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putting 396 in the jimmy

Discussion in '1969-1972 K5 Blazer | Truck | Suburban' started by roostr3269, Oct 18, 2001.

  1. roostr3269

    roostr3269 1/2 ton status

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    just wanted to check if anyone did this engine swap before, was originally gonna go with a built 350, but forgot my brother had this motor sittin in his garage, any tips would be greatly appreciated, thanx....roostr

    live to wheel, wheel to live--1972 gmc jimmy 8 inch lift, 37" ssr's, big n bad
     
  2. Greg72

    Greg72 "Might As Well..." Staff Member Super Moderator

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    The swap is possible....my '72 is using a 396 with a 454 crank. That makes it a 427.....acutally with a .030 overbore is something like 431 or something.....

    I bought mine with the engine already in it, so I don't know what has to happen to make it all fit. The distributor and passenger side valve cover seem awfully close to the firewall, and my K5 has a 2" body lift on it. I assumed that the lift was to help provide some extra clearance for the motor. Otherwise, I think the motor would have to be moved forward along with the tranny and xfer case, new driveshafts would need to be made, special motor mounts, etc.

    Sorry I don't have more specifics, but I wanted to at least let you know that it's been done....and that it CAN be done.

    Good Luck

    -Greg72
     
  3. roostr3269

    roostr3269 1/2 ton status

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    thanx greg, my jimmy has 8 inch susp. lift w/ 3 inch body lift. actually was thinking of taking body lift off until now. could u tell me what drivetrain your running? thanx again...roostr

    live to wheel, wheel to live--1972 gmc jimmy 8 inch lift, 37" ssr's, big n bad
     
  4. ed rex

    ed rex Registered Member

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    Rooster, I put a 454 into my '70 Jimmy. Bolted right in with the exception of the front cross member. Had to extend it 2" lower to accomodate the deeper oil pan. Maybe the 396 won't need this mod. Also, I am just running stock exhaust manifolds. Can't speak to headers and the clearance thereof.
     
  5. Greg72

    Greg72 "Might As Well..." Staff Member Super Moderator

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    The drivetrain is a 427 (as mentioned previously) bolted to a TH350 and NP205. Front axle is stock (10-bolt?) with a 12-bolt rear 3.73 gears, and 35"s (which measure out to a true 33").

    Suspension is a 4" lift with blocks in the rear. I don't know if anything special was done to the driveshafts.

    Something else that might matter....it has twin electric fans instead of an engine driven one. That's a real space saver so if you decide to pull the engine forward to clear the firewall, you may HAVE to go with electric fans.....

    -Greg72
     
  6. SilverJim

    SilverJim 1/2 ton status

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    Ed, do you have an auto or a manual?
    Do you have any valve cover clearance problems at the firewall?

    1970 GMC Jimmy 502HO/SM465/NP205 doesn't run just yet!
     
  7. frito

    frito Registered Member

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    my 71 had a 396 in it before i owned it now its got a 350 but to get the BB in the only thing the previous owner did was cut the driver side frame rail a little bit to clear hedders other wise it should fit my stock 350 sits very close to the firewall anyways ... i didnt think it could fit an HEI but it did BARELY good luck on the swap
     
  8. ed rex

    ed rex Registered Member

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    SilverJim.....not to mislead anyone with the simplicity of the situation here are some more particulars....Jimmy came stock with the 350, Dana xfer case and manual 4-speed. After I ran the p*** out of it, the SB and half-ton running gear had about enough of my s***. A buddy of mine with a 71 Jimmy rolled it and tweaked the bejesus out of the frame. It was unsalvageable. He had a 1-ton rear with Detroit, 3/4T front, 427BB, TH350 and NP205. I bought the whole kit-n-kabootle for a grand. The 427 was tired and he had just bought a 454 Targetmaster from GMC. It was still in the crate in his garage when he toasted his load. I weaseled it out of him for another grand, which then (~1994) was about 1/2 price.

