answering these forums, have they ever raced a car before?
There is no way the engine will stop at the exact same point every time. So checking that the balancer is on 0 won’t do any good…
You check a balancer with a dial indicator on the #1 intake valve the same as you do degreeing in a cam. That’s the only poditive way to verify your zero. If it’s off, move your pointer to correct it. Then you can time your engine accurately.
Have you tried less spark advance? 38 degrees seems a little much for 12.4:1 compression unless you’re running lean. Also I’d check that you are physically getting wide open throttle when your pedal is all the way down.
have you checked your camshaft?
Sounds like you’re timing is to far advanced, pull #1 plug and make sure your timing mark on the harmonic balancer is correct and you really need more than 115 valve springs you may be floating valves.
Yes these 2 things are my bet too
Is it missing or just going flat after 5000. Take 1 valve spring off in place check open pressure see if it’s enough for the recommended pressure for your cam.put fuel pressure gauge were you can see it check pressure over finish line
I had the same performance issue with my 355 stroker. After doing all the routine checks I removed the heads to check valve springs. Upon inspecting the camshaft my problem turned out to be a couple of “flattened” cam lobes
? sounds like valve float. with solid lifter cam it has to be flat cam lobes as already mentioned again check valve springs broken or weak springs check push rods for bent push rod and or valve lash to tight?
also install a fuel pressure gauge and make sure you’re pressure isn’t dropping to much .
I’ve had g force cut fuel pick up between fuel tank and pump. had my fuel pump mounted to high and loosing prime.
Proof that bigger isn’t always better
All the chicks ive been with will argue differently. Like every day their different. Crazy. Thats what they are. Plain crazy. But yeah i do agree with you on size thing. Had a 305 in my camaro. Had wheels come off ground about inch. Stock. But stripped of egr. And bigger carb. 2.5 exhaust. The 350 i put in. Well. It was good too but never the same thrill. I guess like your first kiss compared to 3rd or fourth wife. Just kidding. No.
Torque converter lockup? check the OPs original list of parts. C4 transmission. No lockup converter there.
He did compression check so its not bend pushrods, its not wiped cam lobes.
Has to be either fuel, ignition or valve float.
Fuel: get a wideband O2 sensor to borrow for a few runs. Does it fall flat in every gear or only a the top end? If the latter it may point to a fuel delivery problem (pump, lines, filter), if its falling flat in every gear it could be more to do with Jetting, float bowl settings. The wideband will tell you if its a fuel problem and leaning out or going crazy rich.
Ignition, if your fuel is good then it could be ignition. Timing doesnt sound so bad but are you running the aluminum or Iron heads from world products? You say total timing but do you have a vacuum advance unit on it that could add a few more degrees? Im not convinced its a timing issue but you can try a few different runs with different adjustments easily enough. It could just be breaking up at higher RPM but usually you can hear that because of the misfire – itll pop and bang from raw fuel/air mix going through the engine into the exhaust.
Valvetrain, heres where that spring pressure comes in and my hunch at the problem
assuming you have a solid flat tappet youre still way shy of the recommended spring pressure. if you have a solid roller cam (doesnt look like you do or you would have a lot more lift) then youre way off on spring pressure. But even a flat tappet cam needs more spring.
Without knowing more sounds like valve float. especially if youve done some carb tuning before and can tell what lean and rich looks like, presumably your ignition set up was good for more RPM in the 302. So it kinda points to the stuff thats new, like the heads/valve springs.
Need more info
How heavy is ur car ?
What rear gear ?
It does sound like ur valve springs are a little light prob try a 140-150 lb spring . not sure if ur running a solid flat or roller combo ,,, but if sounds like one would need a roller set to run that type of spring .
The world product SR heads flow right at 260 cfm @ .600 valve lift .. basic cal show u should be good for about 530 hp …
The the single plane Vic JR intake is prob not a good match for that head / cid combo , the performer RPM would prob be a better match for ur combo..
What kind of plugs???