MPG optimised header ideas

[Madact]

Originally Posted by freethink

I have a cheap ebay header on my DX, and i gained power all through the rpm range. The best part is the increase in low-end power due to the longer primary tubes. I can now drive at two to three hundred rpms lower without bogging the engine. Lower RPMs should theoretically equate to better MPG.

Nice - cheaper the better, I've heard, as if you go cheap *enough* they start using realistically sized pipes instead of shiny oversized ones (that choke the engine by reducing gas velocity) "for the JDMs" I'd love to know the diameter of your primaries - got a caliper handy?

Also, if the article on the new Mazda (earlier this thread) is reliable, you may also be able to safely increase your compression ratio (and hence efficiency) a bit, using the same grade fuel - might be worth considering a thinner head gasket if the head ever needs to come off.

Originally Posted by freethink

I would stay away from "ram horn" headers, as they're meant to increase peak HP at the expense of low-end torque. Formula One engineers get away with using these because they keep the engines revved up, thus having no need for low-end power.

The rams-horns I've seen do seem to be designed for that, but AFAICT that's not a feature of the rams-horn itself. I think there's two different reasons rams-horn headers get used (in racing or other contexts):
1) To allow the pipe length required for a tuned exhaust where 'total tailpipe' length is limited.
2) To allow feeding a turbo with a minimum of sharp bends, and also have enough primary length to reduce 'cross talk' between the cylinders.

On a side note, conventional wisdom seems to be "there's no scavenging effect in a turbo engine" - I happen to disagree there's more back pressure from the turbo, but there's also more intake pressure from the compressor, so the in-cylinder dynamics will be pretty similar to NA apart from somewhat elevated pressure / density / viscosity, and turbo or no turbo, if you can get a bit more air-fuel mix into the cylinder, it should make more power. A rams horn eliminates sharp bends for a fairly decent down-pipe distance, and you should get at least some of the inertial part of the scavenging happening, if not the tuned-length effects you get on an NA engine...

Originally Posted by freethink

If you're looking to dump tons of money and time into building a prototype MPG header, look into hydroformed head pipes. Gas flow dynamics are similar to Aerodynamics inside of bent pipes. Round is not always the best shape for gas flowing through a bend. Check out Micron motorcycle exhaust systems. They're engineers had a very good understanding of gas flow dynamics.

I doubt I could get hydroforming consistent enough myself to be better than mandrel bends, and I'm not looking to drop enough money to pay someone who can . I might give sand bending a try (the price is right , and I like learning new things), but I think fabrication will be a welder, grinder, hammer and dremel job...

Those Micron 'serpent' systems look amazing though. The 'flat' bends in particular are interesting, as they should decrease or eliminate Dean vortices... however, that degree of flattening without doing bad things to the cross sectional area profile would take a lot of precision.

I've been thinking about a slightly D shaped cross section - with the 'inner' side flattened slightly - but again, reliable fabrication is an issue. Sand bending around a rigid form might do this slightly, which would be one of those fortuitous side effects, but I'm not sure that amount would make a difference. Perhaps... using an oversized pipe and bending without sand? Accurate preservation of cross sectional area would still be an issue. The most reliable way to do this cheaply I can think of would be to take a 'good' sand bend and use rollers to flatten it to spec - the rolling stage would also make the bend tighter, but you could compensate for that fairly easily by doing a few tests first.

All that said though, for my purposes I think I'll just go for nice consistent constant cross-section bends. I doubt the gains would be all that huge, and I'm better off keeping it simple

[freethink]

Originally Posted by Madact

Nice - cheaper the better, I've heard, as if you go cheap *enough* they start using realistically sized pipes instead of shiny oversized ones (that choke the engine by reducing gas velocity) "for the JDMs" I'd love to know the diameter of your primaries - got a caliper handy?

Also, if the article on the new Mazda (earlier this thread) is reliable, you may also be able to safely increase your compression ratio (and hence efficiency) a bit, using the same grade fuel - might be worth considering a thinner head gasket if the head ever needs to come off.



The rams-horns I've seen do seem to be designed for that, but AFAICT that's not a feature of the rams-horn itself. I think there's two different reasons rams-horn headers get used (in racing or other contexts):
1) To allow the pipe length required for a tuned exhaust where 'total tailpipe' length is limited.
2) To allow feeding a turbo with a minimum of sharp bends, and also have enough primary length to reduce 'cross talk' between the cylinders.

On a side note, conventional wisdom seems to be "there's no scavenging effect in a turbo engine" - I happen to disagree there's more back pressure from the turbo, but there's also more intake pressure from the compressor, so the in-cylinder dynamics will be pretty similar to NA apart from somewhat elevated pressure / density / viscosity, and turbo or no turbo, if you can get a bit more air-fuel mix into the cylinder, it should make more power. A rams horn eliminates sharp bends for a fairly decent down-pipe distance, and you should get at least some of the inertial part of the scavenging happening, if not the tuned-length effects you get on an NA engine...



