Cold intake gas = Good?, Hot exhaust gas = Good? 4

[Gary_321]

thread71-29226

I have a BMW M Roadster and I've been gently modifying using labour and minimal cost - my rules.

I have insulated the intake side of the engine with aluminium shielding and loft insulation and gold insulation tape...

I didn't have any testing software before the exhaust modification (see below), but the "before and after" for the intake modifications show a decrease in the intake temperature and an increase in the air mass flow rate.

Until now, I have been using automobile forums to influence my thoughts and ideas. Since I have found this site, I'd like to seek your thoughts about my future ideas...


I have been looking at ceramic spacers to thermally insulate the throttle body from the engine to further cool the intake gas

Is hot exhaust gas a good or a bad thing?
I have also been looking at spending big bucks on having my stainless steel headers ceramic-coated (Zircotec) to insulate the exhaust gas and further cool the engine bay. Automotive forums think this is a good idea, but engineering forums seem to think it is a bad idea. I'm trying to get a definitive view (with evidence) as to why I should, or shouldn't do it.

I welcome your views (both pros and cons) for my latest ideas.



As an aside. To increase flow (I know that you need a certain amount of back pressure) I have gutted the exhaust mufflers...

Original

Modified

 

[kjoiner]

Another and possibly simpler option for insulating the throttle body from heat is to use a phenolic spacer.

Kyle

 

[EdStainless]

If you have improved fuel economy at cruise, and acceleration at WOT then you have improved efficiency.
Unless your exhaust system was highly restrictive I doubt that it had any impact on performance. If you go to turbo or supercharged and greatly increase air flows then it becomes critical.
I believe that the guys at Engine Masters (YouTube) have done a couple of these where they swap headers and pipes. They even hammered on a set of headers and at normal HP they measured no impact.

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P.E. Metallurgy, Plymouth Tube

 

[Gary_321]

Another and possibly simpler option for insulating the throttle body from heat is to use a phenolic spacer.

Thanks for the steer. I'll phone Tufnol in the morning and see what they say.

[edit] I've just ordered a small 6mm sheet of Tufnol Carp (190mm x 190mm). It has a 130°C continuous use rating, which should be enough. There is other stuff on the web that is only 90°C continuous rated. It will probably be too small to do the job, but it was an off-cut that was being sold off cheap.

I'll see what it's like to machine. It looks like it will be very messy.

 

[Gary_321]

If you have improved fuel economy at cruise, and acceleration at WOT then you have improved efficiency.
Unless your exhaust system was highly restrictive I doubt that it had any impact on performance. If you go to turbo or supercharged and greatly increase air flows then it becomes critical.
I believe that the guys at Engine Masters (YouTube) have done a couple of these where they swap headers and pipes. They even hammered on a set of headers and at normal HP they measured no impact.

I think you are right about the exhaust. It's about as good as it will get. The only improvement would be to remove the catalytic convertor, or to tune the tailpipe length. I don't want to remove the cat as I want to stay legal. Tuning the length is impractical as there is no under-car space to get the pipe to the side of the car, and it's too dangerous to allow the pipe to terminate under the car.

I am intending to gain access to the back of the inlet and exhaust valves so I can measure ACTUAL CAM POSITION v. CRANK POSITION. I'm hoping to use those measurements to determine the optimum RPM setting for the exhaust. I'll then have a go at selecting an inlet ram tube for that RPM - I will probably start a new thread about flow, rather than temperature, when the time comes.

 

[GregLocock]

Tailpipe length has virtually zero impact on volumetric efficiency. The only bit of the exhaust worth tuning for length is the headers.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[Gary_321]

I've done some maths using the equations that I have and the results are puzzling.


Primary Cross-Sectional Area (sq in) = ( Cylinder Volume (cu in) * RPM ) / 88200 [Equation 1] [ISBN 978-1-61325-207-9 p.223]

My headers have a 35mm bore, so the cross-sectional area is 1.49sq in.
The engine is a six-cylinder 3201cc, so each cylinder is 32.6cu in.

From [Equation 1], tuned engine speed is 4034rpm. This seems reasonable.



Header Length (in) = ( ( 850 * ( 360 - EVO° ) ) / RPM ) - 3 [Equation 2] [ISBN 978-1-61325-207-9 p.219]

My header lengths are roughly 500mm (20") and Exhaust Valve Opening (EVO) is 87° BBDC.

From [Equation 2], tuned engine speed is 13900rpm - am I doing something wrong?


Should I start a new thread to discuss this?

 

[EdStainless]

Is your EVO 87deg of engine rotation? that makes it 156deg of cam rotation.
In which case I get 7500rpm, which sounds lot like max rpm limit.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

 

[Gary_321]

Is your EVO 87deg of engine rotation? that makes it 156deg of cam rotation.
In which case I get 7500rpm, which sounds lot like max rpm limit.

This is the approximate timing cycle of the engine when the inlet and exhaust cams are fully advanced.
It is a 720° cycle, with TDC(Compression) at the 6 o'clock position. 0°/720° is TDC when the piston is at the beginning of the induction stroke.

The exhaust opens at approximately 453° of crank rotation, is fully open at 597° and closes at 015°. 453° is 87° BBDC.


There are lots of versions (and interpretations) of the formula on the internet. Last night, I found the source of the equation here on p.283 of the pdf.

Bell's actual equation is

Header Length (in) = ( ( 850 * ( 180 + EVO° ) ) / RPM ) - 3 [Equation 3]

Resolving [Equation 3]: RPM = ( 850 * ( 180 + EVO° ) ) / ( Header Length (in) + 3 ), gives a tuned engine speed of nearly 10000rpm.


Others have suggested that Bell assumed that ( 180° + EVO ) was the full exhaust valve opening time, but it ignores any time the valve is open ATDC.

Using the full valve opening time, the tuned engine speed is 10,500rpm.


Some have further suggested that the duration should be measured not from valve opening, but from when the valve is open 0.050". It looks like people are making stuff up to fit the dyno results!

I've also read that due to engine wear and tolerances, the valve duration can be shorter than the cam duration by tens of degrees. This could explain the 0.050" fudge factor, perhaps.

 

[CWB1]

Some have further suggested that the duration should be measured not from valve opening, but from when the valve is open 0.050". It looks like people are making stuff up to fit the dyno results!

Duration is often defined as between 0.050". Below that is little flow and often compromises with ramp geometry to improve durability.

JMO but I wouldnt put too much faith in simplified formulas relative to modern engines. For older mechanical engines running pretty much the same ignition and valve timing they sorta worked but with VVA and modern electronic strategy a lot of that goes out the window.

 

[inline6]

ceramic coating is great for reducing heat transfer into the engine bay, a back to back dyno test i saw was about 2 hp on something around 500hp so next to nothing as its just the accuracy of the dyno. at part throttle the extra velocity might resist reversion a smidge better so it might be more responsive.