diesel to V8 conversion - PeachParts Mercedes-Benz Forum

deferr · #1 10-03-2004, 03:05 PM

Alright, I was thinking the other day that while I love my 78 300D for cruisin around town and as my daily commuter. I would love to have a car that had a little more get up and go as well. Basically a project tinkering car. So my idea was that If I were to get an older, early 70's maybe late sixties car, and I would like to transplant a chevy 350 or 305 in it with a manual 5 speed. Which model best suits such a transplant. Also how much would I expect to spend on a car such as this. I wouldn't car about the drivetrain condition because I would be replacing it anyway. I would mainly be concerned with the rust issue. Any thoughts anyone.

psfred · #2 10-03-2004, 05:42 PM

V8 won't go into a W115 unless you cut part of the fram out, which I do not recommend.

Look for a 71-72 W108 4.5L, someone (Benz) has already done the transplant for you....

Peter

300SDog · #3 10-03-2004, 11:36 PM

Hell, the '78 300D can be practically anything.... 115, 116 or 123.

I think the 116 will take any MB engine you want including the 4, 5, 6 or 8 cylinder - it doesnt matter because bell housings and engine mounts are the same, but final drive ratios will differ.

Both the 115 and 123 have never had an 8, so you will probably be fighting subframe and engine bay clearances there. Especially think about clearances for the manifolds.

We usually laugh at people who throw Chevy V-8's into the MB as if the Mercedes engine is the worst part of the car, but lately somebody came in here with an excellent Chevy conversion into a 108. He knew what he was doing and has contributed alot of info on this conversion idea, almost matching original MB specs for engine weight and torque.

Surf back a few pages and you will find the multi-page thread and can wake it up to get exact details. Respond and it will be kicked to the top of the list. Around here it usally takes at least a week for threads to get past page one, so nothing gets lost.

He said he used the original MB tansmission and drivetrain. I think his name was Mercedes_68.

Diesel4me · #4 10-04-2004, 02:24 AM

Here's an nice W123 coupe with an equally nice Corvette powerplant.

www.badbenz.com

68_Mercedes · #5 10-13-2004, 04:35 PM

Thanks for your very generous comments 240DieselDog

I have 2 conversions, one being a '67 250 S with a 350, and the other being a '68 250 S with a 229. Both of these are 108 chassis. Both are possible, both work well. Each has it's own advantages and disadvantages. While the 229 is only a V6, it lacks a little horsepower vs a 350 V8. However, I compensated by putting in racing gears, a larger cam, a highrise aluminum intake, Holley carb., etc. So she's pretty well equal to the 350 V8 in the HP department now. Along with that, the V6 gives you sooooo much more room to work under the hood.... and you don't have to scrap the motor-mounted radiator fan. On the other hand, the 350 is more common, a wider variety of parts are available, and all in all, just easier to get parts for. It also works quite well in the 108, and has more than enough horepower stock to give you a great ride... infact, I lit up the tires and left about a 20 ft burn mark on my shop floor.... was just goofing off and wanted to see what it could do... now I know! LOL! Downside is, it eats up most of the room under your hood, you have to scrap the motor-mounted radiator fan and rely totally on an electric one, and if you buy any 108 chassis other than the 280 SE with the 4.5 engine, then you will have to change out the springs and what not to beef up the suspension to carry the weight of the 350.

Any 108 Model chassis can be converted, and I can photo/explain most enything you need to know.... Just be prepared... it is NOT a cheap conversion. If you are mechanically inclined and can do the work yourself it won't be so bad... but if you have to go to a mechanic to have this done, you better have an easy $5K ready to dish out to him for his labor, not to mention the cost of all the parts..... and not to mention the cost of my keene advice.....

