Supercharging a '67 250SE - Mercedes-Benz Forum

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post #1 of 13 (permalink) Old 03-20-2005, 09:28 PM Thread Starter
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Supercharging a '67 250SE

Hey People, I am working on a custom Mercedes project. DOes anyone know how I can beef up the engine? Are there performance parts available for these cars? Does anyone know if I can supercharge it? If so, any recomendations?
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post #2 of 13 (permalink) Old 03-20-2005, 11:20 PM
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RE: Supercharging a '67 250SE

had that idea a few times. havent taken it anywhere yet. i have read others have put v8 and v6 in them. one with a v6 with a vette rear. would be interesting to hear what others have to add. i am also sure u would tick off a few purests.

grez
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post #3 of 13 (permalink) Old 03-21-2005, 04:48 AM
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RE: Supercharging a '67 250SE

As an injected engine it's a good base,convert the MFI to EFI with one of the many kits available ,The japanese have lots of different supercharger aplications where the blower has a clutch like an Aircon compressor.http://www.rodshop.com.au/superchargers.htm
This a link to company who can supply you with everything you need to supercharge your ride.[8D]
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post #4 of 13 (permalink) Old 03-24-2005, 10:36 PM
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RE: Supercharging a '67 250SE

sorry for off topic, but where'd u get the nice artwork pic? are there more? looks awesome. a true stuttgarter gangster car.
post #5 of 13 (permalink) Old 03-25-2005, 12:13 AM Thread Starter
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RE: Supercharging a '67 250SE

Thank you for the compliments. The artwork is of my own. I am an automotive designer.[^]
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post #6 of 13 (permalink) Old 03-25-2005, 07:28 AM
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wow. u do a very good job. remind me to call u when i finish saving up for a total makeover of my Coupe. do u sell pictures like that as posters or such? thats the kind of stuff i'd like to decorate my house with. again, AWESOME, and keep up the good work.
post #7 of 13 (permalink) Old 03-26-2005, 07:33 PM
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RE: Supercharging a '67 250SE

Supercharging is definitely a good way to get loads of extra grunt without a complete engine rebuild but I'm thinking the '67 being so long in the tooth will probably want a good reconditioning anyway if it's not going to let go once you start planting the foot.

Three types of supercharging are available:
Roots-type superchargers are like the classic 6:71 GM style blowers and work like a big fan shoved onto the engine. Gives great low-mid range power and just keeps building boost as the revs rise.
Eaton makes some good low-blow units you can get in variously manufactured kits/bodies for stock and near stock small-medium capacity engines. People like B&M and Weiand make the serious stuff.
Roots-type superchargers can be piped to blow through or draw through your stock throttle body, or mounted to a custom intake manifold for a draw through setup with whatever aftermarket stuff you want to put on it.
The biggest consideration for one of these is making sure you get enough airflow cfm per cycle for your needs (manufacturer guidelines are very rough, better to do your own homework and don't trust the salesmen).

Turbochargers work like an air compressor run off an exhaust turbine. They compress a charge and then release it into the engine, giving a sudden boost in performance and sized right for your engine's needs, maintaining it as the revs climb. Biggest consideration with these is making sure you've got the right compressor diameter for your car, so you get boost at optimum revs.
Also something called an island has a cfm rating that determines the max boost a given unit is capable of on a given engine.
For yours, a 350 island-cfm rating might top out at say 6psi, a 500 at 10 and a nice 800 at 14.
You control the unit-available pressures with a wastegate and blow-off valve (better internal than the generally unroadworthy external ones).
Once again, a little bigger on cfm rating is better than too restrictive, but make certain you get the right diameter compressor piping to bring the boost in just right and then control it on the wastegate and blow-off accessories.

Centrifugal superchargers are like a turbo driven by a belt drive rather than an exhaust mounting, but in action work closest to turbo-supercharging of WWII era fighter design.
Once again they compress the charge before it goes into the manifold but they build up boost somewhere between turbo charging and supercharging and in race applications work best at mid-high revs.
Low-blow units available in these types are a great compromise, delivering a couple of psi at low revs and giving good power gains for stock engines, then hitting strong at mid-range with its designed boost range through to redline.
To drive you can feel them come on down low without any of the lag associated with turbos.
These you have to control a little more directly with their turbo-like island-cfm ratings and get the right one for the boost you want, then control where in the range it comes in with the belt gearing. Also a good idea to pop pressure-release valves on them (works like a wastegate/blow-off valve).

