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Thread: Exhaust manifold crack again

  1. #11
    VCVC Member jrinaman's Avatar
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    x2 on what k.k. said!!! swap the heads, upgrade cam and reprogram the computer. ignore the peak h.p. ratings and select a cam for towing, low end torque and power off idle. headers will help but not much, since yours are cracked already, just buy the headers.
    '64 chevy, 292 40 over, 206/526 cam, 2004r trans. 9.75:1, dual webbers, Langdon cast headers, 1.94 valves

  2. #12
    VCVC Charter Member Vanner68's Avatar
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    Quote Originally Posted by lvjjj View Post
    So this morning, I'm ready to take the Burb 40 miles up in the hills to Loren the mechanic to replace the cracked exhaust manifold. Check under the hood first and see that the other one cracked too. Cancel the appointment cause I can't afford the $100 an hour he's going to charge me to replace both. Plus he'll have to order another one. The manifolds themselves are still under warranty (lifetime), but labor only warranted for 6 months, its been a year.

    Loren agreed with you guys that said I shouldn't be running 4,000 rpm in second towing up hills and that's what causes them to crack. So, I'm going to do the work myself cause we spent all our money on gas on the trip. So, that means we'll be crawling up passes at 3,000 rpm which sucks here in the mountain west. Now thinking headers again cause don't think they will crack????, plus give me a little more power maybe.

    Obviously need a better motor, or smaller trailer.
    The 350 should be able to tow, but you have been used to a six cylinder that has a bore and stroke closer to a 400 cubic inch engine, and a manual trans (IIRC)

    I had a couple F150's with the 300 inch six and 5 speed manual. Both would tow like crazy, but overdrive was useless. My 89 K2500 has a 350, TH400 and 3.73 gears. While it can do 80mph, it's screaming to do so. It likes 60mph best. Even so, the big sixes just seemed to have more guts "seat of the pants".

    If you are cracking exhaust manifolds, you are working that engine hard. I bet they are cherry red when you are pulling uphill.

    Here's the bottom line- comparing your van and the Suburban is apples and oranges. The Suburban easily weighs 1 1/2 times what the van weighs, and you stated you are over the limit of the recommended towing capacity.

    Most manufacturers were going to diesel for the heavy duty towing rigs, so gas engine vehicles weren't really built for it. You have pretty much identified your problem though, you need more motor or less trailer.
    Gregg Groff


    There's no place like 127.0.0.1

    1968 Chevy G20 108 panel Now with 454 power!

    1965 Chevy G10 panel- OHC Pontiac inline 6

  3. #13
    VCVC Member Wookee's Avatar
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    Cool

    Click image for larger version. 

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    Sorry Larry it is ether creature comforts or built to tow horse power.
    You said in the past you built your 292 to tow your travel trailer.
    how ever the wife wanted A/C and a few other things.
    Changing the upper end of the Suburban's SBC with a Vortec top end might answer your issues.
    Be warned after paying a shop to do this you still might still not be happy with the Suburbans performance....
    I know we have foot hills they call mountains out here on the east coast.
    Slow and steady wins the race.

    Around here down and out the back exhaust manifolds are pretty common in the salvage yards.
    The General ran these exhaust manifolds on all of his trucks and vans from the mid 70's till the Vortec engines came out.
    Find a pair and have the guys cut the exhaust down pipes to get them off.
    take them home and work the long studs over with a good penetrating oil & replace them with the same length stainless steel studs and lock nuts..
    Or trade your small block Suburban in for a big block Suburban.

    .......Wookee
    Last edited by Wookee; 06-14-2019 at 08:23 AM.
    Its a "van thing". A life style you have to live to understand!!!!

  4. #14
    VCVC Member joyrde's Avatar
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    agree with all that Wookee shared

    My '67 108' , back in the day it had a "stock" 350 out of "something" running the stock center dump 283 exhaust manifolds, The trans was a 350THM Trans and 3.36 gears, running 30" tall rear tires (L60X15").

    It towed our 25 foot tandem axle just fine - - -ran about 190 highway (60-65)- - - 210 around town

    The Van had a & still has a stock bellypan (dropped 3" in the front) a re-cored stock radiator (4 core), factory fan shroud, 5-blade clutch fan.

    We travelled all over the East Coast - - up mountains & down

    The Van now has a '97 350 Vortec, changed to a carb with a towing camshaft - - 700R trans and a 3.73 12 bolt rear, still running 30" tall tires (275-60X15). Dual A/C, front & rear disc brakes, and power steering. With the power steering an A/C, I guarantee you it would tow that camper trailer, even better now than then

    As Wookie said, get either rear dump, or center dump exhaust manifolds - - 2 1/2" outlets would be best, but stock will do and slow down - - 60-65 tops IF YOU HAVE at minimum a front sway bar and good steering/spring components.

    I would also, as I mentioned before dropping one rear gear ratio - - - my 3.73's combined with the 30" tires and the OD trans works great.

    Slow down, When pulling hills gear down, keep engine rpms below 3000 rpms - - - if the Van slows down pulling hills, just gear down and put the 4-ways on

    Good Luck
    Last edited by joyrde; 05-30-2019 at 03:43 PM.

