[cscottfergus]

Hello.

I would appreciate comments and suggestions on the cam and engine combo. It seems to run rich and doesnt seem as powerful as a 400 2 bbl I used to have, I think it needs some optimization. Runs about 220 deg F idling and seems to have relatively low oil pressure on autometer electric gauges, seems to diesel a little when shut off and has starter seems to have heat soak issues (typical for pontiac?) have not checked cylinder compression lately.

I have a 1967 pontiac Firebird
engine: 400 cu in 0.30 over, Forged pistons, align honed , balanced, about 10,000 miles on professional rebuild
Heads: Factory 670 Heads milled 0.012 compression ratio abt 11:1, stock ratio rockers with polylocks, no port work done on heads
intake: Edelbrock performer dual plane intake (worth keeping?), cam: Crower part no. 60242 389 pontiac 280 HDP "compu pro" advertised duration 280 deg intake 286 deg exhaust intake lift 0.456 exhaust lift 0.466, dur at 0.50
intake 218 deg exhaust 224 deg, lobe separation 112 deg, intake lobe lift 0.305 , exhaust lobe lift 0.312
Fuel: run 93 octane with lead substitute additive, Holley 650 double pumper carburetor with air horn milled off, jet sizes unknown, stock fuel pump, no return line
spark: stock coil, Timing don't remember but open to recommendations, mallory unilite non vacuum advance, stock plugs.
Transmission: THM 400 stock gearing
differential: 3.08 ratio limited slip
tires: stock 14" tires and wheel
exhaust : stock exhaust manifolds and dual exahust non- mandrel bent through stock diameter pipes, dual turbo style mufflers
Thermostat: unknown I believe 180 deg. F

[scoob]

just my opinion but would switch over to a edelbrock 750 ( a lot easier to tune then a holley ) and run a distributor with a vacume advance unit. as far as it dieseling thinking timing also could be reason she is running hot at idle

[torqjunki]

Scott...Is this a street car? THats a lot of compression if your trying to run it on pump gas. Also a lot of compression for a pretty small cam. Not sure if you will ever be able to tame this combo without race gas. A bigger cam with some overlap will help, but a bandaid really. I am in Magnolia, TX and would be happy to help you out with the tune. 281-389-6150 David

[rad400]

Bigger cam and carb for sure. I would say 850cfm carb.

[chiphead]

That engine will ping itself to death if it's really got 11:1 compression and that small of a cam. I would expect cranking compression numbers over 200 PSI with engine warm, plugs out and throttle wide open. That would verify combo of compression and small cam.

A cam with a later intake closing event, about 10-15* more duration and 112-114 LSA would reduce dynamic compression and make more power. That would be complimented by an RPM intake and Q-JET.

We could make timing recommendations, but the timing may be retarded on purpose to prevent detonation. Setting it where it should be may be a bad thing, depending on how sensitive the engine is to detonation. I suspect retarded timing why its so down on power and hot. Check what you have now and post back. We need to know timing at idle and at 3000 RPM.

The engine temps at 220 is too high. It's either water flow, air flow, radiator size or tuning. What are engine temps at cruising? What is the oil pressure at idle and at 3000?

[PontGuy]

As stated all of your symptoms are typical for too much compression - too little cam. A compression test would help confirm this.

Curious though, the numbers that you give for .050 duration didn't sound right so I looked it up and Crower lists the cam at 221 int 229 exh. It doesn't change your situation but are you getting the numbers from the cam card?

[67drake]

Originally Posted by PontGuy

Curious though, the numbers that you give for .050 duration didn't sound right so I looked it up and Crower lists the cam at 221 int 229 exh. It doesn't change your situation but are you getting the numbers from the cam card?

X2. That is the cam I run,and some of those specs are different than my cam card. Might want to double check what cam you are running,or at least the specs.

[screamingchief]

I doubt the CR is @ 11.0:1 here,not unless the short block was zero decked and the heads had been shaved some before being shaved that .012" this time.

The common pistons for these 400 engines sit down in the hole like .020" on average,so that typically puts the CR closer to 10.0:1 when used with most any of the common small chamber big valve heads like those 670's.

Most of those small chamber big valve heads will be over 72cc when "virgin",typically they are closer to 75cc or so,so that .012" mill just puts them 2cc or so closer to the "nominal" 72cc spec that we all know so well.

Besides,there can be a lot of explainations for those sorta symptoms,many of them are related to common tuning chores,others are often related to minor problems like vacuum leaks or such.

I can see a few things I'd change in this combo,but most of what's going on with this is likely things that are only loosely related to those items I would wanna change.

In the right hands,I bet this could be "whipped into shape" in no time.

