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Single 4bbl verses multi carbs

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Red rose racer
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Single 4bbl verses multi carbs

Post #1 by Red rose racer » Sun Sep 06, 2020 10:58 pm

Have the 4bbs manifolds come so far , why are they used more than the multiple carb manifolds, like 2x2 or 2x4 or 3 singles ,even 6 in a row , one per cylinder. With the computer controled engines of today why not more.

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Re: Single 4bbl verses multi carbs

Post #2 by sdiesel » Sun Sep 06, 2020 11:21 pm

Red rose racer wrote:Have the 4bbs manifolds come so far , why are they used more than the multiple carb manifolds, like 2x2 or 2x4 or 3 singles ,even 6 in a row , one per cylinder. With the computer controled engines of today why not more.



we must assume "by computer controlled u might include multi port injection is one per cylinder, and a "bigger 7th nozzle" for those serious enough about speed to include one.


But general answer is cost, 3 carbs cost maybe much more than three times one carb, and 6 carbs is no friend of the weekend cruiser who would rather cruise than lose most of the weekend to tinkering on 6 carbs
And the modern 4 barrels is so darn efficient including here the sniper style efi , simple, q jet excepted, and common, that there is little motivation to go further.
What irritates me is what passes for a performance manifold on the inline. One 4 barrel on a properly designed manifold would rock. This would mean plenum dividers equal length runners and heat risers in each runner, just for starts.
Example, can you envision an upside down header with collector at about same elevation as factory, individual runners to each port. Each of equal length and diameter.
Then a header out of the same design all mated to a common port plate, attached to the head lighter easier to work with, and likely more efficient than those heavy bulky aluminum things we Have now.
Last edited by sdiesel on Mon Sep 07, 2020 4:34 pm, edited 1 time in total.
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Re: Single 4bbl verses multi carbs

Post #3 by THE FRENCHTOWN FLYER » Mon Sep 07, 2020 10:38 am

While I agree that a 4V is much better than the original 1V stocker for performance I have found that using a 2 x 2 setup on a Clifford dual quad intake is better and it eliminated some nagging hesitation problems I had with the 4V. I think even the EFI lower with miltiple carbs offer advantages over a single carb.
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Re: Single 4bbl verses multi carbs

Post #4 by rbohm » Mon Sep 07, 2020 4:16 pm

the big thing as noted is cost. one intake with one four barrel carb is cheaper than one intake and two two barrel carbs. teh aaadvantage of multi carbs though is better air/fuel distribution and control. you pays your money and you takes your choice.
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Re: Single 4bbl verses multi carbs

Post #5 by sdiesel » Mon Sep 07, 2020 8:39 pm

And much of fuel distribution has to do with choice of carburetor maybe? Carburetor tuning,And of course engine health?
a long love affair with the 300 six.
my lastest and final fling is a fresh 300 in an 88 ford f350 dually 4X flatbed

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Re: Single 4bbl verses multi carbs

Post #6 by rbohm » Mon Sep 07, 2020 8:59 pm

sdiesel wrote:And much of fuel distribution has to do with choice of carburetor maybe? Carburetor tuning,And of course engine health?


no actually more about carb location. a single four barrel carb on a long inline six intake means the outer cylinders are going to tend to run lean and the inner cylinder are going to tend to run rich. take two two barrels and position them to where they feed three cylinders each that are closer together, and the cylinders tend to run wore evenly air/fuel wise.
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Re: Single 4bbl verses multi carbs

Post #7 by Red rose racer » Tue Sep 08, 2020 12:59 am

rbohm that’s what I though, 2 2bbls would run slightly cooler and little more power. Now how about if you turbo the motor, 4bbl and turbo, 2 2bbls and single turbo or small twin turbos. Or would you go with injection maybe 2 small snipers.

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Re: Single 4bbl verses multi carbs

Post #8 by rbohm » Tue Sep 08, 2020 1:04 am

Red rose racer wrote:rbohm that’s what I though, 2 2bbls would run slightly cooler and little more power. Now how about if you turbo the motor, 4bbl and turbo, 2 2bbls and single turbo or small twin turbos. Or would you go with injection maybe 2 small snipers.


if i were going to turbo a six, i would use two small turbos, to virtually eliminate lag, and run port EFI. if i had to use carbs, i would use two two barrel carbs in a blow through setup, remember the pop off valves as well as the waste gates.
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Re: Single 4bbl verses multi carbs

