Author Topic: Max Compression Ratio?  (Read 200 times)

Offline NormanMini

Max Compression Ratio?
« on: August 05, 2020, 05:43:26 PM »
Calling all engine builders!
I'm currently building a 1293 for my mini.  The car will be strictly a nice weather, occasionally driven street car.  In the quest for more power, I'm going with a Swiftune SW5 cam.  Now I need to decide on compression ratio.  Is there a consensus on the maximum ratio that will work well with 91 - 93 octane gas?  Thanks for any advice!

Mark Crumpley

Offline 94touring

Re: Max Compression Ratio?
« Reply #1 on: August 05, 2020, 06:04:13 PM »
10:1 all day long on premium.  I wouldn't exceed around 10:5:1 on pump fuel.   

Offline LarryLebel

Re: Max Compression Ratio?
« Reply #2 on: August 06, 2020, 12:47:36 PM »
More power than what? SW5 cam is a mild cam, overated IMHO.

Offline MiniDave

Re: Max Compression Ratio?
« Reply #3 on: August 06, 2020, 01:04:20 PM »
SW5 is a nice street cam, better than stock but still gives a nice smooth idle.
1989 Cooper Racing Green
2009 Clubman S
2004 Audi Allroad 2.7 TT

Offline 94touring

Re: Max Compression Ratio?
« Reply #4 on: August 06, 2020, 01:29:25 PM »
Is a sw5 comparable to a kent 266? 

Offline MiniDave

Re: Max Compression Ratio?
« Reply #5 on: August 06, 2020, 01:57:43 PM »
I think it is.....
1989 Cooper Racing Green
2009 Clubman S
2004 Audi Allroad 2.7 TT

Offline 94touring

Re: Max Compression Ratio?
« Reply #6 on: August 06, 2020, 02:00:50 PM »
Well to the original poster I made just shy of 80 to the wheels on 10:1 compression with a 266, worked head, and 1310cc.  Pulls down low all the way to 6k rpms. 

Offline NormanMini

Re: Max Compression Ratio?
« Reply #7 on: August 06, 2020, 04:20:56 PM »
All right, the votes are in.  !0:1 it is!  Thanks for the input, guys!


Offline MiniDave

Re: Max Compression Ratio?
« Reply #8 on: August 06, 2020, 05:07:54 PM »
The Nural pistons I use are 10.3:1
1989 Cooper Racing Green
2009 Clubman S
2004 Audi Allroad 2.7 TT

Offline 94touring

Re: Max Compression Ratio?
« Reply #9 on: August 06, 2020, 05:59:38 PM »
Any other details on your ride?  I also went with a verto turbo clutch setup and the lightest flywheel available from MED.  Couldn't be happier with it.  Very easy to drive and a few of the guys here can attest to that. 

Offline NormanMini

Re: Max Compression Ratio?
« Reply #10 on: August 08, 2020, 11:19:56 AM »
This will be a pretty conservative build.  I'm running 9.75:1 AE/Nural pistons, an 11 lb flywheel with a balanced rotating assembly, modified cylinder head, the aforementioned SW5 cam, single HiF6 and an LCB/single box exhaust.  Speaking of SU carbs, I'm open to suggestions for a suitable needle for this set up.  While we're at it, does anyone have any experience with an SU-to-Mikuni HSR carb conversion? 

http://www.v-performance.com/products/air_fuel.html.

Offline MPlayle

Re: Max Compression Ratio?
« Reply #11 on: August 08, 2020, 12:58:14 PM »
I did one back in 2012 on a 1961 Mini (Mr. Bitsa-FrankenMini) I had.

I used the 42mm kit from that company.

Getting the throttle and choke cables working right was rather tricky.  It performed well. 

I sold the car a year later.  The new owner had it for 5 years before selling it on.  I almost bought it back.


Offline 94touring

Re: Max Compression Ratio?
« Reply #12 on: August 08, 2020, 08:46:33 PM »
This will be a pretty conservative build.  I'm running 9.75:1 AE/Nural pistons, an 11 lb flywheel with a balanced rotating assembly, modified cylinder head, the aforementioned SW5 cam, single HiF6 and an LCB/single box exhaust.  Speaking of SU carbs, I'm open to suggestions for a suitable needle for this set up.  While we're at it, does anyone have any experience with an SU-to-Mikuni HSR carb conversion? 

http://www.v-performance.com/products/air_fuel.html.


I used a needle recommended from Keith Calverts website for a hif44, and then I had to modify upper stations by filing it down slightly.  I have a wideband installed to see exactly what's going on and I highly recommend one for a fast road build. 

Offline MiniDave

Re: Max Compression Ratio?
« Reply #13 on: August 08, 2020, 09:11:26 PM »
I would start with a BDK or BDL
1989 Cooper Racing Green
2009 Clubman S
2004 Audi Allroad 2.7 TT

Offline 94touring

Re: Max Compression Ratio?
« Reply #14 on: August 08, 2020, 09:19:59 PM »
I started with BDK which was too lean by a lot.  BCE was close for me but needed a smidge more. BDK, BDL, and BCE would be the ones to look at. From his website...
« Last Edit: August 08, 2020, 09:24:32 PM by 94touring »

Offline NormanMini

Re: Max Compression Ratio?
« Reply #15 on: August 08, 2020, 10:37:43 PM »
Great input, all.  Thanks!