Power Upgrade- Triple Sidedrafts or Fuel Injected 3.5

[vince]

Maybe some of you can weight in here...

This Halloween will be the six anniversity of purchasing my '72 3.0 CS. I absolutely love my coupe and, luckly, this summer I was able to drive it a lot. But maybe it's an early 'seven year itch' thing but I'm looking for something more... More Power!!

This winter I'm going to be doing some upgrades, and I have a garage bay full of parts to prove it. Sitting out there is my new (less that 5K miles) 5 speed tranny and shortened drive shaft all ready to go, next to it is my new motor out of a beautifully restored 1985 535is euro (totalled this summer). The motor was gone thru in 2001 and came with a stack of receipts.

Now, I'm having second thoughts. I'm seriously considering putting triple sidedrafts on the original motor. With the exception of a header, the motor is stock. The plus here is that I should get the power that I crave and still maintain the originally and character of the car. On the negative side, I'll probably be tuning them all the time.

Please let me know if you have comments or suggestions on either approach.

Thanks,
Vince

 

[Stan]

My opinion only

Go with the 535 motor, if you want to make it simpler, pull the FI and add the carbutors. Add the 5 speed
drive and smile

 

[jranmann]

HI Vince ...here's my nickel's worth on the engine swap subject.

I've been investigating same issue (using a S38 M Motor) and i have not even bought the shell or the donor car yet and of course am also having some workable misgivings regarding putting that much power into the basic framework of the car.

If I do it, I plan to do it from the basis of building the car up from a shell and that has certain advantages ... I have spoken directly with 3 individuals and their respective mechanics about the various issues of fit, power and available options and routes ... Have you seen this thead?

http://www.bmwcca.org/forum/showthread.php?t=1933

Hello from Ping Tsao in San Luis Obispo, CA. It has been over 17 years since my CS/M5 conversion was published in European Car magazine (Dec '91) and Roundel. It has appeared at numerous BMW Festorics at Monterey Historics after being built by a maverick local mechanic, Tim Rayner (who now lives in Camino, CA). It took hime 600 hours. I think that the project can be reproduced with the right collection of donor parts. We had a whole M5 wreck. My advice is that the more M5 parts you have, the easier the project. Key to the conversion is using the front and rear subframes from the M5 so that the suspension, steering, ABS brakes, and engine mounts are there. Everything lines up, and the bolt sizes and patterns are the same between CS and M5. No sheet metal fabrication work was required except cutting off the front frame rail pads for the old subframe. It is also probably wise to reinforce the differential mount by boxing in between the rear frame rails.


Note: Perhaps not such as issue with a euro motor you have there but it would be a good idea to weld in some extra bracing where the Coupe 'floor' is the weakest ie; under the back seat. This may just help save you from twisting differential mounts off the coachwork as you can then spread the torque out eveny over a much wider area with a greater degree of reliability and security.

The issue of stiffer suspension and larger brakes is one to flush out for yourself as well but depending on your own taste it's something not to overlook.

Your question regarding the triple carb set up as opposed to the FI is a good one. What I do know is that the Tri-Weber set up as use on Duane Sword's conversion (Alpina parts) and other's similar has one fault in the fact that I myself desire a well behaved street machine too.

Webers work well at one setting....wide open and the rest of the time they waste fuel, contaminate your engine oil and are finiky as the rest. 3 of them on custom manifolds sure sound wonderful but unless you do some futrher research into fitting more perhaps a more suitible street carburation set up or perhaps get lucky and find an original Alpina manifold or use Solox etc, the Webers are going to need constant attention too. Also the linkage for them needs to be custom fit, re-designed from the norem and well braced and very solid, all in a space that's limited to the max unless you want to get out the welding torch and buy and fit a hood scoop which would look ridiculous.

Nothing at all wrong with fuel injection... (especially if it's on a aerial platform) and there's alot to be said for it...but it certainly does not look as nice as what you could do..and see here...

Frankly what I plan to do next is to further reseach and view some other types of vehicles that use triple carbs such as the mid to late sixties Ferarri's etc and explore other possibilities that haven't been done with the e9 before.

lastly, what i noted across the board is that these projects often take more than a year for one reason or another, the owners of most no longer own the car and that to me speaks volumes about the good reasons to fully flush this out prior to starting...if not only so you have many happy more Halloweens driving your Coupe in the coming years!


