Rwhp vs engine dyno

[INTMD8]

Ok, instead of having a discussion just skim over what I wrote and call it arbitrary. THAT is being an asshole.

Want me to program my Hellcat to run through the quarter in 2 gears soo you can see the difference?

Never mind power glide is the best. Launch in high gear to save yourself the wasted time of that shift 

[cdr]

Ok, instead of having a discussion just skim over what I wrote and call it arbitrary. THAT is being an asshole.

Want me to program my Hellcat to run through the quarter in 2 gears soo you can see the difference?

Never mind power glide is the best. Launch in high gear to save yourself the wasted time of that shift 

LMAO !!! you are the one not getting it, talking about MPH, not et

[BSB67]

Sorry.  I'm really slow.  

"Keeping the engine at/near peak horsepower maximizes -wheel- torque which maximizes acceleration. "

I don't understand this statement.  I'm looking at my engine dyno results and my chassis dyno results.  My engine makes peak hp at about 5600 rpm. On the chassis dyno my tires are making peak torque at about 4000 engine rpm.   Can you explain why my max wheel torque does not match my peak engine power like you say it should?


"Do you see what the new 8 and 10 speed auto cars run compared to the old 2/3/4 speed autos with similar power to weight ratio."

No, I don't see.  Can you show me?  Preferably same car and engine, two different trannys.

[INTMD8]

Sorry.  I'm really slow.  

"Keeping the engine at/near peak horsepower maximizes -wheel- torque which maximizes acceleration. "

I don't understand this statement.  I'm looking at my engine dyno results and my chassis dyno results.  My engine makes peak hp at about 5600 rpm. On the chassis dyno my tires are making peak torque at about 4000 engine rpm.   Can you explain why my max wheel torque does not match my peak engine power like you say it should?


"Do you see what the new 8 and 10 speed auto cars run compared to the old 2/3/4 speed autos with similar power to weight ratio."

No, I don't see.  Can you show me?  Preferably same car and engine, two different trannys.

I didn't say wheel torque matches peak engine power. I said gearing the car to keep the engine at/near max HP maximizes wheel torque.

Gearing is calculated on any chassis dyno.  This is why you don't see 3000ft/lbs to the wheels if you made a 1st gear dyno pull, gearing is calculated automatically as it knows mph and with an RPM input can automatically calculate overall gearing.

You will see variances in measured wheel hp depending on what gear you run it in as the higher the gear the slower the rate. (RPM per second).  If you are in a lower gear and accelerating 1000rpm/sec you lose more parasitic to accelerating mass, or inertial loss.   Higher gear and 400/rpm sec is less inertial loss.  The other variant is gearing efficiency as 1-1 is generally the least amount of loss vs an under or over drive gear.

As for keeping the engine at/near peak hp. (you want to be at the same horsepower before/after the shift,  when leaving one gear and moving to the next, this keeps it in the highest average hp going down the track). 

More gears equals a narrower window and the ability to keep it closer to peak hp.  Wider gears do the opposite. Of course as mentioned a loose converter will achieve this as well but in the way of slippage (and slippage converts crank hp to heat in the way of heating the transmission fluid, it is power lost that could have went to the rear tires).

Here is a calculator you could use to get a general idea though it will only give you real results for a manual transmission or locked converter. (as rpm drop would be much less than calculated with converter slip)    http://glennmessersmith.com/shiftpt.html

As for a comparison, lets take the Mustang GT.

2017 GT with 6 speed auto has 435hp, 3,800lbs  8.73lbs per hp and runs 12.8-13.0 at 110-112mph

2018 GT with 10 speed auto has 460hp, 3,860lbs  8.39lbs per hp and runs 11.8-12.0 at 118-119mph


You would think the addition of 25hp and 50lbs curb weight might result in 2 tenths/2mph faster but it is much much faster.

There was a drastic jump in performance with only a slight hp gain in the F150's as well when going from 6 to 10 speed.

