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cometguy":221lrg3r said:
With respect to PLAN, the stroke and piston area are off limits in this class. We can play with compression however; the piston is at zero deck with a FelPro gasket that crushes to .042-.043. The allowable limit is any combination totalling .031. The current valve cover set-up has a sealed pcv and one breather doubling as an oil filler. I will check all the rockers as well.
Anything other than the specified manifold and carb for the year of the car (1972) would be considered illegal but most tech guys would not check dimensions, just casting #'s. The exception would be a post record-run tear down or a protest situation. Very unlikely in my case. The current head casting is D5DE-BA(illegal for '72) and I have an unmolested casting from a '71 Maverick, C9DE-M which is OK by the book.
Are you guys suggesting less gear? The rear end is an 8" and less gear will be easier to source than a higher ratio for certain. The trans has minimal mods; stock servo, reverse pattern manual valve body, shift kit and a converter that will flash to 3900rpm.
Great work, your combo is getting pretty well optimized at present!
Your hard work has resulted in moving from a 4.62 ratio and 26" combo with 15.30 and 2.07 60 foot times to a 5.43 ratio and 28" tires for 15.25 and sub 2.01 60 foot times.
The trap speed is around 86 mph now, so your pulling what, 5600 rpm?, when it was 5100 rpm. That may not be power, it's optimization, period!
Your team effort has basically created half a seconds more hp by the changes. Your right into the peak power band with your cam, compression, carb and head flow. That Quarter mile time indicates about 1.1% more effective horsepower, or 2.25 hp.
I still think that a success will be going back on gear to create maximum power at 5600rpm so the combo you've got will give you, say, a 14.8 second pass.
That means you'll have to bring your gearing down from the 15.3 mph per 1000 rpm you have now back closer to the 16.7 mph per 1000 rpm you had before.
I'm thinking that power supply is best at about 5500 rpm with a 1.50:1 rod ratio on the smaller 200, since its a short stroke engine verses what Australians know about 250 engines. Evidence from work done in the late 60's on the 2V Falcon 250 showed that the poor rod ratio on a six in line would lower the rpm peak. Even "port on port" carbs like triple Webers or Dellortos didn't raise the rpm limit to 7500 rpm with a 320 degree cam, 4800 rpm was a magical figure of rpm that the 1.50:1 rod ratio that a long stroke 250 created.
The only whay to make more hp with a 1 venturi carb probaly not rev related. It is to go to finding a cam grind that creates high pressure in the camber (bmep) and a part number perfect carb which flows the most cfm at 3"Hg. For a 200 Ford, the ideal peak rpm for a 1-bbl head might not be 6200 rpm, but 5100 to 5600 rpm on a 200. Past 250 feet per second, you reach very turbulent air flow, and maximum power drops. An example is the F1 engines which rev to 20000 rpm, or NASCAR engines which rev to 7500 rpm. They make less specific power for each rpm than an engine with less air speed.
Anecdotal examples of bending the rules within the rules. The old production stock British Group 2 (later Group A) rules for carbs was that the term "adaptor" and "carb" and "manifold" must be defined. Where it's not, you use that cloud to improve the whole flow to each cylinder by seredipity time on a flow bench. You go through odd ball combinations until you improve the cfm flow and compression (BMEP) to each cylinder, sometimes by reducing CFM and increasing compression to make up for the loss.
If YA or RBG Carter, or the factory replacement Autolite 1940, you have to look at what legal combo of adaptor and intake you can use helps your cause. I'd look at if a stock 1.5" log head could be modified within the rules to a 1.75" log, without technically hand finishing it. You get to scramble the parts to suit. For example, Aussie racer Dick Johnston used to glue to parts of his old 1985 302 Mustang Group A racer's manifold, after reparing the intenal passages for a 1984 4V HO intake, but still use a 1985 EFI roller rocker cam. The 4180 carb and two part Araldite held the combination together and, whamo, there was suddenly 320 hp instead of 260! All within the rules.
Aussies working there old L6 and I6's found a smaller chamber head which is still legal can bump the compression off the scale for some improvement, even a 'bad' casting that trades off cfm flow at 28" H20 may be made up for by a 15% higher compression ratio. That's worth more hp with less cfm. The old 46 cc 138/149/161 uesed to be slapped on a 173/179/186/202 for a big boost in squeeze. What if you used the 52 cc 170 spec head planed?
Perhaps the use of low compression 12cc California spec head, but with 5.5 cc pistons, with the right exhast gas recriculation pump plumbed to
add a 40 cfm free air flow ticket, evenly distributed over a 6 cylinders (like EFI), while the low cfm carb could add fuel from a little California spec 165 cfm leaker.
This could exceed the 185 cfm from a good Carter carb. An engine that makes 195 hp at 5100 rpm beats 196 hp at 5600 rpm if its optimised to suit.
I'm aware of another thing from Aussie Holden and Ford sixes with less than 12 counterweights or cast iron cranks. Crank vibration tends to cause harmonic vibration which hurts the power at around 4500 to 6200 rpm on six cylinder engines in the 3.0 to 4.1 size range. Holden gained about 1000 rpm of safe extra revline (from 4500 to 5500 without cam changes).
To verfiy, you draw two converging lines, horizontal line, and a line 10 degrees to the horizon on the side of the engine block on a white backing, and then data log by video the actual horizintal up thrust at each rev range. (This is used in vibrating table tests for maximum density of gravels by geologists in the Earth Manual). Amplitududes in 1/32" intervals can be logged, and you can see when the in the rev range things go critical. Anyway, it allows you to see that crankshaft vibration is hurting the power. The old four bearing 170 and 200 cranks were about 6 pounds heavier, and sometimes this alters the revs at which the power sapping harmonics occur. I've heared that 1972 was when four bearing blocks were replaced by the seven bearing block from Consumer Guide in there 85 years of Ford history book. Yet this is contrary to what we at Ford Six have found to be the case. Four bearing engins make more power at lower revs than seven bearing engines,as the frictional resistance is less. After a certain point, vibrations hurt power, but a heavier crank usually shifts the point where vibration happens further up the rpm scale.
