The plan.... Does it make sense?
Turbo Mini Forums

Right chaps, perhaps you can advise me.
I have recently bought a car (GTM Rossa) with a metro turbo engine. The engine appears to be bog standard (except its at the other end of the car!), complete with the control module thingy limiting boost during the mid range revs. Alas the oil presure is a bit dubious. So this is my plan. I'd welcome feedback!

Pull the engine and crack it open. Hopefully a new hi Cap oil pump and new shells will improve the oil presurre, maybe re-grind the crank.
Put engine back in
Add renault 5 GT turbo intercooler (just bought off ebay for ?13)
Bin the modulator thing - This will mean that I get a constant boost of 4psi?
Change the err umm whatever spring there is on the wastegate for a stronger one (Avonbar?) to get the 7.5 boost back
Get it on the rolling road.

A few questions:
- does the Metro trubo modulator do anything other than the boost - so I can bin it?
- more boost without reduction in CR is liky of cause detonation
- Are high lift rockers a good invesment
- If I want to up the boost, some head work is the best way to drop the CR?
- the exhaust system looks a bit weedy, how much does back pressure sap bhp?
- what have I missed.

Thanks.
Jimbo

crack open the intercooler and by-pass the crappy flap in the end of it - or flog it and get a different intercooler that needs no work?

Oil pump - get the Avonbar turbo pump. minispares oil pumps are good as paperweights only.
Regarding 1.5 rockers - Your money would be better spent towards a new (ported, lowered CR, unleaded) head. Rockers can be done later...

They have a 'themostatically' operated flap that by-passes the intercooler. These are slow to operate, can stick, or even worse fall apart and into your engine!

You just have to take off the end-cap where the pipes are by prising back the tabs, remove the flap and 'stat assembly, make up a piece that fits between the two halves of the end-cap (16 gauge alloy sheet is ideal), then put it all back together. You need to strap the intercooler together with a few big jubilee clips aswell, as the tangs are near impossible to get tight again.

See what i mean about lots of fannying around?

Take a look at
http://www.turbominis.co.uk/forums/index.php?p=vt&tid=2850

for alternative intercoolers that may suit you...
Also read
http://www.manchesterminis.co.uk/technical...ntercoolers.htm
For hints on selecting good core designs...

You thought about location yet?

I can post pic's of the internals in the morning but i'm not sure you need to make anything to separate the two halfs as this is already molded into the end cap on the one i have and the end cap is one piece not two.

Did they change them at some point dave. ?

Edited by Doodmeister on 30th Mar, 2005.

Two things are infinite: the universe and human stupidity; and I'm not sure about the the universe.

Regards modulater, it just bleeds off mid range boost.

Exhaust, fatter the better.

you want the least amount of backpressure in the exaust in a perfect world NONE.
the genrall Consensus is
forget the 1.5 rockers on a cam above 270 deg

as this just wears the whole valve train out very soon!.............................and makes driveability for a road car an issue. more so wit a T 3

10 psi is the max boost ish.. on standard compression on optimax fuel may be 12 with a GOOD intercooler

When I said 'two halves' I meant two chambers, or however else it could be described...

The endcap is one piece, as you say, but the by-pass must surely leave a hole between the two chambers if you were to remove the assembly?

I'd stick to 7psi... 10 is possible with retarded ignition - hell even 20psi is possible if you retard the ignition enough, but you're making boost, and heat, and not much else.

As i've said before though, stick to 4psi untill it's on rollers unless you're 100% confident of listening out for pinking and have a lambda meter to check the fuelling. It's all very well saying wang it up to 7 or 10psi, but who'd to say the head hasn't already been skimmed, and the engine is already at 9.7:1 ???
Also, imagine the dizzy had been swapped out for one off a 1300 metro, or an MG; you can set the advance according to haynes all day long, but come 4000rpm, it'll be pinking its nuts off...
Basically, don't touch the boost until you've got it on the rollers...

do 1.5 rockers really cause all those probs ??

