| [GMCnet] EFI Question. [message #236499] |
Sat, 18 January 2014 10:13  |
BobDunahugh
Messages: 2465
Registered: October 2010
Location: Cedar Rapids, IA
Karma: 11
|
Senior Member |
|
|
Hoping to get back to that topic on our 403 78 GMC soon. As I have the parts including a 454 TB. I was thinking last night. If a 350 chevy TB can handle the airflow and fuel to 6000 rpm's on that 350 engine. Then why can't that same 350 TB handle a 403 at 4000 rpm's? As this engines are really just an air pump. A 350 at 6000 is pumping more air then a 403 at 4000. The intake valves and runners are about the same size. The 403 exhaust manifold is a little larger. The exhaust pipes are the same size. Anyone ever tried it?
_______________________________________________
GMCnet mailing list
Unsubscribe or Change List Options:
http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
|
|
|
|
| Re: [GMCnet] EFI Question. [message #236624 is a reply to message #236499] |
Sun, 19 January 2014 11:39  |
 |
John Heslinga
Messages: 632
Registered: February 2011
Location: Edmonton, Alberta, Canada
Karma: 4
|
Senior Member |
|
|
Bob:
Simply for the purposes of discussion:
The simple answer is: the smaller throttle body would work, but you would probably be unhappy with the result. It's not really the top RPMs that having more throttle (or air) is important, it's what's happening at full load at the top of the a power curve.
Both the 403 and the 350 (stock) will have a power curve topping out between 4500 and 3500 RPM. (I'm estimating here). Not as much difference really.
A smaller Throttle body will act like your not stepping on the throttle fully.
Much in the same way many engines had options between 2 barrels and 4 barrels for carbs. The 2 barrel would not flow as much air and the performance will be less than a 4 barrel option, that does flow more air. (Better overall gas milage though because you could never ask too much from the engine). That's why anyone who wanted more power would change to a 4 Barrel as soon as they could.
Putting a smaller throttle body bore is like putting in restrictor plates in your engine limiting what it could do. (They did that in NASCAR to make the vehicles go slower) Something you would like to avoid at all costs with your heavy motorhome and also opposite to the reason your shifting to EFI in the first place. (It's been reported that you won't get measurably better gas milage.  )
GM did have a dual TBI option for some of its Models that used 2 smaller throttle bodies. Doing that to one of our Motorhomes sure would have an increased "Cool Factor", but I highly suspect that the results won't be any better than a properly set up Single TBI unit.
Best of luck in your conversion and keep us informed of your progress.
John and Cathie Heslinga
1974 Canyonlands 260
455, Manny tranny and 1 ton, 3:70 LS,
Red Seal Journeyman, DTE, BEd. MEd.
Edmonton, Alberta
|
|
|
|
| Re: [GMCnet] EFI Question. [message #236629 is a reply to message #236624] |
Sun, 19 January 2014 12:03 |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
|
Senior Member |
|
|
One of the motorhomes that I work on for customers has a throttle body that
uses all four bores in the manifold, with four injectors. It has an
impressive throttle response. It will spin the tires at will. I did not do
the install on this coach, so I do not know exactly which manufacturers
products were used. It starts and runs great. It definitely will outperform
a 2 barrel throttle body, or a properly set up Quadrajet Carb. I don't have
a clue as to fuel economy but if I had to guess, I would say it would use
more fuel. If you want to have high performance, you are going to have to
pay for it some way. I am in the middle of an install of a Howell system
with the Progressive Dynamics Embedded Locker Computer. I am learning how
to install custom tailored .bin files that change the run characteristics
of the system without swapping prom chips. A brave new world for this old
dog. Definitely NOT A "PLUG N PLAY" set up, no matter what the propaganda
says. Just my take on it.
Jim Hupy
Salem, Or
78 Gmc Royale 403
On Jan 19, 2014 9:39 AM, "John Heslinga" <rbeeper@hotmail.com> wrote:
>
>
> Bob:
> Simply for the purposes of discussion:
>
> The simple answer is: the smaller throttle body would work, but you would
> probably be unhappy with the result. It's not really the top RPMs that
> having more throttle (or air) is important, it's what's happening at full
> load at the top of the a power curve.
