Head coming off - tuning? - PeachParts Mercedes-Benz Forum

pentoman · #1 05-26-2007, 07:47 AM

I am having the head reconditioned on my 2.5-16. I wondered if, while the engine is in pieces, there's any point to doing some tuning work? I hear talk of exhaust, filter, and cam changes unleashing up to 30bhp or more on other four-cylinder cars and taking them up to 100bhp/litre. Is the 16v not capable of this too??

I know someone who had his head ported & polished (well the car's head, not his!) and I drove his car. There didn't seem to be a big difference to be honest.

thanks

Russell

MTI · #2 05-26-2007, 02:58 PM

The twincam head, being thin walled, has to be addressed carefully. I've read that some of the intake casting work could use some smoothening out, but as you noticed, it won't yield any real HP gains.

Tuning with cams has it's pros and cons. It's taking from one side and giving to another. A cam and upgraded valve springs that allow more revs typically means that you'll lose torque at the low rpm range. Hence the appreciation for variable cam technology.

While not as "rev happy" as the 2.3-16, the 2.5 is usually regarded as a better balanced engine for everyday driving. So, if you want to live like the 2.3 folks (life begins at 4K rpm) then cams are an easy way to go.

pentoman · #3 05-27-2007, 10:10 AM

The 2.5 still has a noticeable step at 4,000 rpm. I'd rather not sacrifice low-down torque for high end power if possible. Maybe that's just asking too much?

maggot · #4 05-27-2007, 04:55 PM

I've recently got my C36 head back from this chap http://www.sabre-heads.co.uk/1.html and am very pleased with the results. They are posted on his site under european cars...c36 twin turbo. Worth a call perhaps ?

Racing · #5 05-28-2007, 04:52 AM

Pento.
IMO,just make sure the head in on spec.
There´s flow enough in that head to suffice way longer than any low budget tuning will ever make power,and chances are that even scared porters might F it up.
Yup.
It flows that well,and the valve sizes of it is HUGE.

If you wanna step power up a tad,the intake and a stand alone is what you want.
The stand alone install is THE mod for these cars,and when intelligently applied..it almost wont show.
As you´ve probably also read the OEM intake sports runners way to long for spirited driving.
No two ways about it.

A sidenote maybe,but a fellow countryman to you has written a good book on the subject.
It´s called "4 stroke performance tuning",and is by Alexander Graham Bell.
My advice..read up..cause the man knows a thing or two that he willingly shares in that book.

pentoman · #6 05-28-2007, 08:28 AM

Thanks guys.

Quote:

Originally Posted by Racing

Pento.
IMO,just make sure the head in on spec.
There´s flow enough in that head to suffice way longer than any low budget tuning will ever make power,and chances are that even scared porters might F it up.
Yup.
It flows that well,and the valve sizes of it is HUGE.

If you wanna step power up a tad,the intake and a stand alone is what you want.
The stand alone install is THE mod for these cars,and when intelligently applied..it almost wont show.
As you´ve probably also read the OEM intake sports runners way to long for spirited driving.
No two ways about it.

A sidenote maybe,but a fellow countryman to you has written a good book on the subject.
It´s called "4 stroke performance tuning",and is by Alexander Graham Bell.
My advice..read up..cause the man knows a thing or two that he willingly shares in that book.

Racing - EFI is indeed what I would do ideally, as I've enjoyed reading what you say about it a few times. I'm sure you're right about the head as well and will just go for standard. I will look for that book - thinking about it my dad may have it.

About the intake runners - are they so long to improve torque? If so where is the torque improved?? Because it never feels like a torquey engine the 2.5-16. In a way I feel I would prefer something like BMW's mid-late '90s 2.5 with 'only' 170bhp. The power figure may be low but the way it's delivered is first rate.

