high CR high boost
Turbo Mini Forums

HOW?!? lol i understand if people want to keep there secrets under wraps, but for those who dont please debate :)

with regards high boost and CR. iv chosen the old school method of low cr and lots of boost, however i'd like to upp the CR, but here is the crux of the problem, regardless of how well you controll fuel and spark (in my mind) if the dynamic CR gets high enough, the charge in teh cylinder will spontaniously ignite no matter what. how do you get around this? whilst retaining reliability? if you have enough controll over cam timign you can alter the dynamic CR, but then you could easily hav ethe same power with less boost and more subtle timing? surely?

i know wrc cars are the classic example of lots of boost and high CR, but i'd put money on none of those engiens keeping there pistons intact if i drove them as a street car for a few months, i jsut cant get my mind around how it would be possible (assumign no fancy fuels, direct injection and fixed cam timing!)

turbo 16v k-series 11.9@118.9 :)

Denis O'Brien.

Hi,
I think it can be done, by working with minimum best advance and timing retard on charge / engine temp. It would take a lot of research, calculation and mapping, an alloy head is apparently a great help.
Cheers,
Gavin :)

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nah i stil dont get it. if you retard under xxx conditions, at some point your going to reach a dynamic CR where the fuel ignites no matter what.

do these engines runn really cool coolant temps!?

turbo 16v k-series 11.9@118.9 :)

Denis O'Brien.

Hi,
Yes you are going to reach that point, but using the "tools" will allow you to get as close as possible, without a melt down.
I missed knock control from my list!
Cheers,
Gavin :)

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octain & efficent intercooler

stock CR with stock pump fuels good intercooler 12 psi and your pushing it

add mapped ignition & you may ewell get 2 points more add octain 20+psi

just been doing some very basic maths.
(well cheating at soem basic maths ..)
http://www.rbracing-rsr.com/compression.htm


vortech S2000 will boost 7psi @11:1 CR

effective CR becomes:16.39:1

My mini at the highest boost i have ran without det/knocking is 20psi@7:1CR

effective CR becomes:16.52:1

std A+ 9.4:1@10psi

effective CR becomes:15.79:1

now this is a pretty big generalisation as the honda has very lairy cams up top so its actual dynamic CR should be a good deal lower up top, but numbers are looking similar ish. all on regular pump fuel. anyone kno wof any examples of higher effective CR on normal fuel?

turbo 16v k-series 11.9@118.9 :)

Denis O'Brien.

Ive been having this same arument wit me dad today.
Is it more efficient to have a mid to high CR wit low boost? Or Low Cr and more boost than all 3 fast and furiouses?

They should in theory replace same amunt of pressure, shouldnt they?

Back once again like a renegade master

10.5:1 LS1 engine will easily run 10psi...more if you want to tread dangerously.

But thats mostly down to a poor piston design.

My last LS1 used 9.1:1 and I was running about 19psi at the top end ( less in mid-range due to blower design )

Current one is slightly lower at 8.7:1, but that was just to make it extra safe, again using about 19psi at 7000rpm.
Combustion chamber shape isnt hugely different to a Mini...just slightly bigger lol.


With proper intercooling, ignition control etc etc etc....its possible to run high CR's.

But every engine design is different. Some are more tolerant than others.

I would say, always use the highest CR you can and making the power you want...but going low does add an element of safety...which cant be ignored.

9.85 @ 145mph
202mph standing mile
speed didn't kill me, but taxation probably will

WRC cars use quite high (and probably very special/well developed) fuel.

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

Hi,
Reading another post on this subject, John talks about good electronic boost control.
This I imagine is going to be a way of controlling those cylinder pressures as you can alter the boost to match the cams varying trappping effiency.
Also as Stevie says some combustion chamber are better than others, I believe the BMW head has a very good design in this respect.
Minimadj ... Higher CR will always be more efficent, it's whether you can get enough boost in for the power you want.
Cheers,
Gavin :)

Edited by Bat on 18th May, 2007.

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Ultimately the limit is the temperature in the cylinder at the point of ignition. I believe this is about 300 deg. C.

Everthing you can do to lower the inlet temperature will allow higher boost and CR.

The dynamic compression adds the greatest temperature rise. The temperature ratio is equal to the pressure ratio to the power of 1.4.

So you need to get the air temperature at the inlet valve as low as possible. This is why rich mixtures help. The fuel helps cool the charge.

You then need a very good intercooler with lots of outside air flow, which is difficult in a mini.

