I went from 2.76 to 3.91 In my Duster yrs ago. HUGE difference all the way around.
“Best” all around axle ratio: ~450hp w/ A904?
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j par
Well-hung Member
Oh boy I'm not even going to bother with the disagree button you know more about my car than I do my hundreds of Time slips mean nothing...
This is probably why my friend with the naturally aspirated Duster that does consistent 8 second quarter miles laughs at me when I talk about a car forum...
Over too many people talk about their math...
33IMP
Well-Known Member
I will only say this about that: IN MY EXPERIENCE, every time I took gear out of my car (I have had 4.56s, 4.11s, and the current 3.91s) there was no significant difference in 60ft or quarter, and every time I moved the shift point down, it went faster. Probably as a result of a severely head limited 440. I've never run a small block mopar, so someone else's experience can be quite different.....
Exactly and why sometimes I don’t argue. The people with there calculator slide ruler and abacus’s can do all the math in the world.
In the real world however……
I get these *** clowns live and just smile and yes them to death.
Besides the rest of the combo I don't have much confidence in a 904 holding up or at least not for very long with that kind of HP. They don't last very well on my experience with 1/3 of that power driving them
Go 727.
Go 727.
dartindanno
Well-Known Member
Small block and Cope Racing 904 trans
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roccodart440
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Well, you changed 2 things there.
YOu can't change gears without a change in one or more of the things I mentioned earlier. Trap RPM or trap gear have to change. x gear at x speed change with gear ratio. That isn't even debatable.
One thing that struck me here was lowering of the shift point. With a big block, most people spin their engines much farther than where they make power. Even my engine with a pretty large roller cam, full ported oversized valve heads, ported single plane, etc peaks at 5,900.
roccodart440
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So you're telling me that changing the ring and pinion on a car won't change the RPM at any given speed?
I'll gladly wear the *** clown badge if it shows I understand simple physics and math
What I’m saying is not the words your putting in my mouth but actual experience in what others say is going to happen doesn’t always happen or even remotely close to there slide ruler calculations.
Nothing more, nothing less.
Your specifics above on your question is not in question.
You can run the calculator and math up the flag pole all day and night long and ridicule all you want, but it may not happen. BTDT
Run the math on tire size due to pressure differences.
Then tell me the changes I’ll see in the 1/4.
j par
Well-hung Member
Selective quoting, putting words in mouth, and ridicule are strongholds of a different part of this forum...
We all need to throw our personal experience away and follow his slide ruler...
I've lost a full second at the track and thought I'd hurt the motor or something I couldn't figure it out for the life of me and then I looked at the air pressure calculator... I was doing exactly what I was supposed to with that air being that bad....
j par
Well-hung Member
The real point here is the op wants a nice medium gear and back to that is where we should be... 410's are a street extreme and 323's are at the lower end... Of course you can go lower and higher....
If you want to hit the middle 355...
If you want to hit the middle 355...
Super-Cuda
MOPAR .. Move Over, Plymouth Approaching Rapidly!
Having done the 3:23's previously , then going to 3:91's, I am now trying 3:55's hoping exactly that.
I'll soon find out if its the sweet spot for me. I don't disagree with the math presented here, engineering is built on it. I also know that real world applications can be a factor in performance as well. Somewhere using both is the answer I'm after.
mderoy340
Well-Known Member
I have found that each gear step is around 200rpm (cruise and 1/4 mile trap), same goes with tire 26/27/28". The other variable is converter slippage.
Aaaaa - What?
Rat Bastid
Dunamis Metron
Like every other thread of this type, the answer is subjective. That’s because the question is subjective.
“All around” means what? All around town? All around with mostly freeway driving? All around with more emphasis on track numbers?
And then you have the issue of what some will live with. Some think any engine cruising about 2200 rpm is abusing it. Others think 70 MPH at 3800 rpm is no big deal.
So the answer is twofold. No one can know what the OP needs because he would have to clean up his question and be more definitive of what he wants and what he can live with.
Part 2 is the math never fails. For a given tire diameter, gear ratio and rpm there is an exact mph. The math isn’t wrong and it doesn’t lie.
