IDF Carb Tuning Guide

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maytag
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Re: IDF Carb Tuning Guide

Postby maytag » Thu Jun 07, 2012 1:13 pm

I have a question related to fuel pressure regulators, and it most closely associates with this old thread. So I;m resurrecting it. :lol:

I'm a little confused by the info above, because the way I understand pressure regulators, if you put the regulator between the pump and the first carb, you are only regulating the pressure between the pump and the regulator, and NOT the pressure at the carbs. the fuel to the carbs effectively becomes just part of the return line at that point.
Unless you are eliminating the return line?

The comments above about blocking the return and then drilling it with a small hole seems to create a situation where the size of that hole is what is determining your pressure, not the regulator.

to my understanding of regulators, the "after" photo posted by Mighty8, with the new location should be correct.

someone help me with what I'm missing here?

Thanks.
I'm no Boy-Racer..... but if I can't take every on-ramp at TWICE the posted limit.... I'm a total failure!

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engineerted
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Re: IDF Carb Tuning Guide

Postby engineerted » Thu Jun 07, 2012 1:50 pm

Maytag,

Regulators regulate the pressure down stream. If the return line has less restriction than the two needle valves in the carburetors then you will not build pressure to flow into the carb fuel bowls. There is no need for a return line on a low pressure pump for IDFs. The only benefit of the return line is that it will keep a cooler supply of fuel coming to the carbs at the cost of the pump working harder all the time, plus it will filter all of the gas in the tank over and over again. So, if you want to keep the return line, put an inline restrictror or a 1-1/2 to 3 psi check valve.


Ted
Ted
1978 124 Spider, Complete Restoration
1974 Fiat 124 F Production Race car

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rlux4
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Re: IDF Carb Tuning Guide

Postby rlux4 » Thu Jun 07, 2012 2:05 pm

So Ted, if you don't have a return line will an electric fuel pump burn out if the needle valves at the float bowls are closed? Or would I have to research whether or not a particular universal electric fuel pump has an automatic shut off feature?
Ron
Ron Luxmore
rlux2n2@gmail.com
'82 2000 Spider: after 26 years between Spiders.

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maytag
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Re: IDF Carb Tuning Guide

Postby maytag » Thu Jun 07, 2012 2:06 pm

engineerted wrote:Maytag,

Regulators regulate the pressure down stream. If the return line has less restriction than the two needle valves in the carburetors then you will not build pressure to flow into the carb fuel bowls. There is no need for a return line on a low pressure pump for IDFs. The only benefit of the return line is that it will keep a cooler supply of fuel coming to the carbs at the cost of the pump working harder all the time, plus it will filter all of the gas in the tank over and over again. So, if you want to keep the return line, put an inline restrictror or a 1-1/2 to 3 psi check valve.


Ted



Thanks Ted!
you just gave me all the excuse I needed to eliminate that return line! :lol:
I'm no Boy-Racer..... but if I can't take every on-ramp at TWICE the posted limit.... I'm a total failure!

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engineerted
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Re: IDF Carb Tuning Guide

Postby engineerted » Thu Jun 07, 2012 2:47 pm

Ron, No they are self regulating and self relieving.
Ted
1978 124 Spider, Complete Restoration
1974 Fiat 124 F Production Race car

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rlux4
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Re: IDF Carb Tuning Guide

Postby rlux4 » Thu Jun 07, 2012 4:26 pm

Thanks Ted, you just helped me solve a problem with a temporary fuel supply on a motorhome I need to move 8 miles.
Ron

PS. Self regulating and self relieving sounds like me drinking a lot of coffee on a long drive. :lol:
Ron Luxmore
rlux2n2@gmail.com
'82 2000 Spider: after 26 years between Spiders.

