Carbs make more power than FI?

[Truckedup]

I can't get rid of a part-throttle rich spot no matter what I've tried, although it's not much of an issue on the track because it's only at that RPM and throttle combination for any length of time on the cool-down lap. It appears that high revs and part throttle draw enough air through the main circuit to pull fuel from that circuit and the throttle is open far enough to draw all it can through the slow circuit, and the two together are too much.

Two items to consider:
A fuel delivery system based on pressure differential is subject to superposition pressures due to pulsed air flow.
At certain engine speeds the inlet air pressure curves will stack to produce both an alternating high pressure and low pressure. High pressure causes a fuel flow reversal while low pressure causes excess fuel to be delivered.

Carbs deliver fuel based on the difference in pressure between the venturi and float bowl pressure which is open to the atmosphere. A partially closed throttle at high rpm will produce a very strong fuel signal.

Once upon a time we built a carburetor flow bench that measured mass air flow, air pressure and fuel signal pressure.
It was not easy to match the fuel signal to the air mass flow. But that was a dry system simulation; the presence of wet fuel would change the numbers more radically.

Bike guys usually call that , right or wrong, reversion....Generally just before the engine starts to come up on the cams....Exhaust and intake work can sometimes tame it down..

[Orr89rocz]

It may be 2018 but carbs still run as good or better than efi and cost thousands less. I think the efi thing is a fad cool thing so people can say they are a tuner and have the latest technology. It’s like the guy that has to have the latest smart phone. Then months later realizing the thing cost a lot more than the old one and isn’t much better.

Since it’s 2018 the one thing that has changed is most engines now have a power adder. Na heads up racing is almost none existent. Due to this efi has become necessary because carbs don’t work as well with boost set ups.

I wish efi was cheaper, and please don’t say stock ecm or some cheap equivalent is fine. Most just include some pieces in the cost but not all. You have ecm $1200, wiring harness $500, injectors$1000, o2 sensors $200, other sensors $300, throttle body $600 and that is no ignition pieces and on the cheap side. Efi done right is expensive.

You are about right on that. Bout the cheapest i can come up with is holley HP with a ls1 wiring harness. Thats about 1650-1700 depending who you get it from (dealer discounts etc). Comes with o2 sensor already. Holley 36-1 crank trigger at 365$ and find some ls coil packs from a donor car or truck, d581 or d585. Seen em for 100$ or so. Gather ls1 sensors for coolant temp and oil pressure, iat sensor etc. 100- 150$ at most there. Efi carb style intake 400-500$ most of the time plus an elbow for 100-200. 130-150 for a decent warr ls1 throttle. Injectors depend on fuel or power level, say na for 1000 hp siemens dekas 80’s can be had for under 400. On gas that will do it.

It will add up some depending how you do it and what you are doing. Boost you kinda need injection imo

Na sbc street machines can do it on the cheap with tpi electronics if you dont mind chip burning. Its old tech but works fine and makes plenty of power as a batch fire system. I have done many and the advantage is packaging of the efi style manifolds under hood, and sensors are cheap. 3rd gen fbodies are my deal

You can also convert sbc to run ls1 pcm and oem harnesses with some mods. Efi connection sells a kit. I ran my twin turbo sbc like this and went 8.2’s at 3750 lbs. never an issue on oem pcm and stuff. Cost is cheaper than standalones but you need to mod the harness to fit so theres work involved. But the coil packs are awesome and cheap


I love the ls1 efi intakes. You get proper length runners for the rpm range up to 7000 which is perfect for street and mild race aps. Plastic light weight and stay cool. Broad torque curve since everything is tuned right with the manifold design. Most all of the setups that go to a carb style manifold with efi or not lose average power and sometimes lose power at peak. Runner length is short and it does not make low to mid range average power. Induction Tuning is not there

[groberts101]

It may be 2018 but carbs still run as good or better than efi and cost thousands less. I think the efi thing is a fad cool thing so people can say they are a tuner and have the latest technology. It’s like the guy that has to have the latest smart phone. Then months later realizing the thing cost a lot more than the old one and isn’t much better.

Since it’s 2018 the one thing that has changed is most engines now have a power adder. Na heads up racing is almost none existent. Due to this efi has become necessary because carbs don’t work as well with boost set ups.

