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  #16 (permalink)  
Old 01-28-2009, 05:50 PM
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Sorry guys...I may have mislead you on my timing numbers above. I had the distributor recurved last summer. Timing is set at 14 initial and 36 total, all in by 2600.

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Old 01-28-2009, 05:51 PM
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Would 4.11 rear gear be too much? Rear Tires are 255/55/17
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Old 01-28-2009, 06:46 PM
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I think a 4.11 gear would be okay. I think your tires are 28" diameter and the O.D. in the trans is a .67. This would put you just under 2,000 rpm at 60mph. A 4.56 gear would be right at 2,200 rpm at 60 mph. How do you want to use the car ?
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Old 01-29-2009, 08:19 AM
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here's a easy to use gears/tires/mph/rpms calculator:

http://www.tciauto.com/Products/Tech...culators.asp#6

(LOL, I'll be "Mr. Conservative" on this thread)

flywheel TQ x tranny ratio x rear gears ratio = force on the tires...
so,,,,
deeper gears is more acceleration force at any/all rpms driving normal or messing around
versus,,,
the bigger cam swap helping add some HP at higher rpms and needs more parts changed to make it work and drive decent on the street....

what is excellent on your present cam is you are at the inital HP peak at only 5,000rpms
the 274 doesn't get to the initial HP peak till 6,000!!!
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Old 01-29-2009, 08:45 AM
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Bow to red65mustang

Great article by Grant. I don't know what came first the AFB or the D-pumper but both are good carbs in their own rights. They have been around a long time.
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Old 01-29-2009, 09:32 AM
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only to illustrate what the "real world" result with a cam swap will likely do:

click on the 268 and 274 cam graphs on this comp dyno mule link which is the same build and CR:

http://www.compcams.com/Technical/DynoSheets/

now plug in the "WOW" 27HP 274 cam gain into the TCI weight/HP =et/mph calculator on the link above...

3400lbs/342HP = 12.44ET/108mph
3400lbs/369HP = 12.12ET/111mph

blink your eyes very quickly once,,,that is aprox 1/10th second...
the 274 cam is 3 very fast blinks quicker (whoopee)

bottem line:
do the gears swap first for the most dramatic improvement and then research a cam swap if you do want more...
(the deeper gears=less load on the motor=more timing sooner is OK=more power,,,,the 268 motor may/may not "want" 18base/18cent or 20base/16cent after the gears swap,,,,the Hg is recovering much quicker (motor wind up is quicker) due to less load)

I'd go with 4.56
risk is that will be so much TQ on the tires at launch you will be fighting for traction on a street surface....
illustration:
413 ft/lbs x 3.0(?**) first gear x 3.55 rear gears=4398 ft-lbs of force on the tires
413ft/lbs x 3.0 first gear x "4.56" rear gears=5649 ft-lbs twisting the hides!!!
(?**=do look up your low gear ratio,,,small difference make a big "total" difference)

footnote:
with the present 4400 ft/lbs of force accelerating only 3400lbs,,,your car should "scoot" darn good as is,,,should be no problem lighting them up from a stop sign...

my car, with only 1ft/lb per lb of car weight would burn the tires to the cords if I let it from a stop sign...

?????
check your timing in 500rpms increments with a timing light to verify the centrifugal curve,,,to indicate the cent is working correct,,,not hanging up
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Old 05-04-2009, 11:37 AM
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Now that the weather is finally good enough to get the car out....I am back to this post.

Car is running great and i have decided to swap the rear gears. Currently running 3.55's with a TH200 OD transmission. Car still has the original (with Eaton POSI) 8.2 10 bolt. Available ratios are 3.73, 3.90 or 4.10.

I am leaning towards the 3.90's but still might be able to run the 4.10's without any issues? I have a 28 inch tire (255/55/17) and at 65 mph would be 2140 rpm in OD?

Am I missing anything?

**MOVED TO TRANSMISSION - REAREND FORUM**

Last edited by wickster; 05-04-2009 at 03:12 PM.
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Old 06-13-2009, 08:22 PM
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You may have some other issues to tackle as well with your combo as far as tuning goes., but the minimum gear for any OD transmission is a 3:73. Anything less will be a dog.
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Old 06-13-2009, 09:27 PM
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Quote:
Originally Posted by wickster
Looking for some input....although the engine runs great...there is just not enough oomph. Runs and drives great...but I really want to be able to smoke the tires off the line.

Was thinking a cam upgrade (XE274 or XE284) and or a steeper rear-gear. Any advice? Or am I missing something>

350 SBC, bored .030
Stock Crank
Spped pro Flat Top (~9.5:1)
Stock Connecting Rods
Edelbrock Performer RPM Heads (#60899), 64cc, Straight Plugs
Comp Cams XE268H Camshaft (224/230@.050, .477/.480)
Performer EPS Manifold
Edelbrock Carb, 600cfm
Mallory HEI
1 5/8" Heddmen Headers
3.55 Rear with TH2004R Bowtie overdrive Tranny
Have you verified your carb is tuned correctly by reading plugs in each mode of operation?

I happen to use the Edelbrock 600cfm carb. I get great torque and good milage; I'm sure I loose some ponies above 4 grand. A larger carb could hurt your off the line performance and lower RPM torque.
600 cfm should be plenty of flow for under about 3500-4000 RPM.

If you want to maximize power above 4000-5000 RPM you could use a bigger carb and perhaps a Edelbrock RPM intake, etc.

I like my Edelbrock carb but I disposed of my Hedman headers.
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