Maximum Compression Ratio
Turbo Mini Forums

Every week there is a question about compresion ratio.

So I've tried to pull together the collective expertise and experience of the forum on this into a single chart.

The chart shows the maximum compression ratio for a given boost. The three curves relate to the inlet closing point of the chosen cam. For example an SW5 has an inlet closing at 48 Deg ABDC and the MG Metro, 56 Deg ABDC so a bit of interpolation is required.

Less than 20 degree inlet closing angle has little effect on the dynamic compression ratio.

This assumes an efficient intercooler.

And 95 RON Unleaded.

http://www.jaservices.co.uk/photos/Max%20Comp%20Ratio.JPG

Edited by Paul S on 21st Nov, 2006.

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."

Well done that man

Edited by Brocky on 20th Nov, 2006.

BTW - I took my buddy VTEC Pete out for a spin this weekend, and even though I am running her in, he gave it a name, the "Brocket"...cause I'm a brocket maaannn, nah nah nah nah nah nah nah nah nah nah nah....

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Edited to clarify octane.

I'll also try and improve the chart.

If anyone feels that it is not right in any particular area let me have the info and I'll tweek the curves.

Edited by Paul S on 20th Nov, 2006.

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."

Great stuff. I can't comment on the accuracy, but it looks pretty realistic for 95RON assuming all other things are equal.
Any chance you can make it a bit bigger though?

And stick your name - or turbominis - acroos it aswell, or you'll have someone else taking the credit for it!

Could you produce it in 3-D and add in the effect of octane level ?

I think that would look cool as...

Cheers

Brocky

Dito about putting your name on it

BTW - I took my buddy VTEC Pete out for a spin this weekend, and even though I am running her in, he gave it a name, the "Brocket"...cause I'm a brocket maaannn, nah nah nah nah nah nah nah nah nah nah nah....

Build thread - http://www.turbominis.co.uk/forums/index.php?p=vt&tid=7483

Katy Mini Owners Club Thread - http://www.turbominis.co.uk/forums/index.php?p=vt&tid=505552

Let's make sure you embarrass at least one VTEC MINI today !

https://www.facebook.com/groups/17557298589...096464253807802

On 20th of Nov, 2006 at 02:54pm Brocky said:
Could you produce it in 3-D and add in the effect of octane level ?

I think that would look cool as...

Cheers

Brocky

Dito about putting your name on it

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."

In short no...

I think it could be done using the chart in the link below, (with the correction factor as added by DC), and populated columns for say 95, 100, and 105 ron the data could be produced and then plotted in the 3rd dimesion, against cr and boost for each curve.

A bit more work than a first thought...

I don't mean to take anything away from what you have already produced, which is fab btw, but a chart like that would allow someone to simply choose a cam and then fuel and would know what boost they could run.

Providing as you assumption state they use and efficient intercooler. Perhaps there may be away of specifying a minimum intercooler requirement.

http://www.turbominis.co.uk/forums/index.php?p=vt&tid=7872

Keep up the good work

As they say back to work....

Cheers

Brocky

BTW - I took my buddy VTEC Pete out for a spin this weekend, and even though I am running her in, he gave it a name, the "Brocket"...cause I'm a brocket maaannn, nah nah nah nah nah nah nah nah nah nah nah....

Build thread - http://www.turbominis.co.uk/forums/index.php?p=vt&tid=7483

Katy Mini Owners Club Thread - http://www.turbominis.co.uk/forums/index.php?p=vt&tid=505552

Let's make sure you embarrass at least one VTEC MINI today !

https://www.facebook.com/groups/17557298589...096464253807802

As far as intercooler efficiency is concerned, it would be pointless stating a value as no one ever measures it.

It would be best to state a maximum inlet air temperature of say 50 deg C.

With regard octane rating, it may be easier to calculate some adjustment factors, rather than a 3d cuve - I'll work on it.

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."

is it me being thick or does that chart show that on hot days with the same comp ratio you can actually run more boost?!

The degrees is for the cam inlet opening angle ...

Although in reality you would expect to be able to run more boost on colder days as the inlet temperature may be lower. But may be negligable.
Although if you live in Scotland like I do, you do notice a difference on the colder mornings

Edited by Brocky on 20th Nov, 2006.

