High compression M20 on Sidedraught Carbs?

[nando]

Thanks for getting in on this discussion...
are you really familiar with Megasquirt? do you have to run coil on plug for best results of will the stock set up work just fine?
What would the down side be to tuning with just 2 injector outputs?
I have tuned cars with Autronic, AEM, Fast, Halltec and various piggy backs and flash software...does MS use a VE table or a pulse width table for fuel?
I think there is a guy on this forum called Ely who does a lot with MS...I think he is quite close to me in Chattanooga TN, maybe I will pick his brain.
I guess the smart thing to do would be to tune the car with MS on the stock set up (banana manifold) first and move on from there as you are right ITBs are a real PITA to set up with a MAP sensor, although when correct they sound GLORIOUS!!!!

no, you do not have to run COP - I wouldn't even recomend it realy, there isn't a big advantage and it uses a lot of output pins that could be better used elsewhere. the stock coil works fine for almost any M20 (even turbo), or a good compromise like wasted spark with 3 coils (which is nice to eliminate the mechanical wear you get with a cap/rotor system).

the only real disadvantage to tuning with 2 injector outputs is in low load/low RPM areas and idle. Especially as injectors get bigger, their pulswidths start to shrink making low-load tuning more difficult to control with batched injection. But it's not impossible - MS2/e supports semi-sequential at least, which is the same thing BMW used on the M20 (motronic 1.3), and it's plenty smooth. at higher loads and full throttle the injectors are mostly on all the time anyway, so the timing of them doesn't matter as much - basically it's not going to make any difference in peak power, only smoothness and economy/emissions. That said, I'd *love* to have 6 full sequential injector outputs, but my car is daily. if it were a track car, I wouldn't care at all.

MS does use a VE table for fuel, and there are a few ways to get around the MAP problem with ITBs. MS1/extra supports blended alpha-n/speed density directly, MS2/extra doesn't officially support it but there's a neat trick you can use with dual VE tables to blend the two together. I would definitely reccomend learning the system on a stock motor with the stock intake - cuts down on variables and makes it easier to tune while you are learning.

as far as ely - he's pretty knowledgable on MS. I'd definitely reccomend hitting him up, he even builds a trick plug and play setup that uses the stock wiring harness to cut down on setup time & troubleshooting.

[Madhatter]

you can run alpha~n and do away with a map sensor. Or as you have said, you can run a MAF sensor like M vehicles. What is the big restriction in a MAF sensor though? you only have a heating element contained inside and the body section is more than large enough. You would be mad to run open trumpets on a road vehicle so you need to run a plenum anyway, a maf at the front isnt going to be a problem. You will still get the throttle response and top end increase due to the throttles, you just need to make sure you size the plenum correctly.

Carbs are going to be more difficult to setup and tune than throttles, with throttles all you have is a stop screw for sequencing. Carbs will require the right jets, chokes, tuning, etc, which is becoming a bit of an art, so finding someone who knows that they are doing with carb setup and selection is getting hard. The difference between a pro and someone getting it close is going to be the difference in peak power outputs, so you need to spend time getting it done right the first time.

Whats the going rate for a 40mm side draft over there? $450-$500 each? then you have filters and tubes, then on top of that, to get them setup for your car, looking at about $8 per jet, $30 or so for chokes if you need to change them. So you are probably talking close to $600 complete per 40 to get them kitted to suit. Thats closing in on 2 grand just to buy and setup the carbs, then you have the manifold and tuning on top of that, its not a cheap proposition either.

You can make it cheaper buying used carbs, but if you are paying someone to do the work, rebuilding them runs to quite a bit of money too. Problem with used carbs is its difficult to tell their condition without pulling them appart, you can open them up and find corrosion has gone to town on them, or the shaft bearings have worn in which case the whole body is junk and needs to be thrown out (you cant get oversized bushes, etc for these, so if it wears the body, its stuffed). Unless they are a good set, restoring an old set can be just as expensive (if not more so) than buying new.

