I've had a lot of discussions with people about compression ratios when running an SC12.
Some people say 10:1 is fine upto 10psi boost and others say 8:8 is good.
Now I'm torn on what to do.
Obviously being a brand new engine I don't want it to blow in a week due to high compression.
I'm looking at these:
http://www.minispares.com/product/Class ... 0to%20shop

What are people's thoughts?
Obviously going +20 on a 1275 plus GR RE13T cam, head work, probably an Aldon yellow dizzy and extractors.
I've talked to one guy that's driven a mini in SA with pretty much the same setup and same compression and he reckons it goes like crap out of a slingshot.
Really I have high hopes, wanting about 130hp out of it.
So any other little tips would be nice to achieve my goal!
So I'm wondering what I should do?
Other peoples Experience is appreciated.
This is my first engine build I want to do it right.

Cheers, Rhys

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2000 Holden Rodeo TD - The Daily
1998 JDM Mitsubishi Lancer Evolution V -The Weekender
1977 Leyland Mini 998cc, 1293cc in the works - The project
1977 Leyland Mini Van - Sold
1966 Morris Mini Deluxe - Sold
2004 MINI Cooper S Chilli - Sold

mine is about 9.4

those pistons look like cheapies

don't use a distributor, you can't control the timing when boosting, use a megajolt

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did I tell you that I won a trophy?

What brand pistons are you running Simon?

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2000 Holden Rodeo TD - The Daily
1998 JDM Mitsubishi Lancer Evolution V -The Weekender
1977 Leyland Mini 998cc, 1293cc in the works - The project
1977 Leyland Mini Van - Sold
1966 Morris Mini Deluxe - Sold
2004 MINI Cooper S Chilli - Sold

Now I'm no expert but IMO only .020" over isn't a whole lot past standard, in regards to metal left between the cylinders you still have a good size there so it's still pretty safe. The head gasket will still have a good clamping surface size.
On a side note if this is the first bore look at getting the bore centers moved out the 0.015thou (I believe it is), cylinder 1 goes towards the waterpump and cylinder 4 goes towards the clutch, cylinders 2 & 3 stay where they are. This will give you more metal in the cylinder walls between 1-2 and 3-4 and lets the block get bored out the 1380 or bigger in the future.
The choice of pistons is important when considering compression ratio. High compressing can cause pre-ignition (pinging) and can damage/burn out pistons quicker, so a good quality piston is essental. Of corse exact and controlled ignition and fuelling you'll get from an ECU can help.
Have you done any reading up on what the UK boys have been doing in regards to turbos and SC's, (boost is boost, it doesn't matter what unit creates it the engine will still react the same).
What boost pressure do you want to run I think the std SC12 makes around 8psi at 5000rpm (correct me if I'm wrong) so you could probably get away with a comp ratio of around 9:1. The lower the CR the less performance you'll have off boost but SC's build boost quicker than a turbo so you probably won't notice and "lag".
Also look at what CR a std 1275 has, 9:1 is about std so I'd say your safe around there. I wouldn't go to 10:1 on a boosted engine unless your going E10 fuel.
If it was my engine I'd go for a std or below std CR of a NA engine and then only run 5-8psi for a long life engine.

What boost do you want to run
Are you planning on using pump fuel (98 or higher).
Are you going to run an intercooler or water injection

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Respect mine and I'll respect yours.

Thanks for the input kennomini.
It's stock standard 1275LS engine.
That will have the bit of work done and the blower on top.
I only want to run the stock boost of the sc as I'm going to run bens kit on it.
Only plan on using normal 91, 98 pump fuel as the others are few and far between in tassie.
I've been told our fuel quality is crap here so don't wanna risk running it to high.
No inter cooler or water injection. Maybe one day!
There is a mini on gumtree with very much the same setup as I want running 8.8:1 as far as I know and I've had someone drive it and it goes bloody well.

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2000 Holden Rodeo TD - The Daily
1998 JDM Mitsubishi Lancer Evolution V -The Weekender
1977 Leyland Mini 998cc, 1293cc in the works - The project
1977 Leyland Mini Van - Sold
1966 Morris Mini Deluxe - Sold
2004 MINI Cooper S Chilli - Sold

I'm using GR's +0.072" pistons, he machined out the dish for me. I think that's is the smallest size he makes. I'd been using Hypatecs before that (with the dish machined again) and they were OK, but the Hastings rings literally fell to pieces when I took them out, they had no spring in them at all. GR reckons they're known for that - the rings can't handle a lot of heat - I did have too much heat being generated

I had the block offset bored as Kenno said, definitely a good idea as you will be rebuilding it again at some point



what fuel was this car using

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did I tell you that I won a trophy?

