["Puddles the Pontiac"]

its been a while since i have posted here, i have been in the world of late model performance for a while. i have recently built a new motor for my '65 Lemans. specs are as follows ;

463 with eagle/scat/SRP rotator.
6x-4 heads w/heavy porting and 1.77ex valve (no numbers but professional work was done)
1.5 JBP roller rockers/pushrods
edelbrock T2 intake
holley 750hp carb

comp cams solid flat tappet custom grind.
lift .558i .580e
dur. @ .050- 260i 268e
110lsa

pertronix hei triggered by Mallory hyfire VI #685
module bypassed.

now that i have that out of the way, i built this motor to to give me high 11sec times and to be used w/ nitrous (i have a cheater kit). and at some point i will be adding turbos.after break in i gave this engine a quick "tune" by ear. i set the timing where the engine liked it and started good, set the idle mixture to the highest rpm. jetted by plug reading after a wfo pass down the road. now the engine barks when i rev it and sounds pretty good... in park. i take it out on the road and i have this frustrating miss. not a back fire or pop but a constant miss. here is an example in typed form if i may...
mmmmmmptmmmmmptmmptmmmmmptmmmmmptmmmm. at cruising speed. and i feel i am missing alot of power. i have changed and tested the coil, pickup coil, module, volts going in, alternator, plug wires. checked cam placement and valve lash as well. i feel this is electrical because i noticed the miss on the timing light while bringing the revs up in park. i installed the mallory unit hoping bypassing the module (hei distributor) and giving the coil a little more push would help things. i gained some power but still had the miss. now, here is another odd symptom, after resetting the distributor by putting the engine TDC on #1 and setting the timing to where it would start easy and idle strong, i checked the initial timing. i was at 50* of advance! i brought it back to 16* and that killed the engine. when i tried to start it it would pop a few through the carb and want to start. but wouldn't. 30* did okay but it wanted 50. if i went past 50 it went into a "blower surge" sounding idle. so i take off the cap, put the engine back TDC on #1, make sure #1 cap terminal matches the rotor, put the cap back on and fire it off. timing is at 30*. so i say to myself "fine, this $400 digital snap-on timing light is screwing with me". so i assume the light is off 30* and put the timing at 45*(assuming its really 15*). the engine likes it. so now i check the mech. advance. i go from 1000rpm to 1500 and the timing advances 10*. odd, i have the stiff springs on the advance weights but okay. i rev up to 2000 and the timing marks go crazy. they did this with the light springs too. oh and the miss is still there. so now i cant set my timing past 2000rpm. and as the engine gets warmer the miss is more pronounced.

so to put this in a nut shell,
my engine wants 50* of initial advance. it has an irregular but constant miss that shows up with the timing light. i cant set timing past 2000rpm. it is low on power. idle gets weak after warmup. and another symptom i noticed is, i can't get this thing to detonate on 93 octane. it was easy to do with the 290b-6 cam, but this one just wont do it.

notes of interest,
the only things distributor wise i didn't change was cap, rotor, and bushing. they all checked out good. as far as mechanically and visually. and the cam was installed straight up (same way i did with the 290b-6 which made alot more steam) crank dot at 12 o'clock and cam at 6 o'clock firing off cylinder #6.

guys, i am out of ideas and pretty down about the whole thing. i have been without this car for 2years. i feel i am a fair tuner but this has got me stumped. please help

[screamingchief]

Safe bet that the explanation for lost power is the reduction of cylinder pressure from the later IC event,coupled with the loss of some overlap from the wider LSA and not adding enough duration to make up for that loss of exhaust scavenging due to OL.

OE/ported pontiac iron heads love overlap in race engines,it helps make up for the weaker ports,as long as the exhaust is up to the task as well.

The reduction of cylinder pressure explains the reduced abillity to detonate.

The loss of overlap also means the VE likely dropped some too when the scavenging was reduced,so the cylinder is'nt filling as well in addition to the later IC event trapping less charge.

Installing the new cam striaght up just compounds the whole deal.

Was the new cam degreed when installed?

What are the advertised specs for that cam?

As for the igntion,my advice is to lock out the advance mechanism and phase the rotor and see how it responds,odds are that will be help a lot,and if you want a curve after that,run an electronic ignition curve box or such.

I would try advancing the cam to a 104°ish ICL and try some 1.65 ratio rockers on it,and run the lash as tight as you feel comfortable running it.

