boost question
Turbo Mini Forums

hey guys

im trying to find out a couple of things


what would be the max boost i could run safely and what hp would it give out?


setup at the min is

988+60
12g295 head big valves and things

mg metro cam
28/36 weber

and its putting out 64bhp

when i get the CR down to 9:3 what would be the max boost i could run on that?

going to be using the biggest intercooler i can get and it will go where the grill is.

what bhp figures could i be looking at?

thanks

I'm not a wizard at this stuff like most on here but may help if you state pistons and gearbox spec

How long's a piece of string. But all things being good, 10psi would be safe and produce 100bhp on a good day.

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

www.twin-turbo.co.uk

would 9:3 be low enough to run 10psi?

none with that compression.

I like to run a bit of a safety margin

also need to make sure its properly tuned (ignition and fueling).

Why none? Standard metro turbo was 9.4:1 and took 8psi with no intercooler.

how much extra boost can run with a intercooler then?

About 2 psi less than blows it up is about right.

Install megajolt system and aim for about 10psi as long as the intercooler has good airflow

Masturbation is not a crime its a hobby

its all down to preference. and what you feel comfortable with.

I did a few thousand miles on my old 1275 engine, it ran a compression ratio of 8.7:1 with standard non turbo metro pistons at 10 psi. it went well and was reliable...but there is always the thought at the back of your mind, mine was regarding the pistons and whether they were up to the job. they were but there is always that doubt there.

if the op was looking to boost his engine, it could be worth considering fitting a std chamber size 998 cooper head to drop the compression. for peace of mind if nothing else.

dan

by no means do i know what im talking about!!

but perhaps look at the intake closure point and work out your true compression ratio

ive herd guys with 12-1 and 15psi BUT the intake valve closes way late so the true compression (dynamic) is only like 9.5-1 or something..

as far as i know, you dont have compression till the valves are closed and the air/fuel have no place to go right?

Yeah I am going to to be running a no diz setup too, renewing all the cooling system and like I said the biggest cooler I can get to go where the grill is,


That 9:3 compression is which my head chambers opened to 27cc(at 25cc ATM)

This info not right?

9.4-1 Standard Metro Turbo compression ratio. Suitable for standard 7psi of boost, a little more if an efficient intercooler is fitted.

9.0-1 Suitable for about 10psi or so.

8.5-1 Suitable for about 15psi or so, efficient intercooler essential.

8.0-1 Suitable for 20+ psi Efficient intercooler essential. Undercrown jets advantageous.

It's only a guide, & is set on the cautious side. There's no hard & fast set figures as there are so many variables.
Charge temps, fuel octane, ignition timing, compression ratio, fuelling, camshaft used, Turbo efficiency etc etc

Phil.

WWW.TURBO-MINI.COM

Well with my setup,

Let's just say Everything is good, fueling spot on, good air flowing cooler.

I want around 100-120bhp


What would you say the best CR would be?

Also in your experience what is the most on average you can you get back out of a head cc wise? 2cc or more?

Edited by coopdog on 18th Jan, 2014.

its hard to tell someone what they should do with there engine, what if it goes bang?

advice is what we can give however

i have used this to help get an idea of where ill be at but i will back it up by measuring it as i build and then run what ever boost i feel safe

http://www.wallaceracing.com/dynamic-cr.php

for instance low compression high boost vs high compression

low boost could make the same power as high but be totally different in the way they drive
low comp is probably much more boggy until boost comes on where as high comp should be more willing to get up and go at low rpm little to no boost

as for fuel choice myself ill be running unleaded 98 octane for the first starting and running in like 5psi then im changing to E85 110-115 octane when the boost gets turned up this requires ignition timing and fueling changes

I'd recommend spending some time reading 998 build threads and seeing what setups people are running and what issues they've ran into.

Learn abit about setups and then make a decision from there. Start simple and slowly progress to where you want to be.

13.95 1/4 mile on a 2.95 fd. Carnt be that hard to beat!

I don't understand why i can't get a straight answer though?

What cr are you guys are running and what boost that's all I'm asking...

Edited by coopdog on 19th Jan, 2014.

Whatever you want. Its your car all people can do is give you they're opinions and experience.
Around 10psi should be fine, its just a bit lower then metty turbo..
Srsight answer enough?

i think if you had mappable ignition and keep charge temps under control cold air makes more hp and makes it less likely to det
id be happy with 9.5-1 CR id think you could make 100hp on about 10psi given the engine is in good shape and has a decant VE

what turbo?

I ran a 998 for a joke once, it was completely stock bar a fast road cam. I ran 8psi and it was a nice fun car to drive.

We could just tell you 14 psi would be fine with around a 9;1 cr but that would need setting up perfectly. So it's down to you in the end.

Phils guide I'd good but as he said its a guide. A turbo project comes down to the user in the end. Treat it properly and with caution regarding your tuning and you'll make a good engine otherwise wise you'll be chasing your arse all day long.

Edited by eden7842 on 19th Jan, 2014.

13.95 1/4 mile on a 2.95 fd. Carnt be that hard to beat!

This is a straight answer.

10psi will be safe. As I don't know enough about your engine, and you writing all the spec won't help, this is what I would advise.

In reality it will probably be happy with more boost, but that's your risk once it's all together.

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

www.twin-turbo.co.uk

Edited by Paul S on 19th Jan, 2014.

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."