2¢ FWIW

Bret P.

[PontGuy]

I doubt the CR is @ 11.0:1 here,not unless the short block was zero decked and the heads had been shaved some before being shaved that .012" this time.

Maybe, maybe not. I do know that I ran a similar cam with RA heads in a 400 years back and though it ran OK I had similar issues- pinging, dieseling, heat soaking, etc. I installed a much bigger cam, one of the old Crane Fireballs, and the engine was a lot happier. But that was on a 4spd car with a big gear and no power brakes, so I could get away with the "racy" cam.

We are all just guessing, and compression numbers would help tell where this one stands.

Though the intake/carb combo, no vacuum advance etc. are not the way I would go and are probably not helping the situation.

[screamingchief]

Originally Posted by screamingchief

I doubt the CR is @ 11.0:1 here,not unless the short block was zero decked and the heads had been shaved some before being shaved that .012" this time.

Well,lots of times when folks say two cams are "similar",they really are'nt all that similar.

The only way to compare two cams is by looking at all the info for both cams and looking at what the valve events are like with both cams.

Beyond that,I never assume anything about cams,there are just too many people that just look at the basic cam info without really understanding where the real differences in cams lie.

You may know what cams you had in that combo,but I have absolutely no idea what they were unless you tell me exactly which two cams you are refering to.

Then I might be able to compare those two cams to the OP's Crower #60242 cam.

Originally Posted by PontGuy

We are all just guessing, and compression numbers would help tell where this one stands.

I dunno about guessing,,,I'm not really guessing about anything I said...

I know I have a pretty good idea what I'd expect to see from any compression test results,if he is infact @ 10.0:1 I'd expect the cranking compression to be around 150 psi (give or take 5-10 psi or so) with that #60242 cam,and if it were indeed up @ 11.0:1 I'd expect it to be closer to 170 psi (again give or take say 5-10 psi).

Now there are a lotta folks out there that would say he should easily be able to run trouble free with those sorta cranking compression numbers,but that's just not always the case,as there are numerous other factors that affect that situation beyond just what psi it cranks out,so honestly looking at those compression test numbers are only going to tell a person if he's way off the mark.

There are combos out there that crank over 200 psi that run trouble free,and the flip side of that is there are also combos out there that only crank 130 psi and they ping like crazy,so there is no "magic" cranking psi that is going to ensure trouble-free results.

A lot of that depends on not skipping over "details" in the build itself,as well as the overall skill of the tuner,and the quality of his work.

Now there may be some info that the OP neglected to mention here,so yeah there is some "grey area" in all this where certain things needs to be taken for granted till he clarifies those further,but the SCR situation is'nt really one of them.

Even if he had that combo zero decked,with a 72cc head that still only gets him to 10.5:1 CR.

And in order to get it to an honest 11.0:1 CR,it would have to be zero decked and the chambers in those 670 heads would need to be like 68cc or so.

That stuff is'nt a guess,that's pretty cut & dried really.

Originally Posted by PontGuy

Though the intake/carb combo, no vacuum advance etc. are not the way I would go and are probably not helping the situation.

I agree with most of ^^^^ that.

I did'nt go into specifics,mostly because I wanted to make the point that the CR was'nt likely as high as was being quoted by the OP,and being discussed amongst the others here.

But I did indeed point out that there were some things that I too felt were not helping this.

Yeah,the first thing I'd do is pitch the non-vacuum advance uni-lite distributor,mainly because I dont care for the uni-lite distributors,and second because I've rarely ever seen a vacuum advance hurt a "street" car in terms of improved performance and driveability.

That mostly relates to the "tuning" end of things,as I mentioned earlier.

Get the timing dialed in and then you can start to figure out the rest of the tuning needs.

Also,the car could almost certainly use some more converter,even with the 3.08 rear gear that cam is gonna want a bit more stall than many "stock" converters will give.

Another thing is that I'm not a fan of the performer intake either,especially with the square bore holley carbs on them,as the Edelbrock dual flange intakes can be prone to vacuum leaks around the carb base with the square bore carbs on them.

I dont really have a problem with the 650 holley DP per-se,as that can be easily made to work by someone with the proper carb tuning skills.

Hands down I'd take the Holley 650 DP over any of the Ecarb AFB clones.

And the cooling system sounds like it may need some indepth attention as well.

But I'd probably double check the electrical guages accuracy by installing some mechanical gauges to get another more accuate reading of the OP & WT.

Though things like high coolant temps and low oil pressure can easily be caused by lots of other things.

Same with things like pinging and dieseling.

Lotta that stuff is often related to one another.