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maytag
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Re: IDF Carb Tuning Guide

Postby maytag » Thu Jun 07, 2012 6:57 pm

rlux4 wrote:
PS. Self regulating and self relieving sounds like me drinking a lot of coffee on a long drive. :lol:



well, other than the self-regulating part... it sounds like a bunch of us on the golf course too!

wait.... that was a different thread....
I'm no Boy-Racer..... but if I can't take every on-ramp at TWICE the posted limit.... I'm a total failure!

fiat218
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Re: IDF Carb Tuning Guide

Postby fiat218 » Sun Jul 29, 2012 7:37 am

deliver a solid 3 psi at WOT <<<< what does WOT stand for
Jim
East Grand Forks MN
1970 Fiat Spider BS1 ( FOR SALE
1969 124 AS Spider
2017 Abrath
2018 Alfa Romeo 4c Spider

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maytag
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Re: IDF Carb Tuning Guide

Postby maytag » Sun Jul 29, 2012 10:05 am

fiat218 wrote:deliver a solid 3 psi at WOT <<<< what does WOT stand for


you probably know it as "WFO" :lol:


WOT = Wide Open Throttle.
I'm no Boy-Racer..... but if I can't take every on-ramp at TWICE the posted limit.... I'm a total failure!

fiat218
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Re: IDF Carb Tuning Guide

Postby fiat218 » Sun Jul 29, 2012 6:42 pm

maytag wrote:
fiat218 wrote:deliver a solid 3 psi at WOT <<<< what does WOT stand for


you probably know it as "WFO" :lol:


WOT = Wide Open Throttle.

lol ok, got it
Jim
East Grand Forks MN
1970 Fiat Spider BS1 ( FOR SALE
1969 124 AS Spider
2017 Abrath
2018 Alfa Romeo 4c Spider

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maytag
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Re: IDF Carb Tuning Guide

Postby maytag » Mon Aug 13, 2012 10:58 am

sptcoupe wrote:Ace - can you post that chart showing the flow increases/decreases through the various horn shapes we typically put on or carbs? I think this is an important element in getting the max out of your carbs. I know when we were experimenting with the FI on the coupe, the dyno showed up to 3 RWHP differences between horns! That is a lot. We ended up doing the custom horns in accordance with that chart, and got the best results that way. I won't be at our home in Dallas for another week, so maybe you can put it up on the this thread? Thanks.


Does anyone have any data like that referenced above? I'd love to benefit from the work someone else has already done (rather than reinventing the wheel) to determine which horns and filters I should use on my motor.

Or tell me what y'all are using?
I'm no Boy-Racer..... but if I can't take every on-ramp at TWICE the posted limit.... I'm a total failure!

pastaroni34

Re: IDF Carb Tuning Guide

Postby pastaroni34 » Sun Aug 19, 2012 6:14 pm

Jeff's car is using custom made super short air horns. The reasoning behind this is that the amount of space above the air horn (head room) is just as important as the horn's shape. There is only about 1.75" inside the air box to work with, so these horns were made 0.45" tall, leaving a head room of about 1.3" See them here: Weber 44IDF Air Horns

For shape, you certainly want a fully radiused horn. Most horns are poorly matched to he carb throats, blending is ideal, or even the type of horns that are machined to go into the carb throat behind the choke.

Also, you want your air correctors to be at the same height as the air horns. Some of them are buried down in the carb, others have extensions so they rise up off the carb body. Its a slight design change and the effect is small but having the air correctors at the same pressure as the throats is ideal.

Length of horns has nothing to do with increasing airflow or reducing restrictions. A long horn flows just as much air as a short horn. Where length is important is with tuning your intake runner length for your engine. This is why there are hundreds of different opinions for hundreds of different engines explaining that X engine made Y more power with Z air horns but putting Z air horns on a Fiat motor may not be the best solution. Where do you want the power to be, up high or down low? Do you have carb spacers? All of these factors are important.

Finally, the number one thing, get cool air into those carbs. If you're sucking in engine bay air, you're leaving power on the table. Not only are you tuning your carbs for hot air, you're tuning the ignition and everything else for hot air.

fiat218
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Joined: Fri May 16, 2008 5:06 pm
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Re: IDF Carb Tuning Guide

Postby fiat218 » Sun Aug 19, 2012 11:43 pm

pastaroni34 wrote:Jeff's car is using custom made super short air horns. The reasoning behind this is that the amount of space above the air horn (head room) is just as important as the horn's shape. There is only about 1.75" inside the air box to work with, so these horns were made 0.45" tall, leaving a head room of about 1.3" See them here: Weber 44IDF Air Horns

For shape, you certainly want a fully radiused horn. Most horns are poorly matched to he carb throats, blending is ideal, or even the type of horns that are machined to go into the carb throat behind the choke.

