Exaust manifold - advice required

[Julian West]

I'm looking to have a new exhaust system fabricated for my GTD and would be grateful for any opinions as to specification.

The engine is an SVO 302, 345bhp & is lowered in the chassis. also I have a roll cage that may obstruct a 'pattern' manifold, hence my manifold will need to be 'bespoke'.

Is stainless steel preferable over mild steel & what are the pros & cons?

I hope to upgrade the engine output at a later date & with this in mind what dia tube would be best ?

I've read through http://www.gt40s.com/forum/tech-eng...ength-formula.html?highlight=exhaust+manifold & there seems little difference in running either 1 5/8" tube or 1 7/8" tube.

Finally jet hot coating in silver looks great but what are the alternatives other than exhaust wrap??

Finally, any reccomendations of companies in SW England that would fabricate the exhaust for me?

I would be grateful for any opinions or ideas!

 

[Julian West]

Bttt....

 

[Simon]

Tony law exhausts, not in the SW, but Leeds, will make a mild steel crossover system from a jig for £1,000 + vat in two weeks.
Simon

 

[Jim Pearson]

Hi Julian,

You have a PM.

Jim

 

[Tye GT40]

Or you can make it by yourself - much cheaper. I ordered a system from Speedwaymotors www.speedwaymotors.com + a couple of bends and put about 5 hours of work to a finished system. Not so fancy as a professional made but it will look OK when painted. Cost in total including silencers was less USD500

Br
Henrik

 

[Malcolm]

You mention primary dia of 1 5/8 to 1 7/8. My car is arguably more BHP than yours some say the same as yours (they know nothing of course!) and I run 1 3/4 pipes which seem to work well. I would suggest 1 5/8 will be restrictive to breathing.

I would also go SS and my local fabricator who I trust to do a good job would charge about £1300 plus vat for the job. That is a complete bespoke exhaust. If you go mild steel, you then have costs of coating etc so do you save overall?

But that is just my opinion.

 

[Paul Thompson 'Hooligan']

I too like the look and 'ring' to a Stainless Steel exhaust, but if you are looking to use on a track, check the noise regs cos stainless systems are generally 2-3 dB louder than their mild steel equivalents - fact.

 

[Ian Anderson]

Paul

You mentioned that an unsealed / leaking manifold would give an incorrect lambda reading.

How so as I would presume the pressure inside the exhaust is higher than ambient and hence any leak would be from inside the pipe to atmosphere.

I think mine has a slight leak and perhaps this is causing the problems with EFi

What is the best stuff in the UK to make a seal?

Thanks
Ian

 

[Jim Cowden]

Ian
They suck as well as blow
When it goes into the negative wave it will draw air in and send that air down the pipe on the positive.
That air changes the lambda reading.
Hopefully the description is close enough.
Jim

 

[Murray Cowley]

Julian,
if you do plan to do your own, try these www.dynoflow.co.uk
There are a couple of people in Cullompton, I have never used them but they should be good for a quote. Double 'S' Exhausts - The Original and Finest Stainless Steel Exhausts Manufacturer in the South West of England, UK. We have been manufacturing quality stainless steel exhaust systems for over 25 years for performance and classic cars. and Longlife Exhausts - Performance exhausts, exhausts, sports performance exhausts, bespoke exhausts, custom exhausts in Plymouth also in Exeter is this lot at Powerflow Exhausts UK Ltd- Stainless steel exhausts systems. Powerflow produces one of the worlds finest ranges of universal fit stainless steel products. Powerflow is the company where you choose the layout, sound and appearance for your system and Hopefully these can give you some idea of a price range. Maybe see you at Exeter?

 

[Ian Anderson]

Jim

Yes many thanks - still amazed that the outside air is drawn in!

Ian

 

[Frank Catt]

In getting air in also adds lot more oxygen into the silencer, most of the early GTD single boxes split wide open because of explosive mixtures of unburnt fuel and added oxygen in the box. Of course, the boy racers do this deliberatley, excess fuel and air looks great in the street on overrun !!

 

[Paul Thompson 'Hooligan']

Jim

Yes many thanks - still amazed that the outside air is drawn in!

Ian

There is a scavenging effect of the exhaust pulses running through the header into the collector. On exhausts where the collector fits 'over' the header end, a loose fit will allow this scavenging to pull in cold air, add a bit of unburnt fuel when lifting off or on overrun and as Frank says many a GTD box has been split open.

On exhausts where the collector ends slip 'into' the headers, this is less likely as the air has to be drawn in, back up the slip joint before it can enter the exhaust flow.. possible, but far less likely. Motec reccommend this style of exhaust design for slip joints...

 

[Julian West]

Thanks for all the info, & Murray thanks for the links. I'll be at Exeter on the Sunday for a mooch. I believe there will be a few exhaust manufacturers at the show to speak to.

Here's what I've learned so far....

I don't fancy making my own, tempting as it may be cost-wise, I haven't really got the time at the moment.

I've spoken to a couple of firms who have made systems for original GT40's & prices vary, right up to £2500 !!

Interestingly one company believe the best performing system would *not* be a crossover type, but a split system with a balance tube. Personally I like the look of the crossover so much I'd be happy to sacrifice a few BHP for looks....

Simpson exhausts sent me this picture of the system they made for Adrian Neweys car (1 3/4"), this is one of the nicest I've seen & also the most expensive!

 

[chris parker]

a very beautiful exhaust i take it the top of the prices you have been quoted it looks fantastic, have you made any choices as who to go with yet?