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Thread: Exhaust manifold crack again

  1. #1
    VCVC Member lvjjj's Avatar
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    Exhaust manifold crack again

    Help, don't know what to do. Every time we tow our trailer with the '94 Suburban something breaks, this time, for the second time, new exhaust manifold cracked. I had had them replaced a few months ago cause the originals were leaking where the bolt heads broke off. When one of the new ones cracked shortly thereafter,I had it replaced under warranty, but just broke again. So I wonder if the mechanic used cheap Chinese parts? But, I can't even find a new Genuine GM part passenger side manifold (350 with A/C).

    We're almost home from a 4,000 mile trip from NW Washington to Prescott AZ on old blue highways including Route 66. The engine still sucks but its doing a lot better than the last time we took a long trip, with the dual exhaust, dual air intake, adjustable timing control, fastchip and AC Delco tuneup parts. Lots of mountain passes, so got around 7 mpg average, pulling lots of hills and passes in 2nd gear at 55 mph. Got that 350 screaming all day long. Luckily when the manifold heats up it quiets down.

    So, I'm thinking shorty headers instead. Any problems I'm going to run into there?

    (God I miss that 292, it never gave me a single problem). Just wish it would tow a 6,000 lb trailer and power a 6,000 lb suburban.
    LARRY OF THE PACIFIC NW
    1965, 292, TH350
    purchased Nov. 22, 1970

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    VCVC Charter Member Vanner68's Avatar
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    I have an 89 K2500 with the 350, just did head gaskets over the winter and replaced the exhaust crossover pipe. This is a 100% original truck, and I was amazed how thin the castings are on the manifolds. They are prone to cracking, especially under stress. Short of trying to find earlier manifolds that are thicker, and having a new y pipe made to match, headers may be the next best option. DO NOT wrap them, they will rust out in a few years. Also, watch out for the oil filter adapter on the driver side, it's pretty tight in that area.
    Gregg Groff


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    1965 Chevy G10 panel- OHC Pontiac inline 6

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    VCVC Member kookykrispy's Avatar
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    just replaced a cracked exhaust manifold on my '99 silverado after heavy towing during our move down the west coast. Cracked manifolds suck, but it happens. You might consider headers, which would give you a little torque increase, and if you eventually swap to vortec heads, the headers will fit



    64' wikivan 230/4 onda tree/2.56 posi
    '64 Red Baron no engine/trans
    '66 "Lucky" 230/3 onda tree/project

    Quote Originally Posted by Vanner68 View Post
    Remember, they're still printing money, but they aren't making any more earlies!

  4. #4
    VCVC Member lvjjj's Avatar
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    I was thinking headers but the ones for $250 at Rock Auto, etc., are probably real cheap and won't seal well. How expensive would I need to go to get good ones? I'd want shorty headers that connect to the stock exhaust pipes with donuts.

    Also, even though the engine did a lot better this time because of the exterior improvements I made, it was frustrating to have to pull it down to 2nd a lot to go up hills, I'd run around 4,000 rpm between 55 & 60 mph. It was screaming but didn't seem to care too much.
    Part of the problem is that its a 1300 lbs over the GVRW rating of the Burb. Its a K1500 and I think the GVRW is 10,000 lbs. We weighed the combo on the way home to day and the rig weighs 11,300 lbs. It's very stable, stops great and runs smooth, its just the lack of power that bothers me.

    Got a friend mechanic/car restorer who suggested I get a 383 stroker that would be built in Spokane to my specs and he thought he could get it installed for less than $5000, total. Real tempted to sell the van in order to get some money to do that. I've heard the 383 is quite powerful and would do a lot better towing than my current 350 cause of its longer stroke.

    As for selling the van, I'm thinking about it cause my HOA rules won't let me keep the van on my lot, I keep having to move it around to different storage units, and its just sitting there deteriorating and I hate to see that. And at 73, I may not have a lot of RV'ing years left so I need to do something.
    Last edited by lvjjj; 05-24-2019 at 04:22 PM.
    LARRY OF THE PACIFIC NW
    1965, 292, TH350
    purchased Nov. 22, 1970

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    VCVC Member kookykrispy's Avatar
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    you don't need a 383. You have a perfectly good running 350, which is a quite capable power plant, just needs some improving. Its just that your 94's stock swirl port heads and stock "peanut" cam basically suck big time. Swap to vortecs and then have delta camshaft in Tacoma custom re-grind your existing camshaft to give your cam a new custom profile to take advantage of the heads. Combine the cam and heads upgrade with headers, and a re-flashed computer and you will see great gains... and it won't cost anywhere near $5k

