Phil H
Posted a lot
Posts: 1,448
Club RR Member Number: 133
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Making a tubular manifoldPhil H
@philhoward
Club Retro Rides Member 133
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I think I used this www.mezporting.com/exhaust_length.html to get some sort of ballpark for tube sizes and lengths and it gives sensible sounding values. You won't be able to it exact, but it's a good starting point given tube generally only comes in predetermined diameters and lengths might be aspirational.. as JB says, you might as well get it as good as you can especially if you've got the space available. 4:1 for a power-based exhaust, 4:2:1 for torque.
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Last Edit: Oct 9, 2019 11:20:01 GMT by Phil H
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funny reading all the powrr vs torque adage, when an engine builder I know uses 4-2-1 om all his engines and they make more power than most, with a nice fat torque band
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Admittedly so, but if the oe one is so awful, surely anything would be an improvement? If you are going to the trouble of making a new one, do it to the best of your abilities 😊 Agreed. However, the best of my abilities might still not be that great 😂
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I think I used this www.mezporting.com/exhaust_length.html to get some sort of ballpark for tube sizes and lengths and it gives sensible sounding values. You won't be able to it exact, but it's a good starting point given tube generally only comes in predetermined diameters and lengths might be aspirational.. as JB says, you might as well get it as good as you can especially if you've got the space available. 4:1 for a power-based exhaust, 4:2:1 for torque. Thanks, ill have a play with that.
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I did cross my mind that making a manifold is the perfect opportunity to stick a turbo on it. Would mean i could stop my search for flat top pistons too. Ive turbo converted a car before though and although i could do a better job now, i know ill just end up pushing the boost till it pops. Which from what ive read, the slant will. Low boost would probably be ok, but i know what I'm like 😂
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tristanh
Part of things
Routinely bewildered
Posts: 990
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In relation to doing it "properly" , No doubt, but it's bloody difficult to match the internal volumes to the nth degree, I don't think having a couple of inches variance across the tubes will matter hugely in this instance.
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Last Edit: Oct 9, 2019 12:29:18 GMT by tristanh
Whether you believe you can, or you cannot, you're probably right.
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No doubt, but it's bloody difficult to match the internal volumes to the nth degree, I don't think having a couple of inches variance across the tubes will matter hugely in this instance. Ill get them as close as space, awkwardness to make, or available materials determines. Hopefully that will end up being reasonably close. I guess i could water fill each primary to see how close they are? When i get chance ill take some pics and some mearurements, then take off the manifold and downpipe and make a jig so i can make it on the bench. Ive been meaning to put a flexi in the downpipe for years anyway so this is a chance to do that too. It will also stay on the stock exhaust system so I'm obviously not going for all out best possible performance. Just get rid of the main restriction. I have a month or so to contemplate my options as this is all prep for winter jobs when it will be unused for a while.
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Last Edit: Oct 9, 2019 12:34:23 GMT by VW
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Depending on how involved you want the process to be, it might be worth mocking something up with PVC pipe as it's relatively cheap and easy to work with, possibly enough so that you could work up a couple of different options to consider.
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Bit restricted in bends though isnt it? Mocking up isnt a bad idea though, could use thin rod to lay out pathways for the center of the pipework and measure between to check the pipe diameter fits.
If it goes like the 2 stoke exhaust i did though ill just chop stuff into handy looking sections then trim and tack till its where i want it. That was just one pipe though so pretty easy.
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The link above provides this...
A reduction in primary pipe Diameter of 1/8 of an inch will move the torque peak down by 650-800 RPM. Conversely an increase in diameter of the header will raise the engine speed at which max torque occurs,by approx the same RPM,for each 1/8 of increase.
Adding length to the primary pipe will increase low speed and mid-range power, with corresponding reduction in power at max RPM.
Shorter primaries give an increase in high speed power, at the expense of reduction in the midrange. However,there will be little change in peak torque or the engine speed at which it occurs.
Now this sounds important to me due to what I'm trying to achieve. Its a van, so torque is important, but the vans main failing, as ever, is going up hill. This is no problem at say under 40-50mph, it will happily accelerate up hills in 4th from 30mph, but at higher speeds it is. The van is quite quick really, considering, up to 40-50mph and has overdrive so will get up to 70 quite happily and sit there all day. But dual carriageway hills end up in donwshifts and high revs and lower speed. So, maybe id be better off with shorter primaries. This suggests torque wont change but any power increase will be higher up. Sounds more like what I'm after really. I wouldnt want to move the torque range though so 4 2 1 with short ish primaries?
