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Old 07-23-2015, 12:07 AM   #1 (permalink)
The brake pedal is evil
 
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My car seems to be P&G resistant.

My car (1994 geo prizm) seems difficult to bump start. If I let the clutch out enough to spin the engine enough that it will start, the engine will consume large amounts of kinetic energy and make some noises I do not like.
Comparison of the civix DX, Si, and VX, geo prizm, and saturn S series (approximate, I didn't research it much,) at 30 MPH. The prizm has gearing that is shorter than even the civic Si and this is after my rubber overdrive (185/70/R14 vs 175/65/R14) using the tallest tire that does not rub the fenders everytime I take a turn fast.

Code:
car	5th	final	revs/mile speed	 clutch rpm
DX      0.702	4.058	890.59	 30	1268.51899122
Si      0.75	4.25 	886.89	 30	1413.4809375
VX      0.702	3.25	912.81	 30	1041.2880075
prizm 	0.815	4.311	833	 30	1463.3581725
SX1   	0.643	4.063	833	 30	1088.1099985
SX2   	0.73	4.063	807	 30	1196.776965
Any idea why bump starting is so hard? I'm suspecting the short gearing shown above, but I may be missing something.

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Old 07-23-2015, 12:52 AM   #2 (permalink)
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What gear are you bump starting in? If its a low gear = no good, I always use 4th or 5th.
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Old 07-23-2015, 12:54 AM   #3 (permalink)
The brake pedal is evil
 
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Quote:
Originally Posted by iveyjh View Post
What gear are you bump starting in? If its a low gear = no good, I always use 4th or 5th.
5th only, everything else is too short.
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Old 07-23-2015, 08:55 AM   #4 (permalink)
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My Renault has the same gearing and no problem bump starting in 5th or 3rd at lower speeds.

I wonder if you're throw-out bearing is bad?
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Old 07-23-2015, 09:44 AM   #5 (permalink)
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From my experience, short gearing actually makes P&G all that more effective because cruising in gear is that much less effective and it also shortens up your pulses.
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Old 07-23-2015, 11:35 AM   #6 (permalink)
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I have to ask, are you double clutching to match revs or just dumping the clutch?

What you describe sounds like my early attempts at P&G, after years of driving autos.
It wasn't pretty

I often clutch start the Mazda in 4th gear at the sort of speeds you mention, without any jerking now.
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Old 07-23-2015, 12:09 PM   #7 (permalink)
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You can't match revs with a bump start. I suspect a clutch issue- the engine doesn't know or care where the force to crank it is coming from, but the hard and noisy start doesn't occur with key starts, only bump starts.
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Transmission type Efficiency
Manual neutral engine off.100% @MPG <----- Fun Fact.
Manual 1:1 gear ratio .......98%
CVT belt ............................88%
Automatic .........................86%

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Old 07-23-2015, 05:10 PM   #8 (permalink)
What brake pedal?
 
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Quote:
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Any idea why bump starting is so hard?
Broken motor mounts??
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Old 07-23-2015, 06:39 PM   #9 (permalink)
The brake pedal is evil
 
Join Date: Jan 2013
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Trolla - '94 Geo Prizm base
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90 day: 29.51 mpg (US)

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Quote:
Originally Posted by digital rules View Post
Broken motor mounts??
The front is broken (I get about 6 months out of the front mount due to a bent frame) but it was just as hard when I had just replaced them.
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Old 07-24-2015, 08:53 AM   #10 (permalink)
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Then it's the bent frame. If it's throwing enough stress on the front mount to kill it twice a year, it's far enough out of kilter to disrupt other things- but since the starter is mounted to the engine there's no problem starting with that because it's always properly aligned with the engine.

The front mount being broken may let things become slightly worse, but even when new it can't keep everything properly lined up.

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Transmission type Efficiency
Manual neutral engine off.100% @MPG <----- Fun Fact.
Manual 1:1 gear ratio .......98%
CVT belt ............................88%
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