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Forced induction A series chat
https://ausmini.com/forums/viewtopic.php?f=5&t=80642		 Page 1 of 3
Author:  Kennomini [ Sun Mar 10, 2013 1:49 pm ]
Post subject:  Forced induction A series chat
I have a couple of ideas I would like answers to so lets see what we can find out.
First question is can the A series take 14psi + and still be reliable? And what would the rough engine and head specs be?

The second question is if you build a 1330 what would be a good comp ratio to run the engine as a N/A or later down the track as a low boost (under 8psi) engine.
Author:  simon k [ Sun Mar 10, 2013 4:11 pm ]
Post subject: 
1/ reliable is a subjective term, I don't think it can be reliable as a daily driver, I think you can expect it to last up to 10,000kms between rebuilds

2/ 10:1
Author:  MattE [ Sun Mar 10, 2013 8:48 pm ]
Post subject: 
I suppose first thing on your shopping list would be forged pistons?

The Metro Turbo A series uses up to 7 psi and is 9.75:1 from factory. If I was in charge it would have come out with lower compression. And a turbo better suited to a small engine.

Remember, the more psi you push in, the hotter the charge gets, and the more you start to need an intercooler or other wizardry to prevent detonation / pistons melting etc.

14psi would be a lot for a daily driver, IMO.
Author:  Boostedmini [ Mon Mar 11, 2013 12:44 pm ]
Post subject: 
I have had my mini turbo charged for over 12 years now in a few various forms and outputs and a lot of this has been trial and error, when i first did it i knew of 2 others here in oz done.
they can be very reliable, but as like anything, you abuse it and it will not last as long as you want i to.

I can say that if you say you will not go over 12psi your kidding yourself, i thought the same but we all get greedy and want to see how well it can go.

Ignition advance is crucial and do not over advance as it will knock/detonate and you cannot hear it so be carefull and do not run over 25ยบ when on boost, otherwise broken pistons, I have done this...

pistons, if you can afford get forged, i have been running Omega ones from UK now for around 7 years and still holding strong.

my motor now puts up with regular hard drives on 18 plus psi and has even been subjected to 22psi, remember ignition has to be brought back even further if you go this high, as for comp ratio the more boost the lower you go, when i built my current engine i always intended on runniing 16+ so my comp is at 7.6:1 i feel its a little low as it is very doughy when taking off but you can run a little more advance to combat this.
I cannot recomend Graham Russell's cam enough plus a well sorted head, no need to go too big on the ports either, build it strong with new ARP bolts through out, 4 bolt or steel centre main cap, good oil pump and regular oil changes and do not abuse it but you can drive hard, there is a difference.

hope it helps.

Grant
Author:  mattsmadmini [ Tue Mar 12, 2013 9:41 pm ]
Post subject: 
Grant,

when you first started did you IC your setup or just run a basic metro turbo set up? if the basic set up... what was your max boost you could safely run?

Ive got a set up here, not sure if i want to start with standard or just go straight to IC and play with boost etc....

Ta,
Matt
Author:  Boostedmini [ Wed Mar 13, 2013 12:30 pm ]
Post subject: 
Hi Matt,

was a std metro setup, std turbo, manifold and no IC.

all different now, only metro item is the carb and inlet manifold.

with hepolite pistons i ran max of 12psi but watch the ignition, with max advance of 20 to 22 degree i think you could go to 14psi.

Grant
Author:  braad [ Thu Mar 14, 2013 5:02 pm ]
Post subject: 
good information from Grant there ^^

also see http://www.turbo-mini.com/index2.html
and check out the UK site turbominis http://www.turbominis.co.uk/
Author:  MattE [ Sun Apr 14, 2013 8:19 pm ]
Post subject: 
Grant,
Interested to know more about how you've put your motor together...

What dish do your pistons have?
What cam did GR prepare for you? A turbo specific one?
Did GR do the head for you? What sort of work went into it?

Cheers
Matt
Author:  Boostedmini [ Mon Apr 15, 2013 11:56 am ]
Post subject: 
Hi,

I am using the OMEGA +20 thou forged pistons in std trim, have been for many years now.
my last 3 cams have been GR test cams and all of them are very good and very smooth the current one is a 286 and it is lumpy but also very drivable, i can sit on 60 in top gear no worries.
the head is a very moddified 12G940 with oversize valves but not as big as MK1 valves, GR did some chamber work to get the CR down for me, i am running 7.6:1 but it is a little too low to be honest, its a little hard to get off the line at lower revs and the cam does not really help either.

Image
Author:  MiniVLT [ Mon Apr 15, 2013 12:06 pm ]
Post subject: 
Grant, from your chamber photo it looks like your not running hardened seats for the exhaust.
Are you using a top end lube or additive in the fuel?
How do you find the seat wear?

Cheers Shane
Author:  Boostedmini [ Mon Apr 15, 2013 3:30 pm ]
Post subject: 
correct Shane,

I have not run inserts ever to be honest and i run 98 BP, i hav enot pulled then valves out for some time for full inspection but the rocker gaps are still fine.
i do put some flash lube in the tank every 3 or so fills for security.

Grant
Author:  MattE [ Mon Apr 15, 2013 8:12 pm ]
Post subject: 
Those chambers look good....
What CR would you recommend, if yours is too low?
The current Omega pistons (offered by MED), are 18cc dish - seems like a lot!
Author:  MiniVLT [ Mon Apr 15, 2013 9:30 pm ]
Post subject: 
Hi Matt,

Compression ratio is always going to be the limiting factor as to what amount of boost you run. Unfortunately it's always a compromise!

The more boost you WANT to run the lower the static compression. However the lower the static compression, the less off boost power you have.
So really it all comes down to what do you want to do with the engine?

A track day car that'll never see anything below 3000 RPM or off boost, or a good everyday car with a nice boost of power that's not over the top!

As Grant says, he reckons at 7.6:1 it's a bit of pig to get off the mark, but he can put 22 psi into it. The factory 9.75:1 only had about 5 psi max.

When I build my motor I'm looking for around 8.8 - 9.0:1, however I'm only looking to put in about 10 - 12 psi with an intercooler. Off boost power is big a concideration for me when boost can only be used for approx 15% of the daily drive!

Cheers Shane
Author:  MattE [ Mon Apr 15, 2013 9:38 pm ]
Post subject: 
Thanks Shane.
Interesting - and it makes sense.
Grant's 7.6:1 does sound low, and the factory's 9.75:1 (Metro Turbo) seems quite high - so somewhere in the middle is probably where it needs to be.

What low compression pistons for big bore engines are you aware of Shane?
Author:  Boostedmini [ Mon Apr 15, 2013 9:43 pm ]
Post subject: 
All depends on boost and turbo being used, small turbo low boost up to 10psi = 8.5:1, bigger turbo up to 16psi 8-8.2:1, up to 18 psi 7.8-8:1
This is not proven ans all depends on cam, ignition system, ignition timing etc etc

Grant
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