Help with 60ft vs MPH vs ET

[wheelsup]

I have never dyno'ed the engine but the lobe sep is 110 so it should be fairly wide. I shift to high at 6800 rpm. Converter efficiency must be around 5-6% (1:1 trans, 4:56 gears, 32" tires = 6500 at 132 mph although I don't know what kind of tire growth I'm getting).

It's not a class car, I want to limit the rpm because I put 150 to 180 runs on it per year and want to avoid engine problems. I believe if I can keep the rpms below 7k it will have fewer issues in the long run.

[T RICK]

Here is somthing to try. Make a few runs shifting at different RPM lower and higher by 200 RPM increments. Compare the 60ft and the 330ft. Is there any change it ET as well. This is a crude way of finding the power band. The shift should occur at the max HP point. And the convertor should stall around the max TQ. This should show the start and end of what I call the acceleration band. Convertor stalls at 5700 and you shift at 6600, this is a 1100 RPM that the convertor is locked up. I think this may be a little short I would like to see 1500 power band used. The problem with this may be that RPM wise you have more at higer RPM and you don't want to use it. The trend in comp and pro stock is raising the power band and not looking for HP gains. The reason for this is simple when you think about it. We measure RPM in a time scale of minutes. Every time a power stroke takes place think of it as a pulse. If a motor makes 500 HP at 6000 rpm in a minute it wll make 3000 pules. if you make 500 HP at 7000 you will pick up 500 pulses more. More pulses make more potental for acceleration. After you determine what potential you have then you can decide what to do about gears. Comments on this appreciated.

[MadBill]

Doesn't look like anyone else wants to wade into the above post, which contains some good advice but unfortunately also a couple of real canards, so in the interests of scientific accuracy with no malice intended:

Quote: "The shift should occur at the max HP point." End quote. Not so. The idea is to maximize the power 'under the curve' and this is achieved by shifting well past the power peak (mechanicals willing). Depending on how steep the drop off past peak HP and the gear ratio splits, this could be 1,000 RPM or more past the peak.

Quote: "More pulses make more potential for acceleration..." End quote
Also no. 500 HP @ 10,000 RPM will give exactly the same acceleration as 500 HP @ 5,000 RPM at a given road speed. (e.g. geared accordingly)

[T RICK]

Bill, Thanks some times I bend things a little, as far as the shift point I agree with you. In this case he is trying to keep the RPM down for engine longevity. My guess is that he says the engine pulls hard at the finish so I get the idea he is trying to shift way below the power curve. A lot of second guessing goes into a comment. Most racers do not have data recorders to specificly know if there is more in their combination and many do not dyno their engines as the expenses is prohibitive. Does the driver shift or auto shift by RPM command. if you hit your shift on the top HP reading and time lag for human response and trans shift time it should be over to some degree. I have no idea as if this is a class car or what?

I also am refering to Reher and Morrisons web site article "Why RPM matters" My wording is different but this is what I understand it to be. Being an ex comp racer my freinds tell me the same.

I take no ofense as I am always willing to learn and in the old days schools did not address anything close as to what is available to day and if I make an incorret statement then I would love to be corrected and learn from the experence. So many thanks for you opinion.

Rick

[impulse]

I have to agree with the thiought that your shifts sould be at peak hp or just below that line. if the engine is finished pulling you will lose a little speed during your shift. It' a fine line and a hard thing to do!

[MadBill]

Perhaps the easiest way to see that this is not so is to work an example, let's say shifting to third with a wide ratio Muncie 4 speed (since I have those ratios at hand): 3rd is 1.28:1 and 2nd is 1.64:1. We'll say your engine makes 500 HP @ 6,000 RPM. You plan to shift at 5,500 and I think a 6,500 shift point will improve performance. The engine drops 25 HP from the peak at each of these points.

After you shift, (it won't affect results, but for simplicity,lets say you're lightning-fast, so the car loses no speed during the shift) the engine RPM will be 5,500 x 1.28/1.68 = 4,190 RPM. After I shift, it will be 4,952. Who's putting down the most power now and getting the most acceleration? Unless you have a mighty strange power curve, it will be me! "But", you say, "I was back into the fat part of the torque curve in 3rd, while you were still revving your guts out in 2nd. I would have gained enough on you then to compensate!"

Lets see: At 6,000 I would be 1/2 way from your shift point to mine, so whoever is ahead on acceleration here probably has the overall advantage. At 5,500 RPM, your engine torque is (575 x 5252)/5,500 = 549 lb-ft., so your driveshaft torque is 549 x 1.28 = 703 lb-ft. My engine torque is (500 x 5252)/6000 = 438 lb-ft. (oops, way down!) But wait: I'm still in 2nd, so my driveshaft torque is 438 x 1.64 = 719 lb-ft. Aha, I'm ahead here too: No contest!
Try this exercise with your actual gearing and power curve. You'll find that the ideal shift RPM (if the mechanicals are up to it) is the point at which the dropping power curve past the peak gives the same HP just before you shift as it does on the rising portion of the curve at the RPM to which the revs will drop after the shift.

[dbusch]

sounds like a couple issues here. first, your converter sounds like it is not multiplying any torque. You should be getting 1.38-1.40 60 fts with 132 mph and ETs in the 10.20s. It is stalling well, and not slipping that much for that tire size and rear gear. That gear&tire should produce WAY more converter slippage than that on the big end. Makes me thing the stator and pump angles are 180* off. You need a looser pump and more torque out of the stator. I agree that you need to gear the car to cross over 7000rpm.

Your engine could be suffering from very low dynamic compression ratio, especially with the altitude you run at. What are your cam specs and what is your compression ratio? A mismatch can kill engine acceleration significantly, moreso at that high altitude.

