so I got this question (Chevy 4spd swap for the GMC 5spd)
Posted: Thu Dec 27, 2007 9:52 pm
This is all about the Hupla or debate regarding the Chevy 4 speed transmision swap for a GMC 5 speed with O.D. in a chevy 1.5 ton 4x4 G506.
Some say it aint worth all the effort.. Others swear by it
(But of course off the board and private emails telling me this)
Probably for fear of public ridicule.. I dont know...
I guess what I am saying is there seems to be two opinions here:
One says its the best thing since sliced bread. The other say its a waste of time, money and effort.
I beleive the later to be hard core 100% restoreres, probably why the responses I got ON LINE on other boards.
I belevie I really nerver got the answers I thought I would get.
So, I found this online automotive calculator.
http://www.bgsoflex.com/auto.html
So, for SH*Ts and giggles, I plug in some numbers.
---------------------------------------
Differential Gear = 6.67 to 1
Transmission Gear = 1.00 to 1
Tire Diameter (Inches) = 36.90
(as listed on the Coker TIRE site for a 7:50-20 NDT
Engine RPM = 2750
Computation Results:
Computed Vehicle MPH is 45
---------------------------------------------------------
I think 2750 is a "managable, working RPM" for a 235/261 straight 6 dont you think? I mean, we are told that the ww2 Chevy trucks are good for 45 mph.. Not sure what RPM is a "good working range" for the "dippers" but a pressure bearing engine I think 2750 is reasonable.
reading engine performace specs they seems to be capable of 3100 PLUS RPM's... Maybe more.
Comments so far?
Now, I take the same calculator and plug in the .79/1 over drive reduction ratio for the GMC 5 speed. I get the following:
--------------------------------------------------------------
Differential Gear = 6.67 to 1
Transmission Gear = 0.79 to 1
Tire Diameter (Inches) = 36.90 (same size again here)
Engine RPM = 2750
Computation Results:
Computed Vehicle MPH is 57
--------------------------------------------------
WOW.... So "technically" the .79 ratio reduction can give me one nice "boost" in road speed. Or, as I would be using the truck, no more than 50-52, I would reduce the "working" RPM's even further.
Am I missing something?
I mean, I have read LOTS of negative responses to why one would not , or should not install this O.D. transmission. "Very Little gain for all the effort" is one statement written.
Heck, I see one helluva advantage just by these numbers.
again, am I missing something? Drag? vehicle weight? Lack of HP?
Is 2750 RPM an "unreasonable" working RPM for a full pressure engine or no?
Its my understanding its fully capable of that RPM... and more.
Tell me your thoughts!
Anyway, I go one step further...
I figure I would NOT want to push this truck past 52 as stated above.
So, here I get:
-----------------------------------------------------
Differential Gear = 6.67 to 1
Transmission Gear = 0.79 to 1
Tire Diameter (Inches) = 36.90
Engine RPM = 2500
Computation Results:
Computed Vehicle MPH is 52
--------------------------------------------------------
Hummmmm..... ONLY 2500 RPM to achieve 52 MPH.
Seems like a good deal to me... So, would anyone here comment that 2500 is EXCESSIVE RPM for this engine?
Thanks all..
(Just looking for truthful, non-biased answers to a swap I want to make)
Some say it aint worth all the effort.. Others swear by it
(But of course off the board and private emails telling me this)
Probably for fear of public ridicule.. I dont know...
I guess what I am saying is there seems to be two opinions here:
One says its the best thing since sliced bread. The other say its a waste of time, money and effort.
I beleive the later to be hard core 100% restoreres, probably why the responses I got ON LINE on other boards.
I belevie I really nerver got the answers I thought I would get.
So, I found this online automotive calculator.
http://www.bgsoflex.com/auto.html
So, for SH*Ts and giggles, I plug in some numbers.
---------------------------------------
Differential Gear = 6.67 to 1
Transmission Gear = 1.00 to 1
Tire Diameter (Inches) = 36.90
(as listed on the Coker TIRE site for a 7:50-20 NDT
Engine RPM = 2750
Computation Results:
Computed Vehicle MPH is 45
---------------------------------------------------------
I think 2750 is a "managable, working RPM" for a 235/261 straight 6 dont you think? I mean, we are told that the ww2 Chevy trucks are good for 45 mph.. Not sure what RPM is a "good working range" for the "dippers" but a pressure bearing engine I think 2750 is reasonable.
reading engine performace specs they seems to be capable of 3100 PLUS RPM's... Maybe more.
Comments so far?
Now, I take the same calculator and plug in the .79/1 over drive reduction ratio for the GMC 5 speed. I get the following:
--------------------------------------------------------------
Differential Gear = 6.67 to 1
Transmission Gear = 0.79 to 1
Tire Diameter (Inches) = 36.90 (same size again here)
Engine RPM = 2750
Computation Results:
Computed Vehicle MPH is 57
--------------------------------------------------
WOW.... So "technically" the .79 ratio reduction can give me one nice "boost" in road speed. Or, as I would be using the truck, no more than 50-52, I would reduce the "working" RPM's even further.
Am I missing something?
I mean, I have read LOTS of negative responses to why one would not , or should not install this O.D. transmission. "Very Little gain for all the effort" is one statement written.
Heck, I see one helluva advantage just by these numbers.
again, am I missing something? Drag? vehicle weight? Lack of HP?
Is 2750 RPM an "unreasonable" working RPM for a full pressure engine or no?
Its my understanding its fully capable of that RPM... and more.
Tell me your thoughts!
Anyway, I go one step further...
I figure I would NOT want to push this truck past 52 as stated above.
So, here I get:
-----------------------------------------------------
Differential Gear = 6.67 to 1
Transmission Gear = 0.79 to 1
Tire Diameter (Inches) = 36.90
Engine RPM = 2500
Computation Results:
Computed Vehicle MPH is 52
--------------------------------------------------------
Hummmmm..... ONLY 2500 RPM to achieve 52 MPH.
Seems like a good deal to me... So, would anyone here comment that 2500 is EXCESSIVE RPM for this engine?
Thanks all..
(Just looking for truthful, non-biased answers to a swap I want to make)