Rolling road.
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Thread: Rolling road.

  1. #1
    Off the Xmas card list kapri's Avatar
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    Rolling road.

    I got the chance to have some cheap power only runs on a Rolling Road today after I messed with the jetting on the A yesterday. Since it's been on the road ( 1000 miles in 4 weeks now ) it seems to stop dead at 70 mph ( 3500 rpm) .
    The rejetting I carried out feels great seat of the pants and the rolling road showed a AFR of around 13.2 , just a little rich.

    The engine is an old Pinto , comp test shows 160 psi so lower end of acceptable. I've added an Injection head and High Torque cam and it also has a 4 branch and 32/36 DGAV, so on a good day in the region of 120- 125bhp at flywheel.

    Stock motor is quoted a 111lbs at 3500 ...96bhp @ 5200

    Mine came out at 120lbs at 2100...80.2bhp @ 3250

    Now the point is that the power stops dead at 3500, drops like a stone hence the lack of any acceleration but not down to aerodynamics as I first thought? The AFR is still good after 3500 even though the power is dropping ? To me that rules out leaning out due to fuel pressure ( stock manual pump with reg set at 4psi)

    The motor revs clean off load and you can hear the second choke come in ( though in top , under load , it feels like you can't ?) .

    One of my thoughts is that the distributor is electronic controlled by water temp and vacuum and aimed at economy ,couple that with the reduced vacuum due to cam change could that be the issue ?

    I might have to revise the jetting though, dropped from 35 to 25 mpg

    Anyone like to throw their ideas in the pot ?

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  3. #2
    I'm a grown up drunk! chevy2's Avatar
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    Fuel supply issue?
    a guy near near me had a s/block powered 34 that kept losing power when nailing it,

    revved fine up to 6000 plus when stationary,
    but after 3-4000 rpm under load it would lose power,

    turned out to simply be a partially blocked fuel filter in the fuel line under the car,
    being only partly blocked it still showed normal fuel pressure,
    the owner didn't build the car so didn't know the inline filter was there,
    the mechanic found it when on the ramp checking the fuel line for kinks.

  4. #3
    My name is Martin 30psi's Avatar
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    13.2 is a bit lean if you are referring to wide open throttle, or did you mean at idle?

    Whats the afr when the throttle is open?

    It does however sound like the timing is wrong. Could be too advanced or retarded to be honest.

    My Datsun has a permanent afr gauge and I also have a portable LM1 unit for sticking up peoples tail pipes They're pretty useful.

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    Off the Xmas card list kapri's Avatar
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    13.2 at approx 3500-4000 and still climbing . No tickover mixture reading , it's an auto which are fun to get readings from. You get a spike at bottom end as it shifts gears.

    It also bogs badly off the line if you give it full throttl ebut that's not apparent under normal acceleration. The DGAS has a power valve and I think the lack of vacuum from the cam is bringing it in too early when you try to boot it from the line. That's usually masked on a manual as you leave at 2k upwards.

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    My name is Martin 30psi's Avatar
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    Could do with richening up a little maybe

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    Official RnS Addict WB54's Avatar
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    kev. as has been said, you could go richer at WOT, plus I think you need more advance, bogging and nosing over are both signs of not enough initial and total advance.

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    Off the Xmas card list kapri's Avatar
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    Thanks for all the input so far. The bit I'm struggling to understand ( and why I initially put it down to aerodynamics) is that the engine will pull 6000 in first and second but only to 3500 max in 3rd ?

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    My name is Martin 30psi's Avatar
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    Does it bog down or hold back at all in 1st or 2nd?

    On the rolling road did they include on the printouts an air/fuel graph? It can really help pinpoint whats causing flat spots etc

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    Off the Xmas card list kapri's Avatar
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    If you open the throttle normally no bogging in first or second, floor it off the line and it bogs before taking off. AFR / bhp graph to mph print out plus torque / bhp against road speed print outs .

  12. #10
    My name is Martin 30psi's Avatar
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    Would be good to see those graphs if you can scan them in.

    If you were local to me I'd suggest sticking my wideband up your tail pipe and go for a drive to work out whats what.

    However, I think it's worth finding out what the total advance is with and without vacuum if possible

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