M103 refresh tips

[Mighty190]

I'm doing a head gasket and rings w/ bearings if it looks like the bottom end needs it on a 3.0 M103. While its out are there any tips/tricks I can do to pick up a little power? We're restricted to running a M103 with the "stock head" in this case but I can mill it and I was thinking about looking into the ports to see if I can clean them up any. I've never been a big believer in expensive multi angle valve jobs but I could be convinced otherwise.

[Sugar Bear]

Sorry no performance tips ... Sounds like you're going racing???

[Mighty190]

Yes we race our 190 in champcar (formerly chumpcar). Its a lot of fun even if they really want everyone under 200hp.

[97 SL320]

Any valve grind is going to be at least 2 angles , the main angle then another to get seat width correct. Many ( production ) shops use a seat cutter and these are almost always 3 angles. Anything past 3 angles isn't worth it.

Back cutting the intake valves can help, this is where you put a 30 ish degree cut on the stem side of the valve face to eliminate the ledge. Leaving a ridge on the exhaust can theoretically offer some anti reversion.

Cleaning up the bowl area of the port can be helpful, just don't take much if any material from the short side radius ( where the port floor hits the valve seat ) as this is needed to get air to turn the corner / prevent turbulence.

Do a leak down on the motor, I'd be tempted to keep the old rings in place if they seal reasonably well. New rings would seal better but have more friction until miles down the road.

I've clipped a hump from oil ring expanders then slightly stretched out the expander to adjust oil ring tension. I shoot for 1/2 of the normal oil ring expansion beyond the bore. If a bore is 4" and a expanded oil pack is 4.20" , I go for 4.10". These are not set in stone numbers , just a " that looks OK and offers less friction ". After doing this keeping an eye on oil consumption is a must. The engines I've done this on see sprint races not hours long events.

Does this engine have rocker arms under the cam like a 2.3 Lima ( Pinto , Ranger , Mustang ) Ford ? If so, shortening the valve tips and raising the lash adjuster will give more lift / duration / change event timing because you are changing the rocker ratio better. Have a look at Esslinger Engineering and Racer Walsh , they were big 2.3 Ford builders in the day and should have some info.

For some really heavy duty stuff, look at old posts on the Speed Talk forum, there are some really high end builders there. Pretty much anything you want to do has been covered in the past.

[MAG58]

What year M103 are you running? What rules do you get for cams, bottom end etc?

Can you run a late (flat top) Bottom end with an early (high quench) head? That should bump your compression. Depending on how "Flexible" the rules are you could even run either .98 M104 pistons which I think have even less dish than the late 103 pistons or run a M104.99 bottom end in the block to get to 3.2. IIRC the M102 early engines had solid lifters instead of the hydraulic lifters but to be honest I never checked to see if they'd work in my M103 because I just went to M104.


Also when you go through the head check the valve guides, the thrust angles on the valves tend to wear them out pretty quickly.

[duxthe1]

I've never flowed one but the 103 head has pretty nice ports as cast. I'd be surprised if there is much, if any, improvement to be had at stock lift and RPM range.


While I wouldn't pull a motor apart to do it, thermal barrier coatings for the piston crowns, head and valves wouldn't be a bad idea with it already apart.

The cam gear has alternate installation positions for +-3degrees. Depending on the tracks you may benefit from power a little higher or lower in the rev range.

What are you doing for engine management?

[Mighty190]

Thanks for the input everyone!

The M103 has rockers over the cam and I have also thought about the M102 rockers or just machining solid lifters for the rockers as I do work in a machine shop. Do these engine have valve train stability issues? That's a big issue with my CA20E powered Nissan.

As far as leak down I do intend to do that before pulling the head and just seeing what I get. If the numbers are good I will leave the bottom end alone. At minimum I need to do a head gasket on this junkyard engine.