    The 3/4 length "shorty" headers should be fine. Here's some chrome ones for $97 shipped. https://www.ebay.com/itm/Exhaust-Hea...EAAOSwuG1c0XIX

    They will seal fine if you use my trick for headers. Put ultra copper hi-temp RTV on both sides of the gasket. Let it set up several minutes before assembling, so the RTV gets tacky and develops a "skin" on it. Then assemble. Letting it set up before assembling, the RTV does not squeeze out when you bolt it down, and makes a nice seal that doesn't leak.
    Last edited by kookykrispy; 05-24-2019 at 07:22 PM.



    64' wikivan 230/4 onda tree/2.56 posi
    '64 Red Baron no engine/trans
    '66 "Lucky" 230/3 onda tree/project

    Quote Originally Posted by Vanner68 View Post
    Remember, they're still printing money, but they aren't making any more earlies!

  6. #6
    VCVC Member joyrde's Avatar
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    First if you are towing in second gear at 55 mph that 350 is screaming, and way pass the max torque - - - - slow down. That mph is cooking exhaust valves, heads and exhaust manifolds

    If I were in your situation I would replace the manifold with another like unit.

    With stock cam, intake, etc the mid '90's engine had low HP & torque - - - IMHO - - the best fix is to change the Final drive gears going down at least one gear ratio - - - if you have 3.36 - - - then 3.55 if you have 3.55 then 3.73, and so on

    If you are getting 7 MPG - - - lower gears will not hurt, may actually improve mileage

    Second gear has a gear ratio of 1.62:1 use the following calculator to figure out what engine rpm is best for your rig
    https://spicerparts.com/calculators/...rpm-calculator


    If you are going to replace the manifolds, I would not go with headers - - - although not cheap - - - Sanderson headers would be the way to go. - - - if the will clear - - - if not - -- slow down - - - keep the engine near the peak torque curve . . . . Most likely the headpipes will need to be made ???
    https://www.summitracing.com/search/...Ascending&ar=1


    My best advice - - install lower Final Drive gears and slow down - - - operate the engine around 80% of peak torque RPM
    Last edited by joyrde; 05-29-2019 at 05:35 PM.

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    VCVC Member kookykrispy's Avatar
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    joyrde makes a really good point about gearing. For a tow rig, you want 3.73 or lower gears. 4.10's are even better. check your gearing



    64' wikivan 230/4 onda tree/2.56 posi
    '64 Red Baron no engine/trans
    '66 "Lucky" 230/3 onda tree/project

    Quote Originally Posted by Vanner68 View Post
    Remember, they're still printing money, but they aren't making any more earlies!

  8. #8
    VCVC Member lvjjj's Avatar
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    I've got 3.73's. Truck has towing package which includes this lower gearing. Most of the time it does fine in 3rd. When the road has a slight rise it will seem to shift down a couple hundred rpm's, I guess that is the torque converter unlocking? One thing I noticed, that if I kept it at around 3,000 rpm in 3rd it had a lot easier time going up those 2% hills. I think I was going around 64 mph (my speedometer is off 3-4 mph, shows faster than I'm actually going). If I kept it at 60 mph at 2700 rpm or so, it would struggle some when the TC unlocked.

    When heading up the mountain passes at 6% grades, it will shift down to second at about 55 mph and I have to stay on the gas to get up the hill, it seems to like high rpm's. We go up the grade at 3900 to 4200 rpm.
    Last edited by lvjjj; 05-25-2019 at 12:02 PM.
    LARRY OF THE PACIFIC NW
    1965, 292, TH350
    purchased Nov. 22, 1970

  9. #9
    VCVC Member kookykrispy's Avatar
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    3.73's are ok. If your primary use of this suburban is towing, you might consider 4.10's.



    64' wikivan 230/4 onda tree/2.56 posi
    '64 Red Baron no engine/trans
    '66 "Lucky" 230/3 onda tree/project

    Quote Originally Posted by Vanner68 View Post
    Remember, they're still printing money, but they aren't making any more earlies!

  10. #10
    VCVC Member lvjjj's Avatar
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    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.
    LARRY OF THE PACIFIC NW
    1965, 292, TH350
    purchased Nov. 22, 1970

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