Of course adding a converter to the 6 speed auto car would narrow the gap but as it is I would say that's a big difference.

You guys seeing zero difference in mph going from very low to very high numeric ratios, that does not mirror my experience unless again, it was compensated for by converter slip or the change to a higher numeric ratio put the engine well past it's optimum shift rpm through the traps.

[c00nhunterjoe]

The bottom line is horsepower dictates the mph, not the transmission or rear gear ratio. The transmission and rear gears can effect the e.t. that is fact across the entire mathematical board.

If your arguement is valid, then refresh my memory of how many gears are in the tranmission of top fuel cars and what temperature they run at?

[c00nhunterjoe]

170-180 mph in the 1/4. Count the shifts in supergas..... so why dont they run 10 speeds?
https://youtu.be/ZD1xX4UR2-U

[c00nhunterjoe]

Your 707 hp hellcat has 8 gears and 150 more hp then my friends roadrunner with only 3 gears and he is a full second faster then your hellcat in the 1/4 mile. Why? You have 5 more gears then him?

[INTMD8]

If those are your actual questions it's clear you've read nothing I've written. Continuing to discuss this with you is pointless.

[BSB67]

Thank you.

I don't dispute the variances in both engine and more so chassis dynos.

I don't dispute the narrowing the engine rpm around peak power improves performance.  I think I've said that twice now.  Bigger improvement in et, less in mph.

I'll further concede that the amount of change in mph will also be a function of that particular engine's power curve.  The narrower shift recovery on the A833 helps a 340 more than a 440 more than a 500 in motor.

Thank you for the example comparison.  However, I'm always a skeptic.  Are those HP figures factory, or on your dyno?  Factory HP numbers are not necessarily apples to apples, even between same model but different years.  Second, they are different cars.  Two different cars with two different motors with two different transmissions are enough variables for me to question the conclusion that the sole reason for the mph increase is the additional gears. Third, were the two track runs corrected to common standard atmospheric conditions?

My comments on final gear ratio come from a lot of personal experience, and confirmed often by others I trust that have well vetted cars that spend a lot of time at the track.    My two very best examples are with me and two of my race buddies.  Similar stories, but ill tell one. Side by side race all the time. My car was slightly quicker, and faster.  He changes gears. Back to side by side racing following week. He hole shot me big time.  Instead of being even up with him, I was a car back.  That all happened in the first 100 ft or so. Then it turned into the exact same race we always have, except instead of me being even, I'm behind a car length. At half track, I start to catch him, which is exactly where I normally start to pull away. At the traps, I recover about fender, the same distance I'm usually ahead.  The time slip shows the same 1 mph difference we've seen in the previous 50 passes together.  We probably made 4 more passes the day, same result.  The beauty of this example is it neutralizes a bunch of variables.  I'll add that neither of these cars are back in their converters on shift recovery.

Anyways, I'll stand by my earlier statements regarding the mph/horsepower relationship.   And when using it to compare similar cars, the delta HP is pretty solid.  I'll add that as the cars become significantly different from on another, the relationship deteriorates.

[INTMD8]

I agree with a lot of what you are saying.  I'm not trying to say an 8 or 10 speed is the -ONLY- way and will make a 10 second car an 8 second car, but it does make a significant improvement.

Agreed that power curve plays a big part in how much it matters, very peaky/high rpm is going to need to stay in a narrower window.

Take the 213ci engine in my other car which makes peak power at 8350, remove the 4.35 final drive and close ratio box and replace it with a 2.35 and wide ratio box, it would be an absolute slug. (you won't realize the potential trap speed vs peak hp if you are going through the traps 4000rpm under peak)

The example was essentially the same car one year later.  Factory numbers, I have not dynoed them.

Another example is an LS2 corvette. Exact car and engine but 4 speed auto in 05 and 6 speed auto in 06.  6 speed auto is 1-2tenths 1-2mph faster even though the final drive went from a 2.73 in the 4 speed to a 2.56 in the 6 speed.

