That has always been the problem and shouldn't be the last thing to change...I'm running way more cam than you and can get 14-16" of hg
at idle with a holley 600 and a dutra fatpack...to make the cam work you
need more compression so the overlap event has something to bleed down...

(230 duration @.050 would run great with 10:1 SCR on pump gas if you dial in the cam and don't get too crazy on the lobe separation)....

I wouldn't fiddle with the carb and just get the cam changed before winter sets in, then go back to the carb...( before too much of an "over rich" condition washes down a cylinder and wipes the rings out).

-D.Idiot

I can get 9.9:1, calculated, with a head gasket change to OEM steel from Felpro in use now; an increase of .4. Back when oversized valves and other head work was done, I shaved head 0.076â€￾.

I think there is an additional 0.02â€￾ adjustment left in rockers, and can resurface head & block with scotch pad by hand for a good seal.

Current duration is 236 @ 0.050â€￾, so quick head gasket change fix may not get the job done.

At this time I don’t have capability to pull engine, and change cam. This winter I could scrounge up a puller, and engine stand. Chances are good I have a ring problem with #5, it is slow to come up to pressure requiring several additional compression strokes during test to match its brothers in the 160 psi range.

_________________
67' Dart GT Convertible; the old Chrysler Corp.
82' LeBaron Convertible; the new Chrysler Corp
07' 300 C AWD; Now by Fiat, the old new Chrysler LLC

More farting around with the old Holley took place today. I have been running with 53 jets for a week or two, and today dropped down to a 51 jet, the one that was installed when I got the car four years ago.


Instead of trying for highest vacuum reading in park which at one point attained 12 inches with a steady needle by adjusting idle mixture screws, I tried using the air/fuel ratio gage as my guide. I was able to turn in the mixture screws an additional half turn for a total of 1 ½ turns out from their seated position, and maintain about 9 inches of steady vacuum moving the A/F gage in and out of ideal territory on the rich side of the gage. Exhaust smells much better at idle now.


Running down the road I see a lot more Ideal readings under very light acceleration, and a gage swing over to first rich under WOT. Steady throttle on flat ground causes A/F gage to read rich. I still can’t tell when the secondaries are opening, but with brown spring can feel a rush starting to build in around 4600 rpm that keeps on until high 5000s.


Tonight I replaced the brown spring, installed plain spring the next step down allowing for earlier secondary opening. It’s hard to test the secondary circuit with no high speed limit roads nearby. Tomorrow I will be heading to a car show about 130 miles north, and will have a chance to test the plain spring. Holley said to keep dropping down in spring stiffness until a flat spot can be felt when secondary circuit opens, and back up to next stiffer spring.


I wonder if perhaps I should drop primary jet a little bit lower to get a bit leaner under steady throttle on the road, as currently A/F gage tends to sit at first rich reading occasionally settling in on center rich light.
I was reading some of the racing information Josh had written up covering different carburetors and a race only Holley 390 with big cam listed 49 jet primary jet, and 52 secondary metering plate. Perhaps I should try a 50 and possibly the 49 jet… A little guidance on this jetting would be helpful.


Since the mixture has been leaned out, tonight I discovered when power braking, under a quickly applied WOT condition, the tires easily break free on bare dry pavement. Previously the car would reluctantly spin its tires on dry pavement as if it were straining. This “Red Neckâ€￾ dyno test indicated there is more low end torque now being developed with this jetting.

Bill

_________________
67' Dart GT Convertible; the old Chrysler Corp.
82' LeBaron Convertible; the new Chrysler Corp
07' 300 C AWD; Now by Fiat, the old new Chrysler LLC

At this point you need to read the plugs...and watch how lean you go...I was able to jet a holley 390 down to 48...the outside temp was 88 degrees that summer so there was "no air in that air" (i.e. density was lower)...as soon as the temp dropped to the 60's the jets went back up to 51's...if tuning the carb with a normal O2 sensor, the reading is fairly tight it will let you know if you are a bit lean or a bit rich...to make sure it's not too far off you will need a wide band ratio...

Also what's your vacc. reading now while driving, if you get a flat spot with the spring, you might also check your PV opening...

-D.Idiot

Power Valve is currently 3.5 due to low in gear idle vacuum of 5 or less with bouncing needle. I’m now resigned to kicking transmission into neutral at lights to avoid loading up even with the 3.5 PV. For most of the summer I had a 4.5 PV installed, perhaps I go back to it, or may try 5.5 just to lessen lean condition at light throttle opening while cruising, and ignore the in gear rich idle for now to increase drivability.

Running down level road below 3500 rpm gives steady vacuum at 16 or so, under light acceleration it dips to 10 inches. Over 4500 rpm adds two more inches to 18 as the cam overlap effect lessens.

Plugs show light tan crust on ground electrode, porcelain is slightly tanish, and rim of thread body of plug exposed to combustion chamber is black. I suspect I haven’t driven enough to clean that surface.

