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what could be causing this? (dyno run w/new cam) 

 

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 Post subject: what could be causing this? (dyno run w/new cam)
Posted: Fri Jul 06, 2007 9:00 pm 
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well... after finally getting the shims right and the car running well after a cam swap (rpd rspec3), i got a dyno run done today.

the picture tells the story - car appears to have picked up a few KW in the top end (and you can definetly feel it), but lost power over most of the rpm range, with a huge hole in the midrange. it doesnt feel half as bad as it looks on the graph, but there is definely a flat spot around 3500-4000 rpm.

couple of questions:
should I have picked up a bit more midrange power?
would wacking the variable gear i have on and playing with the cam timing make a huge difference?
any others with the rpdrspec3 got charts to compare?

what could be causing the big drop in midrange power? the dyno guy couldn't think of anything obvious. he ran it about 3-4 different times and got the crazy graph each time.
I haven't checked ECU fault codes or anything yet, but will.
also suggested was check and adjust base timing.

the car is running pacemaker 4480's, 2.5" reback catback, and minimal other mods (factory 5 spd), same fuel for both runs (95oct, but from different servo;s), and similar weather (damn cold rainy)

the other thread about the cam install here: http://www.fordmods.com/forums/viewtopic.php?t=51646

 

 

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Posted: Fri Jul 06, 2007 9:16 pm 
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your obviously not to far happy to look at it if you come over!

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Posted: Fri Jul 06, 2007 9:21 pm 
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Did you check that the BBM was switching runners. Might have knocked something loose when installing the cam?

 

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Posted: Fri Jul 06, 2007 9:32 pm 
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it wont be bbm youd have a more gradual change..

check your ignition advance and fuel ratios...

looks like youve lost power down low by a fair amount as well...

what ecu u running? chip?

 

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Posted: Sat Jul 07, 2007 2:47 am 
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hey guys, thanks for the replys :D
dynowog, i'll be leaving the city for a week on sunday but i will give you a ring when I get back.

On the BBM butterfly swiching, if I pull the vacume hose off the bbm it switches, (when idling) is there a way to make sure its switching at 3900rpms? or maybe i could go for a drive with the vac. hose disconnected and see if there is any difference... hmmm

running the stock ECU, no chip. looks like A/f's are richer at lower rpm which could account for the power loss down low, but not for the huge flat spot.

 

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Posted: Sat Jul 07, 2007 2:50 am 
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When I was running too little shims in mine (2 in EXT, 2 in INT), it was a dog until 4500 rpm. And then it wasnt much better than stock. But I noticed the 'hole' in the mid range. I reshimmed it and it improved a lot. Not saying you should reshim LOL, but keep it in mind.
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Posted: Sat Jul 07, 2007 2:56 am 
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hehe F**k shims i dont want to even think about them!!!!
atm i am running 3* 1.1mm + 1* 0.9mm on exhaust side and 3*1.1mm on the inlet (+ std ford 1.9mm on each) for a total of
4.2+1.9mm exhaust
3.3+1.9mm inlet

before this i tried running 5.5 ex. and 4.4 inlet and the car wouldnt run properly so im assuming the shimming is fairly close to correct. (or at least +/- 1mm)

 

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Posted: Sat Jul 07, 2007 10:44 am 
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thats pretty weird.. It does somehow look BBM Related. In the stock run you can see the BBM switch point. your graph really looks like it plays up at that point. Vernier gear will not fix this. Vernier is purely for advancing and retarting the cam. what does if feel like when driving and if there is a noticable hesitation what rev range does it happen in?

Dave

 

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Posted: Sat Jul 07, 2007 2:40 pm 
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it feels 'ok" driving, but there is a noticable flat spot in acceleration around 3200 - 4200 rpms... its sorta like, power comes on, has a rest, then comes on hard again.

what rpm does the bbm change?
does anyone have a simple formula to convert the speed to rpm's (3rd gear, 3.23:1 diff, 15/65 tyres)

 

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Last edited by forsaken on Sat Jul 07, 2007 3:04 pm, edited 1 time in total.

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Posted: Sat Jul 07, 2007 2:52 pm 
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Isn't the BBM 'spose to come on at 3,500rpm???, EF & EL.

 

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Posted: Sat Jul 07, 2007 4:00 pm 
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It could be that there is a lack of vacuum causing the slow changeover of the long/short runner butterflys, as you would know these are vacuum operated or there could be a leak on the vacuum side of the butterfly switch.

 

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 Post subject: dyno
Posted: Sat Jul 07, 2007 4:18 pm 
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this is a serious response:

did the dyno operator keep his foot flat

 

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Posted: Sat Jul 07, 2007 4:26 pm 
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hmmm i assume so, lol :?

maybe i'll zip-tie the bbm in the short runner position (i assume that will be opposite to whatever it is at idle...) and see if it has any effect ? (apart from losing power down low:S) and check for vac leaks... hmmm. if i pull the hose off the bbm butterfly switch at idle it changes, so is it a lack of vacume that changes it? or what?

is it possible the computer hasnt adjusted properly or something? it has done approx 250 km's with the new cam installed.

 

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Posted: Sat Jul 07, 2007 10:18 pm 
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I would be getting a diagnostic or some sort of tuning. The AFR's are all over the place and running rich. Was it smokey at all? It may be something simple like a oxy sensor. Looks like it was a bit over the place before as well.

 

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Posted: Sat Jul 07, 2007 11:35 pm 
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ignition problem?

how old are the plugs and leads?

 

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