If any part of the above equation doesn’t match what the math says you have a junk tach (there are many junk tachs out there) or the method of measuring mph is faulty.
“All around” means what? All around town? All around with mostly freeway driving? All around with more emphasis on track numbers?
And then you have the issue of what some will live with. Some think any engine cruising about 2200 rpm is abusing it. Others think 70 MPH at 3800 rpm is no big deal.
So the answer is twofold. No one can know what the OP needs because he would have to clean up his question and be more definitive of what he wants and what he can live with.
Part 2 is the math never fails. For a given tire diameter, gear ratio and rpm there is an exact mph. The math isn’t wrong and it doesn’t lie.
If any part of the above equation doesn’t match what the math says you have a junk tach (there are many junk tachs out there) or the method of measuring mph is faulty.
33IMP
Well-Known Member
...or the converter slip is excessive, or the trans is worn out, or the clutch is slipping, or....
Plan on 10 percent converter slippage
Ot the metric listing for the tire size isn’t exactly what you think it is or what it says it is listed as. Take a stroll through some fire manufacturers listed tire diameters vs others listed tire diameters.
Super-Cuda
MOPAR .. Move Over, Plymouth Approaching Rapidly!
Exactly ! This is where the theoretical world meets the real world. A 26" tire may actually be 26.5 inches so speed at a given RPM would be off.
The math still works though, you just have to be precise about the actual numbers you are using to calculate your results.
So in regards to tires, measure the the actual circumference don't assume what's on the sidewall is 100% correct.
thesiren74
Well-Known Member
3.73
Thank you! Exactly!
There is a host of things that are not on spec or though of “supposed to be” when people do the math. I’ve had individuals tell me the most insane & outrageous things.
Super-Cuda
MOPAR .. Move Over, Plymouth Approaching Rapidly!
How true!
How many times have I heard comments like ... "my car makes 700 hp does the quarter in 8 seconds!.
Old adage still stands..
"when the flag drops, the bullshit stops.. "
Took the wife’s Cuda out to a car show. Besides the gaggle of disparaging remarks of how I screwed the car up royally, I was asked a host of questions on the engine.
I was told I have no clue what I’m talking about and it really makes *** hp.
I never dyno’d the engine and I really don’t care what the hp is.
.030-360 @ 11.5-1
Hyd roller at 224/230 -.573/.569-110
TF heads, rpm intake, 750, TTI headers -2-1/2 exhaust.
I’ve been given “Professional” parking lot HP ratings between 290 & 360 hp and my car can only run a 14- or up to a 12.5 in the quarter.
I did find it amazing how a few guys would rephrase that he same question 2-5 times.
How fast is it.
Never been to the track
What’s the trap speed
Aaaaa- never been to the track
What did it do for a ‘60?
So sorry, never been to the track
So how can you say it’s fast?
Ummmm, I never said it was or anything about how fast it is.
OK-OK, so what did it trap at?
(Repeat the above twice.)
Yea… actual conversation
When asked about the HP. IDK, never dyno’d it, you d guess north of 320? IDK. Then I get all the parking lot “Pro’s” giving me there vast experience…. LMAO!
I’ve been putting engines together since I’m 19/20 YO.
I stink at the guessing posts here. However I’ve been in more than just a few cars. I have a suspicion that this engine makes more than 320 hp….
But every last one said I’m nuts and full of it.
OK! Whatever…. I don’t care… but I’ll take the forums best guess…. It’s most likely better than mine!
LMAO!
Rat Bastid
Dunamis Metron
The tires don’t measure their nominal size and that makes the math wrong?
All it means is that someone didn’t do their due diligence before applying the math.
The math isn’t wrong. The assumption made was wrong.
No, you misunderstand me. But yes on the tires. (As one example) That is to say, if you believe what the manufacturer says what the diameter is. Which is not always true. The diameter varies (actual tire size) from manufacture to manufacture.
Math is math and if you didn’t make a mistake in the math, then your math will be right and the thing your working with should work.
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