Post #9 by pmuller9 » Tue Sep 08, 2020 10:06 am

For twin turbos use two front EFI exhaust manifolds along with the stock EFI intake manifold and multi-port injection.
Here is a good example.
viewtopic.php?p=622393#p622393

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Re: Single 4bbl verses multi carbs

Post #10 by jgregg13 » Tue Sep 08, 2020 2:37 pm

It seems the biggest issue for the Single 4bbl is getting uniform AFR to all cylinders. Though the single 4bbl is cost effective and easiest to maintain and tune. As for achieving equal AFR, the design of the manifold plays a part. Mounting the carb on the plenum of the EFI intake might be good, but not practical in most applications. Of the three or four commonly available intakes I expect the Aussiespeed design should have the best AFR distribution. It's much like the slant 6 intake that worked well as the individual runners are brought into the more central plenum area. Using a carb spacer or not can affect the flow characteristics in the plenum as well as plenum volume. Unfortunately I can't back any of this up with real data, it's just an opinion.
If going to throttle body EFI (Sniper etc.) then a single unit would be the only option unless you've got an insane budget.

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Re: Single 4bbl verses multi carbs

Post #11 by Red rose racer » Tue Sep 08, 2020 7:31 pm

Some very good ideas here, and thank you all. Sometimes responses to a yes or no type of question become very hard for my old school brain. Every good answer , makes me think of two more questions, if you know what I mean.

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Re: Single 4bbl verses multi carbs

Post #12 by pmuller9 » Tue Sep 08, 2020 8:06 pm

Red rose racer wrote:Some very good ideas here, and thank you all. Sometimes responses to a yes or no type of question become very hard for my old school brain. Every good answer , makes me think of two more questions, if you know what I mean.


Are you looking at sand racing a 300 six?

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Re: Single 4bbl verses multi carbs

Post #13 by sdiesel » Tue Sep 08, 2020 8:42 pm

My sole argument in favor of the 4 bbl, or sole carburetor 2 or 4, is
A. Cost,
B.simplicity.
C.efficiency

Efficiency did you say!?

Yes generally an engine in very good condition with fairly equal vacuum signal, and a single 4 bbl carb on the aussiespeed slant six model can return near the same effect as more sophisticated and better systems.

The carb has to be near perfect match for the engine, and tuned mercilessly to the finest of detail. Keeping the fuel in suspension and the multitude of factors that entails is more manifold design (awful in most cases) than carb. Yes two webers will feed 6 inline cylinders better and return greater efficiency, but not by huge margins under general driving conditions. Especially when considering costs involved and this:
Getting afr to equalize with two carbs is more challenging than with one bigger carb. There are 2 times as many variables and conditions to meet.
The saving grace is in the manifold. Shorter distance for the suspended fuel to travel.

But what if we were to build an intake with equal length runners I'm imagining something that would look like the old header mufflers on air cooled volkswagons. A " paperclip" shape, feeding 6 cylinders from one plenum and the plenum can sit on the far side of the engine.or anywhere, cause we are building this intake, small runner from commonly available piping.
The 2jz people make gorgeous exhaust systems in this same manner
I am no engineer and have virtually no experience in this kind of design, but there is a sensibility to it that our favorite manifolds lack. These now in use seem to be designed simply for a perch to plop a 4 barrel on , which conveniently enough could be purchased at the same speed shop at the same time.
Most purchasers were profoundly disappointed in the result.

Edit: the reason my FISH carb is so deadly even atop the factory intake is its single throat , no venture, and atomization in this case is nearly vaporization. The air demands of six cylinders pulling through one 1 7/8 hole for all of its needs creates all the carb needs to turn liquid into very fine mist.

I wish somehow I could let everyone drive a six with a fish - a sixnafish not to be confused with or atunafish....
Anyhow its performance best I can tell is up there in efficiency
Last edited by sdiesel on Tue Sep 08, 2020 10:45 pm, edited 1 time in total.
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Re: Single 4bbl verses multi carbs

Post #14 by Red rose racer » Tue Sep 08, 2020 9:07 pm

Yes sand racing. I have sand and mud raced 460 and521 big blocks in f100 for almost 30 years , love it. Nobody races inline 6s. I believe now I will . starting in lower classes.

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Re: Single 4bbl verses multi carbs

Post #15 by pmuller9 » Tue Sep 08, 2020 9:15 pm

How much power will you need to get started?

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Re: Single 4bbl verses multi carbs

Post #16 by Red rose racer » Tue Sep 08, 2020 10:34 pm

My truck weights 3120, I can shave another maybe 400 lbs Off that. I m thinking 350 to400 hp.to start. I’m kind of waiting on the possibility of the Sr. Head that would be the easiest for me. If not maybe the xflow.

