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Discussion Starter · #1 ·
I have a 69 mustang with a 429 and a c6 with a 3500 stall. Is it possible to lose top end speed because of a weak torque converter. I go through the lights at 6500 RPM and all calculations say I have 5.14 gears. I have verified that Im running 4.11 gears. The math says I should have a much greater top end speed than I'm getting. My 1/8 mile time is around 87 MPH with a 1/4 trap speed of 107. I cant figure out why Im only gaining 20 MPH in the last 1/8 mile of the track. Any suggestions for me? Is it possible to test a converter without dropping the Tranny?
 

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yes. it could also be your trans slipping. but its probably the converter. get a quality new one or have yours redone by a quality shop. the torque converter is one of the most important parts in getting low et's from your combination. i run a big block olds in my race car and use a 10 inch 2800 ATI converter. i think a 3500 is too much stall for a mild big block. as far as speed increase between the 1/8 and 1/4 its usually not alot. my cars best are 96mph in the 1/8th and 121 in the 1/4 so i only gain 25mph. even top fuel cars gain little in the second half. they top 270mph in the 1/8th vs 330 in the 1/4. the faster you are travelling, the harder it becomes to gain speed.
 

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3400 lb car, 107mph trap speed = 325rwhp....384fwhp.....

3400 lb car, say, 120(?)mph trap speed = 460rwhp....541fwhp....is your motor built that strong?

stock it was 335fwhp=102mph

what is the tire diameter and what are the rpms at 70 mph on the hwy

agree with the above, your second 1/8th speed numbers are pretty normal for 4:11 gears and 3400 lbs
 

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Discussion Starter · #4 ·
Thanks for your feedback. Yes i believe it is that strong of a motor thats why I am a little confused. it is a full roller motor with 10.5:1 compression. I am running a 950 cfm holley. Im not positive about the duration but the lift is around .650. The car is set up for NO2 but Im afraid to use when we are redlining at the end now. The 3400 pounds is probably about right it has not been stripped of interior Etc. Im running 28.5 slicks on it. Not sure of the 70 MPH RPM'S . Pulled the 3rd member this weekend, I'll have to see what she does when it goes back together.
 

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is it the tranny? or is it the motor HP? is why I asked for tire size and rpms at 70mph

a slipping tranny will usually show big time at hwy speed

70 mph just cruisin' on a flat road with a 28.5" tire = 3400 rpms.....if the tranny is in very good shape....
 

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Most of the converters made that stall above 3500 RPM have extremely negative impellers. This means they have great stall speed, but as the vehicle acceleration slows (speed increases) the engine WILL have to turn harder (more RPM) to continue to provide a consistent acceleration curve. Lacking that RPM the converter efficiency drops, the slip rate increases and the car will actually begin to slow. This gives you the characteristics described in your post. More careful analysis of your engine combo and car setup will yield the result you desire. The torque curve of your engine has exceed the converters capacity, IMO. Time to get a converter spec'd and matched to your car...
 

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Discussion Starter · #7 ·
Wow I think you hit the nail on the head. That was an excellent choice of words to describe my dilemna.I called yesterday and got the same answer from tech support at a torque converter specialty shop but I was hoping to get some confirmation from this forum. Thanks I got what I needed to hear. I think its tranny pullin time.
 

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holy schmoly RJ. your car should be ALOT quicker than mine. my car weighs more and has a VERY MILD olds motor. i run a 3:70 geared 9 inch and 30 inch tires. my bests are 11.31 @ 121 1/4 and 7.19 @ 96 mph in the 1/8th. my car weighs 3640 with me in it. its run in the 11.30's many times in very good air. it runs 40's to 50's in summer. it has gone as slow as 11.60's in mile high air. but i dont retune for air conditions. i have as mentioned a 2800 rpm ATI 10 inch converter in a stock but rebuilt turbo 400. nothing fancy in it. my motor has stock head, (even has original 1969 valves still in them) stock crank, stock rod, 455 olds with keith black hyperautectic pistons which give me 10 to 1 compression. i run a crane solid cam that is 236 246 512 533. stock torker intake, holley with a proform center. and hooker super comp headers with bullet mufflers. i leave the line at idle (800 rpm) and it yanks the front wheels up and 60 foots as good as 1.60. with 1.63 the most common 60' you should be able to get into the 10's with your car once its sorted out. my car now has over 500 runs on the entire combination. i havnt replaced anything except oil and spark plugs in over 3 years of steady bracket racing. when you get that monster right its gonna fly. heres my car by the way. if anyone was at the division 1 NHRA bracket finals at maple grove last year you may have seen it. i lit the tomato in the 4th round.
 

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No pick up on big end of 1/4 mile

I have a 55 chevy 2 door post that i drag race.I run a 5500 stall and 430 rear end gears.i run through the lights at 10.66 at 126 MPH.I turn 7200 RPM in the lights.How tall are your tires???That changes your gear ratio alot.
You also need big power on the big end to pick up speed.My car goes 91 in the 1/8 and 126 through the lights.doesnt sound like converter
 

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fast chevy, your results are why I am still questioning...is it the motor or is it the tranny

he has 28.5" slicks= [email protected] thru the traps with 4:11's if he has 460r[email protected]

RJ,
you really do need to know the cam spec's.....I don't recall any 429 streetable cams that peak above 5500rpms (stock peak was 4000) and all "big cams" fall off like a brick in hp above the peak with stock heads....
bigger tires/less trap rpms=faster mph cause it is 460hp at 5500
 

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top end speed

red65 Im with you on motor or tranny??? I wander if he is running out of motor.The 429s iv been around didnt like big RPM.They can with lots of work.My friend built a 429 in a 67 mustang and it loved around 5500 RPM.If he reved it over that it slowed down.We really had to play with gears to make it run out on the big end.
 
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