Reworking Holley 950 double pumper

[5122GO]

Hello. I'm new here. I've been following this forum several days now for great advice and information. This seems like a swell place to communicate than moparts, so I felt I should register.  On that note, however, I own a 1971 Plymouth Road Runner.  I hope that's acceptable here.  

Anyways, on to the build information.  As my handle states, I run a 440 based 512 torque monster. This is a street car. Never been to the strip.  Bear with me on the story; figured I introduce myself first.  It's been over a year now since this 512 has been screwed together.   The engine has been through many changes.  The heads are the Edelbrock rpms. The ignition box, spark plug wires, coil, and distributor is MSD. The fuel pump is a Holley unit.  The intake was a Mopar M-1. Now I'm running a Holley street dominator for hood clearance. The valve-train is all from COMP Cams. Lifters, pushrods, valve-springs, and their pro-magnum roller rockers.  This is the cam that is in use.

http://www.summitracing.com/parts/CCA-23-700-9/

I was running a Comp Cam hydraulic flat tappet before this, but that cam soon wiped out a lobe and lifter.  At that point, I figured since we've got to back in, why not switch out to a solid roller. Now is the time to do so! So far so good.  When I was running that flat tappet, I ran a Holley 870 street avenger.  At the time of the cam swap, we swapped carburetors and went with a Holley Street HP 950 double pumper. This all took place five months ago. Seemed pretty good. Since than, it's developed a terrible bog or hesitation when I go full throttle at a complete rest on the street.  Eventually it recovers, chirps the tires, then goes like a bat out of hell!  

With continuous playing around, when I go full throttle on a pace she sure flat out breaks the tires loose, slides sideways, to the point where have to lift the throttle some to steer straight. No complaints in that department.  I'll admit I'm no tuning wizard, so at that point I placed that carb aside and back came the 870 vacuum secondary. My point of view at this moment in time was that the smaller cfm would equal towards more throttle response, which I'm all for.  First time out playing around, same test from a dead rest, the tires broke loose, car went sideways through all three speeds in the 727 with slap-stick shifter in drive.  Grin from ear to ear on that run!  

At this stage, I started watching short clips taken from Holley's tuning dvd on their website and decided I could tune these carburetors.  I quickly got too it.  I already knew about adjusting the idle mixture screws and curb idle, but I had no idea about how to adjust the other components.  I knew there was still a slight hesitation with the 870 at full throttle and on the pace.  I pulled out the squirter to find a #40. From researching, Holley states to use a hollow screw with this size or larger.  I did order this part.  In addition, I placed the pink accelerator cam up into the # 2 position.  I set my curb idle at 900 rpm in neutral. With my vacuum gauge, I read a close to steady 15 reading in park and a shaky 12 or 11 reading in drive.  I did notice afterwards I forget to discount the vacuum advance.  I was pulling the readings from the base plate of the carb.

Bare with me here.  Now that winter is approaching, I have a few short days left to go for more test drives.  I haven't been out with the car since the hollow screw has been placed in or made any more vacuum readings.  Since than, I've been pondering putting the 950 back on to dial that in better.  I've noticed a big difference between the two. With the 870, the idle is very rich and certainly does not run as clean as it had with the 950, though the street hp is the newer of the carbs. I have had the 870 for over a year and it did run atop my father's engine, where it backfired a few times. Before bringing it back on, I cleaned it up some.  Made no difference. It's probably because the transfer slot is exposed.  Also with the 950, start ups after seven pump shots of fuel would wake the engine, but she is cold bloody.  A change in spark plugs could possibly help that matter.  I'm running a manual choke with the 870.

The rest of the drive train consists of a Torque-flight with a 2400-2600 stall converter, which could possibly stall higher behind this 512.  The third member is a Dana 60 from DoctorDriff.  Inside are 3.54 gears. I figured that choice made sense for a street driven car with all the torque that's available.  The rear tires a set of 255/60/15s.  I was thinking of running 245, now I'm thinking 275 to match up with the gears.  The headers are a pair of Dougs' 2in primary into an  h-pipe and out through Dynomax bullets, running a complete 2.5 inch setup.  Real damn loud inside and out!  I also thought about switching out the headers for a pair of 1 7/8 to quiet it down some up front and go with 3in pipes before the bullets and retaining the 2.5in tail-pipes. Possibly a change to a Dnyomax muffler, like the Turbos.

