Custom carb or EFI

[Mike Laws]

I mean, it looks cool, I get the idea behind it. If you were able to lean out the mixture at WOT say to 13.5:1 and set the ECI system to enrichen the mixture to make it 12.5:1 then I could see the benefit. Or also use it for cruise AFR in the same way. Lean the mixture out with the carb and let the ECI enrichen it to the desired AFR. That would be cool as long as its accurate.

This is the exact method I've used. Works perfectly.

[David Redszus]

Get the AFR in the same ballpark the Inlet air temp due to evaporative cooling is better with the carb even compared to throttle body injection. Its enough to overcome the loss of airflow required to get a carb responsive

Maybe not. Throttle body injection is only better than a carb due to mixture ratio control over the entire range of operation (a function of the ECU). It is an obsolete (but cheap) system except for trucks.

For a typical engine using isooctane, 100F deg air and fuel, 85% evaporation, the temperature drop
due to fuel evaporation will be 25.6F deg, resulting in an increase in charge density of 1.36%.

But the reduction in inlet air mass due to fuel vapor displacement would be 9%; a net loss in air mass.

One reason that port EFI could make more power is a result of more even fuel distribution to
reduce cycle to cycle and cylinder to cylinder variations.

But there is a dark side as well. NASCAR dumped carburetors a decade ago in order to reduce the number of engine failures, which it did. But it also allowed NASCAR to dial in the maximum speeds that can be driven because cars were getting too fast for the tracks.

No modern race engine would use carburetors unless the rules required them. And some do.

[Mike Laws]

Get the AFR in the same ballpark the Inlet air temp due to evaporative cooling is better with the carb even compared to throttle body injection. Its enough to overcome the loss of airflow required to get a carb responsive

Maybe not. Throttle body injection is only better than a carb due to mixture ratio control over the entire range of operation (a function of the ECU). It is an obsolete (but cheap) system except for trucks.

For a typical engine using isooctane, 100F deg air and fuel, 85% evaporation, the temperature drop
due to fuel evaporation will be 25.6F deg, resulting in an increase in charge density of 1.36%.

But the reduction in inlet air mass due to fuel vapor displacement would be 9%; a net loss in air mass.

One reason that port EFI could make more power is a result of more even fuel distribution to
reduce cycle to cycle and cylinder to cylinder variations.

But there is a dark side as well. NASCAR dumped carburetors a decade ago in order to reduce the number of engine failures, which it did. But it also allowed NASCAR to dial in the maximum speeds that can be driven because cars were getting too fast for the tracks.

No modern race engine would use carburetors unless the rules required them. And some do.

Sorry to hijack the thread, but a couple of thoughts.

NASCAR dumped carbs because of the tax-credit provided by the government to go-green. It took much testing to get efi to the same performance level of the carbureted engines. (And the carburetors were size-limited.) They just kept increasing t/b size until the power got to the level Nascar wanted. I personally hoped they would allow either system for at least a few years but they wanted none of that. The same with NHRA PS.

Thousands of modern race engines use carburetors in classes that allow any induction system. Easily more than 90% prefer carbs in sportsman drag race classes, when they can use either. Several sharp racers and companies have tried EFI in those classes but always circled back to carbs. EFI or MFI is preferred in most of the boosted classes, primarily because of fuel-flow demand.

[Mike Laws]

Has anyone used a custom carb company? If so, how were the results. I have a previous post on here about tuning in an Edelbrock 750. With y'alls help I got it mostly dialed in. I'm still not completely happy with it though. There are custom carb companies that claim to build a custom carb, built off a particular engine build, that yield 20-40 hp gains over a typical self tuned off the shelf carb. I got a quote from a company called Pro Systems carburetors for a really nice looking carb. Everything sounds great about the build, but i'm unsure of the actual gains from the "custom carb"

EFI is certainly an option, top choice would be a Holley sniper system, but they seem to be pretty glitchy and when people have an issue with them it seems to take weeks to get it rectified. I don't want my truck down that long. Carbs are much easier to get parts for and repair but it's certainly intriguing to put an EFI system on it.

Anyone have possible some opinions or even better, some dyno results of a custom carb?

Both.

Still a best kept secret: https://www.knfilters.com/eci

Summit says that unit is almost $900.00 I got a Fitech that controls the timing and the air fuel is self learning, for just a little more. Seems a waste to not just do the full injection system.

