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Discussion Starter · #1 ·
Will a car with a long stroke engine travelling at 50 mph rev slower than a vehicle with a short stroke engine traveling at the same vehicle speed, all other things being equal between two cars (rear gear ratio, tire height, final drive ratio, etc.)? Another way to look at it would be, would there be any difference in rpm at 50 mph if you pulled a 5.0 out of a Mustang and replaced it with a 351W and didn't do any other mods? This may be a dumb question, but I know there are some serious gearheads on this great board who could enlighten me. Thanks.
 

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Nope, RPM will remain the same. What may have thrown you off is piston speed, which will be faster on the longer stroke engine if I remember right. Think of a record on a record player (remember those?) The outter most edge of the record is moving faster than the inside of the record, but they are still both turning the same RPM. The difference is due to the further amount of travel for the larger circle.

I hope this makes sence.
 

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I think a good point to bring up here is what I did this winter. Last year I ran a 302/c4 in a maverick, turned about 107 at the finish line @ 7000 rpm. I switched to a 393w/'glide this winter, same gears, same tires, same rpm stall converter, but the mph is now in the 118 range, but still at 7000 rpm. What gives? High gear is the same @ 1:1 in both transmissions. Also, motorcycles I work on are kinda the same way, a 600 will have a .93 6th gear, and at 100 mph will turn about 9000 rpm, but a 1200 with the same final drive ratio will only turn in the vicinity of 7500, but it's horse power is nearly doubled (turbocharged). I guess I dont understand it
 

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On 2002-06-29 00:42, mavman wrote:
I think a good point to bring up here is what I did this winter. Last year I ran a 302/c4 in a maverick, turned about 107 at the finish line @ 7000 rpm. I switched to a 393w/'glide this winter, same gears, same tires, same rpm stall converter, but the mph is now in the 118 range, but still at 7000 rpm. What gives?
If both driveline combinations were exacly the same and you are crossing the line with both cranks turning @ exactly 7000 rpms, then the speeds would have to be the same. The difference would have to be in the amount of slippage in the tranny or torque converter. Right?
 

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bluestreek is right. Gear ratio relates input RPM to output RPM. If both transmissions are running the same gear ratio (1:1 in 3rd in an automatic), same rear end ratio, and same tires, RPM HAS to be the same at a given speed UNLESS some slipping is happening somewhere. Same goes for the streetbike example. What you might have been seeing there is a difference in primary reduction between the engine and tranny, or differen front and/or rear sprockets.
 

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Discussion Starter · #6 ·
Thanks you guys. This actually does make some sense to this novice. That's why this board is so great.
 
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