Also, junk those old T2/T3 turbos and go for a more efficient GT17 or GT20. The higher the efficiency of the turbo, the less heat added to the air flow.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

9.85 @ 145mph
202mph standing mile
speed didn't kill me, but taxation probably will

i have run 12 psi regulary with 9.4 cr intercooled and fixed advance at 27 deg which retards to 25. 9.8 10 psi max all on a 1380.

i got 140 on 10 at 9.8 amd 145 on 12 on 9.4 so take your pick.

on 9.4 14 psi seem to det at 4k for a micro second using det cans.

always looking for them bigger bunches of bannanas

Here ya go

http://cgi.ebay.co.uk/1960s-Speedwell-Allo...1QQcmdZViewItem

1/4 Mile 14.3secs 96Mph Terminal 10psi of boost.


Fibreglass Parts? - http://www.tdkracing.co.uk/
Split Rims? - http://www.force-racing.co.uk/

27@9.8c/r 12psi,
which c/r would you approximate for 31° max advance
fab

bloody low mate on full boost. mine was 27 deg 9.8 cr on 10 psi normall running and 12 psi on 9.4cr.

always looking for them bigger bunches of bannanas

if it helps fab ,back in '98 i was running 9.3 to 1 at 4 psi at 32 degrees for best power ,this was 114 bhp @6100 on that boost and timing .

Medusa + injection = too much torque for the dyno ..https://youtu.be/qg5o0_tJxYM

Thanks Robert,
ha

?
...
have you tried to up the boost on that timing ?
it's not a mistake that you found best power with it, it's no more no less (30/31° full ad) what's required on any bb a series, turbo or not, at this timing exhaust/engine is cooler and power can be 10 hp more.
I'm still on the idea to build an high c/r light boost everyday on 95 oct fuell, then swich on high boost on the same cr with e85, already sourced polyethylen fuell lines, and will coat carbs.regardind me it will also be money wise as I will not have to sale 11cc 73.5 to buy 18cc ones.
e85 seem to be the future in fuelling here with easy gas station sourcing, It's so long to build that I wouldn't like to to convert it after.
fab

Interesting thread.

We need graphs!

I reckon that doing everything as much as possible and then running 95 octane fuel is the way to go. Blank off some of your radiator and get it set up on the RR using 0.75ml methyl aniline and 3ml of TEL. Get it a nano amount short of detonating and then unblank the bit of the rad and run 1:4 MA:TEL for safety.

Not sure what octane the above amounts to but it's as high as you can get without using special blend fuel or avgas.

The "red stuff" lead replacement makes a right "muesli" style mess in your chambers. Eventually it glows and detonates. Not good.

The Haynes book on blowers (F860) by humphries (I reckon it's a bible) gives a bleak picture for boost/octane/CR's.

Fuelling it properly is the way to go.

I wonder if anyone has tried rigging 2 injectors (nitrous style) one with more fuel, one with hydrogen peroxide. :)

Bugger off, I'm getting there.

Medusa + injection = too much torque for the dyno ..https://youtu.be/qg5o0_tJxYM

9.85 @ 145mph
202mph standing mile
speed didn't kill me, but taxation probably will

Hi,
It's an engine for hair dressers Stevie
Cheers,
Gavin :)

VEMs Authorised Installer / Re-seller. K head kits now available!

WB/EGT gauges. Click here for customers write-up

Visit www.doyouneedabrain.co.uk

My Mini build diary

Hydrogen Peroxide- H2O2 a good oxidising agent.

I've been thinking that using air as the oxidising agent isn't as good as it could be for out and out race engines. In WW2, they ran rockets on hydrazine (N2H2) and H2O2 and you mix the 2 liquids and BOOM! You wouldn't need any intake or inlet valve gear at all. Bearing in mind the stuff is liquid, you could run 2 tanks of approximately equal volume so consumption would be similar.

I was also reading about this stuff called n-propyl-nitrate which is a mono-propellant, it has the oxygen bound up in the molecule for the fuely bit to burn. If you injected that, you would get a nitrous oxide style boost. However any backfiring could get interesting.

It's merely food for thought but I'm surprised that more people dont do it as people spend a fortune getting mega welly out of their drag cars. Besides, if you were actually able to rig up a dual injection system for H2O2 and N2H2 you basically get nitrogen and water in the zorst... no plant food gas! That would probably make the news as an eco car..... as they always forget the bit about where the fuel actually comes from.

The stuff is quite cheap IIRC but quite nasty, I imagine you would need some fancy fuel lines etc.... :)

Bugger off, I'm getting there.

hrdrazine is well toxic rocket fuel.

in the fire service you need gas tight tight suits when that stuff is involved.

f16's use it as a apu fuel as well.

best bet is liquid oxygen you wouldnt even need spark plugs lol.

always looking for them bigger bunches of bannanas