mid length header collector length for anti reversion cans

[lbs-ft]

Hi All,
After researching ST extensively, I am still uncertain about AR canister instal length. 347 Ford in a 65 Mustang with FPA headers. Exhaust reversion clear to the carburetor. Primary tubes are a short 1-5/8 to 1-3/4. Primaries are different lengths from 18" to 30" to 3" collector about 5" long. 3" exhaust from there. Dumb mistake there. It's a 3" collector about 7 ft. long. Pipemax suggest 28-1/2" long primaries to 17.2" collector. I intend to install Dynatech AR cans to put the ID of the cone at the tuned point. Should I add any length to the collector to make up for the shorter than optimal primaries? Would it be a potential advantage to a street car to add a length to bring the tuned point down to a bit lower rpm than the Pipemax optimal point?
Thank you all very much for your time and consideration,
Lbs-ft.

[F-BIRD'88]

Your camshaft exhaust valve events may not be friendly to the mid length headers.

[lbs-ft]

OK, I'm curious. Thanks. What kind of a change in exhaust events might work better to ward off reversion in a mid length header?
Thanks always.

[F-BIRD'88]

OK, I'm curious. Thanks. What kind of a change in exhaust events might work better to ward off reversion in a mid length header?
Thanks always.

What cam is in it now?
Installed phasing is? (in/ex centerlines)

I have some ideas for you to try out in addition to your anti reversion chambers with cone reducer inlet pipe.

Try this and test: On your headers with 3" collector try adding a similar 3" to 2.5" reducer cone stuffed up in the header collector up against the primaries in the collector.

Cut the 2.50" diameter end of the reducer off at 2.75".

This should act more like a "merge collector" but with a anti reversion effect also at the collector..
That diameter of the reducer cone in the collector may need to be tweeked for effect.. say 2.60" to 2.80" ish..

This should speed up exhaust velocity And create a anti reversion effect too..
This s in addition to the anti reversion chambers further down the collector head pipes..
Try it.

[F-BIRD'88]

If the 3" to 2.5" reducer cone (cut off to +/- 2.75") will slide up into the header collector, even better as you can test it stuffed in a different depths up in the header's 3" collector.

You are going to have to test this out to see how it works for you.. Often the 3" collector is a bit too big on small CID engines..

[F-BIRD'88]

Are these your headers?
http://www.fordpowertrain.com/347step.htm

If so, these seem to already have a merge collector.

What is the pinch diameter up inside the merge collector on these?.

[lbs-ft]

Cam is HR with 224 int. 232 ex. 111 lsa in at 108. .56 int. lift and .55 ex. lift. If my memory serves correctly. It was installed 14 years ago.
This is not my car, so testing is difficult. A reducer in the collector sounds like an interesting idea. The collector has a ball and socket type flange so they are rolled in a bit. I'm not sure if I can get a 3" cone through it. Will have to go check.

[F-BIRD'88]

The black in the intake manifold is from part throttle running and idling reversion .. With a cam, that happens.. May respond to advancing that cam some.
Thats something you have to try for effect.

Does this car lack vacuum advance?

[F-BIRD'88]

If the car sees more idling and low rpm running than racing and the black ex reversion is bother some may want to re cam it. less duration and overlap. Single pattern.
Cam it for how it is actually driven vs trying to make max WOT. power, especially if its not being used anyway. Ya that takes a re-think. It will be more enjoyable with a cam better selected to how the car is really used daily.
A open plenum intake will see more of this than a dual plane with split plenum. Anti reversion in the exhaust may help, but not much if want back at the mufflers.

Was visualizing a different low tech generic 3" collector with no merge shape than what you seem to have there already.

[BLSTIC]

How much power is it making, or trying to make? I'm just thinking of the primaries themselves. 1.625-1.75 is fairly big and during street duties there won't be much reversion fighting exhaust velocity in them.

[lbs-ft]

Very good advice here. Thanks to all who have helped. I appreciate your valuable time.
This motor was intended for road race track days. Not for the street but street legal. It made 450 tq. @4600 and 479 hp @ 6100 on a DTS dyno with 1 5/8 long tube dyno headers. The block is a Ford Motorsports deal that they rated at 400hp capable @6000 rpm. I chose not to rev it higher than that for amateur road racing endurance. The car builder then changed the headers to these without testing. It seems to me that everything in this motor is too big for part throttle street use. Just trying to get it cleaned up enough to keep it from fouling plugs, etc. Changing to longer, smaller tubed headers might be inevitable, but want to give the AR cans a try. Will be changing to an Eddy Air Gap dual plane. Canfield 192 heads might be too big, but I don't know nearly as much as I used to.

[F-BIRD'88]

The headers are not the problem. The heads are not the problem... The dual plane will be nice but the current manifold is not a deal killer. Both could be tried.
The dual plane should have a full divider for best low speed results... What really needs attention is the carb and diz ignition
setup.. Starting at the air cleaner. It may be WOT dyno tuned but it sure isn't street tuned. IMHO the exhaust system needs a re think.. It is too loud and I bet its too restrictive too, as is.
The cam probabily can stay too once if these other factors are addressed to make it street friendly..

Time to street tune it and put a true full high perf street exhaust system on it.. It may well end up faster at the track too. He'll be able to drive it better and hear himself think.

A 3" exhaust system is not neded. Its too big and too loud and contributes to the reversion...
A true 2-½" full system w streetable mufflers and tail pipes is what this race car needs. Could be H pipe could be X pipe.. Cats (if needed to be legal) up near the collectiors.
2.50" in out magna flow or tri turbo type muflers (dynomax)
Full 2.50" tail pipes.
A A-R chambe (2..5") should be BEFORE the cats or built INTO the cats.. When done right this will be a ZERO performance loss ex system.. The A-R chambers may not be needed at all.. but are something you can try.

[F-BIRD'88]

Once re set up both the dual plane and your single plane can both be trac tested to see which is really best overall for this car. Keep an open mind on both.
Diz needs to be vacuum advance type and will need a rework.

[lbs-ft]

Well that's encouraging. It's scheduled for a new 2-1/2" exhaust with magna flows to be installed next week. Dual plane after that.
We'll see if the carb acts differently on the dual plane, but likely will be switched out for a street styled unit with a choke.
Distributor is an MSD that's easily adjustable. It's now at 14 initial, 18 centrifugal @3k and I think the vac is 8 deg. Will check that.
Thanks again for your help.

[F-BIRD'88]

Try 18 to 26 initial. 10 to 14 deg advance curve.
For a single plane more initial is better.
Be agressive But keep the total WOT max timing correct for that motor. I bet that you will find a 10 deg mech advance curve is best.. With your engine combo.

Carb may just need better dialing in.
What is it.? and what is the current intake manifold?

On many racey single plane intakes adding a plenum "turtle" and a plenum divider intergrated to a carb spacer can really transform its street use behaviour. Simple to remove that divider for open plenum WOT running on race day.
May not need to throw out the baby with the bath water on this.. Just "streetify it"
Can be a-b compared to the dual plane for perf effect.
Don't forget the tailpipes.

"with a choke" Why? Does he driveitin the snow.?

Spark plug tip type and heat range may need attention too.