[Dyno4mance]

mainly they are just a pain to tune - especially if you are using speed density with a MAP sensor, it's almost impossible to get a good clean map signal. you can use a MAF instead but then you're sortof defeating the purpose of a low-restriction intake. Or alpha-n, which can also be difficult to tune.

none of these things are impossible, mind you, just something to consider when spending $$$ on ITBs that may or may not give you what you're hoping for. BMW has highly skilled engineers and a virtually unlimited budget to spend tuning their ///M engines to perfection. if any E30 guys even bother going to a dyno (most don't), they might do a dyno pull or two and waste money on things like AFPR's to "tune" their engines.

but since you do work at a shop with a dyno - this might not be an issue. 4-5 hours with MS should be plenty to get a great dyno tune if you're experienced with it. You don't need to use it for fuel - although it would be ironic to use it only for spark, since MS started as a fuel-only computer. It's also ironic because it supports 6 cyl COP but only 2 injector outputs. :p

regarding carbs - I think that there are probably some advantages and "cool" factor to be had. but honestly, do you want to spend most of your time fucking with carbs (that will probably need reset quite often, especially when you have 3 or more), or spend a few hours on a dyno tuning it once and then driving it..

Thanks for getting in on this discussion...
are you really familiar with Megasquirt? do you have to run coil on plug for best results of will the stock set up work just fine?
What would the down side be to tuning with just 2 injector outputs?
I have tuned cars with Autronic, AEM, Fast, Halltec and various piggy backs and flash software...does MS use a VE table or a pulse width table for fuel?
I think there is a guy on this forum called Ely who does a lot with MS...I think he is quite close to me in Chattanooga TN, maybe I will pick his brain.
I guess the smart thing to do would be to tune the car with MS on the stock set up (banana manifold) first and move on from there as you are right ITBs are a real PITA to set up with a MAP sensor, although when correct they sound GLORIOUS!!!!

[nando]

mainly they are just a pain to tune - especially if you are using speed density with a MAP sensor, it's almost impossible to get a good clean map signal. you can use a MAF instead but then you're sortof defeating the purpose of a low-restriction intake. Or alpha-n, which can also be difficult to tune.

none of these things are impossible, mind you, just something to consider when spending $$$ on ITBs that may or may not give you what you're hoping for. BMW has highly skilled engineers and a virtually unlimited budget to spend tuning their ///M engines to perfection. if any E30 guys even bother going to a dyno (most don't), they might do a dyno pull or two and waste money on things like AFPR's to "tune" their engines.

but since you do work at a shop with a dyno - this might not be an issue. 4-5 hours with MS should be plenty to get a great dyno tune if you're experienced with it. You don't need to use it for fuel - although it would be ironic to use it only for spark, since MS started as a fuel-only computer. It's also ironic because it supports 6 cyl COP but only 2 injector outputs. :p

regarding carbs - I think that there are probably some advantages and "cool" factor to be had. but honestly, do you want to spend most of your time fucking with carbs (that will probably need reset quite often, especially when you have 3 or more), or spend a few hours on a dyno tuning it once and then driving it..

[Madhatter]

explain to me whats unreliable about ITB's? would you consider M engines unreliable because of throttles?

[jlevie]

I take your point about the driver really being the key to a fast car although you do have to prep the car first....should I just stick with the stock banana manifold and stock FI config with MS then?
Or bite the bullet and get the ITBs?

I'd stick with the OE intake manifold and use fuel injection. That's simpler, easier to tune (with MS), and lots more reliable than an ITB setup.

[backtrail69]

so even with IMG tags your pics have to be hosted somewhere correct?....
What size turbo is that? do you have custom pistons have you ever dynoed it? I would offer you dyno time but you live in WA state:)

correct. Here is a thread with all the specs on my build JE pistons, Eagle rods, ARP everywhere, holset HX35 turbo from a dodge pickup etc.. Put down 331.5 whp on a dynodynamics and 335 lb ft at only 10 psi.

http://www.r3vlimited.com/board/showthread.php?t=101610

[Dyno4mance]

I think it is safe to say that a properly tuned electronic fuel injection system will outperform carburetors every time. Were that not to be the case you'd find FI being replaced by carbs on every race car where the rules allow. That isn't what we see because FI is superior.

I don't know what your experience level is, but I do know that in a race environment the driver is more important than the car. If you aren't an experienced and successful racer, you could gain a lot from prepping the car to SPEC E30 rules and running it. Because the cars are so equal, a SPEC E30 race comes down to the ability of the driver.