I will say this though... no matter if YOU do the work, or someone else... start with a junkyard engine. The first 229 I put in my '68 came straight out of the junkyard... I paid the guy $150 for EVERYTHING (motor, transmission, and ALL accessories). The motor ran like a striped ape and there was absolutely nothing wrong with it... but came out of a car that was totalled... I rebuilt it later, and not even because I had to, but because I wanted to so I could make it high performance. You could probably get lucky and pick up a 350 the same way... that way you don't invest too much at the beginning.... remember, it might take you several years to complete the project, in which time the seals could dry out, cylinder rust could develop, etc., etc... so get everything set up first with a junkyard engine, then when it is complete, pull it back out if you want to/need to, and rebuild it at that point......

and here's a pic of my '67 with the 350 in it....

deferr · #6 10-16-2004, 10:41 AM

Hey, I read your other post about your conversion. I'm impressed! Very Nice Car!!!!!!!! So anyways one thing that I have heard rumor about when using the 350 is that my front crossmember interferes with the oil pan on chevy motors????? Was this an issue for you? If so what had to be done to make things work? Also.... I plan to do almost all the work myself. My dad owns a laser job/machine shop. So I have capabilities to mill things such as adapter plates for just the cost of materials (I work there too and can have access to most things after hours if I ask real nice

) . Also could you e-mail me some in process pictures????? just some of the main steps. Thank you very much......... You've renewed hope in my "pipe dream" as my dad calls it.

68_Mercedes · #7 10-16-2004, 11:27 AM

I don't know if my particular application will help you much, since these are completely different chassis, but I will be glad to help you all I can.....

In the v6 conversion, there were some probs with the crossmember, which took a wee bit of altering to fix.... In hindsight, it's a live and learn type of thing, which I might have been able to avoid, knowing what I now know, but it didn't affect the performance of the car at all, so it's ok...

As for the 350, the crossmember was NOT altered, believe it or not, and the 350 fits beautifully in to the car. Unfortunately, I do not have any pics from the "in the process" period. Lack of foresight.

I can't tell you whether or not the 350 would fall in to place in your car or not... especially without taking a stroll around it and getting a good look at it and taking some measurements. However, even if the oil pan DOES get in the way, there are ways to fix that. One, you can use an aftermarket oil pan, there are many available since the 350 is used so widely in street rod conversions. I have even seen instances where 350's were switched to be front sump, to avoid clearance issues. Also, if you are pretty handy, you could take off your oil pan, cut it, and custom reshape it to allow it to fit, if this becomes necessary. Thing is, there are many remedies... one just has to look at their particular application and see what needs to be done and what will work best in the long run....

And don't worry about the "pikedream" statements.... I got plenty of those too when I was building my '68! LOL! ESPECIALLY from my dad. It used to be his car, and he was NOT at ALL happy with my conversion idea.... infact, he threw a fit... I HONESTLY had to hide the car from him while the conversions were being done because he was sooooooo against it.... BUT...... after it was done, and he'd taken it for a drive (spinning the tires at every start and every corner), he was thorougly impressed! After his first test drive of the car, his exact words were: "Son, that's the best thing that car could have ever had done to it"..... I think that's the best comment my dad ever gave me.... I suspect if you do a good job, your dad will say something very similar....

Anyway, here is my post about many of my conversions.... check it out. (w108) Non-stock Mercedes wheels and tires, oh and motor too! lol

Before starting this process, do what I did and check weights, HP and torque specifications, etc., etc., as I have listed in my post. It will give a better idea of what problems you may or may not run in to, and will also let you know things you need to do to correctly complete the conversion.

Another good idea... take your car to a scale... say like a trucking scale, and weigh it now as it is. When the retrofit is complete, take it back and weigh it again. It is very likely that you will have to have custom springs built for the front end. By knowing the stock weight of the car, and the retrofitted weight of the car, it will make a spring shop's task simple to retrofit you with a new set of springs....

Also, check the transmission and rear end gear ratios of the particular car you have, vs the typicl transmission & rear end ratios of the types of cars that the motor you chose would typically be installed in. Make sure that the rear end is not geared too high or too low for your application.... With my '68, the chevy motor/transmission did not mesh well with the Mercedes rear end which is why we pulled it and replaced it with a vette rear end. But in the '67, it still uses the Mercedes transmission and rear end, which work well together.

And don't let anyone TELL you that a 350 won't fit in your car... that's not entirely true, more than likely (I had so many people tell me that very same thing.... go figure! lol!)....... But if by chance it turns out that it won't fit, I know someone who can tell you how to convert a 108 chassis to sport a 350 if you would like to do that...