ET vs. MPH question...

Does this make sense to anyone? Cuz it sure doesn't to me...

Some background material:
70 Duster
416
12:1
Solid cam (268/276 @ .050)
OLD Victor
Holley 800 (848 cfm)
RHS heads (improved about 10 cfm over as supplied on both sides)
1 3/4 headers

904
Converter with almost perfect slippage %

4.56's
29.5" tall tire

Weight, right at 3100 race ready

The best numbers are as follows (average of cold weather runs)

1.42 60'
6.41 1/8 mile ET
106.8 1/8 mile speed
10.14 1/4 mile ET
128.6 1/4 mile speed

See anything weird there? I do. I feel the car should be at least 130 at the stripe. Although is doesn't leave hard, the 1/8 mile speed tells me it's making decent power from 60' to 660'. Right?

Warmer weather the car has the same timeslip pattern, albeit a bit slower, of course.

Here's a question: With 4.56's at a finish line 7,000 RPM, do I have too much RPM for the small port heads?? I'm wondering if 4.30's would MPH better, WITHOUT giving up ET. It would change the flash of the converter, but I wonder if it would effect the high gear slippage at all??

Would lack of fuel VOLUME cause the low MPH? The fuel system does need updating if I were a betting man, I'd bet it is an issue. Driver says it's still pulling at the stripe, but I wonder it it's beginning to run out of steam for possibly the to reasons above????????????

Or Is my thinking in the wrong direction??

Like to hear some motor-head opinions...

Thanks!

Try jetting the carb. up enough to slow the car down in the 1/4. I had a similar problem with a Holley 850 DP, list # 4781-7, my car ran 10.32 at 129.7 MPH with .110 neeedles and seats in it I had treid jetting it up two jets sizes at the local 1/8 mile track and it didn't respond. I ended up changing the needles and seats to a set of .120 and tha car pick up .2 ET and almost two MPH at the local 1/8 mile track(2500 Ft elevation)I took it back back to the 1/4 mile track at Woodburn this last weekend (180 Ft. above sea level) with the same jetting as before the needles changes and the car slowed down to 10.44 at 126.03 MPH MPH I have a wideban on the car, it had shown that the car was going lean a little at the end of the 1/8 mile and really lean in the 1/4, the changes verified that is was starving for fuel, not enough to make the car nose over or miss, just not enough fuel supply to not respond the the bigger jets I did change the jetting back down two sizes and that helped a little, it was still way to fat with the new needles and seats I will work on that carb. later, I switched the carb(1050 Dominator) and intake (domimator intake flange manifold) this weekend at the track and the car ran 10.03 ET at 133.45 MPH several times, even in worst weather

I put my speed through the wallace calc and it came up with 10.14, mine is in shocks and tyres though. Do you have a dyno sheet for the motor, it's definitely laying down on the top end somewhere, what do you have for a fuel system.
Mine is only 3/8 line, single holley black pump.
Mick

Its probably your fuel supply... the cam should pull
above the 7000 point so I dont believe its a gear issue...
I have used 1 3/4" headers before and they worked to
higher revs than your pulling... I would look at the
fuel system from back to front and that includes the
needle and seats as Cab said and make sure it flows
the needed amount

I don't see it as being that far off the mark. Maybe 1 or 2 mph? Could be fuel curve at high rpms, slightly high gear ratio.

air into carb optimized at speed?
It wont take more jet, unless it take more air?
what scoop and how high above carb opening.?
jet extensions?

what i see is a combo that runs extremely well. the 4 inch crank takes a lot of head.
those heads arent very big on a motor like that, if it was my car i would put a bigger carb on it and probably put less gear in it,never seen a 4 inch motor that pretty much didnt go faster the more carb you put on it. i suspect about 6500-6600 is peak power on that motor, so it just isnt going to pull hard at the big end at 7000 rpm, even my w5 422 motor was " flat" the last 125-150 feet or so from 7000-7400 crossing rpm.
just my

Thanks a bunch guys! I will sheepishly admit...never thought about the needle and seats. I "thought" I was jetted about right as more jet slows the car down. But the N's and S's are "stock" as for a 4780 carb. The fuel system will get re-plumbed from the regualtor to the carb before next time out, and then I'll be prepared to add bigger needles and seats and THEN start fooling with the jetting again.

Yea, Don I'd like to run the car with a 1000 cfm 4150 carb just for grins as I agree with your theory, but one thing at a time...as time permits.

It's also a little soft on timing at 32 degrees...hmmmmm...

thats pretty damn good,i agree those heads aren't the biggest or best..u might just be outta air with that rpm i think thats hallin for that combo

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thats pretty damn good,i agree those heads aren't the biggest or best..u might just be outta air with that rpm i think thats hallin for that combo

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runs very good