I have a 225 with .100 shaved off the head 280/270 dual pattern cam dual exhaut with headers oversize valves with a 390 4 bbl holley, with a 3200 stall. I'm running the 048 jets in the primaries, did a plug read and seems to be burning good. It seems like the engine is looking for something it can't find. I'm wondering if I should go with a bigger cfm or just put bigger jets in the primary. anybody with experience on this setup, and what carb or size jets you using, that got the most out of it. I don't want to overkill.

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Brian Long

Doesn't that carb come with 51s in the front? That's what I'd start with.

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Slant Cecil

Ditto on that...48's are what they use at the amusement park for the 1 barrel carb on the old tractor motor rides from 196X....

Go 51's in front...after that change secondary spring to Purple...do you know what power valve it has? (6.5 is not good for that build).

-D.Idiot

Power valve needs to be determined by ‘in gear idle vacuum’ if an automatic, and ‘neutral idle vacuum’ if a standard transmission by following Holley’s method. Holley 390 cfm 0-8007 instructions here, and more detail on how to tune here.

If power valve is rated too close to engine’s idle vacuum it will be open more often than needed causing a rich mixture, or the other direction if not high enough, it won’t activate soon enough to be helpful.

I’m running #57 jets with a 2.5 power valve, as my in gear idle vacuum is some where around 6Hg with a fluttering needle 3-8. The cam is a bit lumpy, but the vacuum needle smooth’s out around 1000 to 1100 rpm giving 11 to 12 Hg.


This 10% ethanol blend of gasoline tends to run on the lean side with standard jetting for 100% gasoline. Some engines don’t seam to respond to the difference in the old fuel & new fuel blend, some do.

My plugs show proper color, no bogging with lightest secondary spring, to heaviest at all rpm points & throttle openings. I do suspect a rich condition at in gear idle as vacuum dips to near zero during loping as power valve flutters open & closed.

I have made provisions to install an oxygen sensor, but have not as of yet drilled the hole and welded in the bung. Hopefully that device will sort out any unseen jetting, and power valve issues that at this time I’m not detecting.

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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 had the softest spring in my carb i don't remember off hand but i want to say i had the jets all the way up to 58's bigger pump shot 10.5 pv or the 9.5pv dont remember which one.

Kev

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What's your dist curve like? With that much stall you can probably go in fairly fast, say 30-34 degrees by 2500rpm.

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63 Valiant Wagon
225 - 4 bbl

I put what clifford recomended with the 268 cam I got from them, I changed over the cam to the erson 280/270, and I'm sure I need bigger jets in the prims. I put a 8.5 power valve, and didn't change anything in the secondairies. Do you think I need a bigger pv? It idles around 800 rpms with no problem.

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Brian Long

I think I'm somewhere around 30-32 degrees on the advance with the light spings on the dizzy. I brazed the slots and took about .010 off of them to keep the advance in that range.

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Brian Long

Everything else looks good, if the 280/270 came with the stock LDA (111 degrees)...your idle vacc will be pretty good (mine with the hyperpak was 18" at worse at 900 rpm...but I have a clutch...yours would be in gear idle and probably at 14-15")...The 8.5 PV is a good starting place, but may require an improvement.

The key piece we need to know is your vacc at in gear idle, your vacc at cruise (in traffic)...and your vacc reading while passing on the highway....

For this you will need: about 3' of vacc hose...connected to a vacc gauge and the other end attached to the nipple at the base plate under your primary bowl (that will allow you to see what your carb "sees" while you drive, and if you get good at it, it may give you an idea what the position of your thottle plates are at as well)...

Most street perfomance guys will be able to use the 10.5 PV because they chose a cam that provides good vacc. at most rpms in gear...sometimes this can cause a "gap" if you are under load and still have good vacuum...this can be adjusted a bit by changing to softer spring in the secondaries to get them to "come on sooner" before the PV starts in...

Typically the 8007 comes with a plain spring, and for a hot street motor purple spring is better for street driving...for drag racing you will want to probably switch to a short yellow if the car is still demaning "more" sooner...

The tell tale is watching the vacc gauge while you are floored in 3rd gear on a straight stretch of road...if the gauge is not close to zero...it can use more carb (or the secondaries are not open 100%...).

Plug the gauge in and let us know what you see...

To paraphrase one of the Holley Performance books, you will adjust your idle to get the highest vacc reading possible...if it's not happy at 800...but you gain 3" at 1000-1100rpm then the idle should be set at 1000 rpm...


Personally having been at that level, I never saw a difference in gas mileage or economy between keeping the engine happy at 1100 rpm, and making it grumpy at 800...(1500 rpm idle on the other hand is wasteful as the carb by that time has it's plates high in the transfer slots or has activated the mains...if the plates at idle are into the transfer slots, you have too small of a carb and need to upsize-450/500/600 cfm to put the throttle plates back into proper relationship to the transfer slots and transition to mains.)



2 cents

-D.idiot

the cam center line is 108, and I degreed the cam 3 degree advance. I do however notice this..from an idle take off, or a foot brake take off getting the rpms up to about 1500 to 1800 rpms it takes off with no hesitation, however if i'm cruising at a speed from 20 mph on up to whatever, and floor it into passing, i have a bog and then it takes off. At the lower cruise speed the bog is not as aggressive as when i'm crusing say 50 mph and nail it. Seems the faster I go and let up on the pedal and refloor it the more aggressive the bog gets. After the fisrt initial bog down if i hold it down it keeps climbing with no problem. It just seems like the engine has more potential than the way its performing now. I will try the vac method and let you know what I get. The cam is the one Frank told me to use. Erson E470000 270/280 dual pattern. Intake duration 220.0 and Exhaust 230.0 with a 310 lift on both ends.

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Brian Long

Sounds like it leans-out during transition between the mian circuit and the power enrichment circuit.
You need to install a vacuum gauge into the car and drive it, then find the point (in vaccum Hg) where it does the bog, then check that to the power valve rating.
So lets say the bog starts at 11 inches of vacuum and "clears-up" at 8 inches... that tells me to change the 8.5 PV to an 11.5, so power enrichment starts when the lean condition starts.

A couple of other notes:
Off-idle transition lean-out can be "covered-up" by the accelerator pump shot. You can disconnect the accelerator pump linkage during testing to help get a more accurate "feel" for the PV's "kick-in" point.

These carbs have "Power Valve Restriction" (PVR) holes that meter the added "power" fuel into the main feed circuit. Sometimes these holes need to be slightly enlarged in order to get a smooth transition into the power circuit.
(Be careful, the PVR holes are drilled directly into the carb body so they are easy to make larger and hard to make smaller)
DD

I will put a vac test on this weekend and see whats going on. may change the jets to, and see what happens. When yall talk about the spring on the secondairies, is that the spring in the vac pod that opens the secondairies. Think summit of jegs would have em? I think I got the jets and the pv from jegs, not sure. I have a jet kit assortment, but they start in the 60's range and goes up from there. Thanks for all the input yall givin me, I will let you know on the vac results.

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Brian Long

Are you sure? Should be 230 int/220 exh for the RDP cam...

2¢
CJ

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Part of Tyrde-Browne Racing

Well Ceej, I'm looking at the cam card..and it says 220 intake and 230 exh. duration.
Hmmm could be a typo error or a grind error or maybe an old memory loss on your behalf..I know my memory fades with age..LOL Does anybody elso have this cam..if so, let me know what your card says. May have to make a phone call to Erson if you right.

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Brian Long

Your card is the mirror image of my 280/270 card.............

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Yeah....Im the one who destroyed this rare, vintage automobile.....