I just saw that. Not sure what's going on because Amazon is selling the 4150 and Edelbrock/Quadrajet for $499 and the Dominator for $599. (The pricing I've used.) I sent a note to K&N, hopefully they will clarify.

[David Redszus]

Thousands of modern race engines use carburetors in classes that allow any induction system.

Mike
Which classes and sanctioning bodies are those? Besides low level drag racing?

[hoffman900]

Get the AFR in the same ballpark the Inlet air temp due to evaporative cooling is better with the carb even compared to throttle body injection. Its enough to overcome the loss of airflow required to get a carb responsive

Maybe not. Throttle body injection is only better than a carb due to mixture ratio control over the entire range of operation (a function of the ECU). It is an obsolete (but cheap) system except for trucks.

For a typical engine using isooctane, 100F deg air and fuel, 85% evaporation, the temperature drop
due to fuel evaporation will be 25.6F deg, resulting in an increase in charge density of 1.36%.

But the reduction in inlet air mass due to fuel vapor displacement would be 9%; a net loss in air mass.

One reason that port EFI could make more power is a result of more even fuel distribution to
reduce cycle to cycle and cylinder to cylinder variations.

But there is a dark side as well. NASCAR dumped carburetors a decade ago in order to reduce the number of engine failures, which it did. But it also allowed NASCAR to dial in the maximum speeds that can be driven because cars were getting too fast for the tracks.

No modern race engine would use carburetors unless the rules required them. And some do.

Sorry to hijack the thread, but a couple of thoughts.

NASCAR dumped carbs because of the tax-credit provided by the government to go-green. It took much testing to get efi to the same performance level of the carbureted engines. (And the carburetors were size-limited.) They just kept increasing t/b size until the power got to the level Nascar wanted. I personally hoped they would allow either system for at least a few years but they wanted none of that. The same with NHRA PS.

Thousands of modern race engines use carburetors in classes that allow any induction system. Easily more than 90% prefer carbs in sportsman drag race classes, when they can use either. Several sharp racers and companies have tried EFI in those classes but always circled back to carbs. EFI or MFI is preferred in most of the boosted classes, primarily because of fuel-flow demand.

NASCAR required them to still use a manifold designed for a carburetor.

NHRA spec'ed a subpar system for the Pro Stock, with a spec throttle body and rev limit.

People bolt EFI on an manifold designed for a carburetor or rules spec a system with one arm tied around its back, and people try to use that as evidence.

I think some of the Sportsman issues is 1) the racers are pretty grey and they stick with what they know 2) the builders are pretty grey, and they stick with what they know 3) rules. Drag racing really doesn't place demands on an engine combination like oval or road racing does. It's a bit one dimensional.

When you realize you don't need to design the induction system (and exhaust system) around a carburetor jet signal, it opens up what you can do. None of those systems do that.

[Tuner]

Thousands of modern race engines use carburetors in classes that allow any induction system.

Mike
Which classes and sanctioning bodies are those? Besides low level drag racing?

You might want to keep an eye on the dirt Late Model lap times at Bristol this weekend. The track is covered with clay and carbs are running laps as fast or faster than cup cars on the concrete.

[hoffman900]

Thousands of modern race engines use carburetors in classes that allow any induction system.

Mike
Which classes and sanctioning bodies are those? Besides low level drag racing?

You might want to keep an eye on the dirt Late Model lap times at Bristol this weekend. The track is covered with clay and carbs are running laps as fast or faster than cup cars on the concrete.

Are you really trying to make a real argument about carbs vs efi with this example?

[Tuner]

Mike
Which classes and sanctioning bodies are those? Besides low level drag racing?

You might want to keep an eye on the dirt Late Model lap times at Bristol this weekend. The track is covered with clay and carbs are running laps as fast or faster than cup cars on the concrete.

Are you really trying to make a real argument about carbs vs efi with this example?

No. Are you? I merely answered Redszus' question, "Which classes and sanctioning bodies are those (using carburetors) ? Besides low level drag racing?"

The Late Models race Friday for $10,000 to win and Saturday night will pay $50,000 to win, but that's just peanuts to the average guy racing with EFI.

On Friday, there will be a 30-lap main for Sport Mods that pays $5,000 to the winner; a 30-lap main for the 602 Late Models that also pays the winner $5,000; and a 30-lap Modified feature that pays $7,500-to-win. On Saturday, there will be a 16-lap Hornet main that pays $2,000-to-win; a 30-lap Stock Car feature that pays $5,000 to the winner; a 30-lap 604 Late Model race that pays $7,500-to-win; and a 30-lap Open Modified feature that will pay the winner $10,000. All classes will award payouts to the top 24 finishers in the feature events.

