Swapping the 4/7 firing order on a Pontiac - Pontiac GTO Forum
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post #1 of 6 (permalink) Old 11-01-2014, 12:29 PM Thread Starter
 
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Swapping the 4/7 firing order on a Pontiac

Ok, always looking for new ideas and info on "traditional" Pontiacs on the web that I might incorporate on my engine build/car.

Found an interesting article on swapping the number 4/7 firing position on the engineafter reading the specs on a Pontiac race engine. Apparently it can help with cooling, crankshaft harmonics & life, and smoothness of the engine. The article can be downloaded as a PDF.
MOTOR Magazine Article | MOTOR Information Systems

I then found cams ground specially for this firing order by Howard Cams at Summit. http://www.summitracing.com/search/p...s/make/pontiac

I haven't chosen a cam yet, but have a few choices in mind. Now this puts a different option into the ring. No doubt you can get this 4/7 swap from any cam manufacturer/supplier that offers custom cams.
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post #2 of 6 (permalink) Old 11-01-2014, 12:46 PM
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Learn something every day. Looks to be a fine tune, with a bit more HP with all other things assembled to match:fuel, exhaust, etc. Most beneficial for cars/engines running at peak power for extended periods, like oval track. Still, overall benefits of long bearing life and smooth operation have to add durability over the long haul. Apparently, no down-side. And if the special camshafts aren't outrageously priced, not an expensive mod, either. Makes you wonder why this didn't come up decades ago.
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post #3 of 6 (permalink) Old 11-02-2014, 02:04 AM
 
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Fireing Order Change Up

I read about these changes years ago (that article was written for the BBC engine). AT THAT TIME the cost involved in having a special cam ground was more expensive than the 3 to 4 HORSEPOWER that was gained was worth.

Specially ground cams may be less expensive nowadays, and the change might be worthwhile for engine life or drivability... Depending on cost: it might be something worthwhile to consider during a rebuild, but doing it to a running engine, not so much (high cost, low benefit).
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post #4 of 6 (permalink) Old 11-02-2014, 06:02 AM
 
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Ford racers have done this for a while. Some Ford big blocks have a crank that works like 'normal' GM stuff (1-8-4-3-6-5-7-2) but their cylinders are numbered different. Others were running a crank like ours and seeing big power changes. Ever notice how smooth older Ford engines run? Racers decided screw that and went for power. That was over 20yrs ago. This 4/7 swap, would it make a difference in the character of the exhaust tone? The only big challenge I see in a comp application is the header configuration. Seems like (after reading that) getting headers to work with the firing order (another old idea) would result in mess of tubes under the car, if it could even be done on anything other than road race or open wheel stuff. Still a clever idea for a lot of reasons, and thanks for sharing.
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post #5 of 6 (permalink) Old 11-02-2014, 08:54 PM
 
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We had my sons 68 GTO 400 stroked to a 464 last winter.
Our engine builder did the 4/7 swap and installed a Howards cam in the stroker.

This is the cam they installed
.

Instead of headers we are running Ramair restorations OS round port exhaust manifolds.

Oh btw.....Our engine builder rebuilds a lot of Ford engines

Bill
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post #6 of 6 (permalink) Old 11-03-2014, 07:42 AM
 
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Quote:
Originally Posted by bondobill View Post
We had my sons 68 GTO 400 stroked to a 464 last winter.
Our engine builder did the 4/7 swap and installed a Howards cam in the stroker.

This is the cam they installed
.

Instead of headers we are running Ramair restorations OS round port exhaust manifolds.

Oh btw.....Our engine builder rebuilds a lot of Ford engines

Bill
And how does it perform ?
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