But like I said your engine will want a freshen up anyway, with new bearings and some regrinding and flushing. The bonus of this is you get to improve a few points here and there with a total project in mind, to get the most out of the application and setup you've got planned.
Get low compression, stock flat-top pistons fitted for around 8:1 static compression ratio. With good cam timing this will drop to around a 6.5:1 dynamic compression and is good for mucho boost and massive power gains on supercharging. Throw your manufacturer's guidelines out the window here and go for 15psi street boost for some real wheelspinning action and good quater mile times.
If you're going to go full house (ie. chasing 400hp out of the old 2.5E), inquire about Porsche pistons and rods resized to fit, most of 'em are pretty close to the Merc bores.
You can also flow bench the head for the right intake/exhaust ratios for your supercharger type, getting the most out of the setup (can be worth as much as 20hp just there). And all new double valve springs, etc.
Make sure you have a good flowing, tubular exhaust fitted.

Most of the stock internals are actually pretty good for mid-range performance applications, the Mercs are generally designed to spin to 6500rpm safely as is so can take low-medium boost designs and return high performance without trouble, so long as you get the compression and flow ratios sorted.

Stock Bosch manifolding is good for blow-through supercharging and on a basic setup there's no real need to change the throttle body. You can source larger injectors from other models and you'll need those.
Get some specialized supercharging cam grinds too.
A windage tray fitted to the sump will help. So will an electric fan, gapless piston rings and it is a must to have the whole engine expertly balanced during the process.

And don't forget a bigger radiator. When you're playing around with boost, think about intercoolers and water injection (especially for turbos and centrifugals).

driving a fast car should feel like falling off a building.
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post #8 of 13 (permalink) Old 03-26-2005, 10:52 PM Thread Starter
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RE: Supercharging a '67 250SE

Wow...thank you very much for putting in the time and effort for the information. There is more mechanical info than my brain can handle at once. I am going to print this out and sit down with a few local brains to see where we need to start. I greatly appreciate your effort. One other question that I have is, after making these mods to the 2.5 engine, will the stock 4 speed floor shift work, or would I have to swap that, as well?
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post #9 of 13 (permalink) Old 03-27-2005, 06:00 AM
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RE: Supercharging a '67 250SE

A four speed? RHD? you have a rare car.There werre very few RHD coupes made and nearly all were Autos.The four speed is OK ,it's the same trans they put behind the 3.5 V8[8D]But for all out high performance use,don't bother with the original engine,they are very good engines but i really would go with the 6.3 or 6.9 Plus the trans etc for them,but there is also the 117 5.0 liter V8 engines,from a W126 500Se/SEL.Stock, they are a huge performer in that chassis and it's almost a bolt in fit.If you are going to the trouble to chop the top,the trans tunnel needs to changed to suit the larger #722 series trans.When it comes to Mercedes engine mods,don't mess with the small change,go for the biggest engine you can find....How about a W140 V12 6.0 liter?[}:)][}:)][}:)][}:)][}:)][}:)][}:)][}:)][}:)][}:)]
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post #10 of 13 (permalink) Old 03-27-2005, 08:06 AM
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RE: Supercharging a '67 250SE

Mercmad's got a good point. It all depends primarily on how much cash you've got ready.

Supercharging the stock engine will give you small V8 like performance with a bolt on fitment. Expect to spend a couple of grand plus a freshen up for the old engine.

Swapping for an aluminium 5.0 litre is the nice retrotech option. Bonus is it doesn't weigh much so you can save on brakes and like the man says, should be pretty close to a bolt in fitment.
But you'll have to change the tranny. Maybe the tunnel to accommodate. Go over suspension and rear end to make sure of everything. Change the radiator. Spend money on Jim Beam cans and toolkits, you know, all the usual.
But after all the work it'll leave your supercharged 2.5E standing at the lights. Just it'll cost you.

The 6.3/6.9 option is of course the ultimate. And it'll cost the ultimate amount.

The smart thing to do is have a plan. What kind of performance do you want, and how much are you prepared to spend.
Once you've got that sorted at the start, you won't go wasting money, because you'll be spending what you allocate in the right place.

driving a fast car should feel like falling off a building.
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