I wish efi was cheaper, and please don’t say stock ecm or some cheap equivalent is fine. Most just include some pieces in the cost but not all. You have ecm $1200, wiring harness $500, injectors$1000, o2 sensors $200, other sensors $300, throttle body $600 and that is no ignition pieces and on the cheap side. Efi done right is expensive.

You are about right on that. Bout the cheapest i can come up with is holley HP with a ls1 wiring harness. Thats about 1650-1700 depending who you get it from (dealer discounts etc). Comes with o2 sensor already. Holley 36-1 crank trigger at 365$ and find some ls coil packs from a donor car or truck, d581 or d585. Seen em for 100$ or so. Gather ls1 sensors for coolant temp and oil pressure, iat sensor etc. 100- 150$ at most there. Efi carb style intake 400-500$ most of the time plus an elbow for 100-200. 130-150 for a decent warr ls1 throttle. Injectors depend on fuel or power level, say na for 1000 hp siemens dekas 80’s can be had for under 400. On gas that will do it.

It will add up some depending how you do it and what you are doing. Boost you kinda need injection imo

Na sbc street machines can do it on the cheap with tpi electronics if you dont mind chip burning. Its old tech but works fine and makes plenty of power as a batch fire system. I have done many and the advantage is packaging of the efi style manifolds under hood, and sensors are cheap. 3rd gen fbodies are my deal

You can also convert sbc to run ls1 pcm and oem harnesses with some mods. Efi connection sells a kit. I ran my twin turbo sbc like this and went 8.2’s at 3750 lbs. never an issue on oem pcm and stuff. Cost is cheaper than standalones but you need to mod the harness to fit so theres work involved. But the coil packs are awesome and cheap


I love the ls1 efi intakes. You get proper length runners for the rpm range up to 7000 which is perfect for street and mild race aps. Plastic light weight and stay cool. Broad torque curve since everything is tuned right with the manifold design. Most all of the setups that go to a carb style manifold with efi or not lose average power and sometimes lose power at peak. Runner length is short and it does not make low to mid range average power. Induction Tuning is not there

But when you factor in the reduction in parts cost from not needing a big honkin Holley HP(and all that goes along with tuning one), ignition components(can be BIG $$$ there if you like the better stuff).. it's not like EFI comes at 3 times the cost to build a decently proper EFI setup. People in general are slow to change, due to money concerns and lack of knowledge, and mfgrs are slow to invest in newer designs when they can still sufficiently capitalize on the older technology. Then add the capitalistic greed that comes along with limited availability and "state of the art" prices and it's pretty easy to see why not everyone on your block decides to go the EFI route. Things are improving a great deal with more quick bolt on deals and computer technology.. but the elite stuff is still hella expensive due to minimal amounts of competition. If you want a big stuff controller to gain more design flexibility and potentially make bigger power?.. then you'll have to pay big stuff's prices. Just one quick example but you get the idea.

I'm too lazy to spec it all out on paper here, would be interesting to see it laid out, but simply crunching rough numbers in my head says tells me that EFI is only another G at most. Yet people will dump thousands upon thousands into cylinder heads, blocks, and suspension setups and then worry about the front end cost of a nice EFI setup?

[Orr89rocz]

But when you factor in the reduction in parts cost from not needing a big honkin Holley HP(and all that goes along with tuning one), ignition components(can be BIG $$$ there if you like the better stuff).. it's not like EFI comes at 3 times the cost to build a decently proper EFI setup. People in general are slow to change, due to money concerns and lack of knowledge, and mfgrs are slow to invest in newer designs when they can still sufficiently capitalize on the older technology. Then add the capitalistic greed that comes along with limited availability and "state of the art" prices and it's pretty easy to see why not everyone on your block decides to go the EFI route. Things are improving a great deal with more quick bolt on deals and computer technology.. but the elite stuff is still hella expensive due to minimal amounts of competition. If you want a big stuff controller to gain more design flexibility and potentially make bigger power?.. then you'll have to pay big stuff's prices. Just one quick example but you get the idea.

I'm too lazy to spec it all out on paper here, would be interesting to see it laid out, but simply crunching rough numbers in my head says tells me that EFI is only another G at most. Yet people will dump thousands upon thousands into cylinder heads, blocks, and suspension setups and then worry about the front end cost of a nice EFI setup?