Thanks for listing to my rant there. I would appreciate your help on fine tuning this Holley 950. I have read about the Proform 950. Sounds nice and It seems to run real well.  I believe I am running a # 35 front accelerator nozzle on the 950 with a 31 in the rear. No changes on this carb.  It's straight out of the box. I believe the jets where # 78 in front with a #84 in back.  Not sure on power-valve.  Will get back on that matter.  How does the build-up seem?  I'll hunt for the timing specs and share those as well.  I'm a novice in that field too.  I'd like to learn how to setting timing and work over a distributor.  Thanks for any help.

Adam

[chargerman67]

   I ordered this DVD last week and am waiting for its arrival. It was made by a gentleman on this site named Wayne Smothers, maybe it would be helpful to you as well. I haven't seen it yet but it has been highly recommended by a lot of well respected advice givers on this forum.

   Its called "Performance Engine Building and Carburetor Tuning" you can find the video here:

http://smotherssupercars.com/engineclass.html

   As for your Road Runner you better post up some pics for us 

[firefighter3931]

Try disconnecting the vacuum advance & make sure to plug the carb fitting. Set the base timing to 17* and shoot for 35* total all in by 2500-2800. With the MSD distributor you will need to install the BLACK bushing which gives you 18* of mechanical advance.  

For plugs you should be using an NGK BCPR6ES....that is the correct heat range for a pump gas build. Gap them @ .045

As for the carb ; Holley 950 HP series carbs are designed for radical cam profiles that don't produce much engine vacuum. The boosters are very sensitive. When you use the HP unit with an engine that makes descent vacuum (like yours) the tuning headaches often begin. Your cam is small for 512ci and that's why it makes lots of vacuum  

I've recommended the Proform 950 to several members here who have similar "mild" stroker builds and all have been very happy with the performance. Mike (MFR426) had his 505 on Ray Barton's dyno for the breakin/tuning and the carb was perfect. They didn't even have to adjust the jetting. The dyno operator commented that this was a first...he'd never seen a carb run so well right out of the box.   That's not to say the PF950 is perfect for every big cube build but it does work great on a milder setup. Fuel metering is appropriate for the application.  

I'm not saying that you can't tune the 950 to work reasonably well but it'll never be spot on for your engine....the fuel curve is too agressive. A trip to the chassis dyno would confirm this.



Ron


Ps. Almost forgot ; welcome to the site  We need some pics as well 

[oldschool]

also with a heavy car and your gears,you would see a big improvement, in low end and driveability,with a indy dualplane. i use two of them on my 500" motors,in a heavy charger,with 3.54 gears. awesome manifold for the street...

[BSB67]

As for the carb ; Holley 950 HP series carbs are designed for radical cam profiles that don't produce much engine vacuum. The boosters are very sensitive. When you use the HP unit with an engine that makes descent vacuum (like yours) the tuning headaches often begin. Your cam is small for 512ci and that's why it makes lots of vacuum  

Better suited for less cubes and bigger cams.  To get it right from idle through transition, you'll probably need to reduce the idle feed restriction and increase the idle air bleed.  Reducing the IFR will be a challange if its not an Ultra.  It will be okay, it'll just be rich.

[5122GO]

Chargerman67, thanks for the heads up on that dvd.  You'll have to share your comments on the video when you are through watching it.  It sure sounds packed with various useful information.  That's great somebody can share that knowledge to others that could make real good use of it; like this place.  Very pleasant customer satisfaction thus far.

Oldschool, I looked up that model.  I believe what you have to say, however, I feel I'll run into hood clearance all over again with that one. Do you need to run Indy's valley tray with that intake, though?  I'm sure for the price it's listed for, it performs like it should.  I feel fine with my Holley SD right at the moment.  Happy enough for this street driven torque monster.  I have ran the M-1, and it works just as well, but I grew tired of the height and small filter setup that's needed to make it fit.

Ron,  your right on the money, it has been a tuning headache since day one with this carb.  I'll take your advice.  I've looked this Proform 950 over and it sure seems a real decent piece for the money.  Would those that are currently running this carb know the specifications, such as primary and secondary jetting, acceleration nozzle measurements and power valve size? From researching around, it seems to be the wining ticket for the "mild built" 440 stroker.  I know variables are different across the board on everybody's engine, and a real test & tune should be done on a chassis dynometer, however, what do people find to be an pretty good tune after some tweaking around, if needed?

I thought it be would wise to ask before-hand if I do go with this carb, if I should pick anything else up for tuning, to include linkages and springs?

