CC or not CC
Turbo Mini Forums

Right, ive been seriously hacking at my cyl head, and im still only at 24cc. head looks like VMAX one here but has even more off the side opposite the plug.

didnt really want straighter walled sides, but is this the thing to do?

May have to stick with 24cc.

anyone anymore pics i can use as a guide? Jimster?

R.

Sooperdooperturbocooperexpertengineering!

mail me i`ve got most head pics

Everyone knows that instructions only have to be read if the thing doesn't work....

Cheers Mark. my chambers look bigger than most of thos and im still only at 24cc..... will have to look at some other ways of lowering CR.

Sooperdooperturbocooperexpertengineering!

Have you lowered the roof of the combustion chamber and re-cut the seats?

alex

AlexF

No... but that costs money which i havent got spare. hence the reason im trying myself. may take it out a bit more but worried i will hit the water jacket.

Sooperdooperturbocooperexpertengineering!

Hmm tight budgets and more boost leads to problems...

alex

AlexF

Lower CR and Higher boost will come in the form of my spare head. will get that convwerted to unleaded and have roof machined out at same time.

At the moment, money is going on DV's, bleed valves, boost gauges etc etc.....

Anyone know what the bore diameter and compressed thickness of a Payen BK450 head gasket is? i was working on 82mm by .9mm (giving 4.75 CC)

if its the above i have 8.8CR.... what highest boost i should safely run? (im using zetec jets too)

EDIT - Aww bugger, thats not right!.... diameter is about 74 and 2.8CC...... = 9.2CR.... bugga!

Ross

Edited by mini-marauder on 3rd Jun, 2004.

Sooperdooperturbocooperexpertengineering!

Ross... have a play with

http://www.afracing.com/cr.xls

With 8.8:1 I would guess at 10-12 psi... but do you have an intercooler?

Alex

AlexF

HEY!!... Deck volume! what is it on a bog std Metro turbo lump... i was taking it as zero as im sure pistons were flush. not so sure now!

Sheet is cool BTW.

No intercooler as yet, but is on the shopping list.

Sooperdooperturbocooperexpertengineering!

I recall a BK450 compressed is 3.9cc - at least that's what i calculated.

Got 2.8cc from Minispares site. probably wrong.

if deck is 5.25 then my CR @ 24cc chamber vol = 8.00 as below.

just got to find out what it ACTUALY is.... anyone confirm?

Bore 70.61 mm
Stroke 81.4 mm
Gasket Volume 3.80 cc
Ring land Volume 0.5 cc
Piston Volume 12.00 cc
Head Chamber Vol 24 cc
Deck Volume 5.25 cc
Compression Ratio 8.00 :1

Sooperdooperturbocooperexpertengineering!

You need to measure your deck volume...

If I make simialr assunmptions on my engine I end up with a CR of 7:1... without the deck hight and a different gasket this could be a fair bit higher at 8:1.

Alex

AlexF

OK, but could have done with knowing now as im grinding head. once block is back out of storage, i dont really want grinding grit all over it!!!

Need to get some main and bigend bearings now and do a trial fit.

Sooperdooperturbocooperexpertengineering!

Deck vol is naff all on std turbo pistons...

As regards the BK450, get a caliper out and measure one, but 1mm thick is 3.9cc, 0.9mm is 3.5cc, 0.8mm is 3.15cc and i'm sure it isn't that thin...