7 port head, with high comp - wants to run SC without machining head......
Turbo Mini Forums

Hi All,

Hope to poke the collective TM brain please......

A friend has just finished building his injection mini, using an SC seven port and throttle bodies. Its pretty potent in its current form, but he wants more and would like to go down the road of a blow through SC, using a bespoke plenum and IC. (if it'll all fit under the bonnet)

Problem is at the moment, the compression is way too high for any boost. The obvious solution is to machine the head, but as its a brand new alloy 7 port, he'd rather not.

obviously dished pistons will get him down so far, and fitting a thicker gasket will help but otherwise i'm stuck. Don't want to use the standard decomp plate bodge either - blown head gaskets wouldn't be good with an alloy head......

Any other options? what compression is sensible to run with a M45?

Specs are:

head chambers: 21.5cc
current piston dish: 6cc
Gasket: 3cc (per cylinder?)
Bore: 1312cc

Thanks as always for your advice.

P.S. did try the search bar to no avail....

What is the current comp ratio ?

I would say that 9:1 would be fine with a ally head and FI.

I think most guys on here are of the same opinion, open up the head or dish the pistons.

"So wat we gonna do tonight Brain?"
"Same thing we do evernight Pinky!"
"Try to take over the world!"

i would go a sprintex supercharger.

bit more cash but they are small & efficient & put out less heat & will fit no problems.

research them vs the m45 & how they swap the shity bmw blower out for these.

ill be running one on my A series with a 5port had & injection at 10psi.


as far as the engine, i would change for good pistons that can handle boost & leave the head.

other wise you could be back to pulling it out anyways for better pistons, if you pop a hole in one.

Edited by NickG on 14th Sep, 2012.

Pistons will do the trick,

Quick calcs give 11.75:1 at present.
15cc pistons gives 9.3:1
18cc pistons gives 8.7:1

Thanks Tom - seems pistons is the way to go.

where can you get 15cc +040 pistons from? any reccomendations?

I use a copper plate I had made instead of the de-comp and 2 gaskets (equivalent thickness). Assembled it with sealant and runs 146 bh no problem.

accralite used to do pistons in these types of sizes. last time h had contact via omega they would only produce them in runs of 5 sets. minispeed look to do their own fi pistons, not sure if anyone had tried them on here, i cant comment on what they are like as i too have not used them.

Get some 11cc omegas. They sit 0.040" down the block, so you can deck the block to suite your target CR.

Thanks guys, all very helpful and relayed back to the man with a much bigger budget than me!

I'll put some pics up if I can find any.

Possibly speak to sc as well they may have developed a form of there twin cam sc kit, rough numbers on there 1310 with a stock head and lt cams produced 115bhp and with there sc conversion it went up to 194bhp according to there site also have aome running 240+bhp

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

Searching is all you need on TurboMinis

With my build. A 28cc head, 0.020 cast omegas and standard deck height I worked it out to 8:1. With 0.030 removed from the deck height I got 8.3:1.

It would be best to do the sums for his engine, then dry build and measure before doing any machining.

Thanks Andy

What deck height did you use Tom?

Firstly, don't bodge on an M45 onto this setup. Better to either turbo or maybe rotrex.

Speak to JK, the rotrex can run quite high compression as boot is msde high up where dynamic CR is lower. Infact you need the hight CR to make it work.

The other option is to speak to JK ans see what head gaskets he can offer, he does some nice thick ones for the 16v heads and suggested that he could offer the same for normal stud pattern.

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

Ok so general consensus is the M45 isn't a good option?

I've no experience of SC's so totally blind in that subject.

What the benefit of Rotrex or Sprintex?

The rotrex is a centrifugal pump (just like a turbo). But mechanically driven.

As I see it they are not ideal for ultimate power, but they do make a very tractable engine. Have a look on the Sc website for some details on one he built.

Their advantage is you run them on high comp engines, so good for the problem you have.

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

Thanks for the info Will, I'll look into it.

any other 'ex production line car' chargers that are worth considering?

The unit fitted the the Mazda milenia in other parts of the world is a good choice, as is the sprintex unit - they occasionaly turn up on ebay uk.

Toyota SC12 charger, rare as rocking horse shit though. Had to get mine from New Zealand as they never fitted them to UK MR2s.

What does he want from the engine, why is he so set on supercharging? A turbo set up should be easy on a 7 port.