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Registered:
June 2003
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modifiying original exhuast manifold
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Fri, 26 December 2003 22:19
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how can i modify the original exhuast manifold to house a new turbo?
i was thinking just remove the bolts and weld on the appropriate flange, but its cast iron, and it dont weld well? perhaps 4 small nuts and bolts drilled into the apprioate places?
the question i had is, a few people have said that if you just have the turbo hanging off the manfold without the old turbo crossmember support(turbo bolts onto crossmember) it will crack the manifold, how do i get around this?
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Location:
Bundaberg, Qld.
Registered:
May 2002
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Re: modifiying original exhuast manifold
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Fri, 26 December 2003 23:28
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 the 1st turbo manifold i tried was my old cast exhaust manifold. i cut it where i wanted and got the turbo flange i had cut out of 12mm flat bar brazed onto the cast manifold by a metal engineering shop.
whenever attaching something to cast make sure it's brazed with a oxy set-up. there was no way that my flange was going to crack or fall off. (just a bastard i cut it too low and had oil return problems..  )
you will need a support bracket of some sorts. i made one out of some small square bar, flattened both ends. one end bolts to my block, the other to the turbo flange with the turbo.
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Registered:
June 2003
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Location:
Bundaberg, Qld.
Registered:
May 2002
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Re: modifiying original exhuast manifold
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Sat, 27 December 2003 02:01
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no it wont break off with exhaust temps etc.
you can get it off with a grinder, that brazing is strong shite..
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Registered:
June 2003
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Re: modifiying original exhuast manifold
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Sat, 27 December 2003 02:11
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did you ever run one for any period of time? ive just read so many threads where people have brased or welded a flange on and about a week later after multiple heat up and cool downs the turbo has literally FALLEN off (cause only the weld is holding it) causeing quite some damage, obvisoully i will put a couple of mini bolts through it as well as brasing. but im skeptical from what ive read.
thanks for your input feral, much appreciated.
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Location:
Melbourne
Registered:
May 2002
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Re: modifiying original exhuast manifold
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Sat, 27 December 2003 02:24
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Hmmmmm yeah bronze is fine for non-turbo applications/crack repairs, I would not suggest it by itself for a turbo manifold as it would shurely get soft, if the plate was bolted aswell it would be ok seal it up
Also be shure to get the high grade stuff from BOC (white coated stuff from memory, actualy repaired a broken tooth on a nissan g60 patrol gearbox with that stuff and it held!
Allan
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Location:
Canberra
Registered:
May 2002
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Re: modifiying original exhuast manifold
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Sat, 27 December 2003 03:48
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If the quality of the metal in toyota exhaust manifolds is anywhere near that of nissan's, then there's no problem with mig welding a flange to it. Just ensure that you heat the section that you are welding with an oxy first, to ensure good weld penetration, and preferably bolt the manifold to something solid to reduce warpage. It may still require a surface grind on the head flange afterwards.
Cheers
Phil
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Location:
Bundaberg, Qld.
Registered:
May 2002
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Re: modifiying original exhuast manifold
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Sat, 27 December 2003 05:51
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yeah, i ran it brazed for probably 1 month before i made a steam pipe turbo manifold.
if it's welded most times you will find it cracks as when welding the cast doesnt heat up and cool down properly. when it's brazed it's heated up with the oxy and cools down slowly.
do a some google search researching if you want, thats what i did before i decided that brazing was by far the best method of joining steel to cast.
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Location:
Kita-Ku, Sapporo, Japan
Registered:
January 2003
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Re: modifiying original exhuast manifold
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Sat, 27 December 2003 06:57
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the problem with welding and braxing a cast iron manifold, is that there is a large change in composition across the join, which can lead to a weaker structure.
basically, cast iron has a lot of carbon in it, maybe around 4-5%, whereas mild steels are around 0.2%. between these two compositions there are some brittle structures (basically the hypereutectic compostions with respect to pearlite). it IS possible to successfully weld to cast iron, but it helps to have a filler metal with high carbon content, and to have the correct heating, cooling, and possibly heat treatment steps.
i would suggest that you should always support heavy items with stays.... since you have a few kgs haning off a couple of bolts at a reasonable distance from the motor....
Cya, Stewart
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Location:
Perth
Registered:
September 2003
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Re: modifiying original exhuast manifold
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Mon, 29 December 2003 03:52
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biggest problem is sag - custom turbo manfold suffer from this when they haven't been adequately braced if not heat treated.
brazing will work better than mig or arc welding a plate onto the cast manifold because you have to heat both metals up to a dull glow before welding - a mini heat treating. this changes the properties of the metal and lets it 'absorb' the braze better than say a mig or arc rod being arc-ed onto the metal. if the braze and it's joined metals are run over again to a dull glow after welding (without melting the braze) this will be a heat treated manifold and will last much longer than a mig welded manifold. done poorly though, it will prob crack as soon as you grab second gear. this is the reason most people choose a mig or an arc and brace the manifold. for the extra $100 though, i'd heat treat it all.
remember, a cast manifold will have to take the full weight of the turbo on this one weld. you should also make sure the metal you are welding to the manifold is not more than 50% thicker or thinner than the original manifold metal or it WILL crack.
good luck 
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