Choosing a Carb for Boost

one70six

Active member
I have been scouring the net (including this forum) for tips on blow through carb setups and I came across an equation to determine the carb size that you would need under boost. I am interested in seeing what you guys think about this equation and if it makes sense.

"The size of carb(s) or CFM required for a given application can be calculated by the following formula A: {(CID x RPM) ÷ 3456} x {Boost ÷ 14.7) + 1} = CFM required." Quoted from http://blowerdriveservice.com/faq.php


If the math is correct then my Turbo 200 build would work out as follows...

Bore = 3.68
Stroke = 3.13
Over Bore = .030
Over Stroke =
Cylinders = 6
Cubic Inches = 203.017412606177
Litres = 3.32689990013892

((203 X 6000) / 3456) * ((10 psi / 14.7) + 1) = 592.1792328 CFM

This would make selections in off the shelf blow through carbs a lot easier if I can indeed use 500-600 CFM.

What do you guys think? :thanks:
 
one70six,

If I'm understanding you correctly, you're doing blow through and I believe the calculations you put up are for draw through. There's a difference. Draw through carbs need to be kept larger so as not to create a restriction on the compressor or blower. Figured to work at 14.7 PSI's (normal air pressure).

Now blow through will be working at a higher density (14.7 plus your boost). It can be smaller because the denser air will flow through the carb at about the same speed as the larger carb at NA air pressure. So the speed going through the venturi won't go super sonic and cause a restriction. I don't think I'm explaining this very well, but there's some guys on here that know what I'm talking about and can explain this better. Simply put, blow through can use a smaller carb. If you go large you'll hurt your off boost performance creating lag. I think a 350 Holley would be a good place to start. Ask Will, he knows this stuff.
 
Thanks for the tip drag. I will hit up Will if he doesn't see this thread in a few days. One more thing that I just thought about... What does it take to mod a Holley 350 for blow through or where can you buy one already modded?
 
Go to http://www.theturboforums.com. There is a lot of good turbo information on this site and a how-to with pics on a blow through carb modifications.

I would build my own carb - I wouldn't pay anybody else to do it. Will went EFI - he may have his old one laying around.

Take some time and go through Linc's turbo facts on this page. He's got a lot of good information and links there. I would also recommend Corky Bell's book and Alexander Bell's book. Personally, I like Alexander Bell's book better. This turbo stuff isn't that complicated, but if you don't pay attention to the details you can turn your engine into scrap metal.

You'll most likely have to run a methanol injection kit to keep detonation at bay with reasonably priced gas.

Good luck.
 
Congradualtions on the choice of engine!!! Just a little asside to why the turbo to low mount engine is important. It has some influence on you carb choice, because all 1981, 1982 and 1983 B and X code 3.3's were only an emissions clogged 195 cfm 1946 Holley I-bbl deal, but they came with the best E0, E1, E2 or E3 heads ever, and they are the best hp per dollar combinations you can get, bar none. And a whole lot of 1, 2 and even TBI EFI set ups are direct bolt ons to that later higher flowing cylinder head used on gray and blue sixes. And there are soo many of them around.

Ohhh, a Low mount CJ 232AB six just like Linc's 200. viewtopic.php?f=22&t=24859

(Do you have a part number on that 164 teeth flexplate the gearbox uses. If you do, I'd like one too.)

The low mount block is just the right unit for stand out performance modifications to the 200 I6 because all the common V8 gear goes right on it with just a few important provisos.

My absolute favourite Ford engine of all time!!!!

And my new favourite page is yours, http://samos65.weebly.com/photos.html

To see that engine is a delight. Its become a very common engine due to the popularity of auto 3.3 Fox body cars being trashed in record numbers. See this item here viewtopic.php?f=1&t=68983&p=528578#p528578

I'd a direct mount Holley 350 conversion to the X E2 head using the method Crosley uses. See viewtopic.php?f=1&t=68886. His Ford is putting about about 200 flywheel horsepower without a turbo. The adaptor and head work details are in his posts. Read all of them!

A stock Holley 350 or 500cfm with the mods Crosley and Does10's used will give all the power and good fuel distribution you need. Stock non turbo applications can make up about 350 hp or more with this carb. Practically any carb set up is better than the stock 195 cfm 1946 Holley when turbo'd, although Lincs 200 got a low 13 second quarter mile with about 20 pounds of boost with his stock low mount block before the over lean mixture took out the pistons via detonation. To get fuel economy, you'll be best off using lower boost than the level Does10's and Lincs200 used. The 274 cam will be perfect with 200 cubes and a turbo, but you'll need to change the stock 1650 rpm stall speed on the converter to the 3500 rpm items Crosley, Does 10's, and George (see the Turbo Experiement 250 where he uses a radcal 291 degree cam on his EFI turbo Cross flow 250 on viewtopic.php?f=3&t=43235)

If your going to use the Ford C5 auto (the trans that came with your 1983 200 six), you'll get best results with a better, looser torque converter. Your block takes only the 164 teeth low mount flexplate used exclusively on B and X codes with the CJ 232 AB rocker cover gray 3.3 six found in any 1982 to 1983 3.3 Fox. They were a selected standard engine on certain applications. There were also hgigh mount blue IJ 204 engine placard sixes, which were exactly the same but blue and ran a C3, C4 or C5 automatic, or the SR, SROD or T4 4 -speed transmission in the Fox platform Fords.