BTW - I took my buddy VTEC Pete out for a spin this weekend, and even though I am running her in, he gave it a name, the "Brocket"...cause I'm a brocket maaannn, nah nah nah nah nah nah nah nah nah nah nah....

Build thread - http://www.turbominis.co.uk/forums/index.php?p=vt&tid=7483

Katy Mini Owners Club Thread - http://www.turbominis.co.uk/forums/index.php?p=vt&tid=505552

Let's make sure you embarrass at least one VTEC MINI today !

https://www.facebook.com/groups/17557298589...096464253807802

so does anyone know the inlet opening angle for the phase 2 cam then?

also has anyone got a link that'll tell me how to work out my dynamic CR cos i haven't got a clue...

It's actually 62deg for the phase 2.

Edited by Paul S on 20th Nov, 2006.

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."

You should see if nice uncle Axel will plot it on his graph for you !

BTW - I took my buddy VTEC Pete out for a spin this weekend, and even though I am running her in, he gave it a name, the "Brocket"...cause I'm a brocket maaannn, nah nah nah nah nah nah nah nah nah nah nah....

Build thread - http://www.turbominis.co.uk/forums/index.php?p=vt&tid=7483

Katy Mini Owners Club Thread - http://www.turbominis.co.uk/forums/index.php?p=vt&tid=505552

Let's make sure you embarrass at least one VTEC MINI today !

https://www.facebook.com/groups/17557298589...096464253807802

HA HA i was just going to ask for 60 degree's.

Very useful! good work

axel where did the data for this come from? ,also how many data inputs did you have ?
nice idea this
well done
regards
robert.

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

so...........ill need about 5:1 then.....LOL

Great idea, takes alot of the guess work out.
Now, all we need is some handy so and so to post up a list of inlet opening angles for the usual suspects (could we include a std A+ 998 cam please :) )


jo

"Turbo's make torque, and torque makes fun"

"did you know you can toast potato waffles?"

So how does the RON affect it? Obviously all the lines will move up, but by how much. I use 101RON

As an example, I run 8.3:1 and 15psi with an MG cam (I have easy run 18psi with the T3). that graph puts me at my limit, but I'd be interested to know how 'safe' I am.

Edited by wil_h on 21st Nov, 2006.

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

www.twin-turbo.co.uk

Edited by Paul S on 21st Nov, 2006.

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."

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."

Edited by Paul S on 4th Jan, 2007.

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."

I've corrected an error above.

It is the inlet closing angle that I've used, not opening angle.

It's the point at which the cylinder is effectively sealed and compression starts.

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."

Edited by joeybaby83 on 4th Jan, 2007.

"Turbo's make torque, and torque makes fun"

"did you know you can toast potato waffles?"

this is a bit of an old post but very interesting.

the other week i took the head off. with this head i had 8:1 cr and ran 18psi boost with no problems, infact i think it would take more boost.

out of interest i fitted a standard MG metro head and got 8.7:1cr and could only get about 11psi. i ajusted the timing so 11psi gives the same as it did on 18psi, fueling was still good but still all i could get was 11psi before pinking.

i would have thought i could run more boost at this cr, was it the non ported head? was it the change in valve size?

i was planning on a new head and raising the cr and dropping the boost to make a better road car, after trying this i have to say i need more than 11psi!

any ideas?

i've had a similar experience recently too thats confusing me.

my old head had 26.6cc chambers and i was running 8.7:1 and it was taking 17psi with no pinking issues (24 degrees advance on boost) then it went through into the water jacket after having the seats re-cut.

i bought wil_h's old head off him which was pretty similar to the one i had (almost as much porting, same valves) with 27cc chambers (so bringing my CR down a gnats). but now anything over 12psi and it pinks its tits off and i can't stop it.

have knocked the timing back to 21 degrees on boost and it still does it. running 97 super unleaded same as before too.

my old heads off being welded up at the moment so if it turns out ok i'll be sticking it back on and hoping it'll run as well as it did before cos 12psi just aint enough :(

any idea's why it'd do this?