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Old 11-26-13, 10:24PM   #1
goatwgn
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Default Hughes GM25- GM 20 Convertors

I have a question for some people that may have had real world experience with this. I have a 1966 Pontiac Tempest Custom wagon that has a '73 455 with 9.5 to 1 compression, 4X heads with 1.77 exhaust valves installed, a Hughes GM 25 convertor in front of a TH400, with a Gear Vendors overdrive, and a 3.42 rear with 27.4 inch tires. It presently has an 041 (Melling) cam that I am changing out in a couple of months to improve my idling and low speed driveabilty with the AC, and the fact this is more of a cruiser and not a race car. I am going with a Comp Cams dual energy 275 deh grind. It states I can use a "stock convertor" with this combo, and my engine builder ( a very nice fellow on this site) has also informed me I can go with the stock type convertor, being I am looking for a nice tight convertor on the highway with my GV unit, but at the same time I like the power of the 455. The question I have for you all is have any of you used the Hughes GM 20 convertor in a combo similar to this? Hughes states I can still use the GM25,(and it has been good with this present setup), but if the 20 would work better, I would prefer to do that while I have the engine out. (The "Contenental" convertors sound nice, but are a little beyond my present budget) Taking engine out to do the cam,for some underhood detailing as well. Will be easy to change the convertor while it is out.Thanks for any input.
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Old 12-08-13, 11:28PM   #2
goatwgn
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Ordered the Hughes GM11XTM Convertor. Supposed to work well behind large engines with a lot of torque at the RPMs the engine will have the powerband in after I switch my cam. Has an 1800 rpm stall. Will let everyone know how it does when I get it all going again. Not taking it apart until January or so, but looking forward to it.
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Old 12-09-13, 01:59AM   #3
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Old 01-26-14, 02:23AM   #4
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I did something similar with my 400 except I curently have a 2.73 gear & no OD
When I had the trans built I had the lower 1-2 planetary set put in to help compensate the high rear gear & low stall speed at launch.
I left the passing gear switch disconnected.No good down shifting into a really low 2nd gear at highway speed. That could tear things up.
Car is dual purpose but mostly street use.
Just run plenty of trans cooler for the street.
Pair of Hayden DAWGS in front of the radiator works real good
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Old 03-12-14, 01:19AM   #5
goatwgn
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Sorry it took a while to get back to this. Had a lot of other things going on. Well I got the engine back in the car with the DEH 275 cam, (works great on the 9.5 455). The Hughes Gm11xtm convertor also seems to work very well. It will break the tires loose from a rolling start, yet couples very well on the highway, and actually lowered my cruise rpm a tad over the GM25 I had in there before. Overall, a very good convertor behind a mild 455 in a street car IMO.
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