Custom exhaust manifold

[MarcoGTTurbo]

Hi guys,

Just done a bit of a search for some info but cant seem to find what Im looking for.

I am going to be making my own exhaust manifold out of mild steel, but Im after a bit of advice.

What size tube should I be going for? 1 1/4'' or 1 1/2''?

It will be SCH40 steel steam pipe, and will be for my CT9 tubby.

what would people recommend?

Cheers

MArk

 

[5e colin]

wel mark i use 3mm wall steam pipe l think internal size is 40mm i also made my own merge collector you can go ramhorn for ct9 if u use the 1 size down pipe think ist 36/38mm outer size its big enough for what the ct9 can trow at it

 

[Rev]

38.1mm OD that is 1.5"
The stock mani is 32mm ID but this is an anti reversion design where the mani is larger diameter than the exhaust port to create a slight pressure to discourage back flow probably because the stock mani is quite constricted at the outlet, more so than after market manis. It seems the 32mm was probably designed to maximize velocity between the smaller head plate openings and the smaller outlet venturi.
I have 28mm ID for spool but it does get very hot on higher boost.

If the pipes curve too sharply you can reduce the effective pipe ID so a little over sized is less ideal but can prevent a constriction in this case.

 

[Skalabala]

The pipe ID must be the same as the head port size. You can go 1mm bigger.
The collector Mr Colin is showing is what you want

 

[MarcoGTTurbo]

Thanks for the replies guys,

Right went down to my local steel shop to see what they had.

The smallest they had in steam pipe was the below



OD - 42mm

ID - 34mm

Wall thickness - 4mm

Im guessing this is going to be a bit too big?

Cheers

 

[Skalabala]

Yes that is to big. Standard port is around 31mm. If you do a neat gasket match port job then it will work.
The correct pipe is 1 1/4 inch ID

 

[Rev]

I just can't resist putting some numbers in a formula I found.

For best effect, the gas speed in the primary tube at the peak torque RPM should be about 240 feet per second. The formula to calculate pipe size is: Area of Primary Pipe = RPM × Cylinder Size ÷ 88,200

Using the formula for Stock 4efte cylinder and peak torque of 5000 rpm gives 31.7mm ID

as said 1 1/4 inch ID 31.75mm

 

[MarcoGTTurbo]

Thanks guys,

Well, headed out of town today to a place that had the 1 1/4'' ID pipe and hey presto got some





I got 10 long radius 90 degree elbows and 10 short radius 90 degree elbows

Got the exhaust and CT9 flange on order too

Once they are cut it will be time to put it all together

Cheers for the help guys

Oh and Rev - I can always count on you for the numbers

Mark

 

[Rev]

Looking good Marco. Skalabala makes a good point about porting to gasket
I remember the head port as 29.5mm dia so you may want to check that out and consider your options.

 

[Skalabala]

Looking good Marco
Most important is for the ports to align 100%

 

[5e colin]

are you going ram ???? bit short on corners

keep them pics coming off the build up

 

[MarcoGTTurbo]

Yeah Colin going ramhorn, I bought 10 long and 10 short radius 90 degree elbows.





Think I might just go buy another 10 long radius elbows just to be safe and use the short elbows for a cage or summat.

Colin - have you got anymore pics of your mani build? How did you cut the collectors? Im just thinking of standing the tube upright and cutting at 15* with a metal drop saw. Ill weld a piece of angle upright to hold it in place whilst the saw comes down.

Mark

 

[Rev]

Maybe wrong but if ideal min friction is 15 degs or a little less shouldn't each pipe be meeting at 7.5degs max. to minimize turbulance?

 

[5e colin]

hey mark the way i did it is when you have the stock cat and ct9 bolted to the block lay your ct9 flange ontop now you will nead your 4 merge pipes make sure they are smaller then mine !!!! take 2 of them and slot the bottoms in the flange hole and pul them open ontop for the angel you want for the merge collector this will determen the lenght !!!

you wil nead 12 x 90 and 2x 45 mayby 4x45 depending on the angle of the horns !!!

i think its best to face 2 of the horns more angled to the front of the car to give room for runner 2 and 3 if you face them al 4 to the side you wont have enough room for nr2 and 3 !!!!!

if you have your angel then mark with a marker where the 2 meat that wil be cutting angle as you can see in the pic below



i just did 90 degree turns if u get me i marked a TDC at 12 o clock for the lenght to be cut !!! then i turned 90 left and cut then i turned 90 right and cut and ended up with the merge





checked in the flange for fitment



and i ended up with 4 good 1s in the end had to scrap 2 !!!



mind you if you are doing this like i did buy some fags and a six pack taken me 2 freaking hours to do this with my trusted hacksaw ha ha al hand made and armppump 2 days later

 

[glanzatd04l]

hi lad when I made my ram horn manifold I needed 13 elbows and made it out of 1 1/4 sch40 elbows, manifold has been on car a few weeks now and no problems at all and shes putting out 215bhp.

kevin

 

[MarcoGTTurbo]

Thats grand Colin.

Ive got an indexing tool to mark off all four 90 degrees, so I know the right point to turn to get it to merge neatly.

Im just a bit unsure of what angle to cut the pipe cus I thought it was 15 degrees, but Rev said each needs to be cut at 7.5 degrees.


Ill just try both cuz ive got 10 meters of pipe.

Kevin - do you notice any difference when you put on the ramhorn?

Cheers

Mark

 

[Rev]

Marco there will be a sweet spot for that angle I was trying to say maybe go a little less than 15 if it is practical. 15 degs is for gas onto a hard suface thinking about it some more you are combining two gases at 30degs soft to soft they should be ok as all the gas to hard angles are 15 or less.

Hey Kevin that's a great info good to know what the 1.25" can give. What setup and matching info. do you have ,like torque ,Turbo type, boost or exhaust size ?

 

[5e colin]

im sorry i cant give you any spot on measurements i did al by hand and by eye with my trusted hacksaw pillar drill and welder dont have any degree gauges etc etc

just old school build

what i did have was that it wasnt round on the bottom of the merge more like 4 circles being squashed together !!!! thats probly when the angle and serten degree will play a role ??????????

 

[glanzatd04l]

Marco there will be a sweet spot for that angle I was trying to say maybe go a little less than 15 if it is practical. 15 degs is for gas onto a hard suface thinking about it some more you are combining two gases at 30degs soft to soft they should be ok as all the gas to hard angles are 15 or less.

Hey Kevin that's a great info good to know what the 1.25" can give. What setup and matching info. do you have ,like torque ,Turbo type, boost or exhaust size ?

well im running the td04l 13t turbo, fmic, rrfpr, 2 1/2 stainless exhaust, decat, hks dump valve, ram horn manifold, e manage blue, exedy 3 paddle clutch, civic alloy rad, and relocated air filter. running 1 bar 215bhp 198 ft/lb of torque.

Thats grand Colin.

Ive got an indexing tool to mark off all four 90 degrees, so I know the right point to turn to get it to merge neatly.

Im just a bit unsure of what angle to cut the pipe cus I thought it was 15 degrees, but Rev said each needs to be cut at 7.5 degrees.


Ill just try both cuz ive got 10 meters of pipe.

Kevin - do you notice any difference when you put on the ramhorn?

Cheers

Mark

cant really tell cause bought the car standard which had a crack in the standard mani, cracked wast gate, and a hole in the intercooler so was down in power, so I just went down the td04 route and the difference is night and day.

 

[Skalabala]

Come now Marco, don't tease us like this