The same goes for the 4.4 in the 740i - only 286bhp but it feels much stronger than the 300bhp 4.2 in the Audi A8 Quattro and even stronger than the 326bhp 5.0 M119 in the Mercedes S500 or SL500. I love engines which feel faster than their quoted power suggests (the 2.0 8v M102 is one of those engines). The 2.5-16 is the opposite..

and that's where it disappoints me, for road use anyway. It's not so much being 'off-cam' as just flat and unwilling and not feeling like it has 2500cc capacity. Shouldn't that big valve twin cam head give it more power throughout the rev range, rather than just up top?

I suppose I'll see what the rebuild brings - some of my low down torque was gone away with the compression no doubt. Fingers crossed it will be much improved afterwards!

Racing · #7 05-28-2007, 03:07 PM

I think i see what you´re getting at,and frankly that´d come down to driver preference if you ask me.

I guess you´ve at some point come across the expressions "oversquare" and "undersquare" engines?Most enthusiats do at some point.
Well,the simple truth is that very few engines today are built oversquare(Ie bore much larger than stroke),and the reason for this is that it set the parameters for a less torqie engine(and less fuel efficient seing the revs involved for most stock engines)-but what it gives away down low it regains up top.
I guess what i´m trying to say is that the design parameters of the 16vlv was to make it successful in motorsports,and to make it such you HAVE to rev the little engine to make power.
Just comes with the territory.

Now,mercedes in turn tried their best to "civilize" it if you wish,leaving us with an engine that´s far from the beast it was intended to be from the onset.(A bell rings telling me that when cosworth delivered it to merc it put out something like 267 in NA form)
One way of doing this was to set the engine up with intake runners that indeed emphasize low end torq as best as they could.
Here you have the reason for those extremly long intake runner-that indeed will kill the little engine´s main advantage.Its ability to rev sky high.

If we for a second put things into context a little,at least i am amazed that these engine can be had to rev to....TWELVE THOUSAND rpms..seing that it indeed is STOCK BLOCK racing after all(pure race engines is something else),and as such it indeed did the trick to say the least.
These days,with current state of the art engine management,i´ve been to understand that the little engine that could can be had to develop inxs of 400hp as a NA engine...and in my book that says a LOT for a design that old-cause old it indeed is.
The 16vlv indeed has a racing heritage to fall back on..no two ways about it,and it also takes to higher revs than stock with ease.
However,as with anything mechanical there IS a practical limit,and for a 16vlv that´d in my book be just the other end of 8 grand in street form.(After those 8 you´ll have to swap a LOT of stuff within.Rods might break,valves are to soft,valve spring wont take it asf asf asf)

A 2.5 will however react in a positive manner from the install of an EFI way more than most will believe.
The mere fact is that we these days can make engines run MUCH closer to the edge that we did the odd 20yrs or so ago mainly due to the advent of affordable electronics.
(and if you ask me mercedes should be ashmed of their pricing of parts for these cars as well as other "high end" mercs as there indeed ARE enthusiast around that wants to keep them alive for whatever reason really)

Thing is...
These engines are also setup for 95 octane fuel(euro) OEM,and if you can live with the fact of filling her up with 98+ from here on a LOT can be gained.
Instead of trying to convince you of it...look around the various sites that i know you frequent..and ask..
It aint no lie.
These engines can indeed be had to deliver..
An "average" increase of power for your car from the stand alone install alone would be at the tune of 25hp +...but that´s only half the story really.
What those dry numbers WONT tell you is the difference in throttle response,dynamics,economics asf asf asf....
Closed loop wide bands and MUCH better resolution of the modern systems makes the OEM KE system look like yesterdays news for real.

For instance...exactly what you´re after(If i´ve read your wishes correct)...
Better driveability..
Is a result you can expect from a well setup SA.
IOW,the motor will FEEL much more torqie...as well as being more so.

Rock steady idle.(Hell...if you read the OEM specs merc even states that a closed loop lambda controlled car CAN NOT be had to have a steady state idle!!!!)