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

good point dave

Consensus is mark they do

they may be ok on A N/A engine if you need to extract every last ounce of power.

say miglia engine or whatever then strip and rebuild at the end of a season under 500miles

but the turbo makes the power at lower rpm
than a N/A full race engine.

the rockers dont seem to give you much with the cams mentioned above on a turbo engine
only the problems mentioned buddy

better spend your money on or towards a GOOD intercooler say

just the 1st , 2(?), 3rd, 4th, 5th, fastest cars cars at avonpark all ran with 1.5 rockers

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

I'll stick my oar in now...

I'm using 1.5 full roller rockers.
They are sh1t-hot for making top-end power - my power is up after fitting them.

imagine valve lift, versus crank degrees plotted on a graph - 1.5 rockers will have around 15% more area-under-the-curve at a guess - that's 15% more into, or out of the engine theoretically.
Unfortunatelly, it also increases overlap (area under the curve again)...

As regards cam/follwer wear, well what are the facts? You're basically pushing against a spring 1.2 times stiffer with 1.5's compared to 1.25's

So, is the 1.25 setup THAT close to the limit of failure regarding the cam/foller interface that if a slight increase in resistance is seen it fails? I doubt it persoanally.

Only way you'll test this is on a rig - one cam driving two followers - one follower is acting against a spring 1.2 times greater than the other. Add exctly the same volume and grade of oil for lube, and start the test.

Inside an engine, there are too many variables - none more so than one put together by badboyboost, than one put together by an experienced builder like Steve Gault.
I know SG uses a pretty tall spring 'height' (ie spring not compressed so much), even with 8000rpm engines... Badboyboost on the other hand would buy 240lb springs (begause bigger numbers are better of course) and not even measure or change the spring height...

Regarding wear on the valve/guides, sure 1.5 forged (budget) rockers are going to wear things out due to the increased 'wiping' of the pad compared to 1.25 rockers. But what about the wiping of the pad comparing stock sintered rockers, to roller-tip items? Clearly the side load is less on the roller tip. So that just leaves 'distance travelled' by the valve...
Say a valve moves 10mm with 1.25's, it'll only move 12mm with 1.5's - again, it'll wear out 1.2 (or 20%) times as fast, ignoring wear from the increased velocity of the valve and comparing distance alone...



Basically, what i'm getting across is that I don't believe the 'wear' issue of 1.5 rockers is fully justified... There are too many variables and muppet builders out there who see a failure (which they can't even identify as being from their own incompetence) and blame whatever they suspect of the cause...

Edited by turbodave16v on 30th Mar, 2005.

Dave:
my reply was aimed at the GENERAL guy on TM who fires an engine together not knowing the pit falls "FULLY"
aimed at drivability issues and valve train wear.
(as a SAFTEY MARGIN)

it was just genrall advice:
iam glad you coverd this topic more thoroughly! (as allways)

you have hit the nail on the head!

thats exactley it!!!
bad boy boost biger numbers are better syndrome

with a combination of crap oil (ie) viscosity too thin
excessive spring pressures wearing the lobes,followers out accentuated by 1.5 rockers with modern high lift profiles short durations now adays

MANY engine builders and professional!! builders have
SLOWLEY over the years fallen into the above trap...........................................

how many good engines have been wrecked early by the pitfall above!


theres still the issue of driveability accentuated by the fitting of 1.5 with cams a little over halfe race profiles.

Edited by BENROSS on 31st Mar, 2005.

Thanks for the advice

You need to get yourself a wide band lambda sensor if you don't want to use a RR much....

You have to make sure the fueling stays rich when you plan it or your wallet will suffer!!!

An modification you make to your car to gain more power, that does not make you run lean was not worth doing!!!


Alex

AlexF

jimbo, what the weight of gtm, so we can get a power to weight ratio

I believe the weight is approx 600kg 'wet'. Not too sure though.

Edited by Jimbo on 1st Apr, 2005.

a bit lighter than my mini, that thing should be bloody quick, and with the engine in the right place it should grip well too!

Team Racing

is your weight "wet" ? jim

don't know what does "wet" mean??

Team Racing

paint no dry yet????????????? nice light motor, FUN TIME

with fuel