All I want is a tight box and good head!
Turbo Mini Forums

Hello chaps,

The g/f's mini was running a tired metro turbo lump which the dumped it's box just before Xmas.

Initially she was going to just repair the box and carry on, but I may have planted the idea that as it was off the road anyway why not tweak the set up a little...

So here's where we are currently:

1275 Metro turbo short block freshly rebuilt, cross drilled/ balanced crank, boggo turbo pistons, 266 cam.
2" exhaust.
GT1549 turbo.
Nodiz Pro ignition.
Turbo clutch (20% is out of stock currently but on the list)

X-pin diff, centre pick up, and freshly rebuilt box.

Running on 98RON minimum but she lives right near a Shell garage so 100 is readily available.

The goal of the build is a fun, punchy midrange car. Pitching at a 135-140 range for power with torque not too far behind. Staying fairly conservative to remain budget conscious (Yeah that worked out well...).


So with that in mind, I have a couple of questions for the collective intelligence that is you guys:

I've now read the entire internet (or it feels like it!) trying to get a majority answer on head and boxes.

Firstly the easy one, head! I'm estimating at approx. 8.8:1 cr (also assuming to be around 13psi) but haven't done the solid math yet. Which should equate to about 37cc chamber volume, minus dish and gasket that's only a few cc out the head so easily attainable.
But, porting and peaks?

#I'm not a fan of trimming the peak because of the change in characteristics and it's not a great yield of chamber size, unless I'm bass akwards on that?

#Porting has been suggested as unnecessary on this build and would frankly save a chunk of cash, thoughts?

Next up gearbox, been round in circles on gear set choice. SC or fresh helicals, standard drops either way. If the helicals are going in new does it pay to just go SC and be done with it? Some say yes, some say no... I'm lost frankly. I run auto so I have no experience :p

She's not an aggressive driver and isn't rough with her clutch, the car will be a 2nd vehicle with a majority of summer use.

So there you go, still awake?

Advice please, head and box. What would you do for meaty torque in the 120-150 range with that set up?
I'm really keen on efficiency rather than just adding boost to cover design failings.


Cheerios :)

Edited by Skortchio on 5th Jan, 2017.

GT17 and Megajolt.

Might not have been concise enough, all is done bar the head and box.
Gt15 shouldn't have trouble hitting the mark unless I've totally misread the map and calcs?

If you don't need to remove the beak in the chamber to get the volume, then don't. Just modify the chamber as you would for performance NA use, and to the size you require.
A restriction is a restriction and some port work can only improve things performance wise.

Phil.

WWW.TURBO-MINI.COM

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

Revving out isn't a concern, the build isn't for redlining as it's not her thing. Solid midrange, road based fun, traffic light gp and tons of punch out of corners.

keep beaks , 8.8:1 fine , leave head stock ,use a soft 250 ish degree cam , or stock cam .big intercooler . see what happens. try with helical .

Medusa + injection = too much torque for the dyno ..https://youtu.be/qg5o0_tJxYM

If you don't want to spend a lot on head work, some simple valve and seat work and modifying the chamber as mentioned will yield some decent flow gains.

Phil.

WWW.TURBO-MINI.COM

Ah pap knew I forgot something, 266 cam is fitted.

Biggest problem with the Sc gears is that the ratios are too close for road really. Running a tall diff ratio for cruising on the road hurts your pulling away which is obviously important I'm a road car too.

I don't think you need to pay as much attention to the head as you would on an NA car but it's easy to make a difference so maybe go for the low hanging fruit with a bit of a fettle to remove the bad casting and a back cut on the valves but leave out the expense of seat cutting and guide changing etc. Depends how much you can do yourself I guess?

if your going to run highish compression ratio, with a piston change you can probably run a decent 2nd hand ported NA head.


a decent helical box will be happy at 140 especially if your a bit sympathetic with it ( not too many burnouts from the lights....) definatly fit a cross pin diff though.

Thanks for the input, chaps.

Given the cost of a SC set, may well plumb for fresh helis.
Basic flow on the head seems the route to go too.

Best get on with that and see how it works out!

Is the head the stock 33mm inlet valve one ?
Do you have seat cutters ?

Phil.

WWW.TURBO-MINI.COM

It's a stock Metty turbo head, so I would assume just the larger stems on exhaust.

I was going to drop you a note regarding some cutting and the previous mentioned basic fettle, don't have the tooling for seat cutting or larger valves (if that's of any benefit on turbos).