I will have to double check the casting but we bought it as a 1990 300E engine to go in the 2.6 190E. This is a junkyard engine that I have never seen run but I have had good luck with that in the past. I had a 1991 300E engine apart a while ago and that had a very open combustion chamber compared to the 2.6 engines. What years have a higher compression head? We can always claim this engine as that year.

As for rules the simplified version of this is we can swap in an engine that makes less than 200 hp stock to avoid taking on penalty laps. Swapping heads, cams, manifolds, rotating assembly, etc from that engine will incur penalty laps for the car based on how we have it configured. Milling the head, doing a valve job, cleaning up a casting, using different rings, etc is open and they don't attempt to enforce that. So really we're stuck with a 3.0 M103 that has a long block that was available stock but we can work it over a little. I'm not expecting huge gains but with the more advanced 2.6 spark timing and some little things here and there maybe we can approach 200hp which puts us with the faster M52 swapped BMWs.

It would be interesting to see how changing cam timing would effect overall power. With the way the 2.6 transmission is geared having more area under curve would be very helpful.

We run the stock CIS-E system. Any tips on tuning that for power outside stock parameters? It would be nice to go to a microsquirt setup on a 2.8 M104 engine but that is a more involved project than we want to tackle before we're running the car in April.

[97 SL320]

I just looked at a vid of the M103 valve train. https://www.youtube.com/watch?v=O2RXmJ917t0 Wow, there is massive side loading on the intake valve stems and less but still bad on the exhaust.

About the only way to get more lift / duration without another cam is to reprofile the cam contact pad on the rocker. This is where you move the crown towards the pivot point. A fixture on a grinder is the only way to be consistent. This would also be a try a pair, degree things and decide if there is any benefit.

[Mighty190]

Yes that would be a serious project but this is a good idea. Short of CNC cutting new rockers you're right. I wonder if they're swapable and different from side to side or with different engines.

[MAG58]

I cant remember if it's early or late but 88-89 is the change over

The more closed chamber should look like this:


With these pistons:
should give you the best bang for your buck.

Overall they're pretty stable. Springs are heavy so they tolerate over-rev pretty well. Early (86-88) cams were soft and they would eat cams. When lifters get really old (150k+mi or more) they can pump down over time with pushing the motor. They're hard on valve guides due to the angles so be prepared for that but compared to the nissan engines I have experience with (Z24, VG30) they're better on that sort of stuff.

[Mighty190]

Ok thank you that is similar to the 2.6 head. Do you know the valve sizes in comparison? With the different pistons I guess I can't really swap that on but its still interesting to know.

[97 SL320]

Originally Posted by Mighty190

Yes that would be a serious project but this is a good idea. Short of CNC cutting new rockers you're right. I wonder if they're swapable and different from side to side or with different engines.

The reprofile can be accomplished without CNC equipment. You would need to make a pivot fixture that holds the rocker. Finding out where to put the pivot is the issue so the fixture needs to be adjustable and repeatable.

The rocker pad ( where it contacts the cam ) should have somewhat of a crown, the goal is to move this crown towards the rocker pivot. If you can get a hold of come CAD software / Autocad Inventor you could get some idea of the effects.

Given the complexity of this rocker system, I'd first look into shortening the exhaust " Y " pipe to suit your rev range. For some reason, Euro and Japanese cars seem to like split manifolds on inline engines making what amounts to a tri - Y exhaust header.

Do you have access to a dyno? That is the only real way to determine power gains, anything else is a guess. ( unless you are testing by drag racing but even then there are variables. )

[Mighty190]

I do not have a dyno which is another reason that I would be hesitant to deviate from stock too much on things like headers and cams.

[MAG58]

Originally Posted by Mighty190

Ok thank you that is similar to the 2.6 head. Do you know the valve sizes in comparison? With the different pistons I guess I can't really swap that on but its still interesting to know.

I mean I'd be half tempted to clay the valves on a flat top piston and see if they contact.

[Mighty190]

Thank you that is some good info. I'm grabbing the engine from stroage tonight and going to do a leak down test.