Technical Blown Flathead high rpm miss?

I noticed what seems to be a miss or loss of power at WOT at about 5200 rpm and 6lbs of boost. Never had the problem before. I don't think it's a fuel issue because I can see my A/F is at 12.3 at that point of WOT.
I've had this motor to 6000 rpm a bunch of times with no issues. All three mains have custom caps.
4" crank, forged pistons, Mallory Unilite distr. Holley 415o carb, electric fuel pump
Anyone got any ideas?? Thanks Joe

 

Fuel
Air
valve springs

Plus, ive learnt the hard way not to 'discount' what i think is ok.

Bad plug
Bad lead

Etc

 

Are you using a boost referenced fuel pressure regulator? Could be something there.

 

Remember, you only have three main bearings down there.

 

I would check the valve springs.

 

Try a different ignition.

 

I have boost referenced the carb. I'm not using the boost reference on the regulator. I think my fuel is ok.

 

Yessir, noted

 

I'll keep this as my last resort. The motor ran fine up tp 6000 rpm for over 1000 miles. Definitely not ruling it out though.

 

Care to elaborate?!

 

Will start the checking this weekend

 

I had a blown 283 30yrs ago, I would get a miss, change the plug's fine for a while..
Changed again an thought I smelled gear oil.... WTF
Then It dawned on me, Yep it had factory diesel seals in it when I tore it down, They are not designed for hi rpm...
Not saying this is your problem.
But I spent a week changing distributor spring's/weights an carb work etc.
To find my brand new blower was faulty.

 

Unilite is sensitive to contamination inside the cap. It could be a random misfire on more than one cylinder. This is my experience on older units .

 

I posted about the valve spring pressure yesterday,,,,I think mine was the # 4 post .
I guess someone decided to delete it,,,,I have no idea why ?
You had stated you had about 70 pounds of spring pressure on the seat,,,,,,not enough for a blown application .
And 6000 rpm !

Edit : I just realized my post was on this exact thread over on the Ford Barn .
I knew the details were a little different on the first post,,,,my apologies !

( I do feel better that my post was not deleted after all,,,,LoL .)

Tommy

 

Well there's your problem right there.

Not sure you should ever be at 6,000rpm, let alone for 1,000-miles!

Seriously, you are over-revving. You are endangering the bottom end.

 

Oh, and check the condition of the spark plugs, and make sure that your gap is not too big.

 

I'd try two initial things. Try pointing an infrared gun at the exhaust manifold when its missing and see if there is any difference in cylinder temperature. Run it at night in a dark place and look for any ignition sparking.

 

Have to agree on RPM,s unnless you have light weight lifters and very special valve springs. Be sure you haven"t damaged the cam also, may have pounded the bumps off. If your engine is balanced with steel caps, and you don't go any higher on the boost the bottom end will be all right. The nastiest flatties I know of Boost 12- 21Lbs and three main bearing cranks with a girdle do the job.

 

How did you remedy the situation?

 

Sorry Tommy, I don't know why that happened!

 

Gimp, I'm only hitting 6000 rpm for a split second at 1st to 2nd and 2nd to 3rd shift points. Never for prolonged periods of time.
Ill check plugs and wires this weekend. Thanks Joe

 

Wow good call

 

Point taken!

 

What a pain in the butt! This blower was designed for the flathead and thank god never saw a diesel motor!

 

The mallory I had was a dual point YL that I converted to a Unilite trigger. The technology was probably not close to what you have. I also used a light trigger ignition on a couple Harleys (Evo) and it was in the "nose cone" where it could get some contamination from the cam seal.
I probably shouldn't have commented on your situation as it was "apples and oranges comparison" and I apologize.

 

Ho apology needed. We learn something new everyday! Thanks

 

So I decided to replace the coil and plugs. The wires checked out fine except one that gave me a weird reading so I replaced it. Just got back from a ride and watched the video of the gauges.
The miss is gone and I recorded 7.5 lbs. of boost at 5200 rpm with 12.8 on the A/F.
I also installed a shift light set at 5000rpm to limit the rpm at my shift points.
I believe it was the coil. The temp outside is 40 degrees so we'll see what happens when it warms up outside.
Thanks for the responses!

 

A bad wire can increase the load on the coil, by increasing the spark voltage needed to jump the gap/high resistance in the wire. Eventually the high voltage can make the spark punch through the insulation somewhere, sometimes internally in the coil, giving the spark a simpler way to reach ground. It can still work fine in low load situations as the voltage required is low when cylinder pressures are low, but go full throttle and fill the cylinders compeletely, cylinder pressures go up along with the voltage needed to make a spark at the plugs. The lazy spark selects the easier way straight to ground...

 

"replace(d) the coil and plugs" and replaced plug wire.

I would have started by replacing the plug wire.
Not just because it would likely require may more road tests."
What type of wire,and what were the weird readings?

What was the condition of the old plugs" Cleanliness, gap, electrode sharpness.

Back in the leaded fuel days, lead deposits conductive enough to let the spark sneak to ground.
Even My slightly modified Sunoco 260 fed turbocharged Corvair would develop a full throttle miss after a few thousand miles. A Delta CD ignition improved matters tremendously. Stock coil and maybe even stock type plug wires. Legend was the fast CD spark rise was less susceptible to missing due to minor plug fouling.

 

Wow, I didn't know that! Thanks