Fuel Injection vs Carbs

ecohen2

ecohen2

True Classic
Does anyone have a some actual data or at least a good guess from experience on how much of a difference there is using fuel injection vs carbs on 1500cc engine?

Assuming my fuel injection is working properly, if I do things like add higher compression pistons, better exhaust and maybe a slightly hotter cam will I get lesser benefit? My gut says no because in theory the fuel injection is just keeping the mixture detected by the O2 sensor at an ideal value.

(Yeah yeah @carl I am over thinking this :) )

Thank you for your thoughts...
 
ecohen2 said:
Does anyone have a some actual data or at least a good guess from experience on how much of a difference there is using fuel injection vs carbs on 1500cc engine?

Assuming my fuel injection is working properly, if I do things like add higher compression pistons, better exhaust and maybe a slightly hotter cam will I get lesser benefit? My gut says no because in theory the fuel injection is just keeping the mixture detected by the O2 sensor at an ideal value.

(Yeah yeah @carl I am over thinking this :) )

Thank you for your thoughts...
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What kind of fuel injection?
Generalizations about fuel injection can be extremely vast..


Bernice
 
ecohen2 said:
The stock Bosch system...
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L-Jetronic is specific the oem tune 1500cc, there is some small degree of variability for performance up grades, does not work for
much higher power levels the Lampredi SOHC is capable of delivering. For that there are a number of alternative EFI systems available.

What the oem Bosch L-jetronic system offers is mid band performance (torque) and overall fuel control and the resulting burn-emissions which is much better than the carb setup.

EFI injector placement (single or double injectors), intake track length, slide throttle or throttle plates and more figures into motor state of tune, power band and all that.

Basic question is how much power, what is the needed power band, budget..


Bernice
 
Very generally - fuel injection is just a more precise metering system. If a Bosch system and a carbureted system are both set up as well as possible, there is likely no noticeable difference.

The L-Jet has parameter limits that it can work within. If you modify the engine beyond those, then carburetors may be easier to tune for the new state. However, Once you modify compression and cams beyond the limits you are probably better to consider aftermarket FI and take control of the spark too. Not as hard as it sounds. I have Megasquirt running fuel and ignition on the GTV6. Home brewed for around $1200 including the new injectors.
 
I run one as well. I do plan to increase to a hotter street cam, 1500 Eruo cam would be great but just too hard to find today. I'll install complete higher flow exhaust system and would like to increase the compression. From what I have read and researched this is about the limit of the stock FI. When I do it I plan to install a AFR gauge to assure I am within safe limits underload. The FI can be adjusted to provide a richer mixture, to an extent, which will be required. With proper set up this should prove superior to carbs for city driving.
 
ecohen2 said:
So what would be realistic for the L-Jet to handle, 10% gain%?
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Replacing the exhaust header to a 4-2 with two downpipes alone is good for around 8 HPs (this was confirmed on a dyno) I figured with a freer flowing exhaust maybe another 2 so I am over 10% with that one mode. Increase a hotter street Cam with raised compression should give you 5 to 10HP additional. I'm targeting around 90HP maybe a little more which is realistic. Now I have not done this yet but after researching it I think it is realist.
 
ecohen2 said:
So what would be realistic for the L-Jet to handle, 10% gain%?
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If you do Facebook, you can read this MWB post regarding a recent engine upgrade they performed. My 85 had a 1500 Fi with MWB performance head and header and the combo definitely wakes up the X. I never dyno'd the 85 with that set up, but it was definitely a noticeable bump over the stock engine configuration on the butt dyno.
 
carl said:
Don't ask me, I have no dog in this fight. I do carbs because I like carbs. Don't forget to mention you live in Boulder and have to deal with big elevation changes.
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I believe @ecohen2's X is an 86, so it should have the black altitude sensor on top right corner the Bosch box.
IM002969.JPGIM002966.JPG
 
I have no direct experience with the OEM FI. But, I have read a very large slice of the posts one this forum and it is clear that the OEM FI has a range of reliability issues that are just not present with carbs. Not because carbs are better that FI - but because this specific FI is very old, cheap and limited in modern terms. If you are spending money inside the engine, then I reckon you need to spend some on either going to aftermarket FI or carbs. The aftermarket FI stuff is pretty good and since you are starting with a FI setup, that is how I would go. If you keep the stock OEM FI, it will limit the results you could get from the cash spent t on the other stuff, and it will still be unreliable and difficult to fault find or adjust etc.
 
