Turbocharging NA engines...

[BenzBoy]

I'm building a turbo system for my Merc (!) - I collected the parts a while ago, shelved the idea, then dug them out when I saw the article on turbocharging in Practical Performance Car. Basically I intend to fit a Garrett T25 and blow it (at low boost) through twin SU 1.75" carbs as a stop-gap til I find a big engine (and the time!) to transplant.
Has anyone ever done a turbo upgrade to a non-turbo engine? I've found plenty of sites on the web (such as , so I know that it can be done!
Currently I'm wrestling with fuel pressure problems.
Should be fun when it's done! And if the engine gives up the ghost it'll be a good excuse to stick something bigger in!! ;D

[Revolution 9]

A turbo conversion sounds like a good idea! Apparently this is not a terribly hard job on Imps like mine, and I gave very serious thought to trying it, but look at what you have to do to the bodywork to get the turbo to fit! not unless you extended the bodywork or something, but maybe then it would just look plain ugly!

Here's a turbo Imp, but again, note the rear panel that sits just under where the engine lid finishes is missing to allow that re-angled exhaust to exit clear of all that pipework.


besides, look at the mess of it all, compared to a regular rallying Imp engine bay...


I notice that the turbo Imp has lost it's opening rear window too, shame, as all the saloon models had this and it is one of the most practical and destinctive features of the Imp!

[igbandy]

biggest problem realisticaly speaking is you have to consider lowering the compression ratio, on practically every turbo conversion this is carried out as fas as I am aware, due to various problems like pinking and melt downs ;D

[Revolution 9]

igbandy said:

biggest problem realisticaly speaking is you have to consider lowering the compression ratio, on practically every turbo conversion this is carried out as fas as I am aware, due to various problems like pinking and melt downs ;D

Oh, it goes without saying, but another thing I'd check is that nothing is rubbing or chafing when it's fitted. I mean, it's all very well flying down the road with your car running perfectly, but if your pipework is rubbing the wheelarches or battery or something you'll end up with holes in it and a leaking, smoking mess in your engine bay! That and be careful that the pipework isn't too close to your exhaust, or the air getting in to the engine may be uncomfortably warm for the engine, making it run hotter and causing a risk of overheating. That doesn't just apply to turbo'd cars, I'm going to have to create heat shields for my Imp's carbs because the twin Strombergs I put on it sit very close to the exhaust as it is, and the custom one I'm fitting will make things even worse as it will be closer still.

[BenzBoy]

I love that silencer, bolted straight to the turbo! Must make a helluva sound! I see what you mean about hacking up the bodywork though.

As for compression ratios, I'd only be running a very low boost - 4-6psi, which should be OK for running on Super Unleaded (with a few ignition tweaks and the like) and keeping my 9:1 CR. Manufacturers have started making Low Pressure Turbo engines - they have a standard compression ratio (8.5 to 9.5:1) and the turbo running low boost.
I have to re-route the downpipe to accommodate the turbo - and watch for things getting hot under there!

[GrumpyOldMan]

Turbocharging is very popular around here, due to the foolish Greek car taxing system...


First of all, you have to decide how much money you can spend... This will determine the components you'll have to use and the power output you will get...

Assuming you want a low-budget solution, you'll have to make sure your engine is healthy enough to cope with a significant power increase. If not, it will surely self-destruct...

I don't know much about old Merc engines, but a typical T25 will only be OK if you're aiming at around 200HP and your engine is not over 2000cc...

The easiest way to find an appropriate turbocharger would be to buy a used turbocharger off a car with a similar engine capacity/design to yours. The hardest is to try and find the efficiency maps of different turbochargers and compare them. Or you can always go to your local turbocharger dealer and ask for his advise... though that comes at a price.


I think SU carbs are a bad idea, if you intend to keep the 9:1 compression ratio... Note that the 'low pressure turbo' engines have really-really sophisticated injection/ignition systems, in order to avoid pinking. And their combustion chambers are far superior to those of our old engines.

I would experiment with a Megasquirt injection ECU, which will be safer for the engine, better for power, while being relatively inexpensive.

