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Mystery

General engine tech -- Drag Racing to Circle Track

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fishman
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Mystery

Post by fishman »

Just did first race of the season after refreshing motor and torque converter
I will try to be as informative as possible
First pass . Got time slip 60 foots down normally 1.28 went 1.34 et was 9.38 weather station said should have been 9.22 Mile per hour down 3 mph

Second pass watched one two shift power glide tranny dropped 550 rpm weNt threw traps at 7200 rpm usually go threwv7000 rpm Ran 9.37

Third pass
Wheels up out 10-20 feet felt power cutting back in car tires hit ground power picked back up
Ran 9.41

Fourth pass ran 9.39
Fifth pass did same thing out 10-20 feet felt slight power loss and tire hit ground and picked back up
Ran 9.42

6 th pass car ran 9.38
7 th pass in the finals out 10-20 did the little power loss and picked back up soon as wheels hit ground and ran a 9.45 and I lost

I’ve been talking to my torque converter guy he is saying I’m making more power now that is why the car is running slower. I’m not sure on that

Was thinking maybe it’s electrical
Msd 5a digital,tach,retard box, Rpm actuated switch, tranny brake all hooked to box
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406shark
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Re: Mystery

Post by 406shark »

What do you mean by freshened up the engine and converter?

Any changes made to either?

What were the MPH readings on those passes... compared to prior passes?

How much does the car/truck weigh?

What engine? carb or injected?

Do you document the weather?




Jeff
fishman
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Re: Mystery

Post by fishman »

Jeff
Mph was down 3 mph
Car weight 2317
Did rings,bearings, valve springs, valve seals and valve lapping . Converter was send away to make sure all was good
Motor is 422 ci sbc on pump gas threw a 950 dominator
I use a weather station
Thanks
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econo racer
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Re: Mystery

Post by econo racer »

Do you have slosh tubes on the top of carb? Sounds like a little fuel slosh over.
mag2555
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Re: Mystery

Post by mag2555 »

Does the motor seem to be making rpm faster now since the rebuild, if so you may be revin thru the power band too fast making for the ET loss , but that being said your mile per drop has me concerned.

Did your fire up the freshened up motor with oiled up cylinder walls , or dry

They should have been dry to seat the new rings in nearly instantaneous if they are Moly face.

Where the cylinder walls power honed, or flex honed?
Last edited by mag2555 on Wed Jul 22, 2020 7:59 am, edited 1 time in total.
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Stan Weiss
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Re: Mystery

Post by Stan Weiss »

If your trap RPM is up and your MPH is down. Convertor slippage has increased.

Stan
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Offering Performance Software Since 1987
http://www.magneticlynx.com/carfor/carfor.htm
Do you use engine simulation software that uses cylinder head flow files?
We have a package of more than 3025 DFW/FLW Files
77cruiser
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Re: Mystery

Post by 77cruiser »

fishman wrote: Tue Jul 21, 2020 9:27 pmI’ve been talking to my torque converter guy he is saying I’m making more power now that is why the car is running slower.
I don't think I've ever heard that excuse. #-o You might need a different converter guy.
Jim
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Re: Mystery

Post by rebelrouser »

I feel your pain, issue like that could be many things. On the spark, I use an ignition scope, MSD makes a pattern specific to that type of ignition. This is not fool proof but a simple spark tester can sometimes pick up a problem.
https://www.amazon.com/Deal%E3%80%91Ori ... 955&sr=8-5
Hook up the tester to one cylinder, start up the car, slowly expand the gap until the spark winks out, if it winks out before 20KV you have ignition issues, all good MSD will go to 40KV at least in my experence. Be careful sometimes your finger is an easier ground than the tester. Again not fool proof but the tester is cheap and easy to carry in the trailer.
On converters I don't think they have got down the theory and science yet. I don't buy many converters, they are expensive and when I ask companies to spec one out with my combination, I never get the same recommendations from each company. If the science is right you should get similar recommendations right? If I ask for cam recommendations I get similar cams from many companies. I know lots of racers that buy several to get one that really works right. I have a buddy that pulled his 5 times and they kept tweaking it, before they got it right.
If you just had it freshened, some guys preload the thrust bearings when they assemble, and they have to be run a while for them to loosen back up, but your observations is that it is looser. In the old days they built converters out of OEM cores, today they buy and assemble converters from all aftermarket suppliers. I talked to one builder and he mentioned lots of stators now have much more torque multiplication that older OEM stuff they used to use. Maybe they replaced you stator with a new one and it was at a different level?
JDR Performance
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Re: Mystery

Post by JDR Performance »

You might be uncovering the jets on the launch.
406shark
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Re: Mystery

Post by 406shark »

From your post it sounds like with it now picking the front end up more than in the past. Also stating that when up in the air it feels like it loses power until it comes back down. I'd look the carb over as a starting point. Float levels, fuel slosh, jet extensions, etc... It sure sounds like the fuel isn't being properly controlled with the nose in the air?

As far as the converter goes... it sure sounds like it's too loose. I don't suppose you know anyone that has a converter you could borrow for a couple of passes? You said that it only dropped 550 RPM on the shift... I don't run a power glide, but that can't be a good drop back RPM for max performance. I run a turbo 400 and have right at 1000 RPM drop at each shift.

Your converter guy could be partially correct... making more power can make you go slower if the converter is causing too much slip to get you down the track efficiently.

What was the DA comparing your old quicker runs to the new slower runs?

What is your MPH? Just wondering if you're running numbers consistent with your weight and ET.



Jeff
fishman
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Re: Mystery

Post by fishman »

econo racer wrote: Wed Jul 22, 2020 4:16 am Do you have slosh tubes on the top of carb? Sounds like a little fuel slosh over.
Yes I do
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fishman
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Re: Mystery

Post by fishman »

mag2555 wrote: Wed Jul 22, 2020 7:38 am Does the motor seem to be making rpm faster now since the rebuild, if so you may be revin thru the power band too fast making for the ET loss , but that being said your mile per drop has me concerned.

Did your fire up the freshened up motor with oiled up cylinder walls , or dry

They should have been dry to seat the new rings in nearly instantaneous if they are Moly face.

Where the cylinder walls power honed, or flex honed?
Motor was broke with oiled cylinder walls
Not sure if it feels like it revs up faster
I know it’s revs up more at the 1/4 use to be 7000rpm and now it’s 7200rpm
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fishman
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Re: Mystery

Post by fishman »

Just started working on the car and was going check resistance on wires and check rotor and cap when I was pulling the rotor off the distubtor moved some . I said to myself hum grap the distubtor and tried turning and it moved . The clamp to hold it down has to be all the on the distubtor and it was was back , the bolt was tight but the distubtor could move , it wasn’t freely but had moved. I have a crank trigger so it should just throw out the rotor phasing
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Re: Mystery

Post by fdicrasto »

3 mph slower but 200 more rpm through traps? Car bogging slightly on launch? IMO two issues, convertor slippage and fuel control( jet extensions in rear bowl?)
fishman
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Re: Mystery

Post by fishman »

fdicrasto wrote: Thu Jul 23, 2020 1:36 pm 3 mph slower but 200 more rpm through traps? Car bogging slightly on launch? IMO two issues, convertor slippage and fuel control( jet extensions in rear bowl?)
Carb has jet extensions and yes converter not right
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