    So I pulled my engine, tranny and xfer out and slapped his 'get-up' in, basically to verify form, fit and function. There were no apparent modifications to his truck except for the drop down front crossmember I spoke of earlier, and everything bolted up perfectly. I was running 38.5x16x15 SS's at that thime so I had a 6" suspension lift and a 2" body boost. Everything fit tight. I don't believe the body lift made too much difference in the fit because he was running the BB without one. However, he did initially have the HEI. It is a bit bulkier than the standard dist with points setup and thus, he was forced to beat back and enlarge the firewall depression to accomodate the HEI. With the body lift, I did not. But I ended up going back to points to have the flexibility to really dial that BB in so it is really not an issue.

    I have no valve cover issues at the firewall. The BB I have has the 'low-boy' valve covers and there is plenty of clearance both vertically and horizontally. I'm not sure but the body lift probably helps there, but again, the other rolled Jimmy didn't have the lift and it fit in there. Don't recall if that one had some of the firewall beat back, but I kind of doubt it. Aren't all 68-72 engine compartments the same, regardless of pick-up or blazer/jimmy config?

    My buddy's rolled Jimmy had stock exhaust manifolds which I utilyzed and are still on to this day. There is perhaps 1/4" of clearance to the frame. I think that if you want to run headers, the frame will have to be shaved, header dependant. That's next spring's project!

    The only other thing I would mention is that the fan shroud will need to be addressed. I'm still to this day having grief with overheating. First I put that damn body lift on which I am still regretting. It has caused me more problems than anything else. Anyway, putting the body lift on effectively raised the radiator out of position with regards to the fan. So I had to cut the shroud in half and was just using the top half of the shroud with the 350. Although the engine ran a little hotter than with the full shroud, it was not too bad. The the BB went in and I had to further skin down the shroud, this time I took about 3" off the enginewards side as the BB sticks out further. Now it's no more than a dust cover and consequently, doesn't skin the bulldog. The engine is always too hot. Idling in traffic is a killer. Takes about 15 minutes on a cold day before old faithful starts to blow.

    I have the flexi fan on currently. I have tried single and dual electrics to no avail. Someone suggested that I plug the water pump bypass. I've got the plugs sitting on my workbench at home ready to stuff in but looking at my intake manifold, it looks like that fitting will cause me problems.....doesn't look like it will come out willingly. Anybody have any heat-solving tips to share with a BB hothead? I'm at my wit's end!!
     
  9. Steve_Chin

    Steve_Chin 1/2 ton status

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    Ed, check out the custom aluminum radiator I got from Rodney Red. It has much more cooling capacity than I need when running a 30/70 mix of coolant/water. I also run a high-flow Robertshaw thermostat. From what it sounds like to me, you do need to completely encase the leading edge of the fan in the shroud and maybe get rid of the flex-fan in favor of a heavy duty thermal clutch and 7-blade fan setup.

    <a target="_blank" href=http://www.rodneyred.com>http://www.rodneyred.com</a>
     
  10. ed rex

    ed rex Registered Member

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    Hi Steve....thanks for the link. I attribute a lot of the problems to the lack of shroud. Living up in BFE, the junkyards are picked clean of a viable shroud, or even a candidate for jerry rigging. No way to get a BB steel clutch fan from the junkyard. But I know that the issue of flex vs steel is hotly debated. Thanks.
     
  11. frito

    frito Registered Member

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    i have also had problems with overheating with my SB due to the fact that i put a hole in my 4 row raidiator with a rock and had to put a 3 row in that i had laying around and didnt have a good enuff fan shroud for it ... my truck would be fine when moving but sitting it didint like ... esp.. when wheelin but i got tired of it and soldered my 4 row and put it back in with my shroud and the temp stays at 180.. i have one of those aluminum fans that isnt a flex fan
     
  12. SilverJim

    SilverJim 1/2 ton status

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    Just thought I would mention on this post that 64-77 Chevelle headers for a 396-454 will fit perfectly (they fit on my 502; no x-fer case clearance problems and I already have the rest of my exhaust in place...and with small block motor mounts for the big block...since that is really the only option we have.