392 Challenger went from a 5 speed to 8 speed and was about 3 tenths 3mph faster.

The potential for quicker times is not always realized as much as the Mustang example that goes through the traps in 7th gear.

Hellcat goes through the traps at around 5000rpm in 5th gear as it has a 2.62 final drive.  With a relatively flat torque curve due to the positive displacement blower I wouldn't expect it to pick up much/any trap speed with a gear change vs a naturally aspirated car.

Agreed again it's hard to compare very different combo's.  (Like a top fuel car basically using the clutch as CVT).

As for your race, I don't know any of the details but the combinations I've seen pick up trap speed is a gear change that puts it through the optimum rpm through the traps. Like a 4th gen f-body with a cam, tight converter and 2.73. Go to a 3.73 and put it right at peak horsepower through the traps and it picks up several mph.

If it was 2.73 with a 4400 converter the difference would be less with a gearing change because the rpm difference through the traps would be less due to converter slip.

Would I bother putting a ZF8HP in a 60's Charger? Hell no, probably wouldn't bother trying to put it in anything but still will stand by the fact that more speeds can and in many cases does equal a measurable performance improvement.

[c00nhunterjoe]

A 213 ci 8350rpm peak power engine is not a very good comparison on a 2nd gen charger site.
The ls2 and srt392 comparison is more relative and i would like to know if those 2 runs were made at the same time at the same track? My car's mph will vary as much as 8 mph depending on what track i travel to. While experimenting with my car early on, i had 2.76s in it. I changed to 4.30s and my mph did not change, only my e.t.. runs were made the same day with gear swap done at the track.

[INTMD8]

A 213 ci 8350rpm peak power engine is not a very good comparison on a 2nd gen charger site.

It was a point in response to power curves/gearing obviously.

Please link me to forum members top fuel 2nd gen Chargers 

As for the 392 5 vs 8 speed it's been proven a billion times. Try google.

[flyinlow]

First ,sorry Metcoll did not mean to jack your thread.

So I can take away two statements;

If I input the weight of the .race car and it's Hp. The formula will give me the maximum mph trap speed I should see assuming I have an efficient power train ,tire and I drive it well.

If I I input the weight of the race car and it's trap speed. the formula will give me the minimum Hp. The engine makes.

[c00nhunterjoe]

A 213 ci 8350rpm peak power engine is not a very good comparison on a 2nd gen charger site.

It was a point in response to power curves/gearing obviously.

Please link me to forum members top fuel 2nd gen Chargers 

As for the 392 5 vs 8 speed it's been proven a billion times. Try google.

The top fuel reply was in direct response to your statements. That makes it relevant. Your claim of comparing the power curve of a small cube, narrow band high rpm engine to a b body mopar engine and drivetrain need is absurd. As to your 392 5 vs 8 speed. I see no back to back time slips of exact cars. I see no transmission dyno sheets from mopar dictating the hp used between those 2 engines. This is your claim, and your responsibility to prove. And you cant. If the 8 and 10 speed are the way to go, then the no budget, high dollar race teams would all be running them.

[INTMD8]

A 213 ci 8350rpm peak power engine is not a very good comparison on a 2nd gen charger site.

It was a point in response to power curves/gearing obviously.

Please link me to forum members top fuel 2nd gen Chargers 

As for the 392 5 vs 8 speed it's been proven a billion times. Try google.

The top fuel reply was in direct response to your statements. That makes it relevant. Your claim of comparing the power curve of a small cube, narrow band high rpm engine to a b body mopar engine and drivetrain need is absurd. As to your 392 5 vs 8 speed. I see no back to back time slips of exact cars. I see no transmission dyno sheets from mopar dictating the hp used between those 2 engines. This is your claim, and your responsibility to prove. And you cant. If the 8 and 10 speed are the way to go, then the no budget, high dollar race teams would all be running them.

My example is absurd but top fuel is relevant. I don't care what you believe. You asked for examples I gave them. If you don't want to believe it I simply do not care.

