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Old 10-04-2022, 09:38 AM
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Default No top end mph

I took the 1050 Holley and restrictor plate off and replaced with an 850 Holley. I lost finish line mph. 60;s are 1.33 with an 1/8 of 6.30/107 but only manage 9.9 barely breaking 132mph . Do you think it's the carb being small or should I look at a gear change? Car never had high mph even with the 1050.
I have a 4.10 gear and 30" tire. Shift at 6400 and cross the line at 6800.

I run a 10.00 index and am tired of having the lowest mph. I am always looking behind me to see where they are. Would like to be around 135mph.

Only ran it all out thru the 1/8 once with the 1050 and ran a 6.04/111 with a 1.29 60'. Didn't have enough gear to run it thru the 1/4.

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Old 10-04-2022, 10:58 AM
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Do you have data logging? To me It looks like to much convertor slippage.

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Old 10-04-2022, 11:32 AM
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No data logging. Calculator shows just about 9 percent slippage. Afraid if i put a 3.90 or 3.73 slippage will go higher,
I have an ATI MRT 8" converter stall right at 5000. I leave at 3800 with a trans brake.

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Old 10-04-2022, 11:42 AM
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You should have not done that type of testing without having a vacuum gauge hooked up to view in front of you when making a pass.

Having such would have clearly shown if the Carb is too small.

With any flat out race motor if your approaching your shift point and the gauge is reading 3/4" of Hg or over then your Carb is too small.

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Old 10-04-2022, 12:22 PM
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Quote:
Originally Posted by Mike S View Post
No data logging. Calculator shows just about 9 percent slippage. Afraid if i put a 3.90 or 3.73 slippage will go higher,
I have an ATI MRT 8" converter stall right at 5000. I leave at 3800 with a trans brake.
OK. I did a quick calculation and I came up with between 10% and 11%

I have always run a manual trans. So I can only go by what some others have told me. Using your car as an example they went to a 4.33:1 saw an increase in MPH and no increase in RPM. Maybe give ATI a call and see what they think

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Old 10-04-2022, 02:20 PM
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The reason for the carb change was to get rid of the restrictor plate. I had a 1050 with a 1.550 restrictor plate under it. The 850 throttle plates are 1.75 and have no restrictor plate. I notice with the 850 60's and 1/8 mile is better and more consistent than the 1050 with the small restrictor plate.
Last time out 1/8 mile times varied .004 over 5 runs. I used 1/8 mile because of hitting the brakes in eliminations.

Figured it can't have any more vacuum than the 1050 with the restrictor plate at wide open.

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Old 10-04-2022, 03:58 PM
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Tire size? Just a thought...

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Old 10-05-2022, 12:40 AM
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Quote:
Originally Posted by Mike S View Post
The reason for the carb change was to get rid of the restrictor plate. I had a 1050 with a 1.550 restrictor plate under it. The 850 throttle plates are 1.75 and have no restrictor plate. I notice with the 850 60's and 1/8 mile is better and more consistent than the 1050 with the small restrictor plate.
Last time out 1/8 mile times varied .004 over 5 runs. I used 1/8 mile because of hitting the brakes in eliminations.

Figured it can't have any more vacuum than the 1050 with the restrictor plate at wide open.
My 850 has 180 throttle plates. Are you sure you have a 850 ?
4150 carbs are always going to react better. More consistent 60 foot times over a 4500 carb. The way to go for bracket racing.

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Old 10-05-2022, 09:37 AM
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4150 850(1000HPs) have 1.75 throttle blades.

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Old 10-05-2022, 10:32 AM
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I think the blades are stamped 180 but are 1.75" diameter?
(been over 25 years since I looked at one)



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Old 10-05-2022, 01:44 PM
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have you had it on a dyno to find out where max power is being made -- what rpm.??

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Old 10-05-2022, 03:32 PM
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Quote:
Originally Posted by johnta1 View Post
I think the blades are stamped 180 but are 1.75" diameter?
(been over 25 years since I looked at one)


Yup, I just went out and measured a HP 1000 and they are 1.75 dia with a 180 stamped on them.
I just remembered drilling a 1/8" hole right through the "8" back in the day.
Wonder why they do not have the actual diameter stamped on them ? Has to be some reason.

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Old 10-05-2022, 03:51 PM
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I think they are a part number or ID number.
Seems like the 750/800 had maybe 179 stamped number?
(still been a long time since I saw mine)



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Old 10-05-2022, 04:01 PM
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Never had it on a dyno. Been about 8 years with the same combo. Tried different shift points and likes 6400,. I notice the smallest head wind slows the car down, Not being the most aerodynamic body style. The 2 times I took it out had some low wind, I think this might be some of my problem since I installed the 850.
It did mph a little better when I was running a 30" slick. I switched to a 30" radial 2 years ago. The radials hook a lot better and are more consistent. Not knocking slicks, just radials work better with my car. Stock suspension and 3400lbs.

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Old 10-05-2022, 06:54 PM
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Mph is horsepower.
Mph is down, hp is down.
Going from a 1050 to 850 will slow you down. It may be more consistent, but you will slow down.

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Old 10-06-2022, 12:43 PM
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To many unknowns here-- as in head flow , engine size ect.ect. I suspect the 6800 rpm finish line is well past peak HP. just a thought.

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