17 replies to this topic

[Checkmate]

hi, im going to have my combustion chambers opened up tomorrow... but im not sure what size to open them up to?

can anyone suggest what an 'ideal' size for the chambers or compression ratio is for a mildly tuned metro turbo (standard 12cc pistons, gasket etc.) ? - its a daily driver - dont want it to be very sluggish off boost

and what sort of boost would i be able to run safely with this setup?

(im going to be intercooling eventually by the way)

oh and does anyone know what the standard volume is for a metro turbo head?

thanks

Edited by Checkmate, 20 February 2008 - 08:07 PM.

[Sam Walters]

8.5:1 compression ratio will be fine, 13psi on an intercooler should be plenty enough power, youll need a stright cut drop past this level of boost. actually. 7psi really with a decent flowing head. so 26-28 cc should be fine.

[Ethel]

The standard head is 21.woteva cc's like all other 1275's I believe.

[Checkmate]

thanks guys, would you be able to tell me what sort of power im looking at?

and what about 9:1 intercooled with 12 psi of boost?

and what would the most reliable setup and least sluggish 'off boost'

[Turbo Phil]

The standard chamber volume is 21.4cc, though they can vary quite a bit. If you've got the standard Turbo engine with a compression of 9.4-1, then opening the chambers out to 26cc should pretty much put you bang on 8.5-1.
At this kind of compression you'll be fine running 15psi, no problems, obviously providing the engine is intercooled & properly set up & it shouldn't be to flat off boost. You probably don't need to go quite as low really, but at least you'll have a margin for error, or a possibility to run a little more boost as & when you decide to.
You could probably run 12psi on 9-1 ratio, but it would have to be very carefully setup. There are quite a lot of people running higher compressions now, with the likes of Megajolt helping accurate ignition timing.
I'd personally run it a little lower, as i said above this gives you some margin for error, should something go wrong.

Phil.

[Checkmate]

thank, any idea on what sort of power that will give me?

i have been reading about this megajolt setup thingy, and it sounds like its a worthwhile investment. around how much will it cost for all the parts to convert? and how easy and long will it take to fit?

[mini_turbo_pete]

thanks guys, would you be able to tell me what sort of power im looking at?

and what about 9:1 intercooled with 12 psi of boost?

and what would the most reliable setup and least sluggish 'off boost'

On my Metro Turbo Challenge engine i was running 8.5:1 compression turbo challenge cam and 11psi boost with a T34 turbo it ran 139bhp with 148.9lb torque.

Thats was running a standard Turbo dizzy

This set up was nice, it wasn't too sluggish off of boost and it went well on boost.

I then lowed the compression to 6.5:1 (decompression plate and 26cc head) and wound the boost up to 22psi, it was like driving an 850 that was running on 2 cylinders off of boost but when it was on boost it was grin factor 10... lol..

[Checkmate]

whats the 'off boost' rev range? (*if that makes sense lol).

im basically looking for fast off the line and high boost (but not too much wheels spin)

[mini_turbo_pete]

whats the 'off boost' rev range? (*if that makes sense lol).

im basically looking for fast off the line and high boost (but not too much wheels spin)

My T34 boosted later than a standart metro T3, a standard t3 will boost about 3000rpm. for fast of the line normally a little rev or two just to get the turbo started is plenty enough.

I never really used to get too much wheelspin but i was running a 2.7 final drive on 13"'s

This is a vid of it on the rolling road, the first run in this vid was 7 psi the second was 11psi, you car hear the way the turbo kicks in.

[Ethel]

We have a couple of Megajolt guides on the forum and you can also look at MJ's own site at autosportlabs.

[Checkmate]

hi, just got back from the machinist

heres what ive done so far....

[attachment=51046:IMG_0803.JPG]

ive got them all up to 26cc, and lapped the valves in. i tried to retain the original heart shape as best i could.

tomorrow ive just got to chemicly clean it and put it back together

tell me what you guys think?

and what would be a safe level of boost to run this on with no intercooler for a few weeks?

[Turbo Phil]

Out of interest how much did they charge you to open the chambers ?
If your running without an intercooler i'd stick to about 10psi really. You could probably run a little more, but you'll probably not see a huge gain as the charge temps climb.

[miRon]

have you ported the head whilst its off?maybe worth while,
has i been setup?
you can run20 psi but it wont last long.
get i setup first
then go from there.

[Checkmate]

umm i done it myself .. after speaking with the guy he could see i was genuinely interested in engines and i suprised him with what i knew - im only 17 lol. so he said i could use his shop to do my own work on my head

he himslef has worked there since he was 13 and now owns the shop.it is a really good shop though, he does a lot of trade work, mostly heads, and alot of minis, today while i was there he was doing a stage 3 head with lead free conversion and a full race head for company in france.

if u want i could get you the number and some guide prices etc. place is called vulcan engineering by the way

and i was thinking about porting the head, but wouldnt this mean i should port the exhaust manifold aswell? as they both look kind of the same to me? or by porting do you mean polishing?

[Turbo Nick]

if you do exhaust ports on the head then its definately worthwhile doing the manifold aswell, also attack it where the manifold joins the turbo and the most gains can be had from opening up the turbo elbow too. Might aswell do it whilst you've got the chance, every little helps.