I think most guys are too afraid or intimidated by learning efi tuning and software. I know i was at first but i had to learn because nobody in my area had the ability to tune my setup at the time. 80’s tech was not on everyones list lol. Even then ls1’s were new to the game and very few ppl knew how to work hp tuners

The cost can be higher than carb, and i think theres no debating that but i believe most get more capabilities than they actually need or use and pay extra for no reason but there arent a lot of basic systems out there. Holley hp seems as simple as they get and still can do a lot for the money

A lot of guys dont know how to fully spec out their own combinations so asking them to put together an efi setup it can be overwhelming. Injector and pump sizing also difficult or confusing for a lot of people.

Once done i dont see a reason to ever go back to a carb but i never used a carb, so idk. Even if efi couldnt match the power output i would still do efi because i like the look of efi motors with proper efi manifolds

[Brian P]

I haven't looked at slide cutaway as a tuning option on these carbs, and it's possible that it would have some effect. Problem is that the particular carburetor that I'm dealing with is out of production and the "hard parts" - including the vacuum slide and the diaphragm - are not available. The real fix is to change out the CV carbs with a set of Keihin FCR but it's at the point where I don't want to spend big money and time fine-tuning it given that it runs well enough as is (the part-throttle rich spot doesn't slow the bike down on track). After this coming season, due to the way the class rules are written in the series that I participate in, my bike will become uncompetitive, and it's probably going to be retired to a display in my shop in front of a wall of trophies, and I'm okay with that.

[Truckedup]

I haven't looked at slide cutaway as a tuning option on these carbs, and it's possible that it would have some effect. Problem is that the particular carburetor that I'm dealing with is out of production and the "hard parts" - including the vacuum slide and the diaphragm - are not available. The real fix is to change out the CV carbs with a set of Keihin FCR but it's at the point where I don't want to spend big money and time fine-tuning it given that it runs well enough as is (the part-throttle rich spot doesn't slow the bike down on track). After this coming season, due to the way the class rules are written in the series that I participate in, my bike will become uncompetitive, and it's probably going to be retired to a display in my shop in front of a wall of trophies, and I'm okay with that.

Don't retire the bike, get into land speed racing, the sport for retired men riding retired bikes LOL...The track at the old Loring Maine Air force base is a stones trow from Canada, maybe 7 hours from Toronto?
The slide cutaway has a primary influence between the idle circuit and needle...Did you enlarge the slide "lift" holes on the bottom of the slide near the needle?

[Brian P]

I'm reluctant to modify a part that I can't replace if I get it wrong.

[Tuner]

I'm reluctant to modify a part that I can't replace if I get it wrong.

Particularly with multiple carbs the slides need to be production parts to ensure uniformity.

I was given a nearly brand new snowmobile for a token price because it couldn't be putted around for trail riding without fouling a set of plugs in just a few miles. In deep snow and climbing with predominately large throttle opening, instead of small opening at part-throttle on flat ground trails, it would run several hours, but get back on the flat and put.put..put ... poooph .. change plugs or walk. Changing the slides in the 36mm Mikuni carbs from 1.5 to 2.5 cutaway cured the over rich at small throttle opening problem.

[kimosabi]

In my case and many others you don't have to take it as far as "reluctant to change" or "afraid". I do carbs because I like them, I like the mechanical aspects of them and understanding how they work. My day job is EFi engines, whether it be diesels or gasoline. Got a good understanding on EFi. A buddy of mine is building a 67 Chevelle, he's a master tech at a big dealership. He's going carb on the Chevelle.

Only thing I see the benefits of EFi is that it adjusts on the fly and modern EFi engines adjust so many times and so many parameters over the course of a drive you wouldn't believe. You(it) get better control and it adjusts running conditions to outside conditions and load much better. It is a step forward but I don't see anyone doing carburetors as anything else than enthusiasts.

[Darkdowndeep]

Carbs seem to still have a very slight advantage to EFI in arenas like comp. I.E. where the converter stall is less than 1000 RPM below HP peak RPM. A super narrow range. Everywhere else that I'm aware of EFI is just better.
Anybody remember going outside to start your car on those 20° mornings and having to stay with it until it stabilized. Now, just hit the starter, go back inside and everything's good. I love that.

Most carbs with a water choke don't need attendance at 20f. Try a Quadrajet