["Puddles the Pontiac"]

as far as the cam goes, i had always thought the wider lsa cams had more cylinder pressure because of the lack of overlap bleeding off cylinder pressure. i went with this cam to be more nitrous friendly. i was talking to Jim Butler and we came up with this grind and when i ran it on Desktop dyno this cam actually out performed the 290b-6 by about 10hp peak and anywhere from 5-15 through out the curve. but i do put too much trust in the program. i need to study hard facts better i guess. i swapped distributors to see if there may have been advance issues but either one did the same. i will try locking out the advance. i just have never seen an engine prefer 50 degrees like this.

["Puddles the Pontiac"]

i am not seeing the advertised specs on this cam but [email protected] reads 289i 297e

valve timing is open int. 24 btdc close int. 56 abdc
open exh. 68 bbdc close exh. 20 atdc

specs are for cam installed on 106.0 icl
4 degrees advance ground in from factory.

does anyone else think i made a bad choice on this cam? and what role is this playing with my ignition timing if any? i swear it feels like i am learning this stuff all over again.

[440GP69]

289-297 @ .020 is your advertised dur, thats a fairly large cam, 290B6 would outrun it with the other parts and setup you have now IMHO, Is it possible your ballancer shell has moved at all?, is the dist in right??, is it missing like a secondary ignition missfire or is it popping back through the intake?

["Puddles the Pontiac"]

i checked the balancer and it hasn't moved. it is a romac unit with marks to show if there is any movement. and as far as i know the distributor is in right. thats why i thought my timing light was going bad. with the rotor lined up to the #1 terminal in the cap, and #1 cylinder on TDC, it shows up as 30degrees advanced using the light.

[screamingchief]

Originally Posted by Puddles the Pontiac

as far as the cam goes, i had always thought the wider lsa cams had more cylinder pressure because of the lack of overlap bleeding off cylinder pressure.

Please folks,stop repeating this gem of information,it is not remotely accurate,overlap has nothing to do with cylinder pressure,not in the practical sense of this stuff.

Overlap happens at the end of the exhaust stroke,and the begining of the intake stroke,nowhere near the compression stroke.

The only events that significantly matter to the engine in terms of cylinder pressure is the intake closing,and possibly the exhaust opening events.

The only way overlap affects cylinder pressure is by influencing the VE and helping the engine get a dense intake charge to trap when the intake valve closes,that is the effect called "exhaust scavenging".

But that happens mostly at higher RPM's,not so much at lower RPM's.

And besides,speaking of overlap independantly of duration,LSA,and the actual valve events would be a complete waste of time for the most part.

A fella can have a ton of overlap and still crank out significant cylinder pressure numbers.

And he can do that with either a narrow or a wide LSA if he knows what he's doing.

Especially when taken in context with the given static compression ratio of the engine in question...

Now some honest food for thought.

New cam:Custom;
Spec = in/ex
Adv. dur. ~ 289°/297°
Dur. @ .050" ~ 260°/268°
Lift ~ who really cares...
LSA ~ 110° ICL ~ 106° ECL ~ 114°

Events:Seat (.020");
IO = 38.5° BTDC EO = 82.5° BBDC
IC = 70.5° ABDC EC = 34.5° ATDC
O/L = 73°

Events:@ .050"
IO = 24° BTDC EO = 68° BBDC
IC = 56° ABDC EC = 20° ATDC
O/L @ .050" = 44°

Now the 290b6:
Spec = intake/exhaust
Adv.Dur. = 290°/304°
Dur. @ .050" = 255°/266°
Lobe lift = .360"/.356" Rec.lash = .026"/.028"
LSA = 106° ICL = 106° ECL = 106°

Seat events:
IO = 39° BTDC ~ EO = 78° BBDC
IC = 71° ABDC ~ EC = 46° ATDC
Total O/L = 85°

.050" events:
IO = 21.5° BTDC ~ EO = 59° BBDC
IC = 53.5° ABDC ~ EC = 27° ATDC
O/L @ .050" = 48.5°

The new cam is not what I consider "bigger" than the 290b6.

Now,here's the clues,the intake events are'nt a whole lot different if indeed it did get installed @ the 106° ICL,that is in spite of the added .050" duration,that's all because of the similarity in the seat durations between the two cams,but you definitely lost some overlap everywhere,and honestly that's just what a fella who's gonna use spray normally wants to do,but that's also gonna make it seem a bit "sluggish" on the motor alone,especially if it is/was slightly overcammed to begin with or such.

By widening the LSA you effectively gave the exhaust lobe more time to do it's job.

You do so at the expense of the intake side,and at the expense of the exhaust scavenging when running NA,open the exhaust earlier it's gotta close earlier too for a given duration..

