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IaTR6
Dennis Costello
Central Iowa
(175 posts)

Registered:
12/29/2007 02:53PM

Main British Car:
'73 TR 6 '97 Explorer 5.0

Intake plenum modification
Posted by: IaTR6
Date: March 25, 2021 10:43AM

In making a new intake plenum, I have arrived at the question of whether it is necessary to
radius the exit bore on the plate the throttle body mounts to, or is just the straight bore ok?
I'll try to explain further. The throttle body is mounted to a 1/2" plate on the entry to the plenum.
Should the plenum side of the plate be radiused, or just a 90 degree opening? I've searched for the answer,
but don't seem to find what I'm looking for-maybe because I'm not knowledgeable enough to recognize it.
My inclination is it should be, but what do you think?
Thanks,
Dennis


BlownMGB-V8
Jim Blackwood
9406 Gunpowder Rd., Florence, KY 41042
(6008 posts)

Registered:
10/23/2007 12:59PM

Main British Car:
1971 MGB Blown,Injected,Intercooled Buick 340/AA80E/JagIRS

authors avatar
Re: Intake plenum modification
Posted by: BlownMGB-V8
Date: March 25, 2021 11:04AM

I think you should try it both ways and tell us your results Dennis. Research results are conflicting, some say yes some say no. I think it depends on whether or not the plate is a restriction, If it is then radiusing it should help.

Jim


IaTR6
Dennis Costello
Central Iowa
(175 posts)

Registered:
12/29/2007 02:53PM

Main British Car:
'73 TR 6 '97 Explorer 5.0

Re: Intake plenum modification
Posted by: IaTR6
Date: March 25, 2021 04:51PM

Thank you Jim, and I would like to do a comparison except the plate will be welded to the plenum entry.
This upper plenum project is similar to the one I showed on my project journal, Dennis' Project TR6.
This time, with the higher upper it will be possible to have the "floor" more flat, with only a slight upward
slope to the much less restrictive narrow section just before the area opens to the ports.
I still don't have enough room for trumpets, and as I think more, another design comes to mind but this
one will be it (I think I've heard that before)! Too bad my pattern maker father-in-law has passed, I could really get
going if he was here to help with the pattern, cores and casting.
My next question involves my Ford fuel rail pressure regulator. It conflicts with the gradual curve of the throttle
body to plenum transition, and I was going to replace it with a remote regulator. My concern is the factory
return style fuel system is regulated by a bleed off design, which circulates fuel from the relatively cool
tank to the rail and back. A remote regulator would make the fuel rail a dead-end. I was concerned about fuel heating,
and as I type this it occurs to me the newer vehicles use a variable pump output to regulate fuel pressure
which results in a dead-end rail. So, maybe I answered my question. Hmmm....
Dennis


minorv8
Jukka Harkola

(217 posts)

Registered:
04/08/2009 06:50AM

Main British Car:
Morris Minor Rover V8

Re: Intake plenum modification
Posted by: minorv8
Date: March 26, 2021 03:30AM

My previous modified plenum did not have radius. The current version does not have it either. Canīt really tell if it makes any difference. As for remote regulator, they are available with return connection to tank. Thatīs how I did mine.


BlownMGB-V8
Jim Blackwood
9406 Gunpowder Rd., Florence, KY 41042
(6008 posts)

Registered:
10/23/2007 12:59PM

Main British Car:
1971 MGB Blown,Injected,Intercooled Buick 340/AA80E/JagIRS

authors avatar
Re: Intake plenum modification
Posted by: BlownMGB-V8
Date: March 26, 2021 11:50AM

You can fit a bypass regulator at the intake and connect it to the existing return line. I've bought nice billet ones with a fuel pressure gage for around $30 on ebay. Requires a bit of plumbing but can be put about anywhere.

If you can radius the inlet plate a little bit I think you should. OTOH, I just made a riser for a 4 bbl intake that is an open plenum, no radiusing on the intake openings.A radius plate could be added but I don't think it'll be needed. My attitude is, build for a surplus of torque and horsepower and you can overlook a lot of smaller losses.

Jim


DiDueColpi
Fred Key
West coast - Canada
(1271 posts)

Registered:
05/14/2010 03:06AM

Main British Car:
What if the Hokey Pokey really is what it's all about?

authors avatar
Re: Intake plenum modification
Posted by: DiDueColpi
Date: March 26, 2021 10:02PM

Hey Dennis,
If you realize that the air entering your engine isn't really being sucked in. It's being blown in, that should determine your air flow choices.
Atmospheric pressure is pushing the air into your engine. The draw of your engine is merely providing a pressure differential.
So the exit of your throttle adapter really doesn't affect the quantity of air flow. But with thoughtful and careful shaping it can be used to direct airflow to stagnant areas of your plenum.
After market fuel pump drivers are available, these will give you the variable pump / pressure that a bypass regulator provides.
The problem is as you surmised , fuel heating. OEM variable pump drivers exist to keep the bean counters happy. They are a cheap easy way to control fuel pressure, and if you noticed all of them have done away with a serviceable fuel filter, I mean cheaper . Computer control of the fuel pressure is an asset I agree but they were really just a stepping stone to direct injection.
I still prefer a return style pressure regulator. Put a decent filter in the system, add a fuel cooler if your not in Canada. and live happily ever after.
Live Like You Mean It.
Fred


IaTR6
Dennis Costello
Central Iowa
(175 posts)

Registered:
12/29/2007 02:53PM

Main British Car:
'73 TR 6 '97 Explorer 5.0

Re: Intake plenum modification
Posted by: IaTR6
Date: March 27, 2021 11:18AM

Thanks Fred, I appreciate your advice. I have studied the fuel pressure regulators a little more, and find I was under the
incorrect assumption that the outlet of the regulator had to go to the regulated rail. Because the Ford setup has the regulator on the rail,
and the return is only connected through the regulator, I assumed I would plug the pressurized rail end and then have
a dead-end system. What I have done, is drilled and tapped the factory inlet for the regulator at the mount, and will attach a
6AN return line to the remote regulator. This will control the pressure in the rail, and return unused fuel to the tank.

On the throttle body to plenum connection, I find I'm too many engineering classes behind (none) to follow all that I
read on exit orifices. It seems like a tapered cone would be ideal, but I just can't go there. I did radius the exit side of the mounting plate just for fun.
I used a 1/4" radius carbide bit in a router. I used the same process to radius all the ports in the plenum baseplate to the
lower manifold.
Dennis
fullsizeoutput_c8e.jpeg



roverman
Art Gertz
Winchester, CA.
(3107 posts)

Registered:
04/24/2009 11:02AM

Main British Car:
74' Jensen Healy, 79 Huff. GT 1, 74 MGB Lotus 907,2L

Re: Intake plenum modification
Posted by: roverman
Date: March 30, 2021 01:01PM

Hi Dennis,
Blown-in or partial vacume, when air "trips" on a sharp edge, it will vortescie. This reduces air flow. You could build both designs
and test on a flow bench,( no guessing). Even better with a. smoke tube, b. U-tube or c. yarn. What is the downside of slightly more work with a skilled radius ?
Good Luck, Art.


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