Dave J
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| posted on 5/4/06 at 11:46 AM |
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Final drive ratio
Here's a poser,
I'm currently running a 3.9 v8 in my car with a final drive ratio of 3.63:1.
I've got the opportunity to get hold of a 3.38:1 ratio.
Now I know I'll get more mph per revs, but what I'm not exactly sure of is how the acceleration will be affected. The torque on the v8
comes in at fairly low revs and I can only max at about 5000rpm
Cruising would be more economical, but if the acceleration is radically increased (or would it?)would it be drivable at slow speeds?
What do you reckon guys?
Thanks,
Dave
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smart51
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| posted on 5/4/06 at 12:03 PM |
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a 3.38 diff will give more MPH per 1000 revs in each gear than a 3.62. Acceleration will be slower in each gear by 7.4% but the top speed in each
gear will be higher by 7.4%
You will be revving lower at any speed, in the same gear, you will have to have the thottle slightly wider to maintain that speed and your engine will
be working slighly harder to maintain your speed. This will mean better MPG, a bit.
Think about the kind of driving that you do. Think about the increased max speed in each gear. will the change be worth it? If top speed in 2nd is
raised from 58 to 62 and you mostly drive on b roads then is might be useful as you don't need to change to 3rd all the time. If top speed in
2nd increases from 53 to 57, then it is neither here nor there.
With less acceleration in each gear, you will be less likely to spin the wheels.
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Peteff
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| posted on 5/4/06 at 12:08 PM |
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I doubt if you'll notice the difference with your V8 under normal driving unless you rev out in each gear regularly, which kind of defeats the
object of the engine.
yours, Pete
I went into the RSPCA office the other day. It was so small you could hardly swing a cat in there.
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Dave J
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| posted on 5/4/06 at 01:26 PM |
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You are quite right guys, the gain in speed does not really warrant the sacrifice in acceleration. In second gear at 5000rpm, the top speed on a 3.63
diff is 51.54mph versus 55.35 for a 3.38.
As for economy, well with this engine its best not to even go there
Thanks for confirming my suspicions guys.
Cheers,
Dave
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Guinness
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| posted on 5/4/06 at 02:11 PM |
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But if you have a source of a reasonably priced 3.38 buy it and offer it to one of the BEC lads on here or ebay it!
Mike
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