I'm not sure on the fuel it's running.

I'll probably just use 98 in it.
I'm really wanting to get this build started so need to work out a CR pretty soon!
Have been offered a Megajolt setup without the megajolt ecu itself. Does anyone know where I can get one?
I'm wanting to build a good quick and reliable engine and once built I won't have the money to be throwing new parts at it all the time. As other projects are waiting!

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2000 Holden Rodeo TD - The Daily
1998 JDM Mitsubishi Lancer Evolution V -The Weekender
1977 Leyland Mini 998cc, 1293cc in the works - The project
1977 Leyland Mini Van - Sold
1966 Morris Mini Deluxe - Sold
2004 MINI Cooper S Chilli - Sold

If you are concerned about `Hastings' rings, GR's `Nippon' rings will fit Hypatec pistons. I put a set in the 1412 stroker.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

HI Simon
I now have in stock .040 and .060 pistons for the 1275 motors which make a really good piston for historic race cars.
Graham Russell

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"It's better to be not informed than ill-informed"

forget it....

- if you want to go fast for a low cost, it won't be reliable
- if you want to go fast and be reliable, it won't be low cost
- if you want to be reliable and low cost, it won't go fast

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did I tell you that I won a trophy?

I wish you had them 18 months ago Graham! can you build yourself a time machine and go back and give me a set?

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did I tell you that I won a trophy?

From the way I read his post he's prepared to do it right the first time and he wants something that is quick and reliable. Once it's built he doesn't want to be throwing new parts at it because his new projects will be taking all his money.

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Respect mine and I'll respect yours.

Looking back at your first post again you say you'll be boring the engine out so I'd say give GR a call and see what he has in stock.
Also you could use Hypatec pistons and maybe use the rings Drmini suggested.

You'd want your CR to be between 8:1 and 9:1 IMO.
To get that it's just as much about your head combustion chamber mods as it is about pistons.
Look at getting the head modified (if it needs it) to larger valves, unleaded guides, ported etc etc. The head is where you'll free up the most power in any mini engine.

Next is the cam choice and this needs to be done before the head mods so the cam, valves and rockers all work together. Again if your going to call GR about his pistons ask him about his cams and what he recommends.

If your going to run a ECU for optimum spark control (it's a good idea) there are many options, the only limitations are your hands on skills with tuning the system. Simon k likes megajolt because he's got the knowledge, experience and ability to tune megajolt but there are systems out there that have different tuning styles and features that may be more suited to you or the engine tuners in your area. If your happy diving straight in the deep end and picking it up as you go, buy the system you've been offered and learn as you go or take the time and select a ECU system that suits you or the people that will set it up for you.

Have you spoken to Ben? ask him about the kit you intend to buy. He made it so hopefully he has some experience and suggestions on engine specs and setups.
Also search through some of the UK mini forums and see what CR's and pistons they use in there forced induction engines.

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Respect mine and I'll respect yours.

My old mega squirt is probably not up to scratch as a full ECU these days but it would be fine as an ignition only system. Cheap!

M

That's exactly what I meant.
Thanks for that kennomini looks like I'll probably give GR a call at some point.
As I'd like to get Pistons, cam and maybe even rockers from him.
The block and head will be done buy one person so it's all done to suit and I'm not bolting things on from all over and just hoping for the best.
I've got the kit already and Ben did give me a little information on it but really only what everyone else has said.
I think I might go see my local engine guru tomorrow and have a chat with him about it.
He's just built the 1310 for the race mini and it's looking good so I reckon he will be the go!
Tas engine recos is the place.

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2000 Holden Rodeo TD - The Daily
1998 JDM Mitsubishi Lancer Evolution V -The Weekender
1977 Leyland Mini 998cc, 1293cc in the works - The project
1977 Leyland Mini Van - Sold
1966 Morris Mini Deluxe - Sold
2004 MINI Cooper S Chilli - Sold