Also, you want your air correctors to be at the same height as the air horns. Some of them are buried down in the carb, others have extensions so they rise up off the carb body. Its a slight design change and the effect is small but having the air correctors at the same pressure as the throats is ideal.

Length of horns has nothing to do with increasing airflow or reducing restrictions. A long horn flows just as much air as a short horn. Where length is important is with tuning your intake runner length for your engine. This is why there are hundreds of different opinions for hundreds of different engines explaining that X engine made Y more power with Z air horns but putting Z air horns on a Fiat motor may not be the best solution. Where do you want the power to be, up high or down low? Do you have carb spacers? All of these factors are important.

Finally, the number one thing, get cool air into those carbs. If you're sucking in engine bay air, you're leaving power on the table. Not only are you tuning your carbs for hot air, you're tuning the ignition and everything else for hot air.

So how do u get fresh air to them
Jim
East Grand Forks MN
1970 Fiat Spider BS1 ( FOR SALE
1969 124 AS Spider
2017 Abrath
2018 Alfa Romeo 4c Spider

sptcoupe
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Re: IDF Carb Tuning Guide

Postby sptcoupe » Mon Aug 20, 2012 12:14 am

There are some pictures of the cold air box on the coupe in the "Performance" thread, dated January 15, 2012. Picture # 3 shows it best. The air is taken from in front of the radiator, routed through an enclosed filter box with a K&N filter, then into an air box that utilizes the room available under the hood to the max, and delivers the air from the side, right between the carbs and over the horns. All custom made.

I have a great chart that shows the air flow of various horns shapes, tested on an air flow bench. If someone will give me their email address, I will send them the chart that shows the different air flows on various horn shapes/heights, and you can post it for everyone. I just don't know how to make it work for some reason.

I had three custom sets of horns made for the coupe, all radiused. The tallest made the least HP, the shortest, the most. As I recall, about a 3 RWHP difference on the dyno.

When we fitted the cold air system, I had to go a full step richer in jetting. So after many dyno runs, I have concluded that the space over the horns is more important than the height of the horns (if they are properly radiused. Ideally, you should have as much space over the horns as the width of the chokes - so for 40 IDFs, 40mm would be ideal) and cold air allows you to get more fuel in the cylinders and develop a lot more HP.

I haven't run the coupe on a dyno since I put the cold air box on, but a whole step richer is no doubt a significant gain. I'll post the comparison results (with and without the cold air) when I get to a dyno in October.

fiat218
Posts: 5745
Joined: Fri May 16, 2008 5:06 pm
Your car is a: 1969 124 AS spider

Re: IDF Carb Tuning Guide

Postby fiat218 » Mon Aug 20, 2012 8:16 am

sptcoupe wrote:There are some pictures of the cold air box on the coupe in the "Performance" thread, dated January 15, 2012. Picture # 3 shows it best. The air is taken from in front of the radiator, routed through an enclosed filter box with a K&N filter, then into an air box that utilizes the room available under the hood to the max, and delivers the air from the side, right between the carbs and over the horns. All custom made.

I have a great chart that shows the air flow of various horns shapes, tested on an air flow bench. If someone will give me their email address, I will send them the chart that shows the different air flows on various horn shapes/heights, and you can post it for everyone. I just don't know how to make it work for some reason.

I had three custom sets of horns made for the coupe, all radiused. The tallest made the least HP, the shortest, the most. As I recall, about a 3 RWHP difference on the dyno.

When we fitted the cold air system, I had to go a full step richer in jetting. So after many dyno runs, I have concluded that the space over the horns is more important than the height of the horns (if they are properly radiused. Ideally, you should have as much space over the horns as the width of the chokes - so for 40 IDFs, 40mm would be ideal) and cold air allows you to get more fuel in the cylinders and develop a lot more HP.

I haven't run the coupe on a dyno since I put the cold air box on, but a whole step richer is no doubt a significant gain. I'll post the comparison results (with and without the cold air) when I get to a dyno in October.

Do u have a photo of your set up, thanks
Jim
East Grand Forks MN
1970 Fiat Spider BS1 ( FOR SALE
1969 124 AS Spider
2017 Abrath
2018 Alfa Romeo 4c Spider


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