By "adding exhaust" to the cam you shoved the power curve upwards slightly,this also happens when you increase the intake/exhaust split as SOP.

So what happened,while you made the intakes lobes seem "smaller" for that given cam,so understand what does'nt make it into the engine to begin with,really cant be compressed to make that power later on,ie: if the intake side cant feed the HP,the exhaust side wont make that situation any better.

That's why nitrous and boost are generally less dependant on overlap,they help feed the intake side copious amounts of intake charge!

But in a NA combo,barring a restrictive exhaust system,that extra exhaust scavenging really helps get the intake charge moving in the right direction.

More charge,more power,it's as simple as that.

With big flow heads,and lots of cubes you dont need the scavenging nearly as much as you do with restrictive heads and such,it's almost like boost or juice in the most basic sense of all this.

Like I said in my first post,I would try advancing the cam to 102° to 104° ICL,and understand that absolutely all cams of this sort need to be degreed when installed,I simply cannot stress this strongly enough!

I would do that and as I said earlier maybe try adding higher ratio rockers (at least to the intake side) and try to tighten up the lash,these changes all should add back some of what was "lost" by widening the LSA and not going adding more seat duration,and that should hopefully help make similar NA power as the 290b6 made.

If it slows it down,then I dunno what to tell you,likely something else is amiss,as that should add power to that combo while trying to bring the power curve back down a few hundred RPMs or so at the same time.

BTW,I did'nt say I dont like this new cam,I just said it gave up some in the NA department,,,myself,,,I would have just sprayed the 290b6 and not lost a moments sleep over that deal...

I also think the car should have run a little better with the 290b6 combo,but you did'nt really give a bunch of info on that deal,please tell us more about the whole combo,what gears,convertor,tires,exhaust system,fuel system,that sorta stuff...

Was the intake port matched?

Tried any spacers or such?

The more you tell us the better!

[Geoff]

Constant miss at cruising speed. Are you SURE you haven't wiped a lobe? The symptoms sure sound like it. What brand lifters were they? I have sets of Comp Cams 'premium' lifters, Crower & lifters from JBP all now performing paper weight duty, having wiped after correct break in procedure, correct oil etc. All were solid lifters.

[wrench]

My Snap-on dial timing light did the same thing to me. Setting the timing with this light would not even let the car run?? After borrowing a light and setting the timing correctly, my Snap-on light read something like 80 degrees advanced at idle. Maybe your driveability issue is caused by severely retarded timing? I was running a MSD 6AL when I had this issue. A tech that works for me also had this issue. He had the timing light pick up on cylinder #2 instead of one, lol.

["Puddles the Pontiac"]

Geoff, i had that happen as well. they are comp lifters that came with the cam. with break in lube (from comp). i run Rotella T oil. and checked the lift to make sure a lobe didnt get wiped out. the miss itself is irregular, but its constantly happening. i also noticed the miss with the timing lights light. leading me to think it is electrical. btw, i will be using a different light to set timing. thank you for the responses so far.

["Puddles the Pontiac"]

well, after replacing the cap and rotor i managed to get the miss taken care of. now i am onto rethinking my cam. i am going to take some of 'chiefs advice, run it down the strip and see where it is really lacking. if all else fails, i will order another 290b-6. does anyone see any big issues with my combo as it stands? what should this run? i hate that my '97 LT1 trans am feels stronger then my '65 Lemans with a 455.

[screamingchief]

Dont changes cams till you get a chance to spray it.

Like I said,it may be just the ticket for that use.

I was just saying it's not odd that it felt a little soft,especially if it has'nt had a bunch of tuning time on it.

Easiest this to do is run some lash loops,tighten up the intake lash and see what happens,and go back on the intakes and do just the exhausts,then try tightening up both together,lots can be learned just by playing with the lash.

Then you experiment with the installed centerlines and rocker ratios,that's the whole beauty of solid cams,they are they're own tuning aid.

Only after exhausting all those avenues,should another cam choice be considered.

It's long tedious process,but the results often speak volumes about what the combo needs for improvement.

Did you ever get the timing deal figured out???

HTH.

[Sun Tuned]

Lots of probables here, one for certain.

Go to Sears and buy the 49.99 timing light they have... will be chrome, nothing more than a straight blink light. Never drop the inductive pickup for it and you'll be golden. HEI's do not like the dial back lights at all. I understand the Snap-On light runs about 500.00 if it's the digital job... but guess what??? HEI no likey, haven't seen one yet that was accurate on one. Not knocking it just need to spend 50.00 on a good one and no more problems there.

