What's the latest Dad?

I've been dialing in the holley 390 on mine. I am running 53 jets and the .028 shooter with 8.5 pv. and the secondaries are held shut with the black spring. I have the 02 sensor installed in the head pipe with a volt meter running into the cab. sure makes easy work of watching the exhaust mixture.

It's cruising along well at any speed but still idling madly fast and not giving the punch I would expect in acceleration. It is obviously time to look at the dist curve again

Dealing with vacuum leaks has been a real chore between the hooker header and the offy intake at the head and the cheap transdapt carb adapter that has been replaced with an offy one. The original transdapt adapter and thin carb gasket was allowing so much vacuum to get between the carb and the adapter that it actually ripped the gasket in three places.

So the timing is currently set later than the best vacuum to keep it from advancing too fast on acceleration. It seems to like 16 to 18 btdc but will jump to 50 in no time. I now have it at 10 that is the lowest I can go and still get it to idle in gear. With that it runs at 850 to 900 in drive and a steady 10" of vac. but in park the mech adv kicks in and it will run at 1600 rpm and 18 to 19" of vac. at this setting I'm 30 btdc @ 2800 rpm and 32 btdc at 3000. vac adv is disconnected. I think I may need to limit the total advance by soldering in the slot and stiffen the advance spring to slow the mech advance.

It is the 9.5r governor (I believe and has the yellow spring and the beige spring.

Have you designed what you think will be the best curve for our engines?

It seems like I'm getting really close but without getting it right it wont even be as good as it was before I started.

Thx, Ray

Motogrey,, I have not had the opportunity to do a timed acceleration run,, nor have I wound the motor out beyond 3k under load,
but I can report that:
1) the engine certainly feels crisp,no bog or hesitation, I am running the same 2280 that I ran on the OE cam and prior to the head work, believe that I am on the lean side.
2) the exhaust note has changed,the pulses out the tail pipe are a definite bark, now at idle, you hear every pulse, before it was more of a muted rumble
3) from the seat, it feels to pull harder, before the engine mods at 3k it was done,,have not wringed it beyond 3k, but when you get to 3k, it is still pulling.
4) manifold vaccum readings seemed to have reversed, with the OE engine, had 17 to 20 at idle, then as the throttle was opened the readings would drop, now have 10 to 12 at idle, as less than full throttle is applied the vaccume moves up,,
will know more shortly.

Dad,

what is your initial timing set at? Did you modify your distributor at all?

Thx, Ray

the distributor is a 3874714 with a 8.5R can
that cross references to a 1977 Aspen
no distributor mods so far

initial timing is 6 degrees at 800 RPM
10 @ 1000
28 @ 1500
38 @ 2500

I saw where you said when you set the idle at 850 in gear, it jumps to 1600 in park,, so if you set the idle at 850 in park, does it die when it goes in gear?

I had that problem on a Buick v6 one time, messed with it for two days before I figured out I had two sparkplug wires switched...

I had read somewhere on this forum that the holley 390's need some set up work to run right on a slant,,may want to check with some one that has a 390 running well...

No plugs are switched. I'll check again. I have been fighting vacuum leaks. wow, Yours runs at 6 btdc? , mine won't come close. It's lopey. So my dist. Is likely similar but since it requires more initial advance it ramps up way too Quickly

Yep. I've been getting rather familiar with my 390 holley. It's doing ok atm, but I still need to work with the pump cams. Right now, I need to get my timing straight. Sometimes I wonder if the can was degreed properly by my builder

a couple of ideas

1) vacuum leaks are going to really hurt,, on my 83,, with the stock cam I had 19 to 20 inches of vacuum at idle,, with the new cam at 800 rpm I get 10 inches of vacuum..

what vacuum reading are you seeing at idle?

2) do you have the vacuum advance plugged into the correct port? It should have no vacuum at idle then increasing vacuum as the throttle opens..

3) the 390 4 bbl carb should only be using two venturies at idle,, and those two should be smaller on CFM than the 2280 I am running, so running on the primarys should not be a problem,, but here to I have no experience with the 390's

4) and here I am no automatic tranny guy,, but at 800 rpm ,unless Dodge put in a really low torque converter activation point in the truck trannys, the engine should not be seeing much of a load at all just because it was shifted into gear at idle,,. Don't stock torque converters start pumping around 1000 to 1200 rpm?

