[DeTomaso] Intake Reversion

[John Taphorn]

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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