Max Compression Ratio?

Started by NormanMini, August 05, 2020, 03:43:26 PM

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NormanMini

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

94touring

10:1 all day long on premium.  I wouldn't exceed around 10:5:1 on pump fuel.   

LarryLebel

More power than what? SW5 cam is a mild cam, overated IMHO.

MiniDave

SW5 is a nice street cam, better than stock but still gives a nice smooth idle.
Complete failure at retirement

1989 Cooper Racing Green
2009 Clubman S
2014 Audi Allroad

94touring

Is a sw5 comparable to a kent 266? 

MiniDave

Complete failure at retirement

1989 Cooper Racing Green
2009 Clubman S
2014 Audi Allroad

94touring

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. 

NormanMini

All right, the votes are in.  !0:1 it is!  Thanks for the input, guys!


MiniDave

The Nural pistons I use are 10.3:1
Complete failure at retirement

1989 Cooper Racing Green
2009 Clubman S
2014 Audi Allroad

94touring

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. 

NormanMini

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.

MPlayle

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.


94touring

Quote from: NormanMini on August 08, 2020, 09:19:56 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.

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. 

MiniDave

I would start with a BDK or BDL
Complete failure at retirement

1989 Cooper Racing Green
2009 Clubman S
2014 Audi Allroad

94touring

#14
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...

NormanMini