Well I’m off Littleton, Maine for a show.

_________________
67' Dart GT Convertible; the old Chrysler Corp.
82' LeBaron Convertible; the new Chrysler Corp
07' 300 C AWD; Now by Fiat, the old new Chrysler LLC

I recently returned from the car show with 250 more miles on the Dart. This trip was 95% empty two lane 55 mph country highway. I discovered the mixture leans out considerably (off the gage lean) once rpm exceeds 2700 rpm particularly under light acceleration, or up long shallow hills. Steeper hills dip into power valve. I suspect the lean condition is the result of better scavenging due to higher rpm, in other words, flow of gasses through engine become more efficient the higher the rpm goes.

Tomorrow I shall install a higher value PV to lessen some of the light acceleration lean condition.

When engine went lean I could feel a bit of surging up long grades. At constant steady cruse on level ground the least lean light would illuminate under 2700 rpm. Also coasting downhill the A/F gage read mid rich in drive or second; not fully understanding that condition.

By the time I got 50 miles down the road this morning, it seemed the gas gage was dropping faster than I anticipated, so I reinstalled the brown secondary spring to retard secondary throttle plates from cracking open at sub 3000 rpm. I did notice that with the plain spring the A/F ration gage looked to indicate a much leaner mixture before the spring change… This may just be seat of the pants BS, but I made the spring change anyway.

The car returned 18.4 mpg today. I don’t know for sure, but the car seems to be quieter out on the open road since leaning out the mixture. It is defiantly now a lot spunkier at all speeds, and has more torque off idle.

_________________
67' Dart GT Convertible; the old Chrysler Corp.
82' LeBaron Convertible; the new Chrysler Corp
07' 300 C AWD; Now by Fiat, the old new Chrysler LLC

There's more than just a spring change involved when timing the secondaries on the Holley...you have to pull the carb and see where the throttle plates are in relationship to the transition slot...the plates should just cover the transition slot...if they have a fair amount of distance to cover (i.e. you put upward pressure from your finger on the secondary linkage at the vacc pod...and you don't see the transition slot, it'll lean out until the seocndaries crack open more to get fuel for the air).

So if the plain spring started to crack open the secondaries a bit and there was little or no fuel flowing, and they weren't open enough to bring the boosters (venturies) online, there will show a lean out on the gauge (and possibly loss of 1-2" on the vacc. gauge)

The sad and the bad is if you are getting 16-18" at 3500rpm...the cam's power band is way above where you need it to be for anything other than straight racing...did you map the lobe separation for the cam it almost sounds like it's at 102 or something heavy....a 230@.050 cam with a 108-109 LSA and 10:1 compression should have no problem making 18-19" at idle.

-D.Idiot

[img]http://i294.photobucket.com/albums/mm87/wjajr/1967%20Dart%20repair/Sellers_pinkpanther7.jpg[/img]


DI:
[quote]The sad and the bad is if you are getting 16-18" at 3500rpm...the cam's power band is way above where you need it to be for anything other than straight racing...[/quote]

Yup, I have come to that conclusion.



did you map the lobe separation for the cam it almost sounds like it's at 102 or something heavy....a 230@.050 cam with a 108-109 LSA and 10:1 compression should have no problem making 18-19" at idle.

Last winter I degreed this cam. I’m not sure if my graphing method was correct showing exhaust event to left of intake event with zero degrees running down center of paper mapping lift at lifter, so lift at valve will be greater by 1.5 times, less lash I suppose.
Lobe separation = 211*
Duration:
Exh = 0.236â€￾ at 0.050â€￾
Int = 0.235â€￾ at 0.050â€￾
Overlap at one side of cycle = 26* this number was center of my graph where legs of event overlapped.

Should I have drawn graph with zero degrees at left of sheet starting with intake event, than exhaust, or some other method? The point of this question is to properly understand what I have installed in this engine so to be able to select a cam that may give similar performance at a lower rpm band.

The second question I have not been able to satisfactorily answer is a suspect #5 ring problem. That cylinder takes two to three extra compressions to get to the 160 psi range. With the help of a squirt of oil in that cylinder it jumps to over 200 psi in two compressions. What I have been passing off as a lope, may in fact be a lazy compression problem in one of the cylinders which can be heard from the left tail pipe as weak pulse. The left side pipe produces a crispy tat, tat, ---, tat, while the right is more of a tat, tuf, ---, tat. I now suspect that is contributing to unstable low rpm vacuum readings. This is not noticeable while driving, or over 1300 rpm, as the engine is out of the lope mode.

[img]http://i294.photobucket.com/albums/mm87/wjajr/Dart%20Engine/100_1373.jpg[/img]

_________________
67' Dart GT Convertible; the old Chrysler Corp.
82' LeBaron Convertible; the new Chrysler Corp
07' 300 C AWD; Now by Fiat, the old new Chrysler LLC