Scary day tomorrow

[dopdog]

you are correct Rob, when I was at PDQ I asked about the need for using the standard air filter box from the bike because of the ram air and he told me that it made no difference at all under 100 mph and after that maybe 5bhp ish. Basically unless we can pull over 100mph it is not important to us.

[RobMsport]

I like it , very good Adi Maybe we should spend more money and development on radio controlling our cars , then they'd be less weight and no lack of ' bottle '

[adithorp]

I'm liking the sound of this. Mine does a shade under 150flat out. Maybe I can add some real ram air as well as the imaginary 10bhp.... At this rate it'll be faster than a Veyron before the day is out.

(I've been told ram air 'snot significant untill above 150 so who knows where the truth lies)

Feel free to join in with your own theoretica/imaginary figures.

[deecee]

Would I be right in thinking that ram air only works if the speed of the vehicle is faster than the "speed" of the air being gobbled up by the engine, whatever that may be? Also why does no-one talk about bmep (brake mean effective pressure) these days? It was always mentioned when I was a lad (no don't ask!) in relation to tuned engines but I never see mention of it today. I didn't understand it then and I still don't.

Just thought I would confuse the issue

[Darkspeed]

BMPE is mentioned - but its only in certain circles where engineers gather - If you dont know where that is you are not and engineer and have no right there - Its the law...

As for the ram air - interesting comment about sticking head out of window - no relevance. Hold you hand over your mouth and breath in as hard as you can - Now rev your bike engine at 14000 RPM on the dyno at full power WOT and stuff your hand over the throttle inlet - In the first instance you probably made a farty noise through your fingers - The second instance required your one good hand to dial the ambulance. As an engine the bike is developing 190BHP - you develop about none when sitting with your head stuck out of a window, accordingly the engine needs lots and lots of oxygen - you need sod all.
My flow bench would give your hand a nice port shaped blood blister if you were stupid enough to stuff you hand over a port during a test and that is only about 4kW

You breath at a rate of about 6 litres per minute on average and your full lung capacity is about 6 litres volume. Your engine at 1litre capacity and for simplicity 100% VE (Probably more likely to be 120%+) consumes 0.5Litre per revolution so at 14000RPM thats 7000 Litres per minute - thats more air in one second than you would breath in over 20 minutes.

Ram air also requires the pick up to the inlet to be in an aerodynamically high pressure area on the bodywork to be effective and to give those reported increases at 150+ MPH. Bonnets are almost always in a low pressure area - which is why they fly off when not strapped down. In a car the air inlet would probably have to be just above a front splitter - Now there is a drawback as all the dirt and rubbish sucked up at that point would kill the engine dead or thoroughly block the air filter before you even got to 150mph that and the actual length of the inlet tract would create so much resistance to flow that it would probably reduce power.

With the bike the air inlet is in a high pressure area under the nose cowl and its a short straight length to the carb and ports - still sod all effect.



Then again

[dopdog]

Well explained thank you and also where the duct fits on the bike it is just a foam or rubber seal, so again leaks!!!

[adithorp]

Can I just clarify, I don't beleive ram air has a measureable effect, but I think you're missing the point...
Pub bragging figures have no basis in science... and bragging is what Yamaha are doing when they claim there figures.

That said, there's more than enough air going down an inlet at speed to supply an engine without is having to suck. Stick an unrestricted 4" pipe in a 100mph air flow and over 200,000 lts of air will pass through it in 1min. Think thats more than enough to supply 7000lts into the engine.

[dopdog]

I do not think the point was missed as I am sure we all understand what you are saying, I just referred to you comment on "I've got 190+ 10 ram air" and it reminded me of the conversation I had with the rolling road guy about ram air.

I blame David for bring up BMPE

you are correct about the bhp figures as yes they are just bragging for the pub but to get the correct air fuel mixture must be the most important thing. Your engine sounds like it ran like a dream on the rollers so lets hear about how you like it out on the road. Nice day today so can we expect a report later?

PS my GSXR made 360 BHP on the rollers with 250lb torque

[deecee]

No wonder I don't understand BMEP, I was an accountant (retired thank God).

[adithorp]

I do not think the point was missed ...

...PS my GSXR made 360 BHP on the rollers with 250lb torque

Is that with or without ram-air?

Just done some quick calculations and the difference in figures between...
(A) rounded down wheel hp / rounded up fully laden with camping gear + 2xfat gits weight = >250bhp/t
and
(B) rounded up "bragging power" / rounded down stripped of anything not bolted down (and some that is) weight = <500bhp/t


Unfortunatly real world testing will have to wait as I've been ordered onto decorating duty.

If the mapping Wayne did on my old engine is anything to go by it should be drivable enough, though I suspect (given the cams etc) it'll never be as forgiving as the old one.. It was interesting to see heads appear around corners to watch when we got ontopower runs, 14000rpm still rose some interest even in a workshop filled with high powered supercars (several +500bhp cars sat around).