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FITECH for the MGB?

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pinkyponk Avatar
pinkyponk Gold Member Adrian Page
Berwick, NS, Canada   CAN
In reply to # 3889037 by Gerald O Lots of misunderstandings in this thread.
First, the CFM flow rate of individual twin carbs on the MG cannot be added to compare with a larger carb or throttle body that is dumping into a plenum type manifold. The two twin carbs are not connected by a shared plenum so only one carb is flowing at any given moment.

Second, the flow rate required by an individual cylinder cannot be 'averaged', or taken as 1/4 that of the entire engine. Its peak flow requirement must be met, which is the same flow rate as the entire engine. So if the engine can pump 150 CFM, then each cylinder also pumps at that rate, but in an interrupted manner. Since only one cylinder is drawing through the carb at a time, a single 150 CFM carb cconnected to a plenum serving all 4 cylinders would, in principle, satisfy the flow needs. However, if each cylinder were only fed by its own separate carb, it would still need 4 carbs of 150 CFM each. In the case of the MGB, with two pairs of siamesed intakes, two 150 CFM carbs are needed. This is of course a simplification, as it does not take into account air velocity and momentum effects of the 'pulsed' or interrupted flow, which tends to raise the nominal flow spec required from the carb. In short, the twin HS4 or HIF4 carbs are the right size.

Nice post Gerald! I know the B series can do 170hp on a single 48mm carb (mine makes 140hp on a single HIF6) so it does make you wonder how 500 cfm would be ok. How does that work?

Adrian
(who loves his aluminum flywheel)



Home built Eaton M62 Supercharger with 7.6psi boost, 8:1 compression, custom "supercharger" cam from Schneider Cams, Mikuni HSR48 Carburetor, cold air intake, ported head, matched manifolds, CB Performance computerized ignition, Fidanza 9 pound flywheel, Maxspeeding rods with Teflon wrist pin buttons.

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pinkyponk Avatar
pinkyponk Gold Member Adrian Page
Berwick, NS, Canada   CAN
In reply to # 3889055 by Paul755 I am just passing on what the owner reported. As he is an actual real live driver of a FiTech modified MGB and did seem to be mechanically well versed in MGB engines and perfomance, I will take his word for it.

In reply to # 3889042 by pinkyponk How would fuel injection give a bump in performance? I can see it might drive better during warmup... but beyond that I see no reason how it could produce more power... unless his carbs were too small or not tuned correctly.

Adrian

Fair enough. Just trying to learn. smileys with beer

Adrian



Home built Eaton M62 Supercharger with 7.6psi boost, 8:1 compression, custom "supercharger" cam from Schneider Cams, Mikuni HSR48 Carburetor, cold air intake, ported head, matched manifolds, CB Performance computerized ignition, Fidanza 9 pound flywheel, Maxspeeding rods with Teflon wrist pin buttons.

Gerald O Avatar
Gerald O Gerald O'Docharty
Wake Forest, North Carolina, USA   USA
1978 MG MGB
In reply to # 3889057 by pinkyponk ...I know the B series can do 170hp on a single 48mm carb (mine makes 140hp on a single HIF6) so it does make you wonder how 500 cfm would be ok. How does that work?

Adrian
(who loves his aluminum flywheel)

The 'published' CFM ratings for a carb are measured for 'laboratory' steady-state flow at a specified fixed air pressure difference. The actual pressure across the carb under real world operating conditions however is nothing like that.
Actual performance depends on many factors. Horsepower does not care about flow volume so much as air mass, which varies with altitude and temperature (density). Scavenging effects increase the pressure drop across the carb which increases its flow, as does forced induction.

An engine doesn't care what the fueling method is with regards to how much air it can pump. However EFI systems generally do better than carbs at maintaining correct fuel/air mixture when oversized. Oversized carbs tend to have poor throttle response or 'lag', but oversized EFI throttle bodies tend to be overly sensitive to throttle, as in 'on-off'.

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rocannon Avatar
rocannon Platinum Member Frank .
Clairvius Narcisse Township, Bokor, St. Kitts and Nevis   KNA
1967 MG MGB GT "GT From Hell"
1980 MG MGB "Restored By Photoshop Inc."
Paul,
What’s chance you could post a pic or two of his setup?

In reply to # 3889055 by Paul755 I am just passing on what the owner reported. As he is an actual real live driver of a FiTech modified MGB and did seem to be mechanically well versed in MGB engines and perfomance, I will take his word for it.

In reply to # 3889042 by pinkyponk How would fuel injection give a bump in performance? I can see it might drive better during warmup... but beyond that I see no reason how it could produce more power... unless his carbs were too small or not tuned correctly.

Adrian



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pinkyponk Avatar
pinkyponk Gold Member Adrian Page
Berwick, NS, Canada   CAN
In reply to # 3889097 by Gerald O
In reply to # 3889057 by pinkyponk ...I know the B series can do 170hp on a single 48mm carb (mine makes 140hp on a single HIF6) so it does make you wonder how 500 cfm would be ok. How does that work?

Adrian
(who loves his aluminum flywheel)

The 'published' CFM ratings for a carb are measured for 'laboratory' steady-state flow at a specified fixed air pressure difference. The actual pressure across the carb under real world operating conditions however is nothing like that.
Actual performance depends on many factors. Horsepower does not care about flow volume so much as air mass, which varies with altitude and temperature (density). Scavenging effects increase the pressure drop across the carb which increases its flow, as does forced induction.

An engine doesn't care what the fueling method is with regards to how much air it can pump. However EFI systems generally do better than carbs at maintaining correct fuel/air mixture when oversized. Oversized carbs tend to have poor throttle response or 'lag', but oversized EFI throttle bodies tend to be overly sensitive to throttle, as in 'on-off'.
Thanks Gerald. That clears it up. You have quite a knack for explaining things.