5) also found this tech info at Holley,
http://forums.holley.com/entry.php?429- ... lley-Carbs

The vacuum is happy at 14 to 16 at idle wen the initial timing is happily at 14 to 18 btdc but itramps up way to fast. now I have it at 10 btdc and the vacuum is about 10. just need to recurve dist.

I have the secondaries locked out. I think the real difference between our engines may be the compression.


Thanks for all your help, it's getting closer all the time. Just waiting to hear back from big slat six fan for a spring kit now.

Saved

I have not read all 7 pages yet, but this sounds like there is much excellent information here. I am eager to read and digest it all. Thanks for all. I suspect Duster Idiot bumped this up for me to read.

Sam

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here is a video

https://www.youtube.com/watch?v=lPQ6J0CLbWo]

good so far, has a genuine thump to the idle, gets 20 + mpg on the highway, good response with the tune / carb,,,, I have been in contact with a a local dyno operator,, I also want to see how this compares to the Dyno Sim calculations,, will do the Dyno comparison runs in July, stay tuned..
I have spoke to this local chassis dyno operator,,,,
http://www.cozzolinomotorsports.com/

the muffler is a flowmaster 60 series,, I had a 40 series on it,, was way to loud even for me,, the 60 is much softer,, wife still says it is too loud...

Says this video is private

I have been chewing my through this thread for the past week. Thanks to all who have contributed, but especially Dad Truck for his many graphs and charts. . I have only made it through page two at this point. I have not even opened David Vizard's article yet. I am sure that will yield more insight. This is kind of like reading a good novel, waiting to see how it comes out. Of course I am pleased with the results Dad Truck has been reporting, but am eager to see how he got there.

At this point I do not really understand the trade offs of the various design choices. High lift versus low lift seems obvious, lobe centers, overlap , duration and centerline choices do not seem as clear by far.

It is interesting that later cam grinds offer so much more power than the stock cam. Is this because of compromises the designers of the stock cam felt forced to make or new design concepts and research?

Sam [/u]

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fixed the recent video post, should be viewable

and here is the basic engine build info
* 83 block and head, used an early heavy cast crank, early heavy cast three ring dampner, stock truck manual flywheel, Silvolite .030 over pistons, moly rings, stock rods, new arp bolts, King bearings.
* engine builder OS valves, bronze guides, the machine shop put in nice multi angle valve seat grind, I did a pocket clean up and port match
* stock slant six valve springs, the guy at the machine shop said if the cam was any bigger the stock springs would be in coil bind. Ken at Oregon Cam recommended getting the valve closed spring pressure be adjusted to get it over 95, so there were shims added, which reduced the free space between the coils.
* stock cam re ground by Oregon, on stock 105 LSA, grind is an Oregon hydraulic 1333 intake on the intake and a hydraulic 1527 intake on the exhaust
256 and 250 at .006
212 and 206 at .050
installed cam with a 4 degree bushing and at 100.5 intake center line
43 degrees of overlap
stated lift is intake .447 and exhaust .432
measured from the cam and with 1.5 ratio intake is .448 exhaust is .426
* OE lifters and new replacement lifters had .180 of plunger travel
Stock pushrod preload was .090 to .100, reused the stock push rods, with the cam reground and the milled head and block surfaces,, preload measured at .075 to .080
* stock head chambers were 59 cc, cut .040 off the head to get to 53 cc chambers. Set the pistons at .162 recession. Per the RB compression calculators:
static 8.52
dynamic 8.20
cranking pressure 164
* observed cranking pressure, eary May this year with 1400 miles on the engine
172, 170,172,172,178,175,, running regular gas,, Knock gauge installed, it lights occasionally under load, but no audible pinging.
* 3874876 distributor , Crane 11R can, stock light spring and light Crane spring, 10 degrees initial advance, mechanical is 0 at 1000 RPM, +15 at 1500 RPM and +20 at 2000 RPM, vacuum can is 1/2 turn out from all the way in
* using a Dutra ported oil pump with hardened gear, dual Dutras on the exhaust side, Holley 2280, cold air ducted to the carb and full time hot water heat to the intake carb base via the EGR cavity.

From reading Dad Trucks charts it looks as if the larger valves and ports do not hurt low end torque, but do raise the peak torque from 500-1000 rpm. Estimated torque at 1500-2000 rpm was actually a bit higher with porting and os valves, but 3000-4000 was much higher. So yes, you can build a torque engine with stock valves, but if the estimating programs are worth their salt, you do not actually lose anything down low with porting and OS valves.

Sam

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