Primaries...what size to go for?

topcatcustom · Post by **topcatcustom** » Tue Dec 23, 2008 9:20 am

How did they come out Pete? Was it hard?!

TC

sidecar · Post by **sidecar** » Tue Dec 23, 2008 1:28 pm

topcatproduction wrote:How did they come out Pete? Was it hard?!

TC

Hi TC,

I can never work out how to post pics on this website so here's a link the the Cob forum where I have posted a couple of pics.

http://www.cobraclub.com/forum/engine-t ... aders.html

I found the whole thing to be a lot of hard work, I had to get the headers round the steering rod and other stuff whilst making sure that they all line up with the existing hole in the body work. I wanted them to be equal length but I gave up on that idea about 10 minutes into the job!

By the time that I'd finished the last pipe I reckon that there must have been about 150 thin rings of steel pipe on my work bench, each ring represents a modification to a piece of pipe that was done with a hacksaw!

I had the 'bright' idea of hand filing the welds, this seemed fine on the first two or three. By the time I had done 30 I was quite pi55ed off!

It will be a month or so before the actual sidepipes are done, I hope that it does free up some BHP. The headers that are fitted at the moment are crap!

Regards,

Pete

topcatcustom · Post by **topcatcustom** » Tue Dec 23, 2008 7:19 pm

Will view the pics when I complete reg on the site Pete! I think I will make up my own as I am getting quite into porting the heads now and it seems daft to choke the engine just because of the headers, plus they may have to be a funny design to fit in the engine bay!

4 litres with 6 or so psi boost equates to a lot more gas than a NA engine of any size I guess!

p.s. how did you get hold of the bends (dont have a mandrel bender) and did you clamp the flanges to the heads and weld everything up bolted in place to stop warping? I have a spare engine and heads for that sort of stuff

sidecar · Post by **sidecar** » Tue Dec 23, 2008 8:07 pm

topcatproduction wrote:Will view the pics when I complete reg on the site Pete! I think I will make up my own as I am getting quite into porting the heads now and it seems daft to choke the engine just because of the headers, plus they may have to be a funny design to fit in the engine bay!

4 litres with 6 or so psi boost equates to a lot more gas than a NA engine of any size I guess!

p.s. how did you get hold of the bends (dont have a mandrel bender) and did you clamp the flanges to the heads and weld everything up bolted in place to stop warping? I have a spare engine and heads for that sort of stuff

Hi TC,

I just bought a load of bends and the flanges from PowerSpeed, they are based down in Ashford, Kent.

The flanges did not distort at all when I welded them up, they weren't even bolted to the heads at the time. I did run a file across the gasket faces but they were basically OK. (Each pipe has its own individual flange).

They are made out of 10mm steel, I am also using long studs rather than bolts as my pet hate is steel bolts running into aluminum threaded holes!

I did not think that you had to register on the cob forum to view the posts, if that is the case I will try and post them on this forum.

The rectangular hole in the flanges were larger than standard, they suit my ported heads. Using a hammer and a lump of metal in my vice I basically hammered the round tube into a rectangle before welding it to the flange. I left a 2-3mm step at the top as an anti-reversion step. I also noted that the exhaust track is not at 90 degrees to the exhaust gasket face so I tried to angle the headers to match the exhaust track. (I whittled a lump of wood and bunged it up the track as a guide!)

I also used a dremel with a tungsten carbide burr it match up the other three sides of the flange to the inside of the pipe. The burr cut the steel like a knife through butter but the thin shavings float about in the air and land on stuff. When you then touch anything you end up with steel splinters! I've got at least 10 in each hand at the moment!

I also mocked up my engine bay and the hole in my bodywork around my scrap engine, this helped quite a lot even though it was yet more work!

I'm certainly no expert but if you need any help please ask!

Let me know about the pics!

Regards,

Pete

topcatcustom · Post by **topcatcustom** » Tue Dec 23, 2008 8:44 pm

Sounds cool thanks Pete, will find out more when I look at the pics but did you have to spend much on the parts? I may end up doing a TVR style set-up where the pipes come forewards, but cross over infront of the engine and exit infront of each front wheel! Might be a bit hot in the engine bay though...

sidecar · Post by **sidecar** » Tue Dec 23, 2008 10:03 pm

I think that the pipes and flanges came to about 250, the camcoating came to another 300!

So all in all, not that cheap!

That's not counting the 10 hacksaw blades and 5 files that I wore out!

If you are worried out the under bonnet temperature the camcoating is very good. My mate has it on his 6.3 SBC and he can touch the headers when the engine is running without burning himself.

topcatcustom · Post by **topcatcustom** » Fri Dec 26, 2008 12:27 pm

Well I think I will buy a load of 1 5/8 or 1 3/4 bends (a few 180's should do I guess which I can chop up and use for the whole lot)- I think I will go mild steel and coat them- stainless would be nice but would want to wrap them anyway so not much point covering up expensive gear!

As its blown and exhaust tuning isnt so much of an issue I may go with 1 3/4 primaries, straight in to 3" stainless straight through mains (1 either side) with decent mufflers in the middle somewhere. Hopefully won't be too loud!

Would flanges with holes the same size as the tin gaskets be ok (I will open up the exhaust ports in the heads to gasket size) or am I better off getting bigger ones? Don't know if reversion is an issue with a blower either?!

sidecar · Post by **sidecar** » Fri Dec 26, 2008 1:29 pm

topcatproduction wrote:Well I think I will buy a load of 1 5/8 or 1 3/4 bends (a few 180's should do I guess which I can chop up and use for the whole lot)- I think I will go mild steel and coat them- stainless would be nice but would want to wrap them anyway so not much point covering up expensive gear!

As its blown and exhaust tuning isnt so much of an issue I may go with 1 3/4 primaries, straight in to 3" stainless straight through mains (1 either side) with decent mufflers in the middle somewhere. Hopefully won't be too loud!

Would flanges with holes the same size as the tin gaskets be ok (I will open up the exhaust ports in the heads to gasket size) or am I better off getting bigger ones? Don't know if reversion is an issue with a blower either?!

Hi TC,

I think that all the bends that I got were 45 or 60 degrees. I also got a couple of metres of straight tube.

Infact the tin gakets are over size for a standard exhaust port, my flanges match up to the tin gaskets very well. Having said that I'm not going to bother with any gaskets, I'll just use some silicon sealant.

The lazy gits at Powerspeed did not drill the mounting holes in my flanges, I used a tin gasket as a template. (I did tell them not to bother drilling the flanges as they seem to take ages to do anything and I did not want anymore delays!) They are a good company to deal with but they do take there time.

HTH,

Pete

Paul B · Post by **Paul B** » Sun Dec 28, 2008 4:08 pm

Wotland wrote:The primary diameter should be based upon what the exhaust port flows.
There is design equations from David Vizard for header and muffler. The equations are based what the exhaust port flows at your maximum exhaust valve lift:

OID = SQRT (Ex_CFM * 1.27/FD)
CDiam = 1.75 * OID

where:

OID = optimal internal diamter (inches)
Ex_CFM = exhaust port flow (CFM) at 28" H20
FD = flow density (around 80 CFM/square inch @ 28" H20)
CDiam = collector diameter (inches)

According to my calculations, for my 6 litre FE Ford I need headers 11 feet diameter.

I never was much good at maths.

Seriously though, I've already had the flanges lazer cut, with 1 3/4" holes in, so I will be using 1 3/4" tubing, making them up piece by piece from a bends kit. Mine will be run into side pipes too.

What I really want is something like this, but it won't exactly be practical, so I'll have some sort of collector on them then into the side pipes.