[c00nhunterjoe]

Ok, 3rd time. What is the horsepower consumption of the 5 speed vs 8 speed. And what were the exact track conditions of the 2 runs you reference,  but did not post slips on? Asking for validation of your claims is not absurd, yet you are getting angry. I have nothing to gain nor lose here. I beleive in facts, none of which you have produced.

[INTMD8]

Ok, 3rd time. What is the horsepower consumption of the 5 speed vs 8 speed. And what were the exact track conditions of the 2 runs you reference,  but did not post slips on? Asking for validation of your claims is not absurd, yet you are getting angry. I have nothing to gain nor lose here. I beleive in facts, none of which you have produced.

How would I know the power consumption? They are one year apart, not decades. I'll post some links later when I can get to my laptop.

[c00nhunterjoe]

2 completely different transmissions. Its your arguement, not mine. Like comparing a turbo 350 to a 4l80. Big difference. Also waiting on the time slips and weather conditions for the 2 cars quoted.

[c00nhunterjoe]

Given a brief google search as you suggested, the nag1 uses approximately 5% more hp to turn then the zf8. In your srt 392 example, thats 20 some horsepower... a pretty substantial difference which will account for your 1-2 mph difference between 2 identical cars as you stated, not the 3 extra gear difference. Parasitic loss is the answer to your claim in these scenarios.

[INTMD8]

Here is the problem with further effort on this conversation. If no matter what I say you want to drop the hammer on me what is the point? Gave examples of same car different trans now it changes to invalid because different trans. Really? If you keep raising the bar it's easy to see that you will teach a point I can't get to.

So to be real, obviously if we are comparing 5 vs 8 speed we are talking different transmissions. If that qualifies as not a valid comparison there's really nothing left to talk about.

Said in a different way, this would be more constructive if you were open to discussing the matter at hand instead of being on a mission to bury me.

So you want to talk about it great, but if anything I say or do is not considered or not good enough I'm good with agreeing to disagree.

[INTMD8]

Given a brief google search as you suggested, the nag1 uses approximately 5% more hp to turn then the zf8. In your srt 392 example, thats 20 some horsepower... a pretty substantial difference which will account for your 1-2 mph difference between 2 identical cars as you stated, not the 3 extra gear difference. Parasitic loss is the answer to your claim in these scenarios.

Not sure that's correct as you failed to link source as you placed so much importance on but the admittance of some advantage for the right reasons or not is a step in the right direction.

[c00nhunterjoe]

You said 2srt 392 challengers, identical cars but one with the nag1 and the newer with the fz8. That was your example. I googled the 2 transmisisons and sourced the relative improvement from the nag1 to the zf8. The difference justifies the 1-2 mph change between the 2 cars you posted about. I do not have dyno sheets. I have not tested the 2 cars. I googled the answer as you suggested i do. I am not trying to bury you. I continue to ask for real evidence to back up your claims and you continue to reply with google this and i heard about that. It does not help your arguement. You call me out for not posting offical sanctioned evidence yet every post and example of yours has been opinion?
   If you want to continue the discussion then im all for it. But if you wish to continue by sidestepping around giving factual answers then you are correct, its pointless and does not help your case.

[c00nhunterjoe]

From the manufacture of the transmission's website. 3% reduction in power loss over their previous 6 speed. Still researching the increase from the 5 speed. But i think the point is proven coming direct from the horses mouth. Even they specificly say that the parasitic loss reduction is their biggest improvement across the board.
https://www.zf.com/usa_canada/en_us/corporate/products_services_corporate/highlights_corporate/8hp_automatic_transmissions_corporate/index.html

[INTMD8]

Lmao, I've given several examples. If your search returned nothing relevant I can't imagine your inputs. Do you really think I will not be able to back this up? What you are requesting is not hard to find, pretty much common knowledge.

[metcoll]

Anyways what I was trying to get at since I have never dynoed this motor on an engine dyno,do you guys think this motor has 500 plus hp and tq..no tracks near by