Good post AJ! (#99)
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One thing leads to another... mean 318?
- Thread starter cawcislo
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Got a question, since the torque converter multiplies torque I'm guessing it would have to drop the rpm between the engine and tranny by similar ratio, Eg. your 455 example gave 340 lb-ft at 2600 rpm and 168 hp, so 340 x 1.8 = 612 but 2600 rpm / 1.8 = 1440 rpm, 612 x 1444 / 5252 = 168 hp. So the torque converter is acting like another gear basically ?
Plus I get all your math wouldn't simpler to use a Hp curve.
Take a the 350 Hp curve since we have it "post #81", with a 3.55 rear gear 2.45 1st gear and 29'' tire with a effective gear ratio of .83 = a 7.22:1 overall gear ratio, more important it's pretty much dead on 1000 rpm per 10 mph.
350 * hp rounded to the nearest 5 hp
210 hp @ 3000 rpm
255 hp @ 3500 rpm
300 hp @ 4000 rpm
330 hp @ 4500 rpm
345 hp @ 5000 rpm
355 hp @ 5500 rpm
350 hp @ 6000 rpm
So a standard in 1st gear would be 3000 rpm @ 30 mph, 3500 rpm @ 35 mph, 4000 rpm @ 40 mph etc.. So in this engine at 40-45 mph you would start getting into the powerband and be out by 60 mph until you shift to second.
So with a Torque converter with your estimated numbers of being 1.8 at 2600 rpm and 1.1 by 4000 rpm, would allow the 10-30 mph reach a few more rpm putting it a little higher into the powerband 2000-4000 rpm.
The only missing info is torque converter slippage. Make it zero for now like a manual, due to newer converters being very very good these days.
AJ/FormS
68 Formua-S fastback clone 367/A833/GVod/3.55s
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All my calcs use 5% for slippage at peak horsepower; I usually state it somewhere.
I think slippage would be foolhardy to incorporate most anywhere else, because it would vary with the ratio of power input, to the resistance to change in acceleration everywhere on the output side, just confusing thechit out of everything....... IMO.
At idle, obviously, the slippage is horrendous cuz the car ain't even moving,lol.
I only use slippage for WOT rpm estimations,
and for cruise rpm estimations where I almost always include the proviso; "@zero-slip". I have to use it in my examples because 5% at 6000 is 300 rpm, an easy to spot fubar if I forget it.
At cruising speed the slip can go either way, so I just say @zero-slip. 5% at 2700 is 135 rpm; so, if the car is geared for 65=2700, and the engine is working hard, the slip might be as high as 2835, whereas if the engine is loafing, it could be less than 2700. Zero-slip just saves me typing all thatchit. Besides; 5% at max-power might not be 5% at cruise. Check your TC; brake stall it at 65mph to see what the tack says. Then lift off at 65 and catch the Rs before the speed drops. Now go compare those to the calculated rpm at 65 using your known tire roll-out and various gears. You might find the slippage is higher than 5%... or perhaps less than 5%..
Part of the TC ratio is due to the rise in rpm, where the engine inputs slightly more torque, than at the non-slipping value. So it's already in the ratio.
I like automatics because, they have the automatically controlled extra "gear", in the TC, which has been reported as up to 2/1. This works out to a split of .50.
But typically I read about 1.8 as the norm or 1/1.8=.56%
The splits in a 727/904 are .59 and .69. If you have a lock up, you can expect 200 to 300 drop there so the equivalent of 7 to 10%, or say .085. when you line those all up I get .56-.59-.69-.085, that's 4 splits so 5 ratios.
Lets assemble that into a working model,with 3.23 rear gears, all at WOT.
At zero mph, the starter gear is 3.23x2.45x1.8=14.24,
about 60 ft out, the TC ratio has dropped to maybe 1.4, so, 3.23x2.45x1.4=11.08 .
At the 1-2 shift, the TC might be down to 1.3 so;
3.23x1.45x1.3=6.09
At the 2-3 shift, the TC might be down to 1.2, so 3.23x1.0x1.2=3.88
In loc up the TC is bypassed so; 3.23x1.0=3.23 .
Setting them a-row we get;
14.24-11.08-6.09-3.88-3.23; count them;
I get 5.
Please keep in mind, It is impossible for me to know the actual TC ratios in your combo, so I liberally say; might, maybe, and about. This does not change the fact that the TC is automatically adjusting it's internal hydraulic coupling ratio continuously with power input and roadspeed, the results of which are still 5 ratios!
If you were watching, you have seen the 3.88 to 3.23 transition. The 3.88 is at WOT, don't forget, so the TC is multiplying in there. Whereas the 3.23/loc-up you would not call for at WOT, so is straight thru. Furthermore to be at WOT in Drive,with 3.23s, you are really moving, (I mean 4000 would be ~95mph) and so, as a streeter, you will rarely be seeing that 3.88.