I raced a 1500 in an ITC car (stock cam and valves, header, 11:1 max compression) very few other mods to the engine. I started with a 34 DMTR and it ran well. I switched to the stock Fi with a variable resistor added to the coolant temp sensor. I didn't notice any higher HP (no nhigher top speed). I did notice better drivablity - torque off the corners. Also, I didn't have to deal with the studder the carb had coming off hard RH corners. Also started easier. I didn't go back to the carb. YMMV!
 
MikeHynes said:
I raced a 1500 in an ITC car (stock cam and valves, header, 11:1 max compression) very few other mods to the engine. I started with a 34 DMTR and it ran well. I switched to the stock Fi with a variable resistor added to the coolant temp sensor. I didn't notice any higher HP (no nhigher top speed). I did notice better drivablity - torque off the corners. Also, I didn't have to deal with the studder the carb had coming off hard RH corners. Also started easier. I didn't go back to the carb. YMMV!
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My EFI performance build is on a twin cam. High compression pistons, 42/82 intake cam, stock exhaust cam, big valve, ported and polished head, "abarth" style headers, no cat, Ansa rear. Running a plex 201 ignition. The only thing I modified was the resistance on the coolant temp sensor. Set mixture with a AFR gauge and it runs very strong. I have many well built 1800 and 2000 engines and it is very smooth. Carbs not so much, but better sound and seemingly more power.
 
The stock FI system is designed to run a stock engine with far superior emissions numbers, better fuel mileage, and more power than carburetors, because it's very efficient. In my opinion, it's the way to go on a stock motor if your testing rules will allow it.

You can easily foul the O2 sensor if the performance camshaft you pick has too much overlap. When that happens it tells the computer it's lean, so it spirals towards poor running. I am told this can be solved with a heated sensor. I have never tried it, but Mark Plaia was having good results on his last car.

PBS claimed it worked fine with their very mild camshaft and 124 fuel injectors on a big valve 1600 stroker motor. I plan on building one of those for myself, if I ever get the time.

If you have a performance motor, it's best to go with a fully programable FI and ignition control set up. Mark was going to do it on our race car to replace the 45 DCOEs. But in his research, he kept running into the issue that some folks, who were amazed with what our engine was doing, felt it might be very difficult to match output. On the race car, we didn't care about fuel economy or emissions.
In the end, we kept the carbs.
 
The problems with carbs up here are changing altitude, temperature, and the everpresent E10. With that said, I put dual carbs on my Fiat 124 Spider, got them set properly for Denver, and have driven them adjustment free for years. But hot restarts can be annoying especially if you head uphill in the summer. The fuel evaporates from the bowls pretty quickly if you aren't driving every day. And if you drive the car down to sea level you may want to bring different jets and rejet along the way.

My 86 X has an alquati cam (specs unknown to me) and headers, and the FI works perfectly - but that's a sea level, I haven't gotten the car back to CO yet.
 
As someone who has built and run a hot Bosch FI X1/9, it was built to Charlie Rockwell's specs, I can confirm that it's very comparable to the typical power you get from a dual DCNF setup with a 280 cam and headers. The FI engine has a custom cam he spec'd (all typical hot cams he tested actually hurt power with stock FI), PBS big valve head, ~10:1 compression, '74 X1/9 exhaust manifold and downpipes, cone intake filter (4 HP lost with the stock air filter can), no really. 4 HP. No fiddling with the AFM spring or fuel pressure regulator, never goes lean.

Rockwell got 81HP from this FI motor, and 86HP from a dual carb hot cam motor, both on his chassis dyno at the wheels. So no bullshite, actual measured power. Stock FI X1/9 measured 61HP.

Did I mention this 81 HP FI motor could pass smog? Yeah, it could. Try that with dual DCNFs...

The reason most think you can't get good power from FI is that they all try typical "hot cams" that don't work with FI and can't get it to work right or lose power and then start fiddling with AFMs and bigger injectors and fuel pressure and just make it worse with attempts to "fool" the FI system.
 
MikeHynes said:
I raced a 1500 in an ITC car (stock cam and valves, header, 11:1 max compression) very few other mods to the engine. I started with a 34 DMTR and it ran well. I switched to the stock Fi with a variable resistor added to the coolant temp sensor. I didn't notice any higher HP (no nhigher top speed). I did notice better drivablity - torque off the corners. Also, I didn't have to deal with the studder the carb had coming off hard RH corners. Also started easier. I didn't go back to the carb. YMMV!
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Hi Mike,

Do you have any information on the variable resistor? Thanks
 
How about a pair of IDF style throttle bodies? That of course would require it's own FI system.
 
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