Recheck the timing deal then get back to us.

[silver68]

I don't think you mentioned what static compression the engine has. If you don't know how far down in the bore the piston is at TDC, how many cc's the combustion chambers are, and the compressed thickness of the head gasket, you will only be making a wild guess as to what the compression is (and probably be wrong). For the cam you have you will need 11 to 1 for it run optimumly. That is my opinion and I recommend contacting the cam grinder to be sure. I can tell you for sure you have nowhere near enough converter or gearing, 4000 flash stall and 4.10 gears minimum are what that cam wants, again I repeat minimum. A big cam in a mismatched combination is the number 1 reason muscle cars lose a race to a turbo import car. If you do have enough compression for this cam, adding turbos to this engine will bring immediate fatal results. No problem with NO2, but forgret about boost. Optimimize your engine, driveline, suspension, and tires, and this car should be quick enough with a 150 hp shot of nitrous to require major safety upgrades to race at most tracks. Your misfire at cruising speed (if your timing is set properly) I can almost guarantee, is due to a lean mixture of the idle transition circuit. This can not be adjusted with the idle mixture screws or changing the jets. There is no reason not to have a wideband O2 sensor in any true performance car. Also, if you are reading plugs and using any of the charts in commonly found in repair manuals that show horribly carboned up plugs, you are not reading them properly. racingsecrets.com has a great video and plug reading light for sale. As far as tuning out the miss in your engine, the general tuning forum on innovate motorsports website, will blow your mind with the references and advice available and I recommend everyone with a performance car to visit there. I thought I was real good with carbs until I got a wideband setup and realized how wrong I was and how much I had to learn. However, learning to properly read plugs is still critical.

[silver68]

One more thing, I can explain why you must "degree" the cam. On both of my personal engine builds each cam was off 2 or more degrees. Never trust a timing chain set with multiple keyways. That is especially true of cloyes true rollers.

["Puddles the Pontiac"]

thanks for all your help and i do plan to check out the mentioned web sites.

as for tuning, the plugs look good on all three levels of the porcelain. as well, the electrode is showing that i do have the correct range plug. after rechecking, i had found some of the gaps to be off. all are reset to .045.

an issue i am having is that i am only getting about 10* of mechanical advance (there are no provisions for vacuum adv.) i am looking for a weight set to get me more, i do physically have more room for more advance (via the slots), but the weights are stopping early. i am looking around for stock weights now.

i know i cannot compete with a wide band. but my idle, off idle is great. not a stumble or pop to be found. the engine will "bark" with a quick stab at the pedal. not to mention the thing will start like a new, fuel injected car. i do have serious traction issues and this car is quick.

but the miss is still there. and it is a light miss (not a surge) which leads me to believe it is in the ignition. i can best feel it during "cruise" situations. i plan to change the coil and module. i can see nothing physically wrong inside the distributor.

fyi, i do have the new cam in (290b-6). the cams lobes all survived break in. at a 106 lsa there is no issue with a lack of dynamic compression (thanks screamingchief for the cam lesson last year). these are 93cc 6x-4 heads on a .030 over 455, zero deck. you are right to say i am guessing the static compression ratio when i guess 9.75 to 10-1. and i am going to use a friends inductive light when setting timing. i will get back to all with any new results. again thanks to all.

p.s. does it make anyone else nervous to see their oil pressure drop to 10lbs at idle? i have never gotten over that.

[MikeB'70Tempest]

5-7 cross fire maybe?? Are the wires running next to each other??

[Old Man Taylor]

I have had bad spark plug wires that check out just fine.

["Puddles the Pontiac"]

i forgot to add that while i was going back through my distributor i noticed the shaft had alot of end play, as well, the thrust washer above the gear looks worn. is this an issue for a pontiac since it does spin opposite of what a chevy spins?

this thing fires off like a champ, its just everything after that, it has issues.

[screamingchief]

Any time a problem persists even after attempts to correct it,it's time to drop back on basic engine diagnostics.

Compression test,leak-down test,vacuum gauge readings,that sorta stuff.

Along with close inspections of stuff like the valvetrain and valvesprings and such.

At the very minimum you would be establishing a "baseline" for this combo,that way you can always track the engines "health" based on how it was when it was "fresh".

And you may just find something that needs attention before it gets really nasty.

Timing & ignition really should'nt be all that complicated,mostly nail down the basic set-up and forget it for the most part.

Also agree that degreeing the cam should not have been considered "optional".

And you can throw rocker arm geometry and pushrod length into that "mandatory" catagory as well.



BP.