Ran

 

[abe3.0CSi]

Ran,
Its time for more action and less talking....I want to make sure that you end up with the car of your dreams before I get too old to type this note.
I go with the 3.5 fuel injection...this appears to be a popular upgrade with good resale potential. Unless you just love tunning carburators...I just keep it simple and not mess around. Oh, don't forget to add that little label in the trunk that says CSI.
abe

 

[jmackro]

... but I'm looking for something more... More Power!!

Now, I'm having second thoughts. I'm seriously considering putting triple sidedrafts on the original motor.

Vince:

More carburetors does NOT equal more power. With no other changes to the engine, you can run 3 carbs, 4 carbs, or 10 carbs - it won't make any difference as far as power is concerned. Better throttle response yes, but not more power.

On the other hand, you can't beat cubic inches. Yea, going with the 3.5 will make a real difference.

I have no direct experience, but have observed that triple Webers have a bad reputation among the e9 community. Do a search of this board. If you want to stick with carbs on your 3.5, you are probably better off running dual downdraft Weber 38's.

 

[TodB]

carbs

Back in 2000 when I got my Coupe, it had triple weber 40s on a 3.3L M30. Sounded just awesome and looked great. Went ok.

After a couple of conversations with Carl Nelson and others, I decided to remove the triples and install dual downdraft 38s, the theory being that the the 3.3L did not have the compression to keep up with the triples. "The triples are washing the cylinder walls with gas" someone told me.

Off came the triples and on went the dual 38s. Performance was much better and torque was noticeably better. Still sounded great.

That all said, if I did it again, I probably would go FI. It took a couple of years to get the carbs set up right and even now, it can be a bit rough going at times. None of these issues happen with FI.

 

[decoupe]

Triple vs FI vs 3.5l vs 38/38 DGES

Vince:

I have a 38/38 DGES dual downdraft set up on a 3.5l that is relatively easy to set up, very little needs adjustment and produces decent power with great bottom end torque. Some what low tech, not too fuel efficient and kind of old school Russian technology that sounds like God's own trumpet when you merge into traffic with max gas. Bullet proof, never fails and I wouldn't hesitate to drive it anywhere below 10,000'. A great setup I would recommend to anyone who wants to upgrade any carb setup.

I mention the sensitivity to altitude - which applies to any carb'd engine - because any rejetting is a total pain and this applies to getting it set up as well. Basically you have to remove the carb body from the intake manifold to get at the main and air corrector jets. This is why you should also spend $300 to get a wide band fuel/air ratio meter and save yourself a great deal of f##ing around getting it dialed in. You also get flashing red and green lights and constantly changing readings which is cool - sort of. Another benefit is that because it is a synchronous versus progressive operation there is none (very very little) sync'ing the carbs. Basically a set and forget.

I would say that you get some of the eye candy of triple carb's, most if not all of the power (in the 1500 - 4000 rpm range) and nearly none of the fussing.

As an aside I'm converting to fuel injection over the winter. Go figure.

Doug

 

[jranmann]

Even Alpina gave up on the side draft eventually!

Here's a very good informative article I ran across on the subject...

http://www.racetep.com/webjettune.html

See Abe, an ounce of research IS worth a pound of gold sometimes... and in this so-called 'unsure' economy spending too much for so little (CS Parts, etc) seems silly. I had to pick a color first, anyway as my goal is to not shoot off my foot before it's absolutely necessary... AND soon it may be as I really intend to modify my living will and request that my Coupe (which ever it is) be allowed to serve as the 'vessel of my earthly remains'...speeding me surely toward that ever lasting Nurburgring in the heavens!

PS: Schwarz Black being right up there in the top three, have you all seen this Black Coupe with a blown motor? Heavens to mercy check out the video too! Owner's quoted as saying:

Engine has a blower ,making this car go 11,6sec in 402m
Bosses BMW är en CSi 3.0 E9 -72:a
Motor is 3.6 liter, M5 block, vevaxel
12v M30 topp
Autorotor 2.4liters kompressor ca 1.6bar
ProSpark ignition
FUEL - E85
Viper T56 6speed

http://forums.vwvortex.com/zerothread?id=4034179 (thread)

http://www.youtube.com/watch?v=35RuuWDOmd8 (YouTube video)

No carbs here i'm afraid...!