I doubt I could get hydroforming consistent enough myself to be better than mandrel bends, and I'm not looking to drop enough money to pay someone who can . I might give sand bending a try (the price is right , and I like learning new things), but I think fabrication will be a welder, grinder, hammer and dremel job...

Those Micron 'serpent' systems look amazing though. The 'flat' bends in particular are interesting, as they should decrease or eliminate Dean vortices... however, that degree of flattening without doing bad things to the cross sectional area profile would take a lot of precision.

I've been thinking about a slightly D shaped cross section - with the 'inner' side flattened slightly - but again, reliable fabrication is an issue. Sand bending around a rigid form might do this slightly, which would be one of those fortuitous side effects, but I'm not sure that amount would make a difference. Perhaps... using an oversized pipe and bending without sand? Accurate preservation of cross sectional area would still be an issue. The most reliable way to do this cheaply I can think of would be to take a 'good' sand bend and use rollers to flatten it to spec - the rolling stage would also make the bend tighter, but you could compensate for that fairly easily by doing a few tests first.

All that said though, for my purposes I think I'll just go for nice consistent constant cross-section bends. I doubt the gains would be all that huge, and I'm better off keeping it simple

My ebay header primaries measure 1.66" or 42mm.

Let me clarify the purpose of 'ram horn' headers
1) to make the primaries equal in length. Again, this gives best peak power, but reduced low-end is a consequence of this.
2) to keep a turbocharger oriented in the OEM position, so OEM oil/coolant lines can be retained, along with use of commonly available exhaust down pipes.
3) underhood space limitations.

I would say 'ram horn' headers do not have minimal bends. They have a lot more bends actually and obviously. Perhaps the bends are smoother, but none the less, there are more bends. I would also say the only exhaust system component used to tune resonance is the header. The rest of the components have different purposes. The cat and muffler are for emissions, and the rest is just conduit for transporting exhaust gases to the rear of the vehicle.

I would happen agree with you about there being scavenging in a turbocharged vehicle. Just because there is more positive pressure between the piston and turbine blades doesn't mean there is no scavenging effect. The exhaust pulses are still moving at very high speeds. Remember turbochargers spin at speeds of up to 150,000 rpms. Exhaust gas still has mass and therefore enertia.

As far as D-shaped primaries go, i wouldn't go crazy, but perhaps i might try making the inside radius form slightly wider and slightly oval shaped. Perhaps using a little less sand might do the trick. I wouldn't use oversized pipe though; gas is compressible, so it's not necessary to keep cross-sectional area the same throughout the entire primary. Enertia will compress the gas to the outside of the bend allowing it to squeeze through the smaller area of the bend.

Getting a little off topic here, if you're interested in going further down the rabbits hole, take a look at a technique called Intake Velocity Porting. It involves making your intake ports smaller and more aerodynamic, giving you better volumetric efficiency throughout the whole rpm range. It was developed by a guy named "Motoman" for use on motorcycles, but the same principals apply to any 4 stroke engine.

Hope this helps. Looking forward to seeing a finished product.

[Madact]

Originally Posted by freethink

My ebay header primaries measure 1.66" or 42mm.
Getting a little off topic here, if you're interested in going further down the rabbits hole, take a look at a technique called Intake Velocity Porting. It involves making your intake ports smaller and more aerodynamic, giving you better volumetric efficiency throughout the whole rpm range. It was developed by a guy named "Motoman" for use on motorcycles, but the same principals apply to any 4 stroke engine.

Ha! That's a little different to the more common case where someone goes crazy on their ports with a die grinder, eliciting lots of 'oohs' and 'aahs' (and zero before and after power or torque measurements) on the ricer forums

[freebeard]

Can you put a date to "Motoman"? Because until I hear that, I'd go with Jocko Johnson, Zora Arcos-Duntov, and that guy I can't remember that did head porting in California in the 50s.

HotVWs Mileage Motor had larger exhaust valves and fuel injection intake valves (because they're smaller) for that reason.

Then there is Extrude Honing where you let hydraulics do all the thinking/guessing for you.

[Madact]

Interesting stuff - a "how to" guide is given here: Homework
And some dyno results from someone who did it on a YZ250F with good effect: I tried Motoman's porting... - Page 3 - General Dirt Bike Discussion - ThumperTalk
Another similar concept: CVN High Performance Cylinder Head Design

Tend to agree with some of the statements about "If you can get past how annoying he is (and his website is), there is actually a hint of good information there." and from somewhere else "thinks he invented critical thinking"... but there are lots of positive reports - mostly anecdotal and I don't doubt there's selection bias in there, but a few have data (dyno comparisons) to back them up.