Now if you had a mind to; you could plot your torque or power or popsicle sticks. at say every 4 mph on a graph, running thu those ratios, and see what is getting to the pavement.
Then you could do it over, but with a different gear. See note 1
If you get tirespin, you can't use any of those numbers because the TC automatically readjusts the internal ratio down towards it's smallest ratio. So for instance at zero mph the ratio I used was 14.24. But if she spins, this is automatically gonna drop towards 11.08 or even towards 8.31 (2.45x3.23x1.05), this is why an under-powered combo, stops spinning right away, not enough torque to sustain the spin, with the rapidly dropping internal TC ratio.
I suppose you could think of a TC as a CVT, that continuously varies it's internal ratio somewhere between it's min/max numbers that generally fall between 1.8 and 1.1 at WOT. The ratio is greatest at zero mph and WOT, and least at Part-Throttle and cruise. and falls with decreasing rate of acceleration, and increases with increasing power input. It's a fabulous invention in any case.
Note 1
If you do that often enough, you will see a trend. I discovered that it matters not a hoot from the torque peak in first gear (with no tirespin), to the powerpeak in top gear...... except for two times; namely thru the traps, and from stall to the torque peak in first gear. All of the rest of the time you are just rearranging the numbers. Try it for yourself and see. It is rare that you can optimize both ends, and I wanna say that peak power thru the traps is more important than stall to the torque peak in first,but not being a racer, I don't know that that isn't an over-simplification. What I do know is that the two times I tracked my car it was optimized for neither, and it still trapped really well.
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yellow rose
Overnight Sensation
If it’s a corner deal, you use lowest RPM off the corner and gear for it. You’d be surprised how many drives haven’t a clue what their corner RPM is.
I can say (and I’ve said it before but I don’t want to be redundant but it’s worth repeating) that torque is a giant pain in the *** most of the time. If you have a ton of torque at the gear change, or coming off the corner, you have a harder time getting it hooked up without blowing the tires off of it.
Same with a gear change in a drag car. If you are at or near peak torque on the gear change, it can be a nightmare getting it hooked. That’s why gear ratio and RPM outruns torque and taller gears every single time.
Let’s again look at your example of torque verses HP above.
If you increase the stroke and the HP increases at a lower RPM, what did you gain? If you increase the stroke and get an inverse torque/HP curve, what did you gain? If you increase the stroke and loose useable RPM above peak torque, what did you gain?
If your metric is smoking tires then torque is all that and then some. When performance is what you want, then an over square geometry with RPM and gear is the winner every time.
One more example. Look at the small block mopar. There are 3 different displacements, and Chrysler they had the option to develop the larger displacements with any geometry they thought worth it. And yet, the chose the same stroke and rod ratio but increased the bore. The 360 didn’t follow this because it has smog geometry and it was to deal with emissions more than performance.
I will be home soon and I’ll post all of what Bettes says in his book about TQ and HP.
yellow rose
Overnight Sensation
The dyno operator was dead wrong. Your combo was quicker because the chassis /converter/gearing in your car was better suited to the power curve.
Fix your kids car and it will gap yours. It’s simple really.
yellow rose
Overnight Sensation
I don’t know a single converter or clutch or transmission guy ask about torque. Ever. I just ordered a PTC converter for a buddy and all PTC cared about was application (how much street verses strip time and this particular deal was 75 % street), RPM, HP, gearing and weight. We never discussed torque. We ended up with an 8 inch case with an 8 inch stator...for 75% street use. It will flash to 5100ish, and yet, it drives better on the street than his 11 3500 converter did.
Converter and clutch tuning is done with the HP curve, not torque.
James Clews
Well-Known Member
Well yellow rose I must point out how wrong you are about our torque converters as both our cars were manuals with the same diff ratios .Unless you don't know what a manual is. they don't have toque converters last time I looked!
@yellow rose
All of that is understood but the reply contains to many what if’s. It adjust the what if’s it becomes a matter of build the engine properly for the goal at hand for the arena your going to be in.
Should an engine be built, stroker or not and the power curve starts high, dips low, rises back up with the rpm, it is ether a tuning issue or the build is off balance. This balance will need to be adjusted via ether the engines bore and stroke to use the parts within better or the parts used within and around the base engine.
IE; Wrong intake, cam to large, etc...
Looking forward to this mystery mans thoughts.
All of that is understood but the reply contains to many what if’s. It adjust the what if’s it becomes a matter of build the engine properly for the goal at hand for the arena your going to be in.
Should an engine be built, stroker or not and the power curve starts high, dips low, rises back up with the rpm, it is ether a tuning issue or the build is off balance. This balance will need to be adjusted via ether the engines bore and stroke to use the parts within better or the parts used within and around the base engine.
IE; Wrong intake, cam to large, etc...
