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You quoted "power peaks at 5200 then dips about 10HP and recovers the peak power at about 5600"

I believe this is the nature of stroker motors. My 347 Stroker did the same thing. It peaked at 415HP at 5200rpms and then dropped 10HP and then peaked again at 412HP at 5700rpms.
 

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heads are fine cam is way too small for those cubes. if you look at what the rev range is on the cam chart for a 351 then take off around 600-700rpm top end with those cubes.
 

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the 2.4 cross section will pull nice to around 6500rpm, if you want a higher peak then a 2.5 would be better. youd want to run either minimum 1 3/4 or even better 1 7/8 primary pipes also. with that cam and comp combo the dynamic comp will be quite high wich could be the reason behind the head gasket drama.

<font size=-1>[ This Message was edited by: BOZRACE on 12/10/06 10:11pm ]</font>

<font size=-1>[ This Message was edited by: BOZRACE on 12/10/06 10:14pm ]</font>
 

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if you want a 434ci to pull over 6000+rpm it needs a alot bigger cam then that. whoever chose that cam was way off target. a 240-250 @050 will get the job done nicely.
 

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On 2006-12-10 07:01, BOZRACE wrote:
the 2.4 cross section will pull nice to around 6500rpm, if you want a higher peak then a 2.5 would be better. youd want to run either minimum 1 3/4 or even better 1 7/8 primary pipes also. with that cam and comp combo the dynamic comp will be quite high wich could be the reason behind the head gasket drama.

<font size=-1>[ This Message was edited by: BOZRACE on 12/10/06 10:11pm ]</font>

<font size=-1>[ This Message was edited by: BOZRACE on 12/10/06 10:14pm ]</font>
With those untouched heads, stroke and those cubic inches, I'd just about guarentee it won't run past 6000revs...if that...lets see...
 

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Cam is way to small for the CID of the motor,
The 20 degree split seems way wierd.
what springs are you running?
_________________
1991 LX Mustang 347 C4 combo 11's with the AC on.
1984 Mustang GT 460, Powerglide "Its alive !!!" 10's out of the box, 9's on the way N/A !!
1929 T-Altered "In the works" Easy 8's are on the horizon

<font size=-1>[ This Message was edited by: dfree383 on 12/11/06 10:17pm ]</font>

<font size=-1>[ This Message was edited by: dfree383 on 12/11/06 10:20pm ]</font>
 

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DFI clearing up the problem is very instructive. If nothing else changed, it was fuel delivery. Engines at WOT like to eat .... a lot.

The fact that peak power was down is not uncommon in DFI applications. They usually don't pass as much air as a carb, even accounting for the difference in wet v. dry airflow.

Computers are only as good as the programming. The 'slop' in a good carb will let a little more air and fuel in that can push past the peak of DFI, at the expense of fuel economy and somewhat higher EGTs. More tuning of the DFI that can give more air might help.

It is also possible at 70 psi, you may be getting some spark scatter from the load on the dizzy (which drives the pump thru the hex shaft) if it bogs the distributor enough to throw off the timing. The power required to turn an oil pump is not linear, IIRC, it is geometric. Twice the flow requires four times the energy. That may be enough to cause enough parasitic drag to wreak havoc. A few degrees is a big deal at full load and WOT. I saw a GM ZZ 572/720 V8 on the pump nearly turn into a $14,000 paperweight for almost the same reason.

DFI cleaning up the problem is instructive, my guess is that there is something of a 'hole' in the secondary circuit where the airflow overcomes the ability of the carb to feed it. Might be worth looking at the data trace to see what the vaccum is at that stumble point and what happens to the EGTs.

Things like lifter pre-load are good to check and cheap. Doublecheck the spring pressures, roller assemblies are really heavy and maybe it needs a different damper, it is possible there could be a wierd harmonic moment in the spring that makes it go wobbly, but seeing as how the DFI cleared up the problem, prolly not.

BOB
 
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