Re: 304/290/200R4 - now V8 Fuel Mileage

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On May 9, 2005 Dwight Southerland wrote:

> I have followed this whole thread with some interest to see what input would be shared.  I feel like the original direction of the thread was abandoned somewhere along the way.  I would personally like to hear input on the subject of increasing fuel mileage on an AMC V8 powered car using modern technology and parts that are available.

Me too! I posted the original thread; here's my thoughts:

Regardless of the thought that OD transmissions are more complex, they're still the way to go IMHO.  The key to gas mileage is keeping the engine at or near it's power/torque peak, and OD transmissions offer at least one more gear to do that.

Also, manual transmissions offer the best mileage.  I have a SVO T5 in my American, and a free-if-I-want-it 200R4 available, which is what I'll use for the '65 American project should I tackle it.  I'll sacrifice the 2-3 mpg or so for the auto for this application.  

Matching gear ratio's with the engine power curve on a reasonable budget would require:
>Figuring out the ratio's of the 200R4 (decode s/n of this trans)
>Use rear end gears in the 3.31-3.54 range I'd think would offer the best combination of low end vs highway OD rpm (depends on OD ratio in the 200R4)
>Do the math for reasonable engine speeds vs actual MPH and build the engine accordingly.

For the engine there's plenty of options:
>Cam - flat tappet hyd (cheaper) or roller hyd retrofit (more expensive, but offers better profiles)
>Engine balancing (more reliability + better performance + better mileage, but cost vs value?)
>Compression? match to cam/needs to run regular fuel.
>Intake - need to use a common intake, maybe a S2P? Lower RPM range, but good low end figures.  I'd also use the TBI with GM componants and something like the Megasquirt controller.  I agree that you get 90% of the benefits with a much easier set up of Port Injection.
>Exhaust - use stock manifolds and good dual exhaust (cheaper) or go for the Edelbrock shorty's ($$ - not sure the benefits/cost vs value in this instance)
>Head rebuild/porting? again, cost vs value

The trick, I think, is to absolutely match the engine to the gear ratios.   There's also got to be a diminishing return of higher rpm/higher power vs gas mileage.  

Too little power/too low rpm and the engine struggles too much = lower mileage.

Too high power/too high rpm + poor mileage as well.

Max torque in the ~2500 range maybe?

The goal would be comfortable cruising, power on tap for passing and modern highway speeds, but it wouldn't be the ideal car to take to the strip, but not a slug either, know what I mean?  I think this is doable with a light-bodied American, 304, and OD trans.

Ideas?

My buddy is on nights now, so I'll have to wait until at least this weekend, but I'll go by and see if I can figure out the exact model 200R4 he's got sitting there, and figure out the gear ratio's.  Don't know if they varied all that much, but who knows.  I'm sure the info is readily available online somewhere.  This trans is out of a ~'85 SS Monte Carlo with the 305 engine.

Jim Boone
Mims, FL


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