Super six set up with low comp

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Slantsix64

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i want to do the super six set up to my 64 dart but my compression is about 90 on my cylinders but my car idles great and drives great with the stock 1 bbl wondering if i swap it to the super six would there be any issues? with that low comp give me problems ? would my gas millage change a lot ? my ex pipe is already 2.25 let me know what you Mopar freaks think!!:D
 
You HAVE to do it and then you have to do whatever it takes for the motor.
That's how Mopar freaks roll. :D
 
I dont think it would do anything....tired slants a tired slant. Rebore and mill head .090. Get some!
 
TB; I like your thinking!

However, 64, on your set-up,IMHO, it would not be cost effective in any way. I did just this swap on my 1980 Volare-fb in 95. Bumped the c/r to 9.0 as well, during a rebuild.I think the motor was a tad more responsive. No additional power. Maybe a hair better on gas. All-in-all I was disappointed. Your results may vary.I should maybe mention that I replaced the 80 motor with a 77 Super Six, that I had rebuilt to my specs. which included the 9.0 c/r, and one-size bigger mechanical cam kit. I waited what seemed like forever for the pistons.Ended up with 145psi cranking pressure.I woulda been better off swapping the rear end to 3.23s or maybe 3.55s. But yeah, 90 psi seems low. Just fine for low-performance, but the super six wont change much on your set-up.
If you decide to go for it anyway, make sure you get everything from the donor car.EVERYTHING, includes the gas pedal and cable.Others have tried to make it work with the floor mounted gas pedal. I think they mostly failed.
 
Are all the cylinders at 90 psi? If so, that is a bit unusual for all 6 cylinders to wear out that evenly, and for it to run well with that low a compression all across the board. That would make me question the compression tester and how it is being sealed in the spark plug holes. It could be for real, but I would be looking at some other cause for those readings.

And yes, the 1980 motors were 'hotter' than the early motors so the smaller difference that you found is rational. The /6 cams were changed in the early 70's for example.

For the OP, I would suggest a re-test of the compression, with all plugs out, cranking 5 times per hole, and with the carb propped open, and see if the readings change. If they are that low, then put a teaspoon full of oil in each hole and retest to see if the oil increases the compression readings; if so, then indeed you have worn comproession rings.

Putting on the super six with worn cylinders won't hurt anything, and ought to perk it up a bit, but of course it will still be down on power due to low compression. I would not expect any big mileage change with the exhaust already changed.
 
TB; I like your thinking!

However, 64, on your set-up,IMHO, it would not be cost effective in any way. I did just this swap on my 1980 Volare-fb in 95. Bumped the c/r to 9.0 as well, during a rebuild.I think the motor was a tad more responsive. No additional power. Maybe a hair better on gas. All-in-all I was disappointed. Your results may vary.I should maybe mention that I replaced the 80 motor with a 77 Super Six, that I had rebuilt to my specs. which included the 9.0 c/r, and one-size bigger mechanical cam kit. I waited what seemed like forever for the pistons.Ended up with 145psi cranking pressure.I woulda been better off swapping the rear end to 3.23s or maybe 3.55s. But yeah, 90 psi seems low. Just fine for low-performance, but the super six wont change much on your set-up.
If you decide to go for it anyway, make sure you get everything from the donor car.EVERYTHING, includes the gas pedal and cable.Others have tried to make it work with the floor mounted gas pedal. I think they mostly failed.


Now see, I never said it would help anything.
Only that it has to be done because it can be done.
That is what I meant about how Mopar freaks roll. :D
 
TB, thats exactly how I understood your post, and I had a good chuckle, too.And thats pretty much why I did the swap; because I already had the stuff,It came on the donor motor, and Im a Moparfreak.
.
I guess I do c/r tests a little different than some. I crank the engine until the needle tops out. On lazy motors it might take 8 or more revolutions. Sometimes 10 or even 12. I also take note of the first solid number and how many pulses it takes to reach maximum. I record all these numbers and then when finished I can compare them to eachother.
-Say the first solid number is 70psi, the next is 90, and then 105,115,120,123,123,124,124. The first number I call solid because many times the piston may be half way up on a compression stroke when you hit the key and that number might be 35,or 45, or some other worthless number. So then the 90 tells me quite a bit about the motor, especially when all the other cylinders come in about the same. Then the 123/124 number tells me I can stop cranking, cause weve topped out.Finally, the number of pulses to the highmark being 6 tells me more about the engine.And finally comparing all the cylinders to each other gives the big picture. If you do the test without the carb at wot, all the numbers are a little slow to come up, but the max is usually the same. It just takes a few more revolutions to get there.A high first pulse is desireable because it usually reflects an easy to start engine.
 
Always suspect data. Your 90 psig data doesn't jive with "idles and runs great". If it doesn't burn oil, I certainly question 90 psig. Turn the motor over by hand. If you must fight each cylinder (3/rev), your engine is fine and your compression method is suspect. You need to remove each spark plug tube and use a screw-in gage w/ an O-ring seal. The Shraeder valve in the tip of the gage must be correct and not binding (opens real easy). Gage must be accurate. If a shop that will do the work collected the data, suspect "data bias", i.e. they might have rounded off a 143 psi reading to say 90 psi, or perhaps they have a gage that always reads 50% low, but they like it because it makes a lot of money for them, as they say with a straight face, "the readings were ...".
 
Bill I like your humor. 143 rounds to 90.I nearly died laughing. You are, of course, right. This industry is rife with abuse. I have always tried to conduct my work with honesty and integrity. I have quit jobs over this belief. I have spent very little time unemployed. I never made a bunch of money, but my needs were always met, abundantly.
They say laughter is the best medicine, so Bill, dose me some more.
 
And when I say 5 times per hole, I mean that compression readigns almost always will be at the peak after 5 revolutions. I just wanted the OP to know that you have to crank it over several times per hole before you can get a valid reading. If it takes 6 or 7 to get the max, do that.
 
Compression on all 6 at 90 PSI is probably pretty good. At least it's evenly worn.
That's a good sign. I like a good distributor re curve better than the super six swap.

The super six swap always results in poorer mileage. Since both barrels on the carburetor open simultaneously, it drinks more gas than a one barrel. Now, go for something progressive like a weber and that changes. Of course it's also more money.

If you really want to make a big difference on a stock engine, get a timing set with multiple keyways and advance the cam 4-6 degrees, then re curve the distributor. It will make a world of difference. Then that bigger exhaust pipe will pay off.
 
Just as a point of reference, my mon's 1980 Super Six Aspen wth auto got 22 mpg on the interstate and was fine for mpg in around-town driving; it's mileage was not any lower than the 5 other family Darts that preceeded it, except for the Dart Lite obviously. I guess you could get lower mileage if you put your foot in it, like anything.
 
I have a 79 Volare wagon automatic with the super six and 2.91 rear gears. I used this car for work and regularly got 30 highway MPG. The car wasn't particularly quick, but it got great mileage.
-Matt
 
Yeah, those venturies are pretty small. And nice boosters.Thats why I went for it. Well that and I already had it.I manufactured a 2-stage throttle set-up for it.The first stage allowed the butterflies to only open far enough to achieve 60mph.Then I had to step on it quite a bit harder to open them further.It was a constant reminder that the car was set up to save money at the pump.Its been on there 20 years now.
I was surprised at how little throttle opening it actually takes to achieve 60 mph.
 
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