Hi thanks for your input...the reason I am not building a full spec E30, although apart from the engine it is very close, is that I work on the weekends at the shop and there is no way I could make even a small portion of the races at RA,CMP,Barber,Roebling and the like although I would love to....and you are right spec E30 is a very good and inexpensive series ( as far as road racing goes) and I know a few of the front runners in the SE....Infact Damien Moses uses our dyno for verification of his SE30.

I take your point about the driver really being the key to a fast car although you do have to prep the car first....should I just stick with the stock banana manifold and stock FI config with MS then?
Or bite the bullet and get the ITBs?

[jlevie]

I think it is safe to say that a properly tuned electronic fuel injection system will outperform carburetors every time. Were that not to be the case you'd find FI being replaced by carbs on every race car where the rules allow. That isn't what we see because FI is superior.

I don't know what your experience level is, but I do know that in a race environment the driver is more important than the car. If you aren't an experienced and successful racer, you could gain a lot from prepping the car to SPEC E30 rules and running it. Because the cars are so equal, a SPEC E30 race comes down to the ability of the driver.

[Dyno4mance]

why bother running carbs when you already plan to install engine management. Throttles will give you similar induction noise, clearly thats your thing.

getting them setup and kitted well, you could expect fairly similar peak power outputs, maybe slightly more with injection. Difference is going to be the rest of the rev range, with injection part throttle operation is going to be far superior, producing more power and torque in the mid range, right up to the peaks. Overall, much better operation when you arent spending 95-100% at full throttle.

none that I can think of. Though you might want to think about a decent cam to take advantage of the situation.

yes, but you really should ask yourself, why only go half the way?

dont forget you will need to convert your existing fuel system to low pressure to run the carbs. using restrictors is stupid and only leads to another point of failure, do it right the first time with proper fuel pumps and regs.

All your points are valid and I had thought of most of them....I plan on using a schrick 288 cam in this application.....
the problem is I have never driven an E30 ever!! and I am building this car to quite a high level Cage, Suspension, wieght reduction etc......but I am not sure if I will be content with this engine or if it will not give the flexibility I am after, I have watched spec E30 race series cars and they seem to do quite well...
I guess I was thinking of adding simple carbs to a simple engine
I removed the M42 because I would of had to spend a lot more on that motor...I rejected the M50/S50/S52 option because they seem to be a lot heavier at over 300lbs (136 KG) than the M20 at 258lbs (117 KG) and the increased wieght would definately upset the balance of the car..
On a second look it does look as though ITBs would be an additional $1000.00 over carbs.....I am wondering if that will be money well spent?
sorry for the waffleing....I appreciate your input

[Dyno4mance]

so even with IMG tags your pics have to be hosted somewhere correct?....
What size turbo is that? do you have custom pistons have you ever dynoed it? I would offer you dyno time but you live in WA state:)

[Madhatter]

why bother running carbs when you already plan to install engine management. Throttles will give you similar induction noise, clearly thats your thing.

getting them setup and kitted well, you could expect fairly similar peak power outputs, maybe slightly more with injection. Difference is going to be the rest of the rev range, with injection part throttle operation is going to be far superior, producing more power and torque in the mid range, right up to the peaks. Overall, much better operation when you arent spending 95-100% at full throttle.

none that I can think of. Though you might want to think about a decent cam to take advantage of the situation.

yes, but you really should ask yourself, why only go half the way?

dont forget you will need to convert your existing fuel system to low pressure to run the carbs. using restrictors is stupid and only leads to another point of failure, do it right the first time with proper fuel pumps and regs.

[backtrail69]

I am running 8.5:1 compression because I am turbod.



You use IMG tags [img]INSERT LINK HERE[/img]

[Dyno4mance]

Thanks for the reply....I will be running Megasquirt for ignition timing tuning and I have my own dyno for that job.... ITBs seem to be a simular price as webers....I take your point that webers do need setting up and jetting correctly and takes some time so I can see how you think carbs are finiky but on the other hand so does setting up fuel on a FI standalone setup...
Is yours a m20 2.8....? If so what compression do you run?

How did you post that pic???

[backtrail69]

you still need ignition tuning so i would get itbs with a standalone efi... i also love my webered m10 but its too finiky...