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AH Spares Fast Flow Manifold....

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A friend dyno'd a MKVI BENTLEY with standard manifolds and then carefully crafted headers and thought they might have made 4bhp difference. Far better to get the head properly sorted IMO.
 
EVV - Very amusing and interesting video. There are also some interesting comments posted below the video trying to explain what is happening. One theory is that the area of the tube hasn't really changed, its just gone from round to oval. There are many comments around fluid dynamics which are beyond my knowledge range. The general conclusion seems to be that overall header design does make a difference. This has been proven many times and after market headers are always an improvement on the restrictive systems that come out of the factory.

i also wonder whether scaling up has any effect. This is a very powerful 500bhp engine. Would damaging the pipes in the same way on a 120 bhp engine have the same result?

DW sell two types of headers, one for SUs and one for Webers. The difference is that the manifolds for Webers are straighter when exiting the head. This is because there is more room to do this with Webers installed. This 'straighter' factor is mentioned in the video as being generally beneficial.
 
…forgot to mention. DW claim that their headers make about 8bhp difference on a standard BJ8. No idea how correct this is. You are correct to say you will get more power from head mods and of course a hotter cam, although switching to headers is a simple upgrade. My car still has the headers for SU carbs even though I now have Webers. The cost of changing for a small power increase just isn't worth the money. I'll wait until they've rusted away!
 
Here is one that I photographed at the recent AH National Rally at Victor Harbor, South Australia. image.jpg
 
Hi Steve,
I recently installed a RAWLES manifold and there is a noticeable difference in performance across the rev range but I think
to get the full effect you need the proper camshaft and that might be a good topic for discussion.
I have a Denis Welch DWR 8 cam (rated 3-5,000 for fast street/rally) in my engine and a set of his headers but the engine seems to run out of steam a little before 5,000 rpm.
With a BJ8 cam and the old intake manifold I was able to pull 6,000 rpm if needed without damage to the engine.
For better performance I'm gonna put the OEM BJ8 cam back in which is the cam the factory suggest for racing applications!
I'm still surprised the engine ever ran properly with the OEM intake manifold.
View attachment 43051
Nothing ventured nothing gained.

Good luck with your project.

Peter
 
I'm guessing you are referring to the most sporting cam the engine with take without machining to block to clear the lobes. This tends to run less well below 2000 and Rev more than the BJ8 cam, it's definitely faster but it can make for a lumpy tickover.

My guess is that provided the valve time is spot on, you need to get the car on a rolling road and make sure the mixture is correct through the range. They do need different needles.
 
Thanks for that input Peter. That is helpful. The attachment didn't seem to go.... could you retry putting that in?

Thanks,
Steve
 
Hi Steve, saw this after my recent posts on fuel manifolds. I like the look of this manifold and it is available.
Am I correct that horizontal float bowls are needed on My HD8,s
I will ring SU tomorrow to see if available if required.
Thanks AL
 
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