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Re: Single 4bbl verses multi carbs

Post #17 by jgregg13 » Wed Sep 09, 2020 12:10 am

sdiesel wrote:
But what if we were to build an intake with equal length runners I'm imagining something that would look like the old header mufflers on air cooled volkswagons. A " paperclip" shape, feeding 6 cylinders from one plenum and the plenum can sit on the far side of the engine.or anywhere, cause we are building this intake, small runner from commonly available piping.


Kinda' like this?

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Re: Single 4bbl verses multi carbs

Post #18 by pmuller9 » Wed Sep 09, 2020 10:28 am

Red rose racer wrote:My truck weights 3120, I can shave another maybe 400 lbs Off that. I m thinking 350 to400 hp.to start. I’m kind of waiting on the possibility of the Sr. Head that would be the easiest for me. If not maybe the xflow.

Bruce's time is limited so his focus is on the crossflow head and even that will be a while since it requires a special side cover to be fabricated.
You will also need to fabricate and intake manifold and exhaust header.
It will be a while for the SR head.

What fuel do you use when racing?

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Re: Single 4bbl verses multi carbs

Post #19 by sdiesel » Wed Sep 09, 2020 11:35 am

Yes! But lower profile of course.
Is that the 302 gmc?
Its sad to hear the SR head is awhile in time be for production. A crossfolw, if one must choose is a better use of that time I suppose. I prefer a crossflow, even if I don't need its performance potential. Its a design that just makes sense.
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Re: Single 4bbl verses multi carbs

Post #20 by Red rose racer » Wed Sep 09, 2020 11:57 am

Well, for ford BB 521, I mixed Sunoco GT 104 (2.7% Ox.) 112 then added 10 oz. nltro p . No legal but with low budget, you do what have to do. Had ex NHRA funny car driver help with fuel,chassis, traction etc.

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Re: Single 4bbl verses multi carbs

Post #21 by pmuller9 » Wed Sep 09, 2020 12:31 pm

You can have 400 hp with a DIY big valve ported head.
Are you good with a long nose die grinder?

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Re: Single 4bbl verses multi carbs

Post #22 by Red rose racer » Wed Sep 09, 2020 1:02 pm

I did all the porting on my big block heads, so yes, bought every porting and cylinder head book I could including (gas flow tech ) by an English Guy

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Re: Single 4bbl verses multi carbs

Post #23 by jgregg13 » Wed Sep 09, 2020 1:06 pm

sdiesel wrote:Yes! But lower profile of course.
Is that the 302 gmc?


It's a Buick 8, but that's the idea.

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Re: Single 4bbl verses multi carbs

Post #24 by Red rose racer » Wed Sep 09, 2020 1:10 pm

My big search now is for 240ci rods and head. How much will 6.8 rods take. Am looking for 65 to 68 first

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Re: Single 4bbl verses multi carbs

Post #25 by pmuller9 » Wed Sep 09, 2020 2:06 pm

Red rose racer wrote:My big search now is for 240ci rods and head. How much will 6.8 rods take. Am looking for 65 to 68 first


Yes You only want the 65 to 68 (No oil spit hole in the big end) rod.
If you remove all the forging lines and shot peen the rods and resize with ARP bolts they will certainly handle 400 hp at 6000 rpm.
https://www.dropbox.com/s/95g3bpoga368g ... .jpg?raw=1
They have been pushed to 500 hp at higher rpm but I would look at aftermarket rods at that point.

For turbocharging the small journal BBC 6.385" rods are being used.
https://www.summitracing.com/parts/cpi-b6385ds3b4ah

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Re: Single 4bbl verses multi carbs

Post #26 by pmuller9 » Wed Sep 09, 2020 3:22 pm

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Re: Single 4bbl verses multi carbs

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Re: Single 4bbl verses multi carbs

Post #28 by THE FRENCHTOWN FLYER » Wed Sep 09, 2020 9:31 pm

That piston/rod is like the ones I used to use...
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Re: Single 4bbl verses multi carbs

Post #29 by sdiesel » Thu Sep 10, 2020 1:03 am

jgregg13 wrote:
sdiesel wrote:Yes! But lower profile of course.
Is that the 302 gmc?


It's a Buick 8, but that's the idea.

