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Tubular exhaust manifolds

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blackdog

blackdog

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Anyone know of the do's and don'ts when choosing one of the above for a BJ8. My inclination is to go for a Denis Welch one but does anyone know how their product compares in terms of quality re fitting and improvement in gas flow / power. Or are the ones from AH spares , SC parts Rawles etc any good?

Are there any suggestions from the States?

Does it increase power noticeably, indeed has anyone ever done a before and after dyno?

Mike
 
Jeremy Welch told me that they did a before and after test of the headers on a BJ8 and bhp increased by 6-8.

The BJ8 frame should not need any modification as it already has a cut out on the left front outrigger. Earlier cars need modification in this area.

You will notice a difference in the exhaust sound. Personally I dont think it sounds as good as the original and there is an increase in resonance.
 
Are there any suggestions from the States?

Yep!!-It is not worth the trouble to install them-Keoke :driving:
 
A tubular manifold will probably increase the power. I found with another car (Midget) that the mid range torque felt improved, or maybe it was the better noise, not sure if you'll get the same benefit with a BJ8.
You need to consider if the manifold matches the exhaust ports perfectly, most unlikely, so you should plan to machine the ports to match.
Don't be tempted to go for the maximum diameter, you need to keep the exhaust gas speed up.
It does also depend on if you're doing any other mods to the engine.
With a tubular manifold you get more heat soak in the engine bay so plan to either wrap the manifold or get it ceramic coated.
 
Killjoy! ------------ :laugh:


:lol:-----Keoke

A tubular manifold will probably increase the power. "If" you're doing other supporting mods to the engine.---- :driving:

OH I almost forgot: Thanks AJAX50-- :thumbsup:
 
Thanks everyone, it has been an education. I shall be re reading many times.
Some kind of improved header will most likely be worthwhile , as I have a D Welch air filter, a free flowing side exhaust and a hotter cam, (but p/o didn't know to what spec!)
 
I just read my older post on the link provided by GregW and I see Jeremy Welch told me 10-12 not the 6-8 increase my fading memory thought he said. Although realistically he might have been using just a tiny bit of poetic licence! So lets say 8-10 bhp increase. Still pretty good.

Re-reading those old threads I realise how much Dave is missed.
 
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