Looking forward to this mystery mans thoughts.
yellow rose
Overnight Sensation
I was drag racing sticks at 8500 and up while you are still shifting at 6000. So bite me. I know exactly what a stick is.
yellow rose
Overnight Sensation
LOL it’s not a mystery man. It’s Harold Bettes.
And I agree. Too many guys just decide on engine geometry without a single though of chassis and gearing. That’s insane. Since my first build in HS everything is dependent on how much gear/converter someone is willing to use. Many guys claim to love a set of 4.56 screws, but when they drive it, their butthole puckers and out they go, 3.23’s go in and they can’t understand why it’s a pig.
My cousins husband burned me on that. Car had 4.11 gears and a stick. I spent several hours with him before the build happened and he was dead set on leaving the 4.11’s in there (BBC BTW) so I built the engine accordingly. I make it run, sounds great, runs even better.
Six months go buy and he calls me up and wants a tune up because “the damn thing is down on power”. I’m thinking this joker lost a cam or something. So he drops it off and after work I drive it. What a slug. Wouldn’t pull a hat off your head. I’m thinking what super hero did his last tune up? I’m sitting at a light thinking it over and when I go to leave the light, I realize the thing is acting like it has 3.55 gears or something. Did the dumb *** maybe switch to a close ratio gear box or what?
So I get to a nice country road and wring it out a bit. It will easily run over a hundred in third gear. And it pulls hard once you get it moving.
So I pull over and all him and ask if he changed ANYTHING on the car. Nope. Really? Nope...nothing. Big pause. Well...I did have a guy drop in some 3.23’s for me because everyone said the 4.11’s were too steep for the street!!
This guy makes better than 200K a year, and he just didn’t listen. We used a port I’d have never used if it weren’t for the 4.11’s. And I would have different intake too. And the cam for dang sure would have been different.
The same super hero who told him to change gears told him I was an idiot and gearing doesn’t affect horsepower like that. I said no ****. It affects DRIVEABILITY. And that’s the issue.
The same super hero changed out the heads, cam and intake cousins husband says it still doesn’t run as it good as it did at first! So I told him his super hero was right. I am an idiot. I should have NEVER even touched that job.
So it’s all combination dependent.
Oh FREAKIN - A brother! Holy crap! If I haven’t seen and been victim to those words before! Oh good Lord!
Oh! Never heard of the above fella.
Oh! Never heard of the above fella.
The problem here is people are debating from from very different levels of compromises.
None to very little compromises, what yellow rose is saying holds very true, Hp is King. At any level of compromise Hp is still king but as you put more compromises on your build the more Torque is King and No replace for Displacement becomes true because it becomes the only way to add hp in a NA engine.
Take a street only performance engine, stop light to stop light first gear and maybe a bit of second all done by 60 mph. Most cars seem to be geared 3.23-3.55 which mostly works out to be around 1000 rpm per 10 mph. So we’re talking idle to 5000 rpm and most of the time is gonna be spent between 2000-4000 rpm and even if you step up or down a few steps in gear your still only gonna move that powerband window a few hundred rpm.
2000-4000 rpm is really gonna limit head, cam, cr etc... choices so leaving only one way to increase hp at a fixed rpm by any huge amount will be torque and as we know torque is mainly dependent on displacement.
So yes to increase the hp curve at a certain powerband the only main way will be displacement.
But if your willing to stall and gear and take other restriction off your combo then displacement/torque is gonna matter less and less.
Why I always say “If your willing gear it, build it, if not build larger displacement” or at least know and or be fine with a smaller displacement with average street gear is gonna give lesser results.
Why I’ve added lately, “or take solace in your compromises”.
None to very little compromises, what yellow rose is saying holds very true, Hp is King. At any level of compromise Hp is still king but as you put more compromises on your build the more Torque is King and No replace for Displacement becomes true because it becomes the only way to add hp in a NA engine.
Take a street only performance engine, stop light to stop light first gear and maybe a bit of second all done by 60 mph. Most cars seem to be geared 3.23-3.55 which mostly works out to be around 1000 rpm per 10 mph. So we’re talking idle to 5000 rpm and most of the time is gonna be spent between 2000-4000 rpm and even if you step up or down a few steps in gear your still only gonna move that powerband window a few hundred rpm.
2000-4000 rpm is really gonna limit head, cam, cr etc... choices so leaving only one way to increase hp at a fixed rpm by any huge amount will be torque and as we know torque is mainly dependent on displacement.
So yes to increase the hp curve at a certain powerband the only main way will be displacement.
But if your willing to stall and gear and take other restriction off your combo then displacement/torque is gonna matter less and less.
Why I always say “If your willing gear it, build it, if not build larger displacement” or at least know and or be fine with a smaller displacement with average street gear is gonna give lesser results.
Why I’ve added lately, “or take solace in your compromises”.
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