One your website, you've gotten a manual flywheel for a high mount six; if you want to use that high mount flywheel, you have to convert your low mount automatic only block to a 1990-2011 Ford Explorer/ Ford Ranger v6 or Capri Mustang Fox 2.8 bellhousing for the SROD or T5/Mazda 5 speed. The V6 runs a left hand starter motor to clear any turbo exhast system you want and a tiny 136 to 138 teeth compatable starter motor which should work with might work with 136 teeth 2.77 early flywheel.

I'd strongly suggest using the stock 4.25" diameter converter exhast be reworked to suit a Lincs 200 style turbo.

You've got more options to consider over the gearbox side than the turbo and induction. You'll make the best budget and best performance with the low mount 200 six, and if you use a mild version of the Crosley, Does 10's, and George turbo set ups, you'll spend the lowest dollars and get the highest performance.
 
Wow thanks for the write up X! This is a lot of good information to go off of. I really appreciate it and thanks for checking out my site! I wanted to sort of document what I'm doing to the car for both personal reasons and to help out the fordsix community for future projects.

The part number for the original flexplate is E1BP-AA.

The new flexplate is a 28 oz 157t billet steel flywheel 10.5" from Modern Driveline part number MD-LBS157-28

The new flex plate is going to be mated up with a T-5 trans sometime in the future, I just love banging gears, what can I say. I talked to the guys at Modern Driveline and they suggested this 157 tooth setup because it will work well with the rest of their conversion kit. I'm assuming that the bell housing adapter in their kit is the same as the one that you described for "1990-2011 Ford Explorer/ Ford Ranger v6 or Capri Mustang Fox 2.8 bellhousing for the SROD or T5/Mazda 5 speed." I hope...

It looks like I do have a few choices coming up that I didn't consider so I will have to study the links that you posted to gain some more knowledge.

As far as the head goes, I was planning on getting an aluminum setup from CI along with their intake but since the original head is one of the better ones, should I reconsider? Money plays a factor but I would spend it if I knew that it was the best route to take. I see benefits in weight, cooling, and flow in the alum setup but if a modded original is close or better in performance I might take that route.

Thanks again!
 
one70six":x2fnz7ec said:
Thanks for the tip ... What does it take / can you buy one already modded?

one70six :

I've been on similar project, searches haven't found a source for Blow-Thru modded 2300. I have 7448 350CFM and a 4412 500CFM versions for project.

Quick list at Holley.com shows 4150 as supercharger - blow through ready but no 2300's on list.
http://www.holley.com/data/TechService/ ... erence.pdf

There is a website- hangar18fabrication referred to:
http://www.com/blowthru.html

have boosted fun...

 
The new flexplate is a 28 oz 157t billet steel flywheel 10.5" from Modern Driveline part number MD-LBS157-28

Are you talking about a 28 pound billet flywheel or 28 oz. as in imbalance? If it's imbalance might want re check that or have rebalanced the six uses a zero balance Flywheel. Good Luck on your build :nod:
 
Sweeten's Performance Machining in Pocola, OK is balancing the entire rotating assembly along with the flywheel so it should be good to go from the harmonic balancer all the way back. Thanks for the concern. (y)
 
Just to chime in, I am building a blow through 200 on a daily driver and have decided to use a Weber 32/36. If you are not familiar with this carb, it has a progressive secondary circuit that will allow me to richen/tune the mixture when my foot is in the pedal but maintain decent mileage while staying in the primaries. The engine is on the stand being rebuilt now and the Weber is new in the box and will go on the fresh engine when installed on the test stand with the turbocharger. 8)

Just pointing this carb out as the other carbs mentioned are synchronized and have no secondary circuit to richen the mix thus affecting the fuel sipping characteristics of this engine.

Being a daily driver, this was important to me.
 
One70six,
For the blow-thru carb mods do search for "hanger18fabrication". It's all explained in there.
I did most of the mods to our 350 Holley. I still have that carb but it's trashed! The E85 pretty much ate everything up! Just one of the reasons we switched to EFI.

The main things to remember for a blow-thru carb:
Boost referenced fuel pressure regulator. Gotta have it!
Open up the PVCRs (Power Valve Channel Restriction). The little holes behind the PV. They need to be MUCH, MUCH larger. (at least for a 250. A 200 wouldn't need them as large) This is the secret to making the blow-thru work.

