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Old 03-13-2011, 10:40 PM
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rear gears, stall speed, and street/strip A

With a best of 11.23 at 118mph, I run a 3,300 pound (with driver) Model A Tudor with a 4:71 blown SBC. I hope to run 10.90s in 2011, but without altering the engine setup. (Yes, I have other blower pulleys that add boost but want to try other steps first). This means experimenting with tires, rear gears, and torque convertor.

Current gears in the Dana 60 rear are 3:54 coupled to a TH 350 and a 2,800-3,000 stall B & M convertor. When racing, I run Goodyear Eagle drag radials with a 30 inch diameter. I also drive the A about 1,000 miles yearly on the highway, so will avoid any combo that will burn up the trans or convertor on the street (as in a high stall convertor that slips constantly in street-freeway usage).

So you be the crewchief: is there a tire, convertor, rear gear combination that could yield below 11 second quarter mile runs while also going for groceries, rod runs, and daily driver tasks in this Model A ? So what do you think: F-Bird 88, BentWings, Cobalt, CamaroMan, TechInspector ?

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Old 03-13-2011, 11:05 PM
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A 700R4 transmission could really help ... with its much lower first gear.

3.06 for the 700R4
2.52 for the T-350

A lower rear end gear could help also if you had the 700R4 because of the 30% overdrive feature.

@ 3300 pounds ???
... you must be a BIG guy OR have a heavy Model A ...

MAYBE BOTH
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Old 03-14-2011, 07:20 AM
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700-r4 or 200-4r would give you a great 1st gear as previously noted. 2.52 1st really needs 3.55s or 3.73s at least for a good launch. Ive personally never had much luck with the accuracy of the off the shelf convertors for high performance applications.

If you went to a shorter tire, this would in effect raise your rear axle ratio.

Last edited by AutoGear; 03-14-2011 at 07:34 AM.
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Old 03-14-2011, 08:13 AM
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What are you crossing the line in, second gear?
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Old 03-14-2011, 10:10 AM
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Quote:
Originally Posted by 471A
With a best of 11.23 at 118mph, I run a 3,300 pound (with driver) Model A Tudor with a 4:71 blown SBC. I hope to run 10.90s in 2011, but without altering the engine setup. (Yes, I have other blower pulleys that add boost but want to try other steps first). This means experimenting with tires, rear gears, and torque convertor.

Current gears in the Dana 60 rear are 3:54 coupled to a TH 350 and a 2,800-3,000 stall B & M convertor. When racing, I run Goodyear Eagle drag radials with a 30 inch diameter. I also drive the A about 1,000 miles yearly on the highway, so will avoid any combo that will burn up the trans or convertor on the street (as in a high stall convertor that slips constantly in street-freeway usage).

So you be the crewchief: is there a tire, convertor, rear gear combination that could yield below 11 second quarter mile runs while also going for groceries, rod runs, and daily driver tasks in this Model A ? So what do you think: F-Bird 88, BentWings, Cobalt, CamaroMan, TechInspector ?
Using the calculators at Wallace, your HP computed from your ET (11.23) is 414.48 rear wheel HP and 460.53 flywheel HP.

Your HP computed from your vehicle MPH (118) is 390.79 rear wheel HP and 434.21 flywheel HP.

Being as how the ET shows the HP to be greater than the speed would indicate, the traction, driving and overall set up would seem to be good. It may be impossible to pick up a full 3/10's w/o any more HP. That said, I would bet you can lower the ET from what it is now.

I'd like to know:

Is it a 350, or ? How much carb are you using- vac. sec. or DP? Boost referenced? Fully tuned in?

What RPM are the shifts at? Do you feel the shift points you're now using are ideal- as in have you tried different shift points?

What RPM are you going through the lights?

What are the incremental times, especially the 60' time?

What are the engine specs, including CR and cam specs? Is the cam installed advanced or ?

What is the ignition timing curve? Boost retard box?

Would you consider a water injection system? What about more octane at the track?

I suspect you're going to need a shorter rear gear.

Last edited by cobalt327; 03-14-2011 at 10:34 AM.
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Old 03-15-2011, 11:43 PM
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This A covers the 60 foot on the strip between 1.61-1.65 seconds.

Because the valve train redlines at 7,000, and Crane's recommended maximum rpm is 6,400, I have a 6,200 chip in the MSD spark box, to prevent over revving.

I manually shift the TH 350 off the tach at 5,500 shift points, based on peak torque from engine dyno runs.

I do not have a data recorder on the tach, so do not know what rpm I am running at the 1/4 mark. However, the shift lift is on at the big end, meaning that I am crossing the line at 5,500 rpm minimum.