  5. #15
    VCVC Member lvjjj's Avatar
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    joyrde you reminded me of something maybe weird about the Burb when you mentioned that your 350 ran at 190. That's what mine does, runs real cool all the time even in 2nd gear at 4,000 rpm, never got over 200 and was usually cooler than that. The radiator on the 94 is HUGE, and has oil and trans cooler running thru it (also has stock external trans cooler).

    So I spent most of the day Saturday putting on the two new manifolds (one made in China the other in Vietnam). The mechanic (Loren) who first replaced the manifolds a year ago was an instructer for GM trucks a few years ago and really knows GM trucks. He said that these 350's had no gaskets between the exhaust manifolds and head to aid in cooling. Don't get it but when he fixed them they didn't leak at all. But when I fired it up Saturday, had many small leaks, so guess I didn't get the mating surfaces cleaned up enough. Used a Dremel too with small wire wheel. Wasn't much on them anyway as no gaskets or gasket sealer was used. He advised against using headers but didn't say why. Plus I screwed up the power steering pump bracket by cutting off the left hand prongs so I could get the bolt out. So its all screwed up so myswell try headers.

    I think I'm going to ignore all the well intentioned advice (even though I appreciate getting it) and order some Pace Setter Headers from Summit for $213 and give them a try, reviews were pretty good. I don't want to spend a lot of money for this experiment, don't care if they corrode and rust (no ceramic coating, the Clifford headers on the van and Thorley headers on my '88 454 had no coating and they are still going great) I figure that even if I get Loren to remount the manifolds to get rid of the leaks, I still can't use the Suburban like I want to so its worth it to me to try the headers and hope they will give me a little more power and can pull hills farther in 3rd and maybe run a little more than 3,000 rpm in 2nd. Probably going to sell the Burb anyway unless it does pretty good with headers. It will cost me a lot less to buy and install headers than have Loren re-mount the manifolds to stop them from leaking. I remember that when I installed the headers on the van and '88, the improvement was immense, particularly the early. The condition of the exterior and interior is so good and pristine they will probably overshadow the weak engine and maybe headers will impress somebody to buy it that don't know much like me.
    LARRY OF THE PACIFIC NW
    1965, 292, TH350
    purchased Nov. 22, 1970

  6. #16
    VCVC Member joyrde's Avatar
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    Quote Originally Posted by lvjjj View Post
    The mechanic (Loren) who first replaced the manifolds a year ago was an instructer for GM trucks a few years ago and really knows GM trucks. He said that these 350's had no gaskets between the exhaust manifolds and head to aid in cooling.
    FYI - - I am an ASE Master Certified Tech and taught Auto tech for 30 years - - - small block Chevys have exhaust gaskets - - from the factory - - depends on the year . . used ALL of them the surfaces warp and pit.

    In the kindest possible terms, do what you wish - - - just think of the tens of thousands of small blocks that do not crack their manifolds - - again, IMHO, you need to slow down, run at a lower RPM, and possible lower the rear gear ratio.

  7. #17
    VCVC Member lvjjj's Avatar
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    Yeah, I was really surprised to hear that about the gaskets, or not. Btw- have always appreciated your expert help. My engine definitely did not have exhaust manifold gaskets from the factory. If fact, it still doesn't. Loren replaced them 1 and one half times and I just replaced the cracked manifolds myself (scary) without gaskets and there are no leaks. Well there was cause the donuts that came with the manifolds weren't correct, so they leaked at first, but got the right ones and now working like new.
    LARRY OF THE PACIFIC NW
    1965, 292, TH350
    purchased Nov. 22, 1970

  8. #18
    VCVC Member lvjjj's Avatar
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    So, the Pace Setter headers came and took one look and sent them back. The middle flange area was an eight of an inch higher than the two end ones when I put a straight edge across it. So there was no way they would seal. Get what you pay for, luckily Summit is taking them back.

    Now we're looking for a better tow vehicle or a smaller trailer. Found a Tahoe with a 6.2 liter engine, never heard of that, what is it? Sounds like it might be powerful. I had a 6.0 for a while and it was great. Also located a Yukon Denali XL with an 8.1, but its pretty beat up, temping though.

    My engine education stopped in 1988.
    LARRY OF THE PACIFIC NW
    1965, 292, TH350
    purchased Nov. 22, 1970

  9. #19
    VCVC Charter Member Vanner68's Avatar
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    Have you considered going diesel?
    Gregg Groff


    There's no place like 127.0.0.1

    1968 Chevy G20 108 panel Now with 454 power!

    1965 Chevy G10 panel- OHC Pontiac inline 6

  10. #20
    VCVC Member kookykrispy's Avatar
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    Quote Originally Posted by Vanner68 View Post
    Have you considered going diesel?
    If the primary purpose of this vehicle is towing, I sure would look at diesels. In my opinion, the ultimate tow rig SUV is the 99-02 Ford Excursion with the 7.3L Powerstroke Diesel. Even the '03 and later 6.0L was a good engine too, but the 7.3L is the legend
    Last edited by kookykrispy; 06-14-2019 at 08:14 AM.



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    Quote Originally Posted by Vanner68 View Post
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