A strait 8 Buick!!!??
Helle's belles. Never knew such a thing. Displacement? Must been a very old design.and I see but 3 intake pipes maybe a 4th tucked in behind. That is so very cool. Perfect for my pickup if it will make power, lordy a --8 in my old ford.....
I'm junking my sixes....gimme 8 and make it strait!!!!!!
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Re: Single 4bbl verses multi carbs

Post #30 by pmuller9 » Thu Sep 10, 2020 9:27 am

Highjack content removed.
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Re: Single 4bbl verses multi carbs

Post #31 by pmuller9 » Thu Sep 10, 2020 8:47 pm

Red rose racer wrote:Well, for ford BB 521, I mixed Sunoco GT 104 (2.7% Ox.) 112 then added 10 oz. nltro p . No legal but with low budget, you do what have to do. Had ex NHRA funny car driver help with fuel,chassis, traction etc.


So it looks like big cam and 12:1 compression ratio.
If you want to start something this year you will need to do the head yourself.

What do you do for an air cleaner to keep sand from going into the intake?

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Re: Single 4bbl verses multi carbs

Post #32 by Red rose racer » Fri Sep 11, 2020 12:39 pm

I use the 14 in. 5 in. Tall cotton cloth filter with cheese cloth around that. The tracks were not dusty, water trucks were used to keep dust down. Filters were cleaned and washed good after each race date.

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Re: Single 4bbl verses multi carbs

Post #33 by Red rose racer » Fri Sep 11, 2020 1:02 pm

Oh, the season is nearly done for this year. I am targeting early to mid summer next year to be done, to do all my test and tune maybe get a few races in. I’m getting to old to do the hurry up, hurry up thing. One thing I learned racing try to do it right the first time. Then adjust.

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Re: Single 4bbl verses multi carbs

Post #34 by pmuller9 » Fri Sep 11, 2020 1:42 pm

Red rose racer wrote:Oh, the season is nearly done for this year. I am targeting early to mid summer next year to be done, to do all my test and tune maybe get a few races in. I’m getting to old to do the hurry up, hurry up thing. One thing I learned racing try to do it right the first time. Then adjust.

As you know the engine build can take longer than expected especially during this pandemic period.

You can use the industrial head you have with a small piston dome to get the needed compression.

You can also buy a new bare Engine Quest head with smaller chambers EQ-CH300B and install the exhaust seat for a 1.60" valve, cut the intake seat opening for a 1.94" valve and do port work and some chamber to valve unshrouding.
This is the combination for the SR head.

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Re: Single 4bbl verses multi carbs

Post #35 by Red rose racer » Fri Sep 11, 2020 4:24 pm

Pmuller9. Firstly thank you for all the help. Sand racing. 300 foot laser timed, mud racing 150 foot laser timed. Mud racing may be deceiving, mud is only few inches deep( dark sand , (wet down with hose) in front of Fair grandstands. After a couple trucks go it’s a paved highway, and fast. Most of the dragsters wheelly the course. Piston will be desired by what rod I can find. Racers learn a good bottom end,will keep you racing A lot lot longer.

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Re: Single 4bbl verses multi carbs

Post #36 by pmuller9 » Fri Sep 11, 2020 8:13 pm

Thanks for the racing info. Gives a better picture of your needs.
Are you wanting to start naturally aspirated and go turbocharging later or is this a turbo project from the start?

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Re: Single 4bbl verses multi carbs

Post #37 by Red rose racer » Sat Sep 12, 2020 12:18 am

I will go with the naturally aspirated engine first. I really like the looks of the small twin turbo setup I seen on this site, in progress, turbos at end of 2 front cast exhaust manifolds, late model I6. I have a Bridgeport mill , large old Footbert drillpress. I could make exhaust work very easily.

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Re: Single 4bbl verses multi carbs

Post #38 by pmuller9 » Sat Sep 12, 2020 12:34 am

Red rose racer wrote:I will go with the naturally aspirated engine first.

The 300 industrial engine you have will have the large chamber head that breaths well at valve lifts under .350" because of the unshrouded open chamber.
You can use the SBC 2.02" intake valve with the 1.6" exhaust.
I bolted the head to the bare block and scribed the bore circle to the head surface.
Then I ground the camber walls on the spark plug side out to the scribe line.

Image

This is what the intake bowl area looks like.
The valve guide is narrowed for use with undercut intake valve stems.

Image

The exhaust pocket is cut straight across leaving a shelf before exiting into the port.

Image

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Re: Single 4bbl verses multi carbs

Post #39 by pmuller9 » Sat Sep 12, 2020 9:24 am

The 300 large chamber head will also be the one you will need later for turbocharging where the compression ratio will be restricted to 9:1
I'm assuming that fuel injection is allowed for all the classes you want to run?