>
> Both the 403 and the 350 (stock) will have a power curve topping out
> between 4500 and 3500 RPM. (I'm estimating here). Not as much difference
> really.
>
> A smaller Throttle body will act like your not stepping on the throttle
> fully.
> Much in the same way many engines had options between 2 barrels and 4
> barrels for carbs. The 2 barrel would not flow as much air and the
> performance will be less than a 4 barrel option, that does flow more air.
> (Better overall gas milage though because you could never ask too much from
> the engine). That's why anyone who wanted more power would change to a 4
> Barrel as soon as they could.
>
> Putting a smaller throttle body bore is like putting in restrictor plates
> in your engine limiting what it could do. (They did that in NASCAR to make
> the vehicles go slower) Something you would like to avoid at all costs
> with your heavy motorhome and also opposite to the reason your shifting to
> EFI in the first place. (It's been reported that you won't get measurably
> better gas milage. ;) )
>
> GM did have a dual TBI option for some of its Models that used 2 smaller
> throttle bodies. Doing that to one of our Motorhomes sure would have an
> increased "Cool Factor", but I highly suspect that the results won't be any
> better than a properly set up Single TBI unit.
>
> Best of luck in your conversion and keep us informed of your progress.
>
>
> --
> John and Cathie Heslinga
> 1974 Canyonlands 260
> TC4W "Too Cool For Words"
> Retirement Projects Galore
> Edmonton, Alberta
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
_______________________________________________
GMCnet mailing list
Unsubscribe or Change List Options:
http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
|
|
|
|
| Re: [GMCnet] EFI Question. [message #236648 is a reply to message #236629] |
Sun, 19 January 2014 14:31 |
 |
USAussie
Messages: 15912
Registered: July 2007
Location: Sydney, Australia
Karma: 6
|
Senior Member |
|
|
Jim,
I can "second" what you've noted below. The Blue Streak has a Holley Commander 950 four barrel EFI and goes, as Aussies say, like a
shower of S#!T! ;-)
The PO told me he spent HOURS on the phone with Holley setting it up.
It also has MSD distributor and electronic ignition control.
It leaves Double Trouble for dead and it has a Dick Paterson Q-jet and distributor.
Regards,
Rob M.
Sydney, Australia
AUS '75 Avion - The Blue Streak TZE365V100428
USA '75 Avion - Double Trouble TZE365V100426
-----Original Message-----
From: Of James Hupy
One of the motorhomes that I work on for customers has a throttle body that
uses all four bores in the manifold, with four injectors. It has an
impressive throttle response. It will spin the tires at will. I did not do
the install on this coach, so I do not know exactly which manufacturers
products were used. It starts and runs great. It definitely will outperform
a 2 barrel throttle body, or a properly set up Quadrajet Carb. I don't have
a clue as to fuel economy but if I had to guess, I would say it would use
more fuel. If you want to have high performance, you are going to have to
pay for it some way. I am in the middle of an install of a Howell system
with the Progressive Dynamics Embedded Locker Computer. I am learning how
to install custom tailored .bin files that change the run characteristics
of the system without swapping prom chips. A brave new world for this old
dog. Definitely NOT A "PLUG N PLAY" set up, no matter what the propaganda
says. Just my take on it.
Jim
_______________________________________________
GMCnet mailing list
Unsubscribe or Change List Options:
http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
Regards,
Rob M. (USAussie)
The Pedantic Mechanic
Sydney, Australia
'75 Avion - AUS - The Blue Streak TZE365V100428
'75 Avion - USA - Double Trouble TZE365V100426
|
|
|
|
|
|
| Re: [GMCnet] EFI Question [message #236892 is a reply to message #236671] |
Tue, 21 January 2014 10:34 |
 |
WildBill
Messages: 232
Registered: January 2014
Karma: 1
|
Senior Member |
|
|
The smaller Tbi was used on 4.3 to 5.7l and flows 470 to 500 cfm. The 454 one flows about 670 cfm. The smaller one should get you to 5000 rpm. Different displacements use different sized injectors and some, fuel pressures.
Gearhead-efi.com and other sites have great info on doing this.
|
|
|
|
GMCforum
Search
Help
Register
Login
Home
