Bob, interesting point on the shift points. I understand having the
revs in the sweet spot, but how did the 80% come about.
If I have the stock motor and cam from the 90 5.0L, and its max hp is at
5200 rpm, the the shift point is 6500 rpm. That is quit a jump, and
with stock valve train, mainly springs, I am sure that valve float would
become a problem.
Larry
Bob Palmer wrote:
>
> Chris,
>
> Assuming you fix the problem that's killing your engine over 5,000 rpm,
> let's look at the best recipe for quick quarter mile times. Let's say your
> motor, after it's fixed, gets a maximum of 350 HP @ 6,500 rpm. You will want
> to be able to run as close to 6,500 all the way down the track as possible
> to optimize the output of the engine. That means, you want the engine rpms
> to more-or-less bracket the optimum 6,500 rpm. That means, first of all, you
> will want to use all four (or five) gears. It also means, although not so
> obviously, that you want to use the close ratio, not the wide ratio tranny;
> assuming of course we pick the right rear end gears. So, what rpm should you
> be turning at the quarter mile mark? The answer is about 7,700 rpm; in fact
> you want to make your lower shifts at higher than this rpm so as to keep the
> motor running, on average, at the sweet spot 6,800 rpm. (The jumps get
> progressively closer as you go through the gears.) So, what rear end ratio
> would give you that? It can be computed it pretty accurately, but you know
> from experience that running in the 12's will put you somewhere in the
> neighborhood of 115 mph. So, if we're turning 115 @ 7,700 rpm in fourth, the
> gear ratio is - - - voila!! 4.56 gears.
>
> This little example should make clear a couple of points. First, don't build
> a motor to give its top horsepower at any more than about 80% of the top rpm
> you are willing to run it at. In your case, to get the most out of an engine
> that makes its best horsepower at 6,800 rpm, you need to be willing to shift
> it as high as 8,500 or so to get the full benefit. If the motor isn't built
> to run that rpm, use a cam and other parts that will maximize the horsepower
> at lower rpm, you'll be ahead in the long run both figuratively and
> literally.
>
> Now, I would like to hear what 12-second Dave's recipe is. And, I hope I'm
> not part of the "clic" he's referring to, so any one else's opinions are
> welcome too.
>
> TTFN,
>
> Bob
>
> -----Original Message-----
> From: owner-tigers@autox.team.net [mailto:owner-tigers@autox.team.net]On
> Behalf Of cvaught@hawaii.rr.com
> Sent: Tuesday, February 20, 2001 2:48 PM
> To: tigers@autox.team.net
> Subject: Re: E-Mail me off the list
>
> simple in a tiger. posi unit in the rear with 3.55. gears, wide ratio in the
> tranny, and a some NOS if your engine is stock and some drag radials to aid
> in traction. now i thought this list was full of adults with mostly more
> money
> then brains to spend as much as we do an our cars (me included) let the
> kiddies
> stay at home and off of our list. i think it is funny as hell. maybe they
> sniffed
> to much gas while in garage and forgot how to get along with others.
> chris in mississippi
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