[DeTomaso] Intake Reversion

[Don Thomas]

Check or change out your power valve.

A good starting point for the power valve is -2Hg's below the vacuum at
idle.




On Wed, May 1, 2013 at 7:36 PM, John Taphorn <jtaphorn at kingwoodcable.com>wrote:

> Sean
>
> I am skeptical about the reversion theory at that RPM.  I didn't pick up
> weather it occurred at steady throttle or acceleration; yet, it strikes
> me as the engine is going lean at that transition point.
>
> JT
> On 5/1/2013 6:44 PM, sean mundy wrote:
> > The engine is installed and ran a chassis dyno.  While sitting on the
> dyno you could
> > see the car bucking and moving a little bit back and forth on the dyno
> wheel because of
> > the surging/hesitation I mentioned.   I know spacers of various
> thickness are used to increase the hp
> > and also insulate the carb from the engine heat.  The reversion specific
> spacers I've seen
> > online seemed to be designed specifically for reducing the effect of
> exhaust gases that are pushed
> > back up into the carb because the intake/exhaust overlap is too long.
>  The spacers I've found
> > range from 70-150 dollars so I don't want to waste money if it's all
> hogwash.
> >
> >
> >> From: cengles at cox.net
> >> To: seanmundy at hotmail.com
> >> CC: detomaso at poca.net
> >> Subject: RE: [DeTomaso] Intake Reversion
> >> Date: Wed, 1 May 2013 18:35:04 -0500
> >>
> >> Dear Sean,
> >>
> >>
> >> In my limited engine building experience, the engine dyno is the
> >> place to determine the benefit of a spacer. The match between an engine
> and
> >> a spacer is idiosyncratic and must be tested to determine if it works.
> Some
> >> engines will benefit and some won't.
> >>
> >> It sounds like your engine is now installed. If so, then if you
> >> want to test the spacer angle, then it would be off to the chassis dyno.
> >> If the chassis dyno showed improvement in your HP/torque numbers, then
> it
> >> would be worthy to road test to see if you problem is gone.
> >>
> >> In my limited reading about engines, I can't recall that
> >> reversion can be quickly and simply fixed with a spacer, but I am a
> rookie.
> >>
> >>
> >>
> >> Warmest regards, Chuck Engles
> >>
> >>
> >>
> >> -----Original Message-----
> >> From: detomaso-bounces at poca.com [mailto:detomaso-bounces at poca.com] On
> Behalf
> >> Of sean mundy
> >> Sent: Wednesday, May 01, 2013 5:08 PM
> >> To: detomaso at poca.com
> >> Subject: [DeTomaso] Intake Reversion
> >>
> >> Hey all, I recently had my new 408 Cleveland tuned and dyno'd at the
> shop.
> >> 438/411 hp/trq rearwheel.
> >> Very happy with the numbers but having some issues with how the motor
> runs.
> >> After driving it 50 miles I noticed at anywhere between 2-3k RPM in any
> gear
> >> there was a surging and hesitation in the engine.
> >> I went back to the shop and we worked on the carb (750 Holley) by
> >> increasing the primary jets and adjusting the pump squirters.
> >> We put it back on the dyno and ran it several times. The tech said he
> >> couldn't get good A/F numbers because the sensor placed in the tailpipe
> >> couldn't get past the baffling in the stock muffler. It pulls very good
> in
> >> the top end but he noticed the 2-3k RPM surging and hesitation that I
> >> mentioned.
> >> The tech told me that he thought since my vaccuum reading was so low
> (10-12
> >> in)
> >> at low RPM that I was probably experiencing "reversion".
> >> He said that the lobe separation overlap on my cam specs were probably
> the
> >> cause of this and also a contributing factor was my single plane
> manifold.
> >> Basically he made it sound like I was stuck with what I got.
> >>
> >> My cam specs are:
> >>
> >> GROSS VALVE LIFT .617 .617
> >> DURATION @ .006
> >> TAPPET LIFT 286 300
> >> VALVE TIMING OPEN CLOSE
> >> @ .050 INT 10 46
> >> EXH 60 8
> >> SPECS FOR CAM INST. @ 108.0 CENTERLINE
> >> INT EXH
> >> DURATION @ .050 236.00 248.00
> >> LOBE LIFT .363 .363
> >> LOBE SEPARATION 112.0
> >>
> >> I've done some reading on the internet about reversion and it seems
> like a
> >> real thing.
> >> I read that installing a carb spacer designed to help eliminate the
> phenomen
> >> might work in my case.
> >> Wondering if anyone else has experience with this and what if any
> solution
> >> worked for you.
> >> Thanks, Sean
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