Not that I'm planning to modify my ports (especially on the exhaust side, where even JB weld isn't going to be that great ) but it makes sense that
1) There's an optimal port size for any particular application, and the ports on a given engine may well be either too big or too small for what you want to do with it.
2) Car manufacturers would, in most cases, go for 'safe' rather than 'optimal'.
3) For castings like the P2J head, which is used for the power-VTEC motors and they probably expect will be modded with cams, turbos etc., 'safe' probably means 'big' rather than 'small'...
Another piece of corroboration is that VTEC-e 12-valve mode is not just about swirl, but also maintaining intake velocity. So if you can increase intake velocity without (a) losing your fuel on the bends or (b) overly restricting airflow at WOT (and WOT do we care about that ?), then it may well be worth it.

The HotVWs Mileage Motor was a 2 valve per cylinder design, so I'm not hugely surprised they used larger valves - 4 valve per cylinder engines like the honda D series have a lot more area, in fact if you tried to fit the equivalent valve area with a 2 valve design, you'd have a 42.4mm intake and a 36.8mm exhaust valve. Good luck fitting those in a 75mm bore without them hitting eachother on overlap (you'd need a pretty steep roof on your combustion chamber to start with)

I've seen some stuff on extrude honing - makes me wonder if you could do it with a standard pug mill (I suspect you could)...

[freethink]

Originally Posted by freebeard

Can you put a date to "Motoman"? Because until I hear that, I'd go with Jocko Johnson, Zora Arcos-Duntov, and that guy I can't remember that did head porting in California in the 50s.

HotVWs Mileage Motor had larger exhaust valves and fuel injection intake valves (because they're smaller) for that reason.

Then there is Extrude Honing where you let hydraulics do all the thinking/guessing for you.

Motoman started his website (mototuneusa D0T c0m) in 1999 and it appears it was last updated in 2011. I'd post links, but i'm a noob, so i'm prevented from doing so. PM me for links.

Extrude Honing works great for removing casting imperfections especially in places where a porting tool will not reach.

[freebeard]

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That dates it to no earlier than 2001, and it still uses tables. But I learned how to open whole tube of JB Weld and how to center a sanding mandrel.

I see this as a down-sized D-port head. Granted, there are advantages to 4-valve heads.

Homebrew extrude honing shouldn't be rocket science, just some machine tooling of a jig and correct selection of the media. I think it was two ingredients, like aluminum oxide particles in a matrix.

[rh0]

I just binge read the whole thread! Isn't header design fascinating

Try Engine Analyzer Pro for an engine simulator that includes the exhaust. The demo is fully functional (and doesn't expire if you never shut the program down) and will run many designs in one go. It also calculates bsfc and shows pressures etc. I've either wasted many hours running sims or learned a great deal playing with this program. You can also specify the intake flow to simulate light load cruise conditions. And I believe it comes with a b series file which should help you approximate potential unknowns like bearing sizes.
(I have no financial interest in the company)

Also of interest are these structures inside the 4-2 merges of the OEM header for the 20v Toyota 4age. I've only found a few pictures of them and read even less explanation/speculation about their function.

It's been awhile since I've read motoman so I can't remember if he mentions the old 16v 4ages went from a large intake port design to a smaller one and improved performance.

[Madact]

Originally Posted by rh0

Also of interest are these structures inside the 4-2 merges of the OEM header for the 20v Toyota 4age. I've only found a few pictures of them and read even less explanation/speculation about their function.

Fascinating indeed! There's an old physics experiment involving an incense stick, a vacuum cleaner that can be set to 'blow', and a sheet of perf-board, illustrating Bernoulli's principle - the air flowing on one side creates a low pressure zone and sucks the smoke through from the other side. I'd hazard a guess that's what they're going for here, it may well provide effective scavenging at lower RPMs than a conventional merge.

It may also provide a very small muffling & detuning effect as the initial pressure increase of the exhaust pulse would partially escape sideways through the holes, before the airflow got up to speed and started sucking.

As for the slot, at first I wondered whether it might be to stop some sort of resonance, like the plate itself vibrating at very high frequency then I realised that without any external surfaces, it would get a lot hotter than the walls of the tube - I'd say it's an expansion joint to stop (a) the plate buckling and then pulling away from the walls as it contracts or (b) the plate pushing the tube apart.

[Nigel_S]

I would think it is almost certainly for noise reduction, the OEMs don't increase costs with things like that unless they are forced to do so by regulations!

Although I wonder if it may remove the boundary layer thus changing the main gas flow closer across the other pipe for better venturi effect?

I'm with you on the expansion slot, you sometimes get the same thing on the manifold flange between the primaries if the head and manifold have different expansion properties - it stops everything disintegrating when it gets really hot.