Have fun!
Will
 
Not to hijack this thread but i was on CI carb calc and it was approx 408 cfm for a 200ci with 6000 redline and 115% VE (using a turbo or supercharger) so would it not be better to get the 500 cfm and jet it down than to error on the side of too low? Just trying to get some answers also :unsure:
 
67chrrybucket":10sty52w said:
Not to hijack this thread but i was on CI carb calc and it was approx 408 cfm for a 200ci with 6000 redline and 115% VE (using a turbo or supercharger) so would it not be better to get the 500 cfm and jet it down than to error on the side of too low? Just trying to get some answers also :unsure:


I'm breaking number one rule of Fourms..... repeating what I read not actual exp. This is what I found out and maybe someone that knows will confirm or laugh at my ingorance :mrgreen:

I don't think the VE changes with boost. (75%)
Haven't seen where many that actually turn 6K rpms. (5500)

On the other hand I read that you can't over carb a turbo (with in reason I'm sure).
 
67chrrybucket":1e236fwk said:
Not to hijack this thread but i was on CI carb calc and it was approx 408 cfm for a 200ci with 6000 redline and 115% VE (using a turbo or supercharger) so would it not be better to get the 500 cfm and jet it down than to error on the side of too low? Just trying to get some answers also :unsure:


100 cfm over what is required makes a big difference in the booster signal. It is not a matter of jetting it down, but of total airflow. Cfm ratings do not change with blowthrough. The air being blown through is more dense, but the actual airflow through the carb does not change at all. It seems that those with experience in the tuning of these systems agree that smaller is better for blowthrough as a slight restriction at the carb is not a big deal, but the tuning is very difficult if the carb is sized even a bit too large.

At the end of the day I would (and do) err on the small side. Hence the DGV Weber for this cat. 8)
 
Are any of the Weber's vac secondary? Or any 2v carb? Just thinking and now asking.... Could you reverse that funtion of the diaphram and use boost to push down on the normally vented side and vent the normally vac side.. to open the secondary as the boost comes on and make up for the extra fuel needed????
 
Easy to do.

There is a Weber 28/30 DFTH and 30/34DFTH carburetor, another vac sec 2-bbl fiited to the Pinto 1600 and 2000 in Europe from 1985 to 1988.

The 2 liter one was still smaller than the earlier 32/36 dgv, but inide they had the stock primary was only a mm smaller at 25 and the 27 mm secondary the same size. Its around, its common, and its part numbers are 85HF 9510 CA, DA, CB and DB. It was jetted for 3 way cat and is ultra lean on the primary to make better fuel consumption figures than the DGV.

http://faq.ford77.ru/pdf/sierra/0903-04a.pdf

http://www.geocities.ws/julianvz/Sierra ... _dfth.html



http://www.gowerlee.dircon.co.uk/DFTMspareslist.GIF

Its a slightly smaller Holley Weber 5200 (bascially a smaller Weber DFV, or a reversed Weber DGV). Ford used it to get better fuel economy on the German and British carb Pinto engined Mekurs. See http://atspeedracing.co.uk/products/ind ... 03_115_121


The Russians and Fiat did a way too small 180 cfm vac sec Weber 28/32 ADHA or 28/32 DMHA,

1974 WEBER 32 DMSA 2/100 CARB is http://www.fiatplus.com/images/P/4330931.jpg from http://www.fiatplus.com/1974-weber-32-d ... 95122.html



great little carb based on the Weber ADM 34 found in cross flow Falcons, Fiat 131 and 132's and is used in the sohc 1.1, 1.3, 15 and 1.6liter Fiat 124 based Lada sedans and 4x4's, Nivas, Rivas, Cossacks.

service kit


See http://www.bitsofitaly.com/weber-tuning--jettings
and for the Weber 28/32 ADHA , http://www.bitsofitaly.com/uploadedFile ... 8-8795.gif

http://www.ladaniva.co.uk/baxter/resour ... erSwap.htm
http://cm4x4.blogspot.com/2009/01/manua ... -niva.html

You can get it for a song from the net. Might have some problems with the CIA getting one, or the IRS if you don't pay the tax on importing, but its around in huge numbers

Carburador.jpg
1719_1.jpg
 
X, You truly astonish me with your vast knowledge of this stuff. No joke. :beer:

I believe a modification is required to ensure the closing of the secondaries when configured like this. It seems that once the intake is pressurized, the engine would continue running unthrottled on just the secondaries even when the pedal is lifted. :shock:
 
Does10s":1ojbzl0a said:
Open up the PVCRs (Power Valve Channel Restriction). The little holes behind the PV. They need to be MUCH, MUCH larger. (at least for a 250. A 200 wouldn't need them as large) This is the secret to making the blow-thru work.
I might suggest getting one of Quick Fuel Technologies billet metering blocks that will allow you to adjust the pvcr via screw in bleeds. If you start drilling the original metering block and go too big you can just throw it away at that point. Here is a link to check out:

http://www.quickfueltechnology.com/mete ... ation.html
 
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