RPM TO MPH ratio

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khai_tuan_nguyen

Senior Member
I was just wondering the rpm to mph ratio on a B20 w/ b16 vtec head and LS tranny.

On my setup for example it is about 70 mph on 5th gear at 4000 rpm. Is this about right?

Thanks
 
the motor and head make no difference, it is about the LS tranny. Look up the LS MPH chart, and there is your information
 
The chart does not answer my question. It helps a little, but it says at 5th gear going 5000+ rpm i should be at like 180. I don't think with 1000 rpms more i would be going 110 mphs more. Right now i am at 70mph at 4000 rpms in 5th gear with 17 inch TSW revos.
 
Originally posted by khai_tuan_nguyen@Aug 4 2003, 11:51 AM
The chart does not answer my question. It helps a little, but it says at 5th gear going 5000+ rpm i should be at like 180. I don't think with 1000 rpms more i would be going 110 mphs more. Right now i am at 70mph at 4000 rpms in 5th gear with 17 inch TSW revos.
Click to expand...

Your speedo is WAY off.....

Top speed on the LS with the proper sized wheels @ 8000 RPM is around 160 REAL MPH
 
Originally posted by AllMotorMonster+Aug 4 2003, 05:30 PM-->
AllMotorMonster @ Aug 4 2003 said:
khai_tuan_nguyen
Click to expand...
AllMotorMonster @ Aug 4 2003 said:
@Aug 4 2003, 11:51 AM
The chart does not answer my question. It helps a little, but it says at 5th gear going 5000+ rpm i should be at like 180. I don't think with 1000 rpms more i would be going 110 mphs more. Right now i am at 70mph at 4000 rpms in 5th gear with 17 inch TSW revos.
Click to expand...

Your speedo is WAY off.....

Top speed on the LS with the proper sized wheels @ 8000 RPM is around 160 REAL MPH
Click to expand...

171mph is top speed with a stock LS tranny and enough power to get it there
 
is it possible to be throwing them that off though? IS there anything else that could be throwing them off?
 
Also I just remembered i do not think (but not sure) that it is the tires, because when i bought the car it had the 17s on them and it had the stock hx engine (and tranny) and when i drove in 5th gear at about 3000 rpms it was like at 70-80 mph. Since then all i did was the B20b/ B16 engine and LS tranny swap... Any ideas?
 
tire diameter and width definately throws the readings off, also, honda spedometers are about 5 mphs off especially at high revs, or as i've heard.

there are tire size/width, final drive, gear ratio actual speed calculators online that you can find via google.com.
 
thanks for the help guys, i understand that the tire size messes up the mph. Does it mess up the reading on the speedometer (i.e. if it says 65 mph am I really going 80) or does it just make the car slower (i.e. smaller tires = faster mph at specific rpm) or both. Also can anyone account for the other engine and trannies rpm to mph ratio compared to the new swap both with the same tires?

thanks again
 
Big rims only throw off your speedo if the tire diameter overall is changed. When done properly, your old fat tire will just be thinned down and filled in with more wheel. The overall diameter doesn't change. That is when it is done properly though, when done improperly, it throws things off. I have this handy image I just made to show it.

on the left , you have your stock rim with fat ass tire. On the right, you have your new set up dubz with thin tires. Notice the overall diameter of the tire never changed, just how much rim is on the inside. Your car for all intents and purposes is perfectly calibrated in this situation.

s3f2fe57390028.jpg
 
the thing is it would only be low if the vehicle speed or RPM sensors were messed, or your tires were actually SMALLER than the originals.
 
I believe my rpms and mph is right, meaning when it says 70 mph it feels like i am going 70. What i mean by the problem is that the ratio of the rpms to the mph seems like it is wrong (70 mph at 4000 rpms in 5th) I think it could be something wrong with my setup or something. I think the sensors are reading right and all.
 
Thanks Dman but the rims + tires of the TSW 17s are the same as the rims + tires of the stock honda. I just have lower profile tires. So it should not make a difference. Could I have a different tranny and not know
 
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