Post your performance mod ideas! - PeachParts Mercedes-Benz Forum

Tomguy · #1 04-29-2004, 03:13 PM

Rather than clutter up other threads, post your performance mods for any vehicle here - just say what engine you're modding!
Here's what I have so far for the 4.5, as for stuff that isn't normally done (outside of modernizing the ignition or EFI system) Assume that you have an infinite bank account and that all parts needed are easy to come by. No engine (block) changing allowed!

4.5 D-Jet (1971-1975), in order of smallest to largest:

_+Replace the throttle body with a larger diameter unit. To take further advantage, either cut off the air horn before the point where it narrows to an ID smaller than that of the new TB, and if desired (to keep a more "stock" look) add a new end to it with larger ID. Or, remove the air filter ass'y and custom-fit a K+N tube filter.
__-Disadvantages: Non-stock look with either, unless air horn mod is done very well, it'll stick out.

_+Custom-made exhaust system (dual pipes like stock look) with pipe ID changed from 1.75" stock to 2.25" (1.65x stock volume) or 2.5" (double stock volume). Custom headers, as well. Crossover in the pipes right before where they normally come together (2-3'? before the 1st muffler). Eliminate the first muffler and a custom (high-flow) muffler at the 2nd muffler's stock location
__-Disadvantages: None, really - only the most discerning eye would really be able to tell without closer examination of the exhaust system (to view the crossover). Of course, it will sound different, but once again, only people who know 4.5's will be able to tell (As long as it's still quiet inside, I'm happy - my 4.5 is silent inside but growls like crazy outside!)

_+Swapping the heads, cams, and pistons from a 3.5 into a 4.5, raising compression to about 12.6:1. Bore is the same diameter - direct swap, no boring out or sleeving needed. Assuming no other mods have been done, this is the ultimate "Sleeper mod" - not even the most expert MB fan would know without pulling the valve covers and comparing the part numbers for the camshafts! Even then, they might assume only cams have been changed!
__-Disadvantages: Raising compression to 12.6:1! Expect pinging from any gas under a high octane (96? 100?) and detonation with 87! Possibly backing off the timing can resolve this (to a point).

_+Supercharging (or turbocharging - more work involved) - by this point you probably have already changed from D-Jet to modern EFI but it is possible using D-Jet - at the end of the MAP, where the mixture adjustment screw is, is where it "senses" atmospheric pressure. You must run a line from here to the output of the boost (before the throttle body) for it to call the boost pressure atmospheric pressure, and the difference between boost input and manifold pressure levels is how it would adjust the mixture. Presumably, you'd need to richen the MAP a lot, but it should still adjust mixture per load and throttle correctly.
__-Disadvantages: It'll look nothing like stock. You will need to make mods to the intake you cannot hide, and if using a turbo, major mods to the exhaust as well. For a supercharger, you need to find a place to mount it for it to be powered, and for the turbo, either header modification or relocation would be needed.

This is all I can think of at the moment, shy of machining your own new (custom) heads and cams with larger valves, better combustion chambers, etc.

j9fd3s · #2 04-29-2004, 06:22 PM

also routing the intake snorkle to the front to get some cold air would be helpful, although not easy (maybe).

on the one hand its nice because mercedes gave us a well engineered package, on the other you cant put a 3" peice of pipe on the exhaust and gain 65hp like an rx7 turbo....

tosbt · #3 05-01-2004, 03:15 PM

Just how hard would it be to move to the D-Jet? Seems that would be simple compared to replacing the cams with a 3.5. Does anyone custom make headers and exhaust for the 4.5 for performance purpose?

Tomguy · #4 05-01-2004, 07:35 PM

3.5 cams would be really easy if you grab them from a junkyard - just get them and the towers, and either tape the rockers to the corresponding lobes or buy new ones.
Moving from D-Jet to a modern EFI system would probably be really easy, just cost-prohibitive. If it gets rid of the trigger points as well, all the better.

As for custom headers/exhaust, I'd imagine you would need a competent muffler shop to do it for you.

j9fd3s · #5 05-02-2004, 05:40 PM

there are a couple ways to move to modern efi.

easy way: find the female side to the efi harness and plug the new ecu in. the cons of this are that you still use the trigger points and 30 year old wiring. nicer ecus like the haltech e11 let you set the sensor ranges so it can use the stock temp sensors, and maybe the tps (it only needs it for idle, and accel pump)

hard way: use the harness that comes with the new ecu.
lets you wire it up the way you want it, the problem is you have to know how you want it. trigger points can be used although others can be (sometimes needs to be). you also either have to drill and tap for gm (this is what most aftermarket ecu's use) sensors, or find/reuse the plugs for the stockers

tosbt · #6 05-02-2004, 08:31 PM

Lets say you just do the cams, will the car run as smooth as it does with the stock 4.5 cams?

Tomguy · #7 05-02-2004, 09:13 PM

tosbt: You may notice a difference, you may not. It might idle better or worse. Acceleration and cruising should be just as smooth as now though, if not smoother. Going from the smogged (low-output) cams to the stock 4.5 ones (higher output) made my idle a LOT smoother.

tosbt · #8 05-03-2004, 07:47 PM

OK . . let me get this straght, I'm running about 225 HP in my 72 300 4.5, it I put the 3.5 cams in I'll pick up about 25 HP? This sounds easy, any downside?

Tomguy · #9 05-03-2004, 08:31 PM

Downside is that you need to find (and buy) 3.5 cams in good used condition with matching towers and rocker arms, or buy (one or more) components individually, new. Stock is 230HP and 280 ft.lbs., IIRC. 3.5 cams I would guess give around 245-255/290-300

tosbt · #10 05-03-2004, 08:41 PM

Why do I need the towers and rocker arms? Could I not just use what I have in the 4.5?

Tomguy · #11 05-03-2004, 11:04 PM

The thing is that they don't wear the same. I suppose if you buy NEW cams then the used towers won't matter much (but used rockers would probably be worn enough to warrant replacement anyway). If you buy used cams, you really need the matching towers for 2 reasons:
1) The journals in the towers wear with the cams - if the one grooves, so does the other. If either your tower or your cam has a groove and the other doesnt, it will cause it to wear signifigantly faster
2) m116 and m117 cams and towers had 2 different cam oiling designs - one has the groove in the rear tower, the other has the oil groove in the cam. These designs are NOT comparible and using the wrong ones together will result in swift valvetrain failure. For example, the smogged 450 cams have the groove in the tower, the 280 4.5 has them in the cam (it might be vice-versa but you get the idea)

#12 05-05-2004, 10:10 AM

http://www.autospeed.com/cms/A_1/article.html

tosbt · #13 05-05-2004, 04:27 PM

Well ..........would be nice to find a system designed for a 71-73 4.5. I tell you if it were reasonably priced and easy to install, I would be a buyer ...but so many others I expect!

j9fd3s · #14 05-06-2004, 01:16 AM

it really wouldnt be that hard to do one, ive done a few on rx7's and its like installing 3 radios back to back....

granted making it run is a different thing altogether

#15 05-06-2004, 03:23 PM

thanks Tomguy en Tobst and others.

Humpert from Holland