    1970 GMC Jimmy 502HO/SM465/NP205 doesn't run just yet!
     
  13. Greg72

    Greg72 "Might As Well..." Staff Member Super Moderator

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    SilverJim,

    You'd better get some photos of that rip-snortin' K5 up on this board soon.......!!!! [​IMG]

    The rest of us are getting impatient. Maybe some engine shots, exterior shots, and a shot of it doing a 4-wheel drive burnout!!!! THAT would be cool.....

    -Greg72
     
  14. SilverJim

    SilverJim 1/2 ton status

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    that part in my signature about how it "doesn't run just yet" isn't a joke...sorry

    i posted some crappy pics a couple of weeks ago, i'll try to post some better ones soon

    1970 GMC Jimmy 502HO/SM465/NP205 doesn't run just yet!
     
  15. Klef72K5

    Klef72K5 1/2 ton status

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    Ed Rex,

    To your over heating problem, What thermostat do you have in there? A 160 degree will open too fast and will not allow the fluid to cool fast enough in the radiator. Please dont say you there's not one in there! Try a 180. Another possible cause is the timming.
    I had a flex fan in my Jeep and was over heating. The problem was at the sand dunes when I'm climbing hills I'm turning 5000 RPM and not going fast enough to let the air pass through the radiator. I put Dual eletric fans on and it stays on 180 unless I push the motor hard for a long time then it gets to 220. Best of Luck!

    <a target="_blank" href=http://wsphotofews.excite.com/031/rw/Jo/og/t488200.jpg>http://wsphotofews.excite.com/031/rw/Jo/og/t488200.jpg</a>
     
  16. ed rex

    ed rex Registered Member

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    Hi KLEF, thanks for the tips. Due to a defective manifold bolt hole, I had not removed the thermostat housing for as long as I could remember. In fact, in retrospect, it has always been on ever since I took it off the 427 and mounted it to the 454. So last night I attempted removal. The driver's side bolt snapped leaving a 'stud' protruding from the manifold about 1/2 inch. The other side unscrewed without incident. The thermostat was a 165 and it was in poor shape. Also timed it to 8 degrees before this past weekend, it was previously at 4. Not exactly sure where to time it at but it runs like a raped ape at 8. Ran good at 4, but much better at 8. Now I just have that snapped bolt to deal with........any suggestions? It's an aluminum manifold and a steel bolt piece. Heat it up? Cut it flat and drill it?
     
  17. Triaged

    Triaged 1/2 ton status

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    Can you get a stud remover on it? I would try that first. If not try a ez-out.

    '71 Blazer CST w/ a 400sbc, 4" lift, 36" Supper Swampers, and alot of rust
    <a target="_blank" href=http://community.webshots.com/user/triaged>See it Here </a>
     
  18. ed rex

    ed rex Registered Member

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    Yup, found this killer penetrating jizz. Comes in a tall yellow spray can with all sorts of testimonials on the side. Almost looks like a cartoon strip. I forget the name, it's at home, I'm at work. Anyway, gave it a spritz, tapped it a few times and the robo-grips got it going. Looks like a job for the helicoil now.

    Ordered one of those thermostat housings from SummitRacing.com that has an o-ring instead of the traditional gasket on the advice of a buddy. Anyone have any experience with these?
     
  19. frito

    frito Registered Member

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    i use a chrome o-ring water neck on my truck and it held up to 260 Deg overheat and i have taken it on and off 3 times now and it still works perfect .... but i also have a brand new intake manifold, i have an old torker manifold that will always leak unless you use an iron water neck and gasket with RTV on it .... (no doubt because the mounting surface isnt flat) none of your local auto parts stores selll that water neck? i live in fremont, CA and 3 or 4 of them sell them for 5 bux and you cant go wrong for 5 bux =)
     
  20. ed rex

    ed rex Registered Member

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    Yeah, I'm here in Grass Valley.....'bout 45 minutes NE of Sacto. Not exactly the mecca for car parts. I looked at a few places, but then just ordered online. Paid double what you did, plus s&amp;h which made the grand total quadruple!!!

    My manifold is an old torquer. Hope I don't have the same issues as you did. The mating surface on it looks to be fairly flat.....
     

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