Engine problem on big end

[1147]

Like the title says. I get the car in to high gear and get to the 1100 foot mark and the engine goes flat, but its not every pass, its only about 6100 rpm. My engine is EFI, 347 ford with Roush 200 series heads, 10.5 compression, hdyralic roller cam, trick flow track heat intake, 32 pound injectors backed by a AOD camshaft. Any ideas would be greatly appreciated. Fuel pressure is good, oil pressure is great. New plugs gapped at 35. new cap and rotor.

[Ethyl Cat]

Total timing? Have you moved it?

You say pressure is good, but does it fall off even a little? A fuel system can lose nearly 50% of it s volume(what you need on the big end) without affecting pressure much.

Do you have a wide band?

Steve

[merk]

by chance have you checked valve spring pressure? Weak springs will make the thing fall on its face and is most noticable in the harder slower rpm sweep aka high gear .

[PaceFever79]

Because it doesn't do it all the time, I'm going to suspect a fuel issue.

By the time you get to the big end charge, you're using a sustained high volume.

What pump are you running? And how much fuel is in the tank (when it runs out on the big end)

[Ethyl Cat]

Also,

Which AOD camshaft did you buy, the Motorsport one or Roush's new one?

:

[1147]

Its an aeromotive pump. Pressure holds strong at 42 all the way through. My 5 gallon fuel cell is filled a couple of inches from the top when i start and only goes down 2 inches per pass. Timing is locked at 38. Camshaft is a Comp Cam.

[shifter]

Try less timing...car may pick up.

I'm also thinking a possible valve spring issue...

[1147]

I will get the tester and where they are at. Thanks

[brianj]

Figure this out yet?

[1147]

Will be going to the track this weekend. Been busy working and tball. Before we will check valve springs and I did put a new coil on and checked and repaired any wires that looked liked they could be a trouble. So we will see what happens and will update about springs and track times if changed.

[1147]

Well also put a coil on it. Valve springs are 95 pounds when they are warm. Valves are lashed properly. So went to track and still does it. So I releaned all fuel filters again and it still did it, fuel pressure is good. So I will take injectors out and get them cleaned, I clean the mass air meter every weekend, the fuel pressure is good though. The plugs look lean, I up the fuel pressure and they still look lean, so it makes me wander about the injectors or the meter.

[merk]

Is this a hydralic roller cam ? I completely missed this. 95 psi is def on the low end those heads in the hr trim are spec `d at being a 125 seat pressure . Even comp specs theire cams for any hr cam ment to go to 6000 at being at least 130 psi

[1147]

At what temp is there rating taken. I took my reading right after I made a pass they were very warm and the colder the spring gets the rating goes up.

[1147]

I am going through the entire car now and so far I found a caliper hanging up on the front, not sure how i totally missed it.

[merk]

usually springs are tested at room temp . But the heat will make a difference but not over 30 psi seat pressure . Any idea what cam it is ? Alot of what comp has in the old catalog arent really ment for much more that 6000 rpm another thing to look at it could be a lifter problem as well what lifters are in it ? Some of the down sides to hr set ups some lifters cant take the rpm .

[PaceFever79]

Most hydro roller lifters are too heavy to rev past 6000 rpm without floating.

That would be especially true with a fast ramp, and valve springs of marginal pressure.

I can't for sure but that does sound like it could be your "problem".

[merk]

spring are def the problem here . In most hydralic roller motor I build that have anything of nice agressive ramp like damn near every cam out there now days i try to stick around the 200 lbs seat pressure + or - depending on lifter wieght , pushrod weight, valve weight and rockers used and if possible use a short travel lifter to achieve any real rpm

[1147]

Yeah its valve springs. Changing them out, and all the shims are beat to crap too.

[droopie85gt]

I was going to mention look out for aeration in the fuel cell from the return line. If it's too close to the pickup or too low in the fuel it will bubble the crap out of the fuel and cause aeration.

[1147]

Just to update we put the valve springs in, i called the engine builder and they gave me the part number of the springs they used, so we got them in and for the first three passes it did not breakup on the big end. Then we got to first round and it fluttered on the big end, we still got the round win somehow, then we lost second round and still had a flutter. So call the engine builder back and he said he wanted to test the springs we just put in and the old ones, he tested them and the old springs were actually a higher pound than the new ones, even though they were the same part number. The old springs had 250 passes on them and the new ones only had 5. They let me return the new springs and trade them for a spring with a slightly higher pound reading.

[1147]

Thankfully the heavier springs worked. Thanks for all the replies.

[merk]

glad you got it all figured out

[Johnny]

Nice!!