Spark Scatter @ High Rpms

[wsa111]

When checking total advance at high engine rpms 4000-5000 i am starting to get some spark scatter which anyone with chevy experience is the norm because of the distributor at the rear of the camshaft getting harmonics & from driving the oil pump. On the chevys i run a moroso anti-cavitation oil pump which cuts the scatter in half.
On the small six im thinking it may be due to the duraspark distributor having no lower bushing & i am getting fluctuations from shaft flex.
I replaced the pickup coil in the distributor but noticed no change. both pickups ohmed out at close to 600 which is in the middle of the correct ohm range.
My option is get a distributor from Performance distributors which has the full length bushing for better shaft support.
The camshaft drive gear is starting to show some wear, but the distributor gear looks perfect.
When some of you members get a chance put a timing light on your engine at high engine speeds & let me know what you find & what distributor are you running.
Spark scatter is the timing mark jumping around & is not rock steady like it should be at high engine rpms.
I may give Mike a call & purchase one of his rebushed distributors with a full length bushing.
I know he sells motorcraft remans, but they probably lack a lower bushing.
Advise next time you put a timing light on your engine. Thanks

 

[thesameguy]

I have had the same problem on my Lima 2.3t at high RPM, which is part of the reason I went EDIS on the Falcon. I wish I could do the same XR4Ti, unfortunately the nice smog folks in California won't let me. No mechanical parts yields really nice timing.

 

[rbohm]

8) i say go with the full bushed distributor as even the front mounted distributors on small block fords have issues with spark scatter.

 

[woodbutcher]

Hi WSA.Had that same problem with the 302 in my 74 F100 with a DS2.solved the problem easily.Just had some new bushings cut for the shaft.Had them made out of oil-lite.Cost?$3.50 for the oil-lite.Friend cut them for free on his lathe.
Good luck.Have fun.Be safe.
Leo

 

[xctasy]

Your a smart man to find that. You'll note the scatter is cyclic and happens at certian periods, rather like the Nissan Skyine GTR's twin turbo DETT26 engine which would go haywire at 3700 rpm. On our long stroke 250's, it happens at 5300 and 6200 rpm, which coincides with crank harmonics and oil pump cavitation.

EDIS will eliminate it all, but within the stock confines of the Ford ohv six, you can take a leaf out of the 335, 385 and Windsor upgrades offroaders have done ever since Adam was a cowboy.

According to one Aussie guy back in 88, (an Outback Modified Bronco driver, with NASCAR block and A3 heads) spark scatter is a combination of

1)timing chain wear and
2)the macaroni drive off the High volume oil pump, and
3)the shear pin, which is too small for heavy duty service.

Australian off road racers have gunned the old Cleveland engine to death in the roughhest races, and those guys have found the small shear pin and hex drive to be the cause a reaction off the drag from the high volume oil pumps to preload and unload the distributor drive, like some kinda freewheeling dynomomoter counter weight. It is has a torsion effect, much like a rack and pinion power steering torsion bar, but yielding to the transient harmonics of the cam, timing chain, hex drive and oil pump and shear pin loads.

I personally don't think an extra support is the answer, as a stronger, better fortified link/mechanical contact between the driving force of the crank and the distributor should eliminate most of the play. I suspect a full on think up on the points 1,2 and 3 above will show you the validity of that Aussie 600 hp Bronco punter showed, and then investigate yourself.


Your solution is to replace the 1/8" drive pin with an Accel 5/8" upgrade (fixes 3), and see if you are able to get a better quality hex shaft (fixes 2), and then invest in a Diecrest gear drive (fixes 1). They don't make a 200 cubic inch American engine gear drive because the Aussie 200/250 cam from 1971 to 1992 is 25/32ths further out than the US 144/170/200.

But they can make anything if the market desires.