Adrian



Home built Eaton M62 Supercharger with 7.6psi boost, 8:1 compression, custom "supercharger" cam from Schneider Cams, Mikuni HSR48 Carburetor, cold air intake, ported head, matched manifolds, CB Performance computerized ignition, Fidanza 9 pound flywheel, Maxspeeding rods with Teflon wrist pin buttons.

matt167 Matt D
Prattsville, NY, USA   USA
I think a slick setup would be throttle bodies for a Harley 883 sportster. It's all GM Delco sensors, so easy to get ECU and tune

Denis Avatar
Denis Denis Hill
Bearii, Nth Victoria, Australia   AUS
A side draft version might be nice on a supercharger, Their sight info mentions boost capable; Having no float system may allow it to lay down. Denis



68 B roadster, Daffodil yellow, supercharger, Burgess SC head, SC cam, Mikuni HSR 48 carburetor and engine built for supercharging.

73 BGT V8 conversion starting with a bare shell. Built the engine "3.9L Rover" early in 2016 with high comp pistons and a few other nice bits, plus a T5 ford trans. Started on the body late 2016 and complete late 2017, Did all the work myself, mechanical, body. paint etc.
Finished and going well, great to drive and quick. Now has a nice 3.23 LSD.

NOHOME P P
O, ON, Canada   CAN
1967 MG MGB GT "Maggie (GT From Hell)"
In reply to # 3889529 by Denis A side draft version might be nice on a supercharger, Their sight info mentions boost capable; Having no float system may allow it to lay down. Denis

I have actually thought about this for the MGB; in theory the throttle body does not care if you mount it upside down or sideways.

B-racer Avatar
B-racer Jeff Schlemmer
Shakopee, MN, USA   USA
1950 Willys Jeep Pickup "Ratrod"
1971 MG MGB ~ For Sale ! ~
2014 Dodge Charger
In theory and in practice. Remember we're dealing with 50+ psi injectors, not a bowl full of fuel delivered at 4 psi. I'll be installing a "vertical system" soon, of different manufacture.



jeff@advanceddistributors.com

Mustangsix Avatar
Mustangsix Gold Member Jack Collins
Orlando, FL, USA   USA
And we're considering a horizontal system. Results soon.



Edited 1 time(s). Last edit at 2019-02-11 07:26 AM by Mustangsix.


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B-racer Avatar
B-racer Jeff Schlemmer
Shakopee, MN, USA   USA
1950 Willys Jeep Pickup "Ratrod"
1971 MG MGB ~ For Sale ! ~
2014 Dodge Charger
Here's Jenvey's Weber replacement setup. The thin throttle bodies leave plenty of room to build a good manifold and velocity stacks as required for any given motor.



jeff@advanceddistributors.com


Attachments:
Jenvey.jpg    57.8 KB
Jenvey.jpg

B-racer Avatar
B-racer Jeff Schlemmer
Shakopee, MN, USA   USA
1950 Willys Jeep Pickup "Ratrod"
1971 MG MGB ~ For Sale ! ~
2014 Dodge Charger
Attached are a couple FiTech installs I've done, which are both good representatives of an oversized system on a small motor. Both are the 1000 cfm 4-barrel system on a 350. One Olds, one Chevy. Simple installs, both started before the 4th revolution of the engine, both continue to self-tune and run better with use. I have found that using setting #4 for the camshaft, which is considered the most radical, results in faster self-tuning for the baseline, and you DO need to adjust the throttle stops front and rear to get the IAC readings to fall into the much needed "5-10 step" range. They're set up with a high throttle opening to aid in initial starting, which needs to be reduced for a better overall tune. You can tell its set wrong when you hear the IAC pulling massive amounts of air from the open port that would usually be the fuel bowl vent at the top of the throttle body.



jeff@advanceddistributors.com


Attachments:
nova.jpg    81.1 KB
nova.jpg

olds.jpg    58.5 KB
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Rick Fawthrop Avatar
Rick Fawthrop Richard Fawthrop
Langley, WA, USA   USA
What are you running for ignition on the Nova?
How are emissions on coldstart ?

Paul755 Paul H
Fairfax, VA, USA   USA
1974 MG MGB MkIII
1979 MG MGB MkIV "Nemesis"
I'll go the the next "Cars 'n Coffee" and see if the B owner is there. I should have asked for his email .

In reply to # 3889145 by rocannon Paul,
What’s chance you could post a pic or two of his setup?

In reply to # 3889055 by Paul755 I am just passing on what the owner reported. As he is an actual real live driver of a FiTech modified MGB and did seem to be mechanically well versed in MGB engines and perfomance, I will take his word for it.

In reply to # 3889042 by pinkyponk How would fuel injection give a bump in performance? I can see it might drive better during warmup... but beyond that I see no reason how it could produce more power... unless his carbs were too small or not tuned correctly.

Adrian

Paul755 Paul H
Fairfax, VA, USA   USA
1974 MG MGB MkIII
1979 MG MGB MkIV "Nemesis"
I called FiTech and they tell me that there is no reason unit will not work horizontally.The initial prime pulse can be disabled to stop any fuel running out at startup as the injectors are above the throttle plates or just put a 10 degree slope on the carb mounting flange if you want to keep the initial pre-start prime pulse. Might be a fun project to hack up a standard twin SU inlet manifold and/or Cannon Weber manifold and would clear the brake booster.....


In reply to # 3889563 by NOHOME
In reply to # 3889529 by Denis A side draft version might be nice on a supercharger, Their sight info mentions boost capable; Having no float system may allow it to lay down. Denis

I have actually thought about this for the MGB; in theory the throttle body does not care if you mount it upside down or sideways.

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