Hi All
just got fresh engine installed. 9.5cr, 390 Holley, long runner manifold, 264 comp cam, electronic ignition 60 thou oversize, standard valves mild port, tube type headers, 904. Premium gas. Straight off ran pretty well with slight pinging. Retarded the ignition a bit and ran it in then off to the dyno tuner. He re graphed the dizzy to take the timing down to 26 degrees all in. Up a couple of sizes in primary jets and off I go. He told me it behaves like it has a lot more than 9.5 to 1. Must say when it spun up high it did pull hard. Still pinged ever so slightly so back it went. Dizzy re graph back to 16 degrees all in and now it doesn't feel right. At higher revs it sounds like it is back firing from the exhaust ports. I have rechecked calculations and CR should be 9.5. Did a compression test and they went 160 psi. What could make it behave like this? Could I have messed up the cam timing? Want all options before the head comes off again.
Thanks in advance Craig

Sounds like a fun motor and a sensible buildup. Welcome to the site! Glad you could join us.

160 psi cranking pressure sounds like roughly in the 9:1 range and should be just fine on premium gas.

What is your AFR? If you do not have a WB O2 gauge, get an AEM 30-4110 and find out what your mixture is doing. I have had these gauges on 4 vehicles and they are bulletproof and very informative. WELL worth the $.

I wonder if you have a slipped damper/timing marks? Probably that is less likely since it is backfring from exh (retarded timing symptom). You should be able to run 26-30 deg adv all in with no trouble.

What is your cam and how did you degree it?

All the best,

Lou

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Home of Slant6-powered fun machines

There are so many things that aren't in good shape here from your description and having experience running clifford and Dutra hyper paks....

Lou brings up a fair amount of very good points, and I have others to add in:



Right off the bat I am going to berate the dyno guy... long rams do need to go up a couple of jet sizes to help the carb anticipate the load so it doesn't lean out when the go pedal is used... that being said, he also should have upped the jets on the secondary side the same amount to assist when you are under load and trying to pass... being the 8007 is a 4160 with the 'plate' instead of a metering device, he should have remove the secondary bowl and installed a secondary metering block kit for tuning... that way you could go from #52's equivalent in the back to #55's (if the primaries went to #53's...)... another part of this same issue, is the long ram manifold will need some kind of manifold heat or all the gas will puddle and stream down the runners as a liquid causing a lean out anyway... with headers you won't have any options for direct heat like a dutra setup could have...and will need a water manifold heat box if you intend to run it on the street...if the outside temps are below 50 degrees it's not going to run well until there is proper manifold heat.

Another issue to note, is he should have been reading the vacuum on the dyno run and like lou recommends with the O2 sensor see when the lean out occurs and read the vacc gauge and note what the reading is, and replace the power valve with the correct one (typically the carb comes with a 6" power valve... and I normally have run a 10" on the street for the 8007)...

Another item I worry about is your head.... the pre-1967 head has the dime spot casting in the chamber and could cause an issue if the mix is running lean with pre-ignition... would have been nice to grind those out when porting the head, or switch to a later head for the build...

We do need to see what your cam timing is (you degreed the cam in right?), Comp Cams are notorious for having a 110 LSA causing a tight overlap event, and if advanced too far you will be running race gas on a 9:1 engine... (one of the reasons why running a dynamic compression ratio calc for the build will tell you where it sits at....)

The distributor... what EI core are you running? You should be able to run mech + initial at 26 all in by 3000 rpm and have room for 17-20 degrees of vacc. advance for economy...(what vacuum can is on your distributor?), 16 is much too low...unless you have a turbo...


Get back to us on the questions and we can help drill down on your issue.

Thanks Lou and DI
I did degree the cam to the recommended 106 degree inlet centre line but I
did question myself as the cam had to be set on the six degree advance keyway on the crank to achieve the 106 centre line. My target dynamic CR was 7.93 for the build but with your comment DI on the cam advance I may have made a mistake with the cam timing. Any advice on technique for checking cam timing in car would be great. AF ration from the first dyno run above 3000 rpm was constant at 13.5 with a slight lean condition below 3000 which the tuner addressed with going up with primary jet size. He did not rerun the AF ratio again as he was trying to address the timing issue. The dime spots were removed when I ported the head also. It is coming on summer here so ambient temp is 80 degrees F or more so manifold heat shouldn't be an issue. I have a bad feeling about the cam timing.
Thanks again Craig

Yep... pull park plugs, and fan belt, and Valve cover... going to have to install a degree wheel on the damper, and install a 'pointer'... install a stop for the piston in #1 plug hole and zero the wheel... pull the stop, and install a fixture to measure the lift at the intake pushrod... the worst part will be if you can't see the wheel you may have to drain the radiator and remove it and peer through the grille... have your cam specs ready to corroborate the intake valve events by readings on the wheel.