Cam is a Crane blower grind hydraulic roller (HR-230-359-2S-12.90-IG) with advertised duration 292 intake, 300 exhaust, lobe separation 112 , lift at the valve 539 intake 558 exhaust. Cam timing is 230 intake 238 exhaust duration, maximum lift 107 intake 117 exhaust. Cam is installed straight up.

Carbs are dual 600 cfm Holley boost-referenced blower carbs, part no. 0-80575S. Jets are 75 primary 80 secondary. Power valves front and rear are 4.5. Accelerator pump cams are maroon/red with .010 " clearance.

Lastly, while I have smaller blower pulleys, I currently am running the street pulley which overdrives the blower at 1.33. From static compression of 7.5:1 on my SBC, the 1.33 pulley produces boost of 8-9 pounds with resulting dynamic compression 10.6-11.6 psi. Since NHRA prohibits overdrive higher than 1.60 on Roots-style blowers (which my Weiand is), the highest ratio I legally can run on the Weiand is pulley number 921004 with a ratio of 1.56. Working again from static compression of 7.5:1, the 1.56 pulley would yield 12-13 lbs of boost and dynamic compression around 14:1. The latter is high enough that it would, at least as I understand it, require substantially differing tuning than running the blower at 1.33:1 and dynamic compression peaking around 11.6 to one. Since I drive the A to the track, bolt on slicks to race, then remove the slicks to drive home, having to change tuning to accommodate higher boost and higher dynamic compression is undesirable. Which, then, brings me back to where I started: seeking from a best of 11.23 to run high 10.90s using rear gears, stall speed, and convertor, instead of higher dynamic compression. Yes, I recognize that 24 hundreths is a bunch to pick up without adding horsepower but this is, after all, hot rodding where trying to get there (where "there" is) is part of the magic....
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Old 03-16-2011, 02:26 AM
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Is the B&M converter you have an off the shelf converter, or was it made specific to your combo??

If it is a shelf job you could easily get what you need time wise from a good custom converter.
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Old 03-16-2011, 08:50 AM
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Quote:
Originally Posted by 471A
This A covers the 60 foot on the strip between 1.61-1.65 seconds.

Because the valve train redlines at 7,000, and Crane's recommended maximum rpm is 6,400, I have a 6,200 chip in the MSD spark box, to prevent over revving.

I manually shift the TH 350 off the tach at 5,500 shift points, based on peak torque from engine dyno runs.

I do not have a data recorder on the tach, so do not know what rpm I am running at the 1/4 mark. However, the shift lift is on at the big end, meaning that I am crossing the line at 5,500 rpm minimum.

Cam is a Crane blower grind hydraulic roller (HR-230-359-2S-12.90-IG) with advertised duration 292 intake, 300 exhaust, lobe separation 112 , lift at the valve 539 intake 558 exhaust. Cam timing is 230 intake 238 exhaust duration, maximum lift 107 intake 117 exhaust. Cam is installed straight up.

Carbs are dual 600 cfm Holley boost-referenced blower carbs, part no. 0-80575S. Jets are 75 primary 80 secondary. Power valves front and rear are 4.5. Accelerator pump cams are maroon/red with .010 " clearance.

Lastly, while I have smaller blower pulleys, I currently am running the street pulley which overdrives the blower at 1.33. From static compression of 7.5:1 on my SBC, the 1.33 pulley produces boost of 8-9 pounds with resulting dynamic compression 10.6-11.6 psi. Since NHRA prohibits overdrive higher than 1.60 on Roots-style blowers (which my Weiand is), the highest ratio I legally can run on the Weiand is pulley number 921004 with a ratio of 1.56. Working again from static compression of 7.5:1, the 1.56 pulley would yield 12-13 lbs of boost and dynamic compression around 14:1. The latter is high enough that it would, at least as I understand it, require substantially differing tuning than running the blower at 1.33:1 and dynamic compression peaking around 11.6 to one. Since I drive the A to the track, bolt on slicks to race, then remove the slicks to drive home, having to change tuning to accommodate higher boost and higher dynamic compression is undesirable. Which, then, brings me back to where I started: seeking from a best of 11.23 to run high 10.90s using rear gears, stall speed, and convertor, instead of higher dynamic compression. Yes, I recognize that 24 hundreths is a bunch to pick up without adding horsepower but this is, after all, hot rodding where trying to get there (where "there" is) is part of the magic....
You mentioned the shift point being referenced off of the torque peak. You need to run it out past the HP peak to get the most out of the engine. I'm guessing that this is what you are now doing, as the torque peak isn't at 5500 RPM- but there's a chance that shifting at a higher RPM may lower the ET.

Personally, I wouldn't hesitate to shift at 5800-6000 RPM for a comparison. But I can say w/relative confidence that, given the 3.54 gearing, that you'll need to step out past the power peak before shifting to account for the relatively large drop in RPM at upshifts. This is something I'd be interested in first running through some good software to see what the results or trends would look like, before running it at the track.

