Will my compression ratio be to low
Turbo Mini Forums

Hi I'm building a 1330 supercharged engine I'm trying to learn as I go. I have a cylinder head with 26cc chambers and pistons with 18cc dishes. Will this combination work or will the compression ratio be to low for the supercharger I no I need to lower the compression but is this to much?. Sorry if this Is a dumb question

Thanks

Hi

Get someone else to check the maths also.

I get 332.5 + (26+ 18+3.8+.8+approx3)/C

=7.44

Sounds about right earwax unless the pistons are flush with the block at TDC but still under 8 so you can run massive boost pressure but wouldn't expect the gearbox or diff to last long with the kind of torque a supercharger will put through it. Straightcut drop gears, minispares clubman straight gear set, LSD, 10" wheels and a nappie

So I need some more pistons or a new cylinder head then.

I would have used 10cc pistons, think it will be a bit low, i expect off boost it will be a little sluggish

how about a turbo on high boost?

Hi if you use 10cc pistons the CR rises to approx 8.6 ( need exact measure of dist piston from lip as wolfie says to be sure), that sounds more ball park for a SC unit. although i would still opt for forged quality pistons even though boost wont be in Turbo realms

If i would have all that stuf i would look for a descent gearbox and primary gears and go turbo... (yes i am supercharging a mini but being on here made me go favours for turbo)

you can do anything if you set your mind to it...
i rather blow it up winning than keep it together losing.

finish date set for project 1... march 2018

I did think about going turbo after joining here but I don't fancy cutting into my freshly restored shell.

I will be running 10" mini special split rims.
My parts list so far for the engine is.


Cylinder head is an unleaded 12g940, with 26cc chambers, 33mm inlets (with 30° back cut), 29mm exhausts, bronze guides, 180lb double springs, ported and polished.
The guide bosses have been completely removed & the ports reshaped

Block is centre main strapped with 11stud fitting currently been freshly bored and honed to 1293. Cam is a Kent 266.

Gearbox I haven't got many parts for yet apart from a x pin diff but wanted centre pickup and clubman gear set. I also have my charger

I do have the 1330 18cc omega pistons.

What do you guys think I should do?

Sorry but this is not clear, are you implying that supercharged engines make huge torque and "need" the below items?

It is well documented that minis with 200bhp+ use open diffs and std drops some with an oil feed mod " look at sprokets build" .

Drives
-Ford S-max Mk2 Ecoboost
-Rover 100 VVC #2 - track project

Searching is all you need on TurboMinis

If you want sc go sc but you do not need tocut the bulk head when going turbo, infact I think most don't now.

My questions
1. Is the block being bored and honed to a set of pistons?
2. The cam is fine but on a sc engine I would go for a 286 as sc engines use cams that are more similar to n/a engines (search for jonnysti)
3. Why get the block bored to 1293 when you have 1330 pistons?

Spend a few days/weeks searching what you want on the forum, most things have been covered

Edited by Paul R on 21st Jul, 2013.

Drives
-Ford S-max Mk2 Ecoboost
-Rover 100 VVC #2 - track project

Searching is all you need on TurboMinis

Engine stuff is so confusing all my other minis have only ever been standard 1000cc engines

I brought the block and crank from wrlondon on here this was the spec

1275 block rebored to 1293 (never even had a piston in it)
drilled for 11 stud, has centre main cap too

Hardened, wedged and polished crank, new bearings

I brought it as it was cheaper than getting the crank done myself. So I intended On getting the block re bored to to my pistons. I do have another 1275 engine in bits as well

I no my first mistake was just rushing into buying things thats why I have 3 heads 2 short engines I should find out a good spec engine and build to it rather than buy parts and hope they work together

Edited by Clive1330 on 21st Jul, 2013.

there is no need to cut the body to fit a turbo im doing a side mount for that reason
i have wondered sometimes about a belt driven turbo on a mini i think it would be grate the instant get up and go of a blower with the boost that a turbo can make = D
as for your CR Delmor how about having the block/head shaved down a bit? depending on how much you may need to shim the rockers back up tho to maintain the geometry
easier still sell your pistons on to a guy that wants a high boosted turbo and buy the right pistons for your build

I was toying with selling them as I think it will be the cheapest thing to do or even swap them with someone :)

ideally clive you'd sell that block back to me

i'd sell the 1330 pistons and buy some 10cc omega's, keep that head
and then decide if your going turbo or supercharged
then choose a decent cam!

if you want to go turbo and not cut into the bulkhead mirage to manifolds for £300+

Reading up on RTS Clutches

Lol not selling it just yet will probably sell the pistons if I can find them as they seem to have disappeared at the moment

Sell the head and get one with a better chamber shape

Nothing wrong with the chamber shape. You could always skim the head to bring the compression up. This would be the cheapest option.

WWW.TURBO-MINI.COM

Cheers Phil I best find the pistons first as I seem to have misplaced them :(

This is one of phils heads

Edited by Clive1330 on 21st Jul, 2013.

Phil, I think we could argue that all day long.

We could, but as there's people making over 200hp on the same chamber design I'd say it's not to much of an issue.

WWW.TURBO-MINI.COM