All those cars have carburetors except the 4-cylinder Hornets which are mostly newer compact cars, Civics, Jettas, Neons, etc. If a Pinto makes in into the Hornet main it will most likely have a carb.

[Mike Laws]

Thousands of modern race engines use carburetors in classes that allow any induction system.

Mike
Which classes and sanctioning bodies are those? Besides low level drag racing?

Hi David,
The NHRA has 40,000 licensed competitors. There are probably 100 or so of those that are 'Professional' and semi-professional (Including TAFC, TAD, PM) but let's make that number 1000 - all of which are injected. Of the 39k left; perhaps another 1000 are class-mandated to use EFI. (SS & Stock) The remainder are the sportsman racers (SC, SG, SST, etc.)

The IHRA is going to be 25%-50% of the NHRA.

The Big-money bracket races typically draw from 400-600+ cars per event and can use any induction system. I've been involved as a sponsor and a racer in many of these races and a generous number of non-carbureted entries would be 20 per race.

Edelbrock builds about 450 carbs per day and Holley's number is close to that.

The majority of circle track racing is still running carbs by rule. EFI is advantageous in road racing when permitted.

[Mike Laws]

NASCAR required them to still use a manifold designed for a carburetor.

NHRA spec'ed a subpar system for the Pro Stock, with a spec throttle body and rev limit.

People bolt EFI on an manifold designed for a carburetor or rules spec a system with one arm tied around its back, and people try to use that as evidence.

I think some of the Sportsman issues is 1) the racers are pretty grey and they stick with what they know 2) the builders are pretty grey, and they stick with what they know 3) rules. Drag racing really doesn't place demands on an engine combination like oval or road racing does. It's a bit one dimensional.

When you realize you don't need to design the induction system (and exhaust system) around a carburetor jet signal, it opens up what you can do. None of those systems do that.

To be fair; Nascar also required a single carb setup that was size-restricted before EFI. A few NHRA racers bought those engines, installed 2 carbs and picked up BIG power. It would have been interesting to allow both induction systems to compete head-to-head, but we'll never know... Same with NHRA PS. I'm with you though; no limitations on either system, let them compete best to best.

[Racer71]

The late models that will be running at Bristol are mandated to run carbs and are also 430 cubes vs napcars 358 so not much a comparison. I’ve never seen a ls engine pick up power going to carb and I’ve personally witnessed a handful on the dyno.

[JDR Performance]

A lot of Pro Mod racers have tried injection and gone back to carburetors.

[JDR Performance]

The late models that will be running at Bristol are mandated to run carbs and are also 430 cubes vs napcars 358 so not much a comparison. I’ve never seen a ls engine pick up power going to carb and I’ve personally witnessed a handful on the dyno.

What carburetors did you use? There can be big differences between them.

[Orr89rocz]

Get the AFR in the same ballpark the Inlet air temp due to evaporative cooling is better with the carb even compared to throttle body injection. Its enough to overcome the loss of airflow required to get a carb responsive

Maybe not. Throttle body injection is only better than a carb due to mixture ratio control over the entire range of operation (a function of the ECU). It is an obsolete (but cheap) system except for trucks.

For a typical engine using isooctane, 100F deg air and fuel, 85% evaporation, the temperature drop
due to fuel evaporation will be 25.6F deg, resulting in an increase in charge density of 1.36%.

But the reduction in inlet air mass due to fuel vapor displacement would be 9%; a net loss in air mass.

One reason that port EFI could make more power is a result of more even fuel distribution to
reduce cycle to cycle and cylinder to cylinder variations.

But there is a dark side as well. NASCAR dumped carburetors a decade ago in order to reduce the number of engine failures, which it did. But it also allowed NASCAR to dial in the maximum speeds that can be driven because cars were getting too fast for the tracks.

No modern race engine would use carburetors unless the rules required them. And some do.

Most dyno tests of typical engine combos guys use, comparing a decent tuned carb to a decent tuned efi system, carbs have made more peak power and yes it is most likely due to cooling of intake charge. Its been pretty well displayed in many tests. Sometimes its very close. Port efi usually makes alittle more average power in other areas off peaks. Richard Holdener and even Steve Morris have done videos on the tests