Cheers!


Ran

 

[abe3.0CSi]

Ran,
If I would have been as patient as you and done my homework I would not been screwed so badly by the guy who sold me the car....he didn't even use vaseline!!!! Luckily, coupeking did a good job restoring the car.
abe

 

[jranmann]

ahhh....as Maxwell Smart always mused to 99 (Barbara Feldon) The ollldddd NOOO 'vaseline on the 'shoe phone' trick!
Shhh...I'm considering either Ceylon or Colorado flames on the schwarz black doors@@!!

My common sense says otherwise and have Hugh (the body/sunroof God in the UK) convert this Verona Red example
with 17,000 actual miles (unrestored and unmolested) to LHD for me... but talk about Coupe pedophiliac
molestation with possible prison time, eh Abe? Almost a cardinal (unforgivable) sin in some circles...

Then again, I could always hock my house twice over? hmmmm....
One thing's for certain there will be no further need for CSI Inc as they don't have the savvy... or the parts!

http://www.classiccarsforsale.co.uk/classic-car-page.php/carno/74730


G'nite Abe!

 

[Bill Riblett]

I have one car with a Korman stage 2 3 liter including triple 40DCOEs. It was built in 1980 and probably has around 100K miles on it now. It was dynoed at 230HP when new.
It is very loud. It is also pretty fast. It gets a little over 20mpg on trips with the leanest of 3 sets of jets. It gets much worse mileage with the rich jets and in-town driving. I rarely ever (almost never) tinker with the carbs, but then I don't put many miles on it. The guy who had the motor built used it as a daily driver and also tracked it.

It is fun, but the other car will eventually get a stock 86 Motronic 3.5. Same engine as in my 86 635. It is quieter (but sounds great under hard acceleration) with stock exhaust system; starts right up regardless of weather temparatures, has good torque at lower rpms and seems more in keeping with the basic E9 character.

Think about how you will drive the car and what you want from it. Also, I personally think you really need more than stock pistons and cam to get the most out of sidedrafts.

 

[AndyM]

I'd keep the injection and do the D-Jet or L-Jet manifold conversion if you want to maintain some of the original character of the coupe. It's not a painless conversion, so if you plan to do it yourself, be prepared to tackle a number of small (but not insurmountable) issues.

 

[DougE]

Sidedrafts versus Sidedrafts

My experience with sidedrafts was on a four cylinder but I'm sure it's much the same on a 6. To start, continually adjusting the carbs is nonsense. Once the mixture and the idle speeds are correctly set leave them alone. Sidedrafts do not come out of adjustment during running but with time as the engine wears they might need to be tweaked.
One thing about sidedrafts is in an average engine with a mild cam, headers and maybe a compression bump those are 6 large holes to fill with air so when you stomp on the accelerator at low speeds it takes those big throats time to create enough vacuum to perform, so… you need to feather your prop so to speak. At speed they perform beautifully although they are kind-of thirsty. If that's what you want I say go for it.
Fuel injection is more sensitive and more forgiving in many respects. It cold starts more easily; it maintains engine idle speed better cold or hot, better fuel economy. But the sidedrafts are mighty sexy and they do have that throaty sound and without a doubt they are whats called at times. Well that’s my 2 cents, which ever you decide I hope it makes you smile a little broader every time you drive your coupe and crank it up, good luck with which ever you decide

Doug

 

[jranmann]

Doug's assessment seems reasonable and well stated...

I wonder what he or anyone else also thinks of decoupe's assessment (italics below) of the down-draft
Weber configuration also shown here on a 74 3.0CS?