Also, on the matter of timing, when the cam was stabbed in and a test run done, she pinged under acceleration.  Now, between the cam swap there was a three month dead period where old fuel sat dormant with some gas treatment poured in the tank and allowed to circulate.  We ran the engine with that old gas after the swap.  Mistake on are part.   After that run, the timing was backed up to 10* and 34* total.  Worked with the old gas on second run. Placed fresh gas in the tank after that and I do not seem to notice any problems, though it's a loud running beast.  I'm trying my best to keep this baby screwed together so I don't end up back at the drawing board.  Long story short, try anyways, I blew the past stock stroke 440 I was running with.  Wiped out the cam, one piston, and a connecting rod went a round with the short-block and brand new Hemi 6 quart oil pan.  You already now who was the Juggernaut on that exchange.  Kept the pieces.  I'll be sure to share some photos, plus some of the car, that's still kicking, no internal or exterior damage done.  Already over a year thus far with this engine.  I did have a serve oil leak that I'm sure contributed to the wiped out flat tappet.

Turns out the rear main seal took a discounted-elevator trill ride down the shaft to hell and was leaking a gallon of oil at a horse-race pace.  I was on a trip with a buddy when that stirred up.  A gallon of Lucas oil after another with their slippery oil treatment along with it.  Kept it going on the trip with frequent oil changes and check-up after each stop.  Then one day when I went to go start her, she sure gave me problems.  It was a hint something was up, though I believed it could have been due to the cold weather; this was going on through the frigid dead of winter in North Carolina; feed her some more gas to ease her on another cycle of cranking and then there was a huge knock and my oil pressure went flat-line. I shut her down and that is what led me to the solid roller this past summer.  I had previously switched out the deprecated rear main seal and went with a 440source billet main seal and she buttoned up beautifully.  There were a few leaks, but this piece has settled in and I'm happy for that. I run Brad Penn high-performance oil now.  Seems to be real good stuff.

Well enough of the rant, just thought I would explain the back story on my experiences thus far to introduce myself.  Thank you for the generosity.

Adam

[firefighter3931]

Hey Adam,

Try working that ignition curve to reduce the mechanical advance to 18-20* as this will allow for more base timing. Keep the total at 34-35* and get the initial up to 17-18* @ idle. This will pick up the vacuum and make throttle response much sharper/snappier off idle. 

As for the PF 950 carb ; just install the Holley pn 20-7 throttle linkage adapter to maintain proper throttle ratio. This bracket should be installed on your current carb. If it isn't then you likely don't have full throttle with the gas pedal to the floor.

Nothing wrong with the Street Dominator intake manifold.....those are very capable of moving enough air to make 600 HP 



Ron

[5122GO]

Ron,

Thanks for the advice.  I've been getting the parts together, thus far.  As far as initial timing goes, for that, do I move the distributor clockwise or counter-clock wise to advance timing?  This will be my first go at setting timing on my own and I want to be sure I nail it down.  Now if I set my initial timing after the adjustment, I'll have to reset total timing, correct?  If do that that, that will alter my initial again.   Is this correct?   This part confuses me.  In addition, do I need to play around with the advance springs?

Thanks,

Adam

[firefighter3931]

Can you post the pn of the distributor you're using ? The MSD distributors use bushings to limit mechanical advance. The initial timing is wherever you set it....the mechanical advance is added onto the initial (base timing) which then gives you the total advance.....Base + Mechanical = Total 

The trick with performance builds is to use as much initial timing as the motor will tolerate and then not allowing it to overadvance. Too much "total" advance will lead to spark knock & engine damage.


You should get a copy of Wayne's DVD....it explains  all this and much more. An excellent resource for novice engine tuners. 

http://www.dodgecharger.com/forum/index.php/topic,62311.0.html



Ron

[5122GO]

Ron,

That part number is "MSD-8387" for the distributor.  By tomorrow the Proform 950 should arrive.  The other today I was able to purchase those NGK plugs you recommended.   I'll be trashing away by this Friday afternoon out in the garage.  Hopefully I'll have her buttoned up by nightfall, or by midnight. 

I'm going to get in touch with Wayne and see if I can purchase one off of him with free shipping, if he still offers that for members.  It's certainly worth-while having!

My plan is to attach the "black" bushing and then dial in the initial to 17*.  With the bushing change, the total will come to be 28* with the current 10* initial.  With the change to 17* initial, I should be back up to 35* total.  This is my understanding of how it will pan out.

Thanks for the help Ron,

Adam

[firefighter3931]

Here are the instructions for the 8387 distributor : http://www.msdignition.com/uploadedFiles/MSDIgnitioncom/Products/distributors/8387_instructions.pdf

I like advance curve "d" which uses two light blue springs and has the total advance all in by 3000 rpm. I would block off the vacuum advance and tune without it for now. INMO vac advance has no place on a stroker. 