Back to the possibility of modding an mx5 manifold then maybe.
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Last Edit: Oct 9, 2019 13:01:19 GMT by VW
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For no particular reason, this is the original and the space available.
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Tbh you are going to have to spend a fair bit on bends , flanges and pipe. And if your going to do with a mig your going to want to go for thicker stuff which will cost more . And most bands are stainless which is not ideal for your situation . I really thick you would be better off if you could get your mate with a tig to do it and you buy the parts. All you would have to do would be to measure the gaps around where the manifold is then remove it and he can work within that . Trouble is , if you going to buy £ 100 worth of bits , and he has to spend x amount of hours doing it then how much would that cost ? Either that or try to get hold of another manifold from somewhere and adapt it. I wouldn't try cutting and rewelding oem stuff , you just don't know what it's made of and how it will behave .
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Tbh you are going to have to spend a fair bit on bends , flanges and pipe. And if your going to do with a mig your going to want to go for thicker stuff which will cost more . And most bands are stainless which is not ideal for your situation . I really thick you would be better off if you could get your mate with a tig to do it and you buy the parts. All you would have to do would be to measure the gaps around where the manifold is then remove it and he can work within that . Trouble is , if you going to buy £ 100 worth of bits , and he has to spend x amount of hours doing it then how much would that cost ? Either that or try to get hold of another manifold from somewhere and adapt it. I wouldn't try cutting and rewelding oem stuff , you just don't know what it's made of and how it will behave . My mate only has mig, but his welding is superb. His labour wont cost me, unless i ask him to do something super complex. Ill work out what bits id so i can work out costs before i make any decisions.
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Oct 13, 2019 10:32:12 GMT
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I've used www.mezporting.com/exhaust_length.html as well. You will find that the lengths given are longer than expected for stock-ish engines. Here's mine I made for my Standard 10 1600cc side valve. It's about four foot long!
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Last Edit: Oct 13, 2019 10:33:03 GMT by crockpot
Proton Jumbuck-deceased :-( 2005 Kia Sorento the parts hauling heap V8 Humber Hawk 1948 Standard12 pickup SOLD 1953 Pop build (wifey's BIVA build).
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Oct 13, 2019 10:58:34 GMT
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I've used www.mezporting.com/exhaust_length.html as well. You will find that the lengths given are longer than expected for stock-ish engines. Here's mine I made for my Standard 10 1600cc side valve. It's about four foot long! Looks good. Whats the kink for in 1/4 secondary? Just to get the lengths matched?
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Oct 13, 2019 11:01:07 GMT
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Oil filter! The kink is not as pronounced in the flesh.
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Proton Jumbuck-deceased :-( 2005 Kia Sorento the parts hauling heap V8 Humber Hawk 1948 Standard12 pickup SOLD 1953 Pop build (wifey's BIVA build).
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tristanh
Part of things
Routinely bewildered
Posts: 990
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Oct 13, 2019 22:43:05 GMT
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Wow those primaries are so short, and secondaries so long!
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Whether you believe you can, or you cannot, you're probably right.
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If you look at the Mezporting site you will see that " all primaries are 15 inches long" so that's what they are. Secondaries are a function of low max rpm and mild side valve timing (although it has a Newman cam).
Edit. There is 4.5" of port in the block, this makes the actual tube lengths very short!
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Last Edit: Oct 14, 2019 8:28:43 GMT by crockpot: Added info on port length
Proton Jumbuck-deceased :-( 2005 Kia Sorento the parts hauling heap V8 Humber Hawk 1948 Standard12 pickup SOLD 1953 Pop build (wifey's BIVA build).
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If you look at the Mezporting site you will see that " all primaries are 15 inches long" so that's what they are. Secondaries are a function of low max rpm and mild side valve timing (although it has a Newman cam). Edit. There is 4.5" of port in the block, this makes the actual tube lengths very short! I assume the stock manifold was awful, but do you feel the design suggested by mezporting works well?
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