Do you have your build numbers? (deck height, head gakset used, combustion chamber volume).


Another question before we start pulling everything to check degree... have you pulled the vacc line off the advance pod, plugged with the golf tee or bolt, and taken it for a drive strictly on mechanical advance? Does it ping there too?

Thanks DI,
yes it has been run without vacc advance. Build numbers are
52cc chambers
Felpro gasket
.1 deck height
plus 60 thou overbore

Will recheck cam timing Monday and will report results. I need the practice!!

Cheers Craig

Assuming a 225, given your numbers you are at 9.64:1 SCR....

if you are at 4 degrees advanced -106 centerline...(and not having the cam ground at 4 degrees advanced and another 4 degrees by accident)... then your DCR is 8.09 which would be fine.... and shouldn't be pinging with a normal curve.... so something is 'amiss' as they say.

What about operating temperature? If your engine is running hot, it will ping much more easily. You have a reliable temp gauge and the passages are all clean and open inside the engine. If you have hotspots in head or top of block that could increase pinging.

Just thinking again...

Lou

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Home of Slant6-powered fun machines

Hi Lou and DI,
I changed out the distributor with mechanical advance wound back for a standard unit with pertronic conversion and set base at 7 degrees btdc and went for a country drive with no vacuum advance. I cannot make the engine ping low down in the rev range but at 60-65 mph with throttle application as the secondaries start to open it pings readily.
Any help please. I will still double check cam timing tomorrow. Need to borrow degree wheel and dial indicator.
Thanks Craig

I will definitely defer to Lou and DI on the distributor tuning, but I have another possible suggestion for the cause of the "pinging" you are hearing.

Have you verified that the rocker arm shaft is oriented correctly? Several years ago I installed a new head on a slant six. I had had the head cut significantly to raise the dynamic compression ratio. I immediately noticed that under load and at higher RPMs it sounded like it was pinging. I retarded the timing, changed the advance curve in the distributor, nothing ehlped.

I later took the head apart and discovered that I had installed the rocker shaft 180 degrees out of proper orientation and as a result the rocker arm tips were not getting enough oil flow and the tips were clattering against the ends of the valves at higher RPMs. The rockers weren't getting enough oil because the oiling grooves in the rocker arms were not properly aligned with the oiling holes in the rocker shaft.

Just something to check since your motor was assembled by a machine shop and even experienced engine builders can make this simple mistake on a slant six.

Now that Reed is on a roll... another question to ask is what did the hot lash get set to? Comp Cams typically 'states' they like .012... but that is sometimes a bit tight.... if the lash is too loose... it will get a little noisy like rattling/pinging.... my comp 252 liked things better at .013-.014

Thanks Reed and DI
I did check the lash hot and left them set slightly looser at .011 and .013 and yes the goose who bolted down the rocker gear got the shaft upside down at first but I must take the blame for that. It sound normal in the valve train. Sadly it does sound like detonation. Can it be running lean as the secondaries open as this is the time it makes the noise?
Thanks Craig

That's too tight, back them all off to .013 hot, there is no difference in the lobes on the cam unlike the mopar cam that has two lashes depending on intake or exhaust.



One way to check this is to replace the secondary spring in the pod with the black painted spring... this will lock out the secondaries and then you can see if the symptoms occur only on the primary side... if it doesn't ping then you can work on the issues of lean secondaries and or the transition of the secondaries opening.... that also being said, long ram manifolds require a longer duration pump shot to keep them happy during this transition... all of my holley's on the clifford hyper pak setup have required the use of the pink acc. pump cam and moving up to a slightly larger shooter (if .025, you may need to go .028 or so...).

i'm keeping a close eye on this thread. i have a similar setup and also am experiencing pinging at higher rpm with secondaries coming into play.
quick fuel 450 vacuum secondaries - 55 primary jets, 56 secondary (was 60)

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70 Plymouth Valiant 4dr

I am also... "keeping an eye on it!" LOL

I was just thinking about mine and to the best of my memory,
my cam calls for .018 on both sides of the aisle???

It's been so long now and I do not remember what the F I have in here now!
I know I got it from ISKY!!! lol

I hate losing gray matter...
crs


lol

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"I may be slow, but at least I'm not very fast!"
'69 A108 - 225, 727, 3.55, MSD6AL, a.k.a.-the brick