Previous by DougE:My experience with sidedrafts was on a four cylinder but I'm sure it's much the same on a 6. To start, continually adjusting the carbs is nonsense. Once the mixture and the idle speeds are correctly set leave them alone. Sidedrafts do not come out of adjustment during running but with time as the engine wears they might need to be tweaked.
One thing about sidedrafts is in an average engine with a mild cam, headers and maybe a compression bump those are 6 large holes to fill with air so when you stomp on the accelerator at low speeds it takes those big throats time to create enough vacuum to perform, so… you need to feather your prop so to speak. At speed they perform beautifully although they are kind-of thirsty. If that's what you want I say go for it.
Fuel injection is more sensitive and more forgiving in many respects. It cold starts more easily; it maintains engine idle speed better cold or hot, better fuel economy. But the sidedrafts are mighty sexy and they do have that throaty sound and without a doubt they are whats called at times. Well that’s my 2 cents, which ever you decide I hope it makes you smile a little broader every time you drive your coupe and crank it up, good luck with which ever you decide

Previous by decoup: I have a 38/38 DGES dual downdraft set up on a 3.5l that is relatively easy to set up, very little needs adjustment and produces decent power with great bottom end torque. Some what low tech, not too fuel efficient and kind of old school Russian technology that sounds like God's own trumpet when you merge into traffic with max gas. Bullet proof, never fails and I wouldn't hesitate to drive it anywhere below 10,000'. A great setup I would recommend to anyone who wants to upgrade any carb setup.

I mention the sensitivity to altitude - which applies to any carb'd engine - because any rejetting is a total pain and this applies to getting it set up as well. Basically you have to remove the carb body from the intake manifold to get at the main and air corrector jets. This is why you should also spend $300 to get a wide band fuel/air ratio meter and save yourself a great deal of f##ing around getting it dialed in. You also get flashing red and green lights and constantly changing readings which is cool - sort of. Another benefit is that because it is a synchronous versus progressive operation there is none (very very little) sync'ing the carbs. Basically a set and forget.

I would say that you get some of the eye candy of triple carb's, most if not all of the power (in the 1500 - 4000 rpm range) and nearly none of the fussing. As an aside I'm converting to fuel injection over the winter. Go figure.

Thanks!

Ran

 

[decoupe]

Ran:

My opinions of course.

You left out the part about converting to FI.

Doug

 

[jranmann]

Apology for quoting you out somewhat of context decoup,,,(his last sentence buried at the very end his posting was the crux of his solution, and I errantly omitted that sentence!)

Seems to be repaired oK now... ??

Cheers!

Ran

PS this is an issue close to my heart and important for me to understand your experience... Thanks for sharing it!

 

[vince]

Thanks to all of you for your comments, ideas, and suggestions. I love this site!

If the triple sidedrafts didn't look and sound so dang cool, I probably wouldn't have considered them.

All of your feedback has convinced me to stick with my original plan and go for the 3.5 FI swap. Now, I need to source the tii brake booster, fuel sending unit, etc...

Thanks again!

Vince

 

[gazzol]

Properly set up sidedraft webers will probably make more power than stock FI purely because the inlet tract is straighter and not so convoluted but the emphasis here is on "properly" the fact is that most aren't properly set up because there are very few people that can do it and get it right in all areas. The most critical area is the progression holes these have the greatest bearing on driveablity. Ultimately carbs (of any type or configuration) are a compromise good power or good economy but never both and rarely as good as FI at either. If it were my car I'd have FI every time, it gives the best drivablity and fuel economy period.

 

[jranmann]

I need to source the tii brake booster, fuel sending unit, etc...

That booster is the cat's meow for the conversion...PM shannon for that member's comments on same. My attempts at finding a unit lead me to
CSI and it became clear that the $950.00 they want for one they don't even own is clearly some of my reasoning on the 'it's the little things' thread I posted several days ago.

If I run across one for say the more normal $300.00 shall I let you know?

Ran

 

[E9Wayne]

Fuel injection for sure

Having lived through reasonably well tuned Zeniths and my first E9 for the last year, there is still no question in my mind that FI is what I need. This Saturday, my '73 CS is going in for the powertrain swap: B34 Euro high compression motor with L-jetronic fuel injection, Motronic 1.3 engine computer and a Dinan chip, along with 5 speed G265. 240 hp with smooth starting, no balking under full throttle or weird antics from the carbs going around fast corners or down my steep driveway. Good luck!

Authenticity is fine, but refined manners and better performance are worth more to me.