Are you allowed to run E85?
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Re: Single 4bbl verses multi carbs

Post #40 by Jesse73 » Sat Sep 12, 2020 9:36 am

If you are going drag racing and not driving on the road, that changes the whole picture in my mind. No part throttle economy needed, simply full throttle power and a small amount of low throttle drivability to get to the line. Why not take the old timey route and use stack fuel injection? You could cheaply buy 3 stock intakes, cut the center out and cap the ends making three 2 cylinder intakes (someone has photos of this, maybe FTF?) or you could also make intakes at home. Then install a fuel pump and 3 Hillborn style fuel injectors for the mechanical guy, or three throttle body’s and electric fuel injectors for the computer minded guy.

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Re: Single 4bbl verses multi carbs

Post #41 by THE FRENCHTOWN FLYER » Sat Sep 12, 2020 9:38 pm

I have posted pics of 3 x 1 intakes made this way.

Or - Algon actually made a mechanical stack injection system for these engines. I had one once. Nice piece if you can find one.
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Re: Single 4bbl verses multi carbs

Post #42 by Red rose racer » Sun Sep 13, 2020 2:38 pm

Yes, we can use E85. Some classes just say pump gas.

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Re: Single 4bbl verses multi carbs

Post #43 by pmuller9 » Sun Sep 13, 2020 8:12 pm

What I'm thinking is when it comes time for turbocharging E85 will let you run without an intercooler.
It's also a good fuel for naturally aspirated racing.

For proper E85 mix you would need to buy drum E85 rather than pump station E85.

This is the style intake manifold I would use along with fuel injection for both naturally aspirated and turbocharged use.
This is just an example. Could be made from six lengths of tubing and a sheet metal plenum.
It gives similar results as using stack injection but with a single throttle body and single air filter.

Image

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Re: Single 4bbl verses multi carbs

Post #44 by Red rose racer » Mon Sep 14, 2020 10:30 pm

Looks like that intake manifold is for crossflow head. If not how does it work, no place for exhaust man. I was thinking of making intake from lower injection manifold

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Re: Single 4bbl verses multi carbs

Post #45 by Red rose racer » Mon Sep 14, 2020 10:42 pm

Pmuller9 your susgestion of 12 to 1 compression ,how will E85 handle that high compression. And roughly how big a cam lift.

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Re: Single 4bbl verses multi carbs

Post #46 by pmuller9 » Mon Sep 14, 2020 11:05 pm

I was just using that manifold picture as an example for manifold style.
Yours would be similar but using a Ford 300 six intake flange.

The Ford EFI intake was designed for peak torque at 2000 rpm making the runners on the lower half too small in diameter for all out drag racing.
You are looking at peak torque above 4500 rpm with peak engine rpms around 7000 and need much larger diameter runners.

The camshaft .050" specs are in the 260 degree range with valve lifts around .600" with an LSA of 108 degrees.

With that large of a cam E85 would have no problem with a 12:1 compression ratio.

Red rose racer
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Re: Single 4bbl verses multi carbs

Post #47 by Red rose racer » Mon Sep 14, 2020 11:11 pm

Another check on my OK list,thank you.

Red rose racer
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Re: Single 4bbl verses multi carbs

Post #48 by Red rose racer » Thu Sep 17, 2020 7:06 pm

Naturally aspirated, I would then port inject head, what size injectors, and then I only need one air inlet. You said bottom standard injection tubes are to small, how much bigger would tubes have to be. I’m sorry with all questions, never ran injection before. I’m at ground zero with injection.

pmuller9
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Re: Single 4bbl verses multi carbs

Post #49 by pmuller9 » Thu Sep 17, 2020 8:44 pm

The size of the injectors is based on the horsepower.
For 500 hp naturally aspirated the injector size is around 50 lbs/hr

The throttle body mounts to the inlet of the intake manifold plenum as shown by the four bolt holes in the example manifold above. post #43

After the head gets ported the intake manifold runners needs to match the port size in the head.
Since you are trying to make power above 4000 rpm the runner can start larger than the intake port and funnel down to the intake port size at the head.

Red rose racer
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Re: Single 4bbl verses multi carbs

Post #50 by Red rose racer » Fri Sep 18, 2020 12:18 pm

What would you suggest in a book I can order about fuel injection that would be the most informative and accurate. When I started racing many years ago I got together all the books I could find, they told me how to do stuff but also what not to do . I enjoyed the research Nearly as much as building the motors.

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