There is likely something to be had by working w/the ignition timing, and a boost retard would take the guesswork out of things nicely- but at a price. Personally, I wouldn't run w/o one- at least not if I wanted to get all I could out of my combination.

Is race fuel an option? That alone will safely allow a significant timing change (detonation being the bogey here).

Running w/o mufflers could help some, but w/o modifying the exhaust system to make this an easy task at the track, it might not be worth the trouble. May require different jetting as well.

All these suggestions have been around the idea the carbs are dialed in pretty close the way they are. Do you feel that you've gotten all you can from them?

The short times seem decent. Is there a problem w/traction and have you tried different launch techniques? This is another area where a sim program would help show trends.

What were the dyno results?
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Old 03-16-2011, 12:12 PM
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You don;t have near enough rear gear or converter stall.
You are shifting way too soon.

For 30" tires you need at least 4.33:1 gears. Get a 8" 9" 4500stall.
Shift at 6000+++rpm You need to trap at least at horsepower peak rpm. You are riding on the converter all the way down the track. ( not near enough gear, shifting way too soon.)

The blower drive ratio rule is intended and only enforced in the pro competition classes. In street eliminator or Time trial lanes (street cars)
They don't care.

You'd be much better off with a solid street roller cam. Blower motors like
to rev. A hydra-rev may help.

Last edited by F-BIRD'88; 03-16-2011 at 12:23 PM.
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Old 03-17-2011, 09:44 PM
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As always, I find hugely valuable comments from the subscribers to Hot Rod Bulletin Board. Thanks to all who have responded. One reminder: this Model A intentionally is a street-strip compromise, which means trade-offs along the way. For example, I cannot run a 4,500 stall convertor and run down the freeway at 65 mph, even with 26 inch rear tires, and avoid overheating the convertor. It appears, that even at 26 inch rear tires, stall speed must be not higher than 3,200-3,500, and even with 4.10 Dana 60 rear gears. So, based on the comments so far, I am considering a 3,500 stall convertor (Yes, my current convertor is an off-the-shelf B & M 3,000 stall) and 4.10 gear change from the 3.54 in my Dana 60. While you are evaluating that, also consider whether there is any reason to adopt a manual valve body in the TH 350 trans. This is, after all, about having fun. Without boosting the blower, I just want to see whether there may be a quarter-mile "10" in this A sedan. Engine timing, by the way, is now locked at 34 degrees advance which, thanks to Firebird88, solved a huge problem with constant backfiring on starts and through the carbs.
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Old 03-17-2011, 09:59 PM
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In response to some unanswered questions along the way, here is some added data. The engine is a 355 SBC. Engine (not chassis) dyno runs on the current 1.33 overdrive pulley on the 4:71 blower yielded peak HP of 502.8 at 5,000 rpm, falling off to 463 HP at 6,100, and peak torque of 462.5 at 4500 rpm. With the current 2,800-3,000 B & M convertor, the A wants to "creep" on the tree, meaning that I basically launch somewhere at or below 2,500 rpm. The dual Holley 600 cfm carbs are boost referenced and, tuned off of a chassis dyno, run 4.5 HG power valves and jets at primary 75 and secondary 80, and accelerator pump cams are Holley maroon/red. Timing is locked at 34 degrees advance.
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Old 03-17-2011, 11:43 PM
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Correction. Peak HP was at 6,000 rpm, not 5,000 as typed earlier.
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Old 03-18-2011, 01:09 AM
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If you did nothing more than shifted at about 6300 RPM you'll see the numbers, or damn close to it.

If you ever drive any considerable distance, the 4.10's will get old. As an alternative to 4.10's, you could lose the TH350 and go w/a TH2004R. Third in lockup would still be the same effective ratio as you have now- except with lockup added. The effective ratio using 3.54's w/the 2004R in OD will be in the 2.5:1 area. The expense would be a hit at the onset, but the rewards would be there for the duration.

A looser TC is a given in your case. A decent compromise would be a "tight" 10".
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Old 03-18-2011, 02:54 AM
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Quote:
Originally Posted by sqzbox
What are you crossing the line in, second gear?

hello?
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Old 03-18-2011, 03:13 AM
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Quote:
Originally Posted by cobalt327
If you did nothing more than shifted at about 6300 RPM you'll see the numbers, or damn close to it.
Given the drop off after 6K RPM, you might want to shift closer to 6K than that.

Given 118 MPH, 3.54 gears and 26" tires (is this what they are?), the trap RPM (w/o TC slip) will be almost 5500 RPM (120.18 MPH = 5500 RPM, w/o slip).

You mentioned the shift light set at 5500 RPM is lit as you go through the lights. If your tires are larger diameter than 26", this indicates excessive slippage of the TC.
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