[Joe Mendelis]

Quote: "More pulses make more potential for acceleration..." End quote
Also no. 500 HP @ 10,000 RPM will give exactly the same acceleration as 500 HP @ 5,000 RPM at a given road speed. (e.g. geared accordingly)

MadBill, I agree with you 100%. A lot of people are under the mistaken impression that if you make the same power higher, you will multiply the will torque proportionately to whatever the increase in rpm is (because you use more gear. There are advantages to gearing, but putting more power to the ground isn't one of them.

[Ed Wright]

I'm trying to figure out if my combo has any more left in it. It has a slow 60ft at 1.57, a mph of 132, and an ET of 10.50 - with no tire slip. (track is at 5800 ft)

I have a 3000 lb car, roller cammed 454, 5700 stall, 1:76 glide, 4:56 spool, 32x14.5 tires, ladder bars, 6600 rpm at the trap.

I'm wondering if I change the rear gears to 4:71 (to keep it under 7000 rpm) if it would imrove the 60ft, lower the mph and leave the ET unchanged? Or do I just have a mismatch somewhere?

It just seems that with 132 mph the car should be quicker. Any ideas?

I'm wondering about your converter also. My car is similar weight, runs similar MPH, and RPM. I have a 383" LT1. Now, I'm not at 5800' either. In the heat (DA about 4000') mine usually runs 127 to 128 MPH. Normally goes 10.30s/10.40s then. If the DA gets down to 1000' or so, I usually run 130/131 mph, my et will normally be 10.20 to 10.teens. My 60' times are low 1.30s. I have a 4400 ATI converter, and I leave at 2000 rpm with the foot brake. I still use the factory PCM, which throws it hands up about 7300 RPM. so I shift it at 7200, and cross the finish line close to that. If your car dead hooks, and you have enough power to run 132 mph, I would be looking at the converter. With that many cubic inches, I would not expect it to be a lack of torque. I would call ATI, and tell them to send what they recommend. Best (besides, maybe, the dampener they sold me) I ever spent. To me, that sounds like a lot of stall speed. Closer to your shift RPM than anything I was ever to make work.

Good luck, Ed

[dbusch]

like i said, a lot of stall speed, no slip, no torque multiplication. poor converter design for the app. you would need to gear this thing to the moon to get a good 60ft.

[STK 758]

The 1050 in my opinion might be hurting the motor in the area of acceleration . A good 850 or even a 750 might perk that baby right up ! I look at the speed vs the mph . @ 132 you should be running quicker I would think. My stocker is a different animal but speed vs mph should be closer. I hope this helps.

Barry

[mbogina]

Racing at Bandimere is a completely different animal than comparitive performance at sea-level based tracks. High altitude tracks kill the motors torque production, yielding results simular to a low torque, high RPM motor at lower altitudes. Inherently, these combinations have poor 60 foot times and dis-proportionate ET vs MPH. In my SS car, the MPH is consistently 2 mph or more higher vs the ET when we race at Bandimere. All that notwithstanding, your 60 foot times need considerable improvement. With the 60 foot times stated and since you said that the car does not spin the tires, the car is not leaving "cleanly". You also stated that the 3 speed auto and the lower gearset first gear in your powerglide yielded worse 60 foot times, thus torque production is probably not at fault. We found the same to be true in our SS Car- the lower gearsets actually slowed the 60 foot times vs the standard "sea-level" sets. You have stated that the car pulls well in the last half, also indicating sufficient torque. It appears to me that taller first gears will not work but increasing final gearing by approximately 6% should help a little all the way down the track. The biggest problem appears to be in the motor combination. The car probably leaves well, lays down a car length out, and then "picks up" further down the course. I suspect that the 1050 is too large for this combination and/or the tuneup is "off". IMO, your 60 foot times on the mountain for this combo should be in the 1.41-1.44 range, based on our experiences is Stock and SS at Bandimere. Don't expect that your ET will ever match your MPH when racing at Bandimere. From our "sea level" style tune-up, we will normally advance the timing 4-6 degrees, lean the jets 2-4 sizes, loosen the lash .015 intake, .010 exhaust, and slow down the secondaries in the carb, in addition to adding a looser convertor (we lose 800+ RPM stall on the mountain), removing the wheelie bars, and softening the shock settings. It is actually harder for us to hook the car at Bandimere because we don't have the torque available to properly apply the suspension. Work on making the car leave the starting line correctly and you will see the greatest decrease in ET.

[dbusch]

interesting you say that about the lower gearsets for the Glide. My 1.76 tranny has given better 60fts than my 1.94 tranny. Seems like the 60 should be better, but maybe the overall ET the same as the 1.94. How could more 1st gear hurt the 60ft unless the car has too much torque to the tire on launch?

[mbogina]

It appears that if your engine has a flat torque curve that you need less first gear, giving the car the ability to "lay" on the convertor longer, resulting in better overall accelleration. Engines with peaky torque curves seem to like steeper gears. Manual transmission cars can work great with a low torque or peaky torque engine, but the same engine with an Automatic can be a real slug. For a SS example, a friend of mine has a SS/I car that will run 9.7-9.8. After converting to a high dollar auto setup and a lot of flogging, the same car ran 10.05-10.15. On the dyno, the motor made great HP but was a real slug for torque compared to most SS auto engines. Remember, torque is what moves the car, HP is just a function of torque as applied over time. At the other end of the spectrum in SS is the Hemi cars. With large amounts of torque and flat torque curves, these vehicles are typically quicker with an Auto than a manual.

[F1Fever]

As mentioned several times already, the stall looks large for this application. It should flash right at your peak Tq number.

on the gear thing...I spent some time road racing for a bit and we learned a lot about gears and shift points as it happens so often when road racing.

The following is a must read:

http://www.hotroddersauctions.com/tech/ ... p#setgears