[DeTomaso] Ford 392 rev limit?

[Sean Korb]

I would stick with the 6100 rev limit.  Actually I might go down a bit
too.  I think after checking the car on the dyno you should be able to find
your maximum power and where it is.  That's where you should consider
shifting to the next gear anyway.

Without knowing how the valve train is configured, there's no reason to
think it can withstand going over 5500RPM for an extended period.  The
camshaft, weight of the valves, spring pressure, valve train stability
gadgets (roller rockers, guide plates etc) all contribute.

I'm a little sensitive to that since I had an early experience with a 351C
in my Mustang.  Everyone told me I should remanufacture the heads with 1
piece valves, but I thought all I had to do was put rollers into the rocker
fulcrums and I could do 6100RPM (just like your rev limiter).  Big
mistake.  My car swallowed one of those ancient 2 piece intake valves and
the cylinder wall had an argument with the piston.

It's best to find someone who has already destroyed a few motors, take
their setup and go a tick under what they were doing.  You *will* break
parts if your motor doesn't have some thought put into spring pressures and
valvetrain girdles.  We only have 2 valves per cylinder and they're *heavy*.

That said I have a 375W in my Cougar with roller rockers and a flat tappet
cam that has seem 7000RPM (an accident) with more to go but I feel a
lot safer down at 6100RPM.  On the dyno I start to plateau at 4800RPM and
it falls off at 5500RPM so I shift well before than anyway.  I've tuned it
more since than so I need to go back to find my new shift points.
http://www.bacomatic.org/~dw/engine/dehaven/dehaven.htm
On Wed, Sep 4, 2013 at 10:40 PM, <MikeLDrew at aol.com> wrote:

> Hi guys,
>
> During the dark days when the forum was down, Jeff Cobb posted a query and
> it was rejected, so he asked me to post it for him (below).   There are
> actually two posts--start at the bottom one and work your way up.
>
> Mike
>
> ====
>
> From: JEFFREY COBB <zumzum at cox.net>
> Subject: Re: 351 rev limit
> Date: August 29, 2013 1:54:13 PM CDT
> To: "detomaso at poca.com List" <detomaso at poca.com>
> Cc: Jeff Cobb <zumzum at cox.net>
>
> Hello again about the rev limit question,
> The engine specs are:
> Ford Racing 392 Windsor stroked,
> 360 hp at rear wheels from the dyno sheet
> GT40 Heads--9.7:1,
> Mighty Demon 750
> Ford Racing steel flywheel
> Tremac TKO 3550 5 speed and 3.73,
>
> Any help would be appreciated,
> Thanks,
> Jeff
> _________________________________________________________________________
> On Aug 29, 2013, at 6:13 AM, Jeff Cobb wrote:
>
>
> Hello group,
>
>
>
>
>
> Hope you all can provide info.
>
>
> A 2000 Superformance Cobra came back in yesterday for some finish up work
> while I was tuning up a 57 Ford Fairlane Skyliner with a Police Interceptor
> 392 engine.
>
>
> Just bought by a faithful customer and he wants me to do what I want to do
> to make it better and faster.
>
>
>
>
>
> My question to you guys is about the safe rev limit. It has a 351 taken out
> to a stated 392, the largest Demon carb I've ever seen and a MSD 6AL with a
> 6100 rpm limit chip.
>
>
>
>
>
> Problem is that this strong engine will instantly bang off the limiter too
> quickly in the first three gears. Engine is very smooth at high rpm's and
> feels as if it would rocket well past past 6,100 with no problem.
>
>
>
>
>
> I do not know cam, rear end ratio, compression or any other specs and I
> will try to find out today. Torque peak feels the  strongest about 3,000 to
> 4,100 with 6,1000 coming in too soon.
>
>
>
>
>
> What rpm limiter chip do you all recommend for what I have described?
>
>
> I have little history with higher rpm ceilings of large FORD engines.
>
>
> Owner is a 64 year old just math professor hot rodder who drives little and
> want to have fun before his last personal rev limit.
>
>
> We don't desire to scatter his engine and he might buy and use some of my
> VP 110 leaded race gas which will also help.
>
>
>
>
>
> Thanks for any input,
>
>
>
>
>
> Jeff Cobb
> _______________________________________________
>
> Detomaso Forum Managed by POCA
>
> DeTomaso mailing list
> DeTomaso at poca.com
> http://poca.com/mailman/listinfo/detomaso
>



-- 
Sean Korb spkorb at spkorb.org http://www.spkorb.org
'65,'68 Mustangs,'68 Cougar,'78 R100/7,'60 Metro,'59 A35,'71 Pantera #1382
"The more you drive, the less intelligent you get" --Miller
"Computers are useless.  They can only give you answers." -P. Picasso