DIY_EFI Digest            Friday, 23 February 1996      Volume 01 : Number 052

In this issue:

	Re: Turbo Lag
	Re: Intake runner sizing..

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From: arthurok@xxx.com (ARTHUR OKUN )
Date: Fri, 23 Feb 1996 01:23:32 -0800
Subject: Re: Turbo Lag

you mean like an old j47 "ithink" that they use in a t33
i think the original "whittle" engine was similar to that but it used 
multiple combustion chambers "small ones" . i dont believe you could 
get more than 15 lbs of thrust out of a car turbo unit thats 15 jet 
horsepower. one thing im sure of is that a gas turbine is fuel 
injected.

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From: Mark Boxsell <mrb@xxx.au>
Date: Fri, 23 Feb 96 20:50:49 +1100 (EST)
Subject: Re: Intake runner sizing..

>
>"Why use RPM sensing? The tuned length should change with air temp, 
>pressure, etc."
>
> No, the character of the curve you get with a given intake geometry 
>changes with RPM only. Air temp and pressure can be considered DC 
>offsets for that curve.

Correct. The speed of sound in air is hardly affected by changes in
temperature due to atmospheric factors.  A tuned exhaust however is a
different ball game!

>
>"I would assume that greater air flow would lead to  higher MAP values
>and the ECM would adjust the fuel mixture  accordingly."
>
>Greater airflow does not necessarily relate to greater MAP pressure 
>because most MAP sensors are located in the plenum of an intake. If 
>you improve the airflow downstream of the plenum, the MAP sensor will 
>never know it. Furthermore, a nicely tuned intake will not affect MAP 
>yet can really boost engine performance, particularly at low rpm where
> airflow is low and corresponding flow losses are negligible.
>

The pressure waves travel so fast that measuring it with a ("normal") map
sensor is out of the question. Anyway that's what you have a VE table for.

                                regards,
                                                Mark Boxsell
                                                MRB Design.

VE = Volumetric effiency.

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