If you really have to use SU's, the cheapest [and not really correct, but usually works] solution is to use a thicker head gasket [or even a pair of them] to lower the compression ratio... Of course you'll have to measure the combustion chamber volume and do some maths, in order to decide exactly how thick the new gasket must be...

An intercooler is always a good idea, but not really necessary.

Make sure the exhaust manifold is as short as possible, to reduce turbo lag, and use the most free-flowing exhaust you can get, since turbochargers work as silencers.

And make sure that you use the recommended 'struggling' part [I'm not aware of the correct term for this] in the oil feeding line of the T25, to avoid leaks.

[Davenger]

You can run up to 0.8 bar without changing your compression ratio.
but the thing I'd be more concerned about is hooking it all up to your twin carbs
I doubt it will be easy

[BenzBoy]

Thanks for the responses! Psychodriver - very helpful in depth advice! My engine is only 2.0, and the T25 is from a Rover 820 Turbo, so they should be a close (ish) match.
I see what you are saying about the SU's - they will be a pain in the as :os, but things are on a very tight budget! I'd love to go for a Megasquirt injection ECU, but it's gonna be £££, and if I were to spend serious cash I might as well get a V8 (amd turbocharge that!!)
The SU's were free, and the T25 only cast me £25 so you can see what sort of budget I'm on!
dminifreak - as you say, plumbing it all in will be a headache, but what I intend to do is build the whole system without modifying my original setup, so if it all does go wrong at least I can unbolt it all and carry on as if nothing has happened!!

[Davenger]

Oh yeah, where did you get your SU's from in the end?

[GrumpyOldMan]

BenzBoy said:

Thanks for the responses! Psychodriver - very helpful in depth advice! My engine is only 2.0, and the T25 is from a Rover 820 Turbo, so they should be a close (ish) match.
I see what you are saying about the SU's - they will be a pain in the as :os, but things are on a very tight budget! I'd love to go for a Megasquirt injection ECU, but it's gonna be £££, and if I were to spend serious cash I might as well get a V8 (amd turbocharge that!!)
The SU's were free, and the T25 only cast me £25 so you can see what sort of budget I'm on!

I see... At least try your best to get the fueling right, to minimise the possibility of an engine meltdown... And -of course- make sure the SU's can work in a blow-through setup (as do the ones that are used in Metro turbos).


A rolling road session would be ideal. If you can't afford one, you can always get a heated lambda sensor and a halmeter (DIY or even a simple voltmeter), and drive around with a friend in the passenger seat, taking note of the air/fuel ratio in various rpms/loads... This will help you decide on the SU needles you have to use, and I suggest you tune them a bit rich, for safety reasons.

Plumbing the whole setup is not that hard... The hardest parts are fabricating a plenum chamber to feed the SU's with air and making a downpipe that will withstand the weight of the turbocharger and the high temperatures without cracking...

Good luck with your project !!!

[MWF]

I have a XR4x4 which was originally NA and now turbo'd and I'm in the process of turbo converting my NA XR4i.

Not really a lot I can say that hasn't already been said. Although I feel an intercooler is essential and not hard to sort out. Have a look at the MG Meastro and Montego, and also the Renault 5 turbo as those all blew through carbs.

[BenzBoy]

dminifreak - I got the carb off of eBay for 99p! I think the guy was hoping for more - he was a bit disappointed when I came to collect.
I have to find a Malpassi rising rate fuel pressure regulator but these are a lot of cash new, so (for the chapskate option!) I have to find one from the suggested cars (MG Metro / Maestro / Montego Turbo, Ren 5 Turbo...)
Good point about the Lambda sensor - my T25 has one built in, which makes things easier!
MWF - I'd be interested to know how you get on! I'll keep you posted on my project also.

[Davenger]

99p ;D
Top job mate

[Revolution 9]

99p! Well done that man! Although I'd have probably have got guilty and gave him £5. Strange, anywhere I get cheap parts the guy selling normally says "a fiver'll dae, mate" so it's become a habit!

[BenzBoy]

I felt awful! I did offer him a fiver but he refused - even gave me 1p back!! Talk about a guilt trip....