Re: Is this a good deal?

[Squash <realsquash@yahoo.com>]

I don't get this argument.  If your engine takes 750cfm to run at WOT/5000 rpm, and 500cfm at
WOT/3500 rpm, how can a 750cfm TB be better than a 900cfm at anything but WOT/5000?  Anything
under 5000 rpm and you are over-sized with a 750cfm unit, right?  Is a 900cfm unit at WOT/3500
worse than a 750cfm unit at WOT/3500?  Or WOT/2000?

Squash

--- JTesta1966@aol.com wrote:
> In a message dated 5/23/00 2:15:25 AM Eastern Daylight Time, bob@tecmark.com 
> writes:
> 
> << Reason for this is that I came across a "Air Research" aftermarket TBI
>  system for about $300 - includes the controller (set with buttons on front
>  and small LCD display, no laptop connection), BIG MAF sensor, *900* CFM
>  throttle body (4 barrel) with 4, 85lb/hr injectors which shoot in from the
>  side,  >>
> 
> Too big is bad in NA engines as they rely on the vacuum for airflow. a 
> injected car might be less suseptible, but still need a certin airflow to 
> keep the air/fuel flowing in the right direction. A TB too large will 
> possibly create positive pressure in the manifold (depending on your RPM 
> range) and hinder actual airflow into the cylinders. This is more important 
> on carbed engines where you need the pressure differential to make gasoline 
> flow out of the carb, but I'd haveta think it'd make a difference in an 
> injected engine as well. maybe you can use a throttle stop to limit the 
> available CFM until the motor is built to require the 900cfm you have 
> available. An olds engine wont rev that high, their not known for their 
> bottom ends....I build a few pretty healthy Rocket 350's and did a decent 
> amount of research on what works with them. Assuming you have a healthy 403, 
> which wont see much duty above 6500RPM you'd want more like a 700-750CFM TB 
> to assure proper airflow. maybe you could fabricate a stop at a little more 
> than 3/4 throttle, and scale the TPS to make THAT point WOT. 
> 
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> Jim Testa                                                         TType86 on 
> #BuickGN
> ASE Master Technician                                     
> buick.fiendish.net:6667
> L1 Advanced Engine Performance                          NJ Lic MV Inspector
> jtesta1966@aol.com                                  NJ Lic Emission Repair 
> Tech
> http://members.aol.com/jtesta1966/buick.htm
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=====
Trains, Trucks, and EFI at http://www.trailrunners4x4.org/users/realsquash

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