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post #1 of (permalink) Old 08-31-2002, 12:05 PM
427jimmy
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Need some tech info

Hello everyone I am new to this board. I just purchased a '74 GMC 6500 Tow truck. It has a 5 speed with dual PTO's. Eaton split rearend. Oh and of course a 427 CI that hadn't been run since '89. My truck is a '90 GMC Jimmy with a 350 and the granny low 4 speed + np241 case. I'm planning on putting the big block into my jimmy and need to know if the input splines on the 4 speed will fit into the crank on the 427. I know that I'll need a bellhousing. Could I use the one from the 5 speed? Not really familiar with the older big blocks so any input would be appreciated. Thanks
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post #2 of (permalink) Old 08-31-2002, 02:00 PM
 
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Re: Need some tech info

<font face="Times New Roman">
<font color=green>Maybe you're new to engine and tranny work, or maybe you just had a brain fart, but the crank doesn't have splines for the input to the tranny, the clutch has the splines. You need to figure out the clutch, find a clutch disc that has the correct spline count. It should be pretty easy to do, it's likely just a standard 12" SM465 clutch. I'm pretty sure that SB and BB Chevys use the same bellhousing also.
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post #3 of (permalink) Old 08-31-2002, 07:19 PM
 
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Re: Need some tech info

i don't think it'll work. correct me if i'm wrong, but isn't this a tall deck engine?? chevy made tall deck big blocks in that time period (366 &amp; 427) for trucks over 1 ton in the 70's. mainly torque monsters, but their all done by 4,000 rpm. it may bolt up to your mounts, trans won't be a problem, but you will have clearence issues with the steering, firewall, possiably brakes. and you can forget about off the shelf exaust. custom headers, etc.if this is indeed a tall deck, presonally, i'd sell it and get a standard deck big block. a couple tips to tell if it is a tall deck is, thermostat housing looks like 2 housings in one, this one is fuzzy, but you can compare a standard deck to a tall deck by measuring the distance from the top waterpump bolt to the deck. i believe standard is around 3/4". tall deck is about 1" or better. the only things that will swap to a standard deck is the cam and maybe heads.like i said before, correct me if i'm wrong.hope this helps out.
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post #4 of (permalink) Old 08-31-2002, 09:59 PM
427jimmy
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Re: Need some tech info

yes it appears like it has two thermostats. It has a big fourbarrel. Dual belt altenator/waterpump. Says 396/427 on the emissions exemption sticker on the valve cover. Glove box says 327 CI and then it says option 427 CI GAS, and all the other heavy duty stuff. Whoever used it before had the tach set to 6000 rpm. And when I drove the thing it appeared to have quite enormous top end power. I have a three inch body lift in my jimmy and I don't think the steering or brakes will even come near it. (because they are miles away from the 350) I have a fair bit of space between the firewall and the back of the engine as well. Does anyone else have any ideas?
post #5 of (permalink) Old 08-31-2002, 10:13 PM
 
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Re: Need some tech info

well, it appears to be a tall deck, possiably a govenor style holley on it.
with the body lift you may have snuck past a couple problems, but one big one exists. exaust. with the tall deck, the heads are moved out away from the block which makes exaust interesting. not having personal experence on this, just here-say.
any other opionions?
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post #6 of (permalink) Old 08-31-2002, 10:24 PM
427jimmy
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Re: Need some tech info

tomorrow I'm going to measure the framerail distances and see about the exhaust. The manifolds on the 427 are pretty tight to the block and seem as though they would have decent flow. They have tons of space on the truck its in, but mine could be a different story. Right now I have hedders on my 350 and I have plenty of room, well, its not tight. Really would like to make it work. Truck is strictly for torque, so this block would be better than the non industrial blocks. I could be overbored and cammed up good right?
post #7 of (permalink) Old 08-31-2002, 10:36 PM
 
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Re: Need some tech info

if the manifolds are in good shape, won't hurt to try. as for hop-ups, normal stuff still works on this. cam should be a no-brainer, pistons may be special because of the longer con-rod. intakes don't exist for these engines unless you use spacers from wieand.
in your case, all you want mainly is bottom end torque, if the engine runs fine as-is, try it then see where you want to go next, (little bigger cam, etc).
keep us posted!
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post #8 of (permalink) Old 09-01-2002, 04:00 PM
Kendog454
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Re: Need some tech info

Why would they be done at about 4000 RPM if the bore and stroke is the same as a conventional 427?
post #9 of (permalink) Old 09-01-2002, 06:20 PM
 
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Re: Need some tech info

ah, but remember, tall deck. the bore-stroke numbers are not the same as a standard deck 427.
if i had a manual, i could find the exact numbers for you, but when you add a good 1/4 inch of new stroke area, the figures won't be the same.
remember, this is a torque monster made for trucks (only) that are a step down from a semi. you got alot more weight swinging around in the crankcase that don't like alot of speed. i've driven these things, they move a bunch of weight pretty quick.
you'd basically treat this engine like a diesel, alot of power, not much rpm.
dose someone have a early heavy truck manual to find the specs on this monster?
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post #10 of (permalink) Old 09-01-2002, 11:41 PM
427jimmy
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Re: Need some tech info

Well whoever was driving it before was taking it up to 6000. I just need to have it to at least 5500 for street use and good mudslinging torque! How much power do you think one of these things has stock? How about when its juiced up a bit?
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