What´s more is that YOU are left with full and total freedom of control.
Ie;bring the laptop out and go at it..
If something´s at fault...just plug the laptop in and have a look at what it might be.
What´s more...if and when something breaks down...it won´t cost an arm and a leg to replace.Screw merc from that perspective.

I absolutely guarantee..the day you´ve had your SA installed...you will NEVER look back...yup..it´s THAT much of a difference.

On the subject of runner lenght.
I don´t recall the exact numbers atop of my head,but OEM i believe the intake runners are something along the lines of 500mm+.
Now,we know for a fact that an engine that is supposed to be shifted around 7500 need runners approx 330-350mm total..(one measures this from the valve seat out to the trumpet end)
So..all in all,what happens is that the OEM intake will to the letter rob you of power as revs go up.
Hence why it makes for such a difference to build a shorter intake.

I guess you´ve seen some of mine on occasion,and yes..they indeed do improve power.

Valve sizes are tremendous for this engine.
38mm in and 33 out.
To put it into context...
It almost has the same diameter OUT that a similar 2,3.16 volvo has IN.

If there´s anything you want me to clear out for you to the best of my knowledge...please let me know,and i´ll do my best.

Jesper

Racing · #8 05-28-2007, 03:17 PM

Pento.
As for the headflow.
Power is always within the head,and the heads ability to flow vs its swirl and port/valve dimensions.This is a tradeoff to an extent,but where cosworth really knows their **** is when it comes to getting stupid amounts of flow out of relatively small holes.
For the sake of argument...
The merc 2.5 head will flow inxs of 350 cubic feet per minute at a mere 14mm of valve lift on the stock diameter valves.
K.
Log onto one or several of the aftermarket head casting companys for the big american V8s...
Look the flow numbers up,but have in mind.....
Those 350+cfm for a stock more or less untouched head are there to supply a mere 600ccs of cylinder.
Do the math,and please also have in mind that this is done over two 28mm large holes.(reall really minescule when compared to the others).
Now...now you´ll appreciate why not to let Cpt Klutz go near the head with his die grinder at the power level you´re at.
In short...let me assure you...cosworth did it right the first time out..

pentoman · #9 05-30-2007, 11:38 AM

Ah yes, of course I forgot it's an oversquare engine.. I suppose me wanting good torque from it makes no sense!

A variable-length intake device would be a very nice feature to have...

Will certainly leave the head untouched.

pentoman · #10 06-09-2007, 05:48 AM

For those interested some quick pics

Put away before work started

Radiator removed, valve cover off

Drivetrain coming out

In special company today

Head off

Valves

This is the worst cylinder. and it's not bad really

That all-important marking!

pentoman · #11 06-12-2007, 06:15 AM

So there we are.. finally all stripped down, valves removed. I really feel that while I'm here I should be doing something to give me a chance of keeping up with all those fast modern cars! EFI is becoming more tempting...

Getting the head off wasn't too hard, plus I have a masters degree in computer systems engineering, so maybe I could manage an EFI project ok....?

Racing · #12 06-12-2007, 03:02 PM

Most def.

Pento.
I´m NOT saying that it is it...but visit;
www.vems.se
..and download the software.
Very,very similar to the MS.
Get comfortable with it.
Don´t gret the config parts of it,just play around with the software and if you need it..just say so and i´ll be happy to send you a base NA map to fool around with.

matsalleh76 · #13 06-16-2007, 12:26 PM

Visit Silvercosworth's e-Bay store for the required fuel rail, injector adaptors, trigger wheel, etc for EFI your conversion. Good stuff that will work with VEMS, MegaSq, Wolf, etc, etc.

Yes, I have an interest in Silvercosworth --- he is a personal friend, sincere, a real 16V enthusiast and makes & sells quality bits -- have a look.

bobf.

pentoman · #14 06-21-2007, 05:06 AM

Spot the problem....!!!

Racing · #15 06-21-2007, 05:18 AM

We´ve had like 3 or 4 heads at the shop with cracked valves too.
IOW,it seems like a half frequent problem.