[DeTomaso] Intake Reversion

[Paul Timko]

While the dyno shop's O2 sensor would make it past the baffles in the 
exhaust, it isn't a big deal to add a O2 bung to your exhaust and leave 
it plugged when not on the dyno.

Paul
#9270

On 5/1/2013 9:36 PM, John Taphorn 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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