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  1. #1
    Join Date
    Dec 2019
    Location
    amersham
    Posts
    126

    Exhaust manifold fitting

    I have just received my exhaust manifolds and exhaust pipes for my AK cobra build. i have a rolling chassis and the body work is mounted above the chassis on supports. i bolted the manifolds onto the engine with the intention of lowering the bodywork onto the chassis. When i look at the setup its clear that the bodywork will foul the manifolds when lowered , speaking to AK they said fit the body work and then the manifolds.
    The question is at what stage do i fit the main pipes and weld the supporting brackets to the chassis, is it before lowering the body or after.

  2. #2
    Join Date
    Aug 2007
    Location
    Bournemouth
    Posts
    383
    I don't have an AK but the arrangement I think is similar to a Dax.
    Lay the body onto the chassis and locate it where it will be permanently fitted. Then fit the headers to the engine. From there you can see where roughly the header exits will need to pass through the body. This is where you need to be careful as you ideally want to keep the aperture in the body as small as possible but large enough to allow for engine 'rock' during driving conditions. Once you have the holes in the body the side pipes will fall naturally along side the body and give you your pipe mounting positions. I suggest you do this with the body on as well so that you can get the distance between the body and side pipes correct. Mark with chalk where the side pipes are fitted over the header pipes.
    Remove body and continue with your side pipes mounting positions to the chassis.
    As I said, this is how I did it with my Dax. The AK I think should be similar but I may stand corrected.

    David.
    Life is driving the Cobra. The rest of the time is just waiting.

    Wessex region caretaker rep.

  3. #3
    Join Date
    Sep 2007
    Location
    Peak District
    Posts
    366
    I found using a dremel invaluable. It's brilliant at opening out holes in Fibreglass in a (semi) controlled manner.

  4. #4
    Join Date
    Dec 2019
    Location
    amersham
    Posts
    126
    Thanks
    Darnpistonbroke
    I have offered up the near side pipe to the exhaust manifold and looked at the position of the mounting brackets, when i am satisfied they are correct i will weld them to the chassis. Afterwards i will then remove the side pipes and lower the body to enable me to cut the correct apertures in the front wing to allow the exhaust manifold pipes to exit.
    One thing that is not so good is the exhaust pipes exiting from the manifolds are just kissing the chassis, when the engine settles on its rubber mounts this could be a problem which gets worse as the whole exhaust system will be resting on the chassis. Ideally the design of the manifolds need to change so that there is more clearance.

  5. #5
    Join Date
    Aug 2007
    Location
    Bournemouth
    Posts
    383
    Depending on how brave your feeling, gently heat up each tube and tease them away from the chassis rail until you are happy. Then start the side pipe fitting process.
    My headers are close to the chassis but don’t touch it.
    If the headers you have are from AK then I’m surprised they touch the chassis?
    Are a different design of engine mount available for your engine to make it stand slightly taller in the chassis? You may only need to find an inch or two.

    Cheers,

    David.
    Life is driving the Cobra. The rest of the time is just waiting.

    Wessex region caretaker rep.

  6. #6
    Join Date
    Dec 2019
    Location
    amersham
    Posts
    126
    Good idea Dave, I think perhaps some packing under the engine mount rubbers could be a solution, the same may be required under the gearbox mount, I don’t fancy any heating of the pipes it’s to chancy.

  7. #7
    I have just gone through first part of this process with my AK & just about to fit body.

    I don't think it would be a good idea to attempt to weld the tabs with the body in place as the body is in contact with the chassis rails you are welding to!

    Temporarily fit the sidepipes before fitting the body, making sure the sidepipes are parrallel & around 8.5cm from the chassis rail by clamping tabs with G clamps to chassis rail to locate the correct tab positions. There is quite a bit of adjustment & trial & error to get the positions correct. Then remove sidepipes from tabs & weld tabs in place. I marked tab positions with masking tape on side of chassis rail then removed tabs to grind some powder coat off bottom of chassis rails for welding. Refit sidepipes to check & then remove again before fitting body.

    Gradually open up holes in body before refitting pipes. Not got to this stage yet, but can imagine it must be very trial & error.

    Mike

  8. #8
    Join Date
    Mar 2020
    Location
    Fleet
    Posts
    19
    This was my biggest fear, however i now understand the process.
    See www.russhowell.com for pictures of my build. I did the exhausts approx 2 months ago.
    Some points:
    Fit\line up pipes with body on, as it likely sits off to one side by 15mm, so you cannot do this just based on the chassis.
    The J pipes MUST be fitted at right angles to allow pipes to slide on, so dont think a few degrees off is good.
    I cut small scallop out of the cats AND end of the exhausts to allow them to snug up better and close up any gaps.
    Exhausts must enter the body low as poss according to AK BUT keep off chassis by around 10mm, else it will always be clanging against it.
    Likely the passenger side manifold will hit passenger by wall. I was advised to cut out a section and reverse it and glass it in. See pics.

    Feel free to message or call me if you want a facetime or more info as this was hardest thing about the build and i could have done with more info
    Cheers
    Russ

  9. #9
    Join Date
    Dec 2019
    Location
    amersham
    Posts
    126
    Russhowell
    I think my setup will be slightly different because i have a carb. engine so no cats, my problem will be getting the pipes off the chassis , i think the most i can get will be about 6 mm to 8 mm clearance by putting some packers underneath the engine mounts any more than 8 mm and the studs protuding from the avm,s wont be long enough for the nuts. another method would be to relieve the chassis locally to clear the pipes but this would be a last resort.
    the exhaust manifolds could be returned for modification to AK but it all takes time.
    The clearance between the bulkhead walls and rear end of manifolds also looks to close for comfort and i fear that some mods may be required there also.
    Speaking to AK i was assured that they would fit but i have my resevations.
    i will have a look at your pictures.
    regards
    Martin

  10. #10
    Join Date
    Aug 2007
    Location
    Bournemouth
    Posts
    383
    Don’t forget if you plan to use packers between the engine mounts and block, if the mount pads on the block are at an angle then packers won’t work. It will throw the geometry out and the bolt holes between the mounts on the engine and the mounts on the chassis won’t line up.

    Regards,

    David.
    Life is driving the Cobra. The rest of the time is just waiting.

    Wessex region caretaker rep.

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