You are correct, with the black bushing installed dial the initial timing in at 17* and recheck the total....you should have 35* at 3000 or less rpm. Then it's on to the carb....

As for the carb, just make sure the float level is adjusted halfway up the site glass and adjust the idle mixture (1-1.5 turns out) and idle speed (800-850rpm in gear). I bet the jetting is just about perfect right out of the box. 

Let us know how it turns out.....i'm sure it's going to feel like a whole different car. 



Ron

[5122GO]

Ron,

I purchased this distributor back when I still had the stock stroke 440 in place.  I figured I'd hang onto it instead of purchasing another.  Someday I'll make a replacement.

I'm looking forward to tuning this beast.  I'm also draining the oil to go along with the rest of the tune-up.  Sure is a sweet feeling taking care of your own engine.   I'll keep you posted on the results.   

I've included some photos of my 1971 Road Runner.  Enjoy.   

http://smg.photobucket.com/albums/v181/rrunr3/71%20Plymouth%20Road%20Runner/?action=view&current=DSCN0935.jpg

http://smg.photobucket.com/albums/v181/rrunr3/71%20Plymouth%20Road%20Runner/?action=view&current=DSCN0942.jpg

http://smg.photobucket.com/albums/v181/rrunr3/71%20Plymouth%20Road%20Runner/?action=view&current=DSCN0941.jpg

http://smg.photobucket.com/albums/v181/rrunr3/71%20Plymouth%20Road%20Runner/?action=view&current=DSCN0931.jpg

http://smg.photobucket.com/albums/v181/rrunr3/71%20Plymouth%20Road%20Runner/?action=view&current=DSCN0945.jpg\

Adam

[firefighter3931]

Adam, no need to run out and swap the distributor anytime soon....the MSD RTR distributors work great. Just work on tuning it for your build and it will work just fine 

Man, that's a sweet looking ride ! 

My Buddy Rick has a plum 71 GTX with a 472 Hemi in it and i luv that car...10.80"s in the 1/4 on pump gas 

Have fun wrenching and please report back 


Ron

[knitz01]

Welcome WE love ALL B-Bodys

[Brass]

And all Mopars!  Welcome, Adam.  Nice Road Runner.     (Glad that Ron, as hospitable as always, is helping you out.)

[5122GO]

Well, I decided to swap out the carb this evening.  Right about the box the Proform 950 was spot on.  Idle speed and quality was great.  No rich smell or smoke.  Then I dived in and starting tweaking.  Reset the float levels, backed out the mixture screws to 1.5, then 1 turns.  I readjusted the idle speed screw to bring the rpms down to around 800 in park.  Now the tune seems off a good bit.  The rich idle is back and there is smoke once again.  The driver side bowl sight glasses show under a half, while the passenger side sight glasses show midway for both primary and secondary.  Plus, the idle speed fluctuates slightly, where before it held steady at 800.    

She seemed just fine out the box; I took a good notice of that.  The float levels were higher than midway though when I started, just slightly seating below the top of the sight glass. 

Also, do you know where I could hook up the vacuum advance on this carb?  I seen two front vacuum ports.  In addition, I'm looking for a port for my vacuum gauge.  I tried two of the front ports, but the gauge would not read. 

Not sure what's going on.

Adam

[firefighter3931]

Try going back to the out of the box tune and see how it runs. The vacuum fittings on the baseplate should be full time vacuum....at least one of them anyway. Try not to use the vacum advance. 

Did you install the black bushing and set the timing up as suggested ? I Allways nail down the ignition tune before moving to the carb.


Ron

[5122GO]

Ron,

I have not adjusted the timing yet.  Once I have the carb dialed back in, I will get right down to it and go from there.

Adam

[firefighter3931]

Ron,

I have not adjusted the timing yet.  Once I have the carb dialed back in, I will get right down to it and go from there.

Adam

Adam, there's no point in adjusting the carb until you get the timing nailed down because the carb settings will be wrong. That is why i recommended adjusting the timing curve first. 

Just trying to save you some headaches and unnecessary work 


Ron

[Manifold]

Ron,

I have not adjusted the timing yet.  Once I have the carb dialed back in, I will get right down to it and go from there.

Adam

Adam, there's no point in adjusting the carb until you get the timing nailed down because the carb settings will be wrong. That is why i recommended adjusting the timing curve first. 

Just trying to save you some headaches and unnecessary work 


Ron

Spot on advice!  You'll be chasing your tail with the carb if the timing isn't done first.