comp ratio Vs boost
Turbo Mini Forums

What CR to run with different boost, opinions please?

12-15psi 9.4:1+!!!	3 Votes - 0%
12-15psi 9.0:1 to 9.4:1	2 Votes - 0%
12-15psi 8.5:1 to 9.0:1	2 Votes - 0%
12-15psi 8.0:1 to 8.5:1	6 Votes - 0%
12-15psi 7.5:1 to 8.0:1	0 Votes - 0%
15-18psi 8.5:1 to 9.0:1	1 Votes - 0%
15-18psi 8.0:1 to 8.5:1	6 Votes - 0%
15-18psi 7.5:1 to 8.0:1	1 Votes - 0%
15-18psi 7.0:1 to 7.5:1	0 Votes - 0%
15-18psi 7.0:1 to Don't bother using a head gasket	2 Votes - 0%

https://www.facebook.com/pages/Fusion-Fabri..._homepage_panel

www.fusionfabs.co.uk



1/4mile in 13.2sec @ 111 terminal on 15psi

Ive been reading through various threads about CR and amount of boost possible to run with these, and there seems to be a variety of opinions?

These figures are based on a road legal mini, but also used on track days. (this seems to be what the majority of people use there mini for)?

Would be fitted with IC and Mapped ignition

Edited by matty on 21st Aug, 2006.

https://www.facebook.com/pages/Fusion-Fabri..._homepage_panel

www.fusionfabs.co.uk



1/4mile in 13.2sec @ 111 terminal on 15psi

i've gone for 12-15 psi on 8.5-9:1 as thats what i plan on going for on my new build.

It depends on more than just boost!

Like what cam and the use the engine will be put to!

Alex

AlexF

Have a look at this for the boost verses cr vs octane

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

Generally dropping the cr lets you run higher boost for a given engine spec.

Increasing the octane can allow you to also run increased boost but with out dropping the cr.

Intercooling is a must as this alone can allow you to run may be 2 psi more without changing either of the above.

It is a must to make sure the bottom end can take the extra torque though and that you use a high boost needle and spring.

Careful optimisation of fuel mixture and ignition timming must also be undertaken.

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

Sorry I forgot to mention intercooler etc, i was trying to keep it as simple as possible (if thats possible).

It goes without saying that you'd have to use an IC and sort the bottom end etc.

After reading that some are taking head chamber sizes to 28cc and using 15/18cc pistons that gives REALLY low CR figures, depending on bore/stroke they average out around 7.1:1 to 7.3:1!!

My engine:

Bore 71.18 (1293)
Stroke 81.23 (AFRacing)
Head 21.40cc
Gasket 3.8cc
ring land 0.5cc (AFRacing)
Deck 5.25cc (AFRacing)
Piston dish 8cc

= CR 9.3:1 ish

After inlarging chambers to 28 cc it gives a CR of 8.1:1
After dishing pistons to 14.5cc it gives a CR of 7.2:1!!

Edited by matty on 21st Aug, 2006.

https://www.facebook.com/pages/Fusion-Fabri..._homepage_panel

www.fusionfabs.co.uk



1/4mile in 13.2sec @ 111 terminal on 15psi

thast not that low....

Cossys run 8:1 as std irrc.

Alex

AlexF

Hi,
I know someone on here has ran 9.4:1 / 10psi with IC and a locked dizzy. So maybe with the mapped ign you could push it to 12.
If you use MS and utilised the boost control, you could map the boost too. This would allow you to map in more boost after 4.5K when the torque starts to drop off......
For road use I'd always go for high compression, less lag, turbo spools quicker, better fuel economy
Cheers,
Gavin :)

Edited by Bat on 22nd Aug, 2006.

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

matty do your calculations on alexs website to get the CCs required in the head to run.........

8.3:1 IMO

leave the pistons alone on this one

let me know

iam in the same boat as i wanted to run 12 - 14 psi boost with the stock turbo pistons. but not have to mill the pistons down. what is the most you can run with stock cc dish. and perhaps the chambers opened up on the head with cossie intercooler...i dont have mapped ignition, and the car would be the occasional fair weather machine / track car.

Richie

Edited by Richie on 23rd Aug, 2006.

______________________________________________________
TRADER HALL OF FAME
BENROSS...MINIMARK..WOLFIE (comic genius).....CARL....MARTPAUL.......AXEL
______________________________________________________
TRADERS OF SHAME
1 user....pm me 4 details

LEGENDS
MikeRace, Mini13

8.3:1 its is then as that seems to be the best comprimise.

Hopefully Benross can srape enough meat out of the head and won't need to touch the pistons.

https://www.facebook.com/pages/Fusion-Fabri..._homepage_panel

www.fusionfabs.co.uk



1/4mile in 13.2sec @ 111 terminal on 15psi

i run 8.3:1

so far good results good brivability

Didn't BL keep the CR deliberately high to keep the bottom end torque?

Yep, & help economy.

WWW.TURBO-MINI.COM