If it's running rich and hot as SOP right now,odds are there is a $#!t ton of carbon build-up in the chambers and on the tops of the pistons,and understand that all it takes is one small piece of that carbon to glow red hot and that'll certainly cause those sorta pinging and dieseling issues.

That sorta thing often has absolutely nothing to do with the static compression ratio...

And proper plug choices plays into this as well,if too hot a plug is being used that could explain some of those sorta problems as well.

And if one is running a thinner wt. oil with a fair amount of miles on it,well a "warm" running engine likely is'nt helping the oil pressure much either.

Not to mention if he's running way too rich,it's entirely possible that the oil is getting fuel contaminated as well.

Or even worse yet,maybe he has a Fram oil filter on it that has collapsed internally or such.

Again those would not necessarily have anything to do with the static CR.

Sure sometimes there is indeed a cause-effect relationship to those sorta things,but sometimes it's just coincidental too,so one is often best served by trying to keep an open mind,and working thru these sorta deals before just going out and throwing more parts at the problem trying to fix it.

All I'm saying here is this:
Often it's a failure to get all those simple things "right" that causes the biggest problems.

FWIW

Bret P.

[torqjunki]

Well said Cheif....Thats why I avoided any real detailed info....this car needs to go to someone who knows Pontiacs and tuning..... Go see the Screamin chief or someone who can methodically diagnose and fix it. Money well spent.

[cscottfergus]

Thanks for the responses.

I need to shake the cobwebs out of my head since it has been 20 years since the rebuild.
Has had these problems as long as I can remember so probably not related to sitting up

I need to move all the kids toys and pull it out of the garage.

I will check oil pressure, timing and cranking pressure soon.

Useage:

This is a street car that sees maybe 200 miles/year use and is not a daily driver anymore.

I would like to drive it more often once I get it sorted out.

Oil has been changed 10w40, I think and is not thinned out due to gas, has happened before though with backfire and blown power valve in carb. car was not driven after this happened.

When I run this car I end up smelling like car exhaust fumes pretty quickly this is a strong smell that stays with you unless you take a shower. ( running rich, I believe)

It leaves black soot marks on concrete(ground) where exhaust pipes exit back on car if it has been sitting idling for a while.

Started regulary to maintain running

rebuild: The engine was professionally machined and then reassembled by the friend of a friend about 20 years ago (no idea of his skill level but he was experienced with Pontiacs and engine assembly). At that time had q jet and factory intake and distributor. The distributor was replaced because it was worn out. I do not now why mechanic recommended that distributor. He is an experienced BUICK GN tuner. The intake and carb were put on because they were offered to me for 75$ and that was cheaper than a rebuilt q jet at the time. I still have old parts. engine has never really been tuned or sorted out.I have never changed jets in carb

Cam: the specs I quoted were off a blue rough 5 by 7 sheet of paper from Crower and match that paper it has a hand written date of 11-9-87 on it. I double checked numbers and card matched my post

The 11:1 ratio was from memory and possibly erroneous. I think it came from information that I have seen that stated factory cr of 10.75 to one for these engines and assuming higher cr with head milling.

I am now looking at the machine shop invoice with my own hand written notes after interviewing machine shop owner.

TRW forged pistons 0.30 over , flat top, part L2262 F-30, no idea if zero decked but that does seem to ring a bell so to speak., sealed power molly rings.

have a hand written note about cr 9.94:1 in 406 ci with 72cc heads , does not account for 0.012 mill on head..

hand written note on cam specs on invoice 60242 .422 intake .466 exhaust dur at 0.50 220 and 229 deg, this differs from blue cam card

cloyes true roller double timing chain

lifters: speed pro ht 951 hi rev anti pump up lifters near 0 lash

stainless proline intake valves 1.77 dia S2638, stainles exhaust valves 2.11 dia u2638
valve springs 108 lbs at 1.656, coil bind at 1.050, travel 0.606

stock rods with arp bolts

more about distrib and coil : mallory unilite 3758001 part no mech advance, mallory coil 29217

tuning: was tuned by mechanic but has been a while and I have changed timing. Timing, has been a while but from memory I set it to maximize vacuum and avoid pinging. I will check it and report back.

Radiator is factory radiator recored about 20 years ago.

well I'm off to go check out those pressures, etc.

[cscottfergus]

Ok update

Thank you to everyone for your thoughtful responses.

I checked a few things

No choke on holley 650
plug wires mallory pro-sidewinder

AC Rapid-fire # 7 25171346 on box , old plugs saved from last change are AC R46S , these are not on car.

pulled two plugs no 1 and no 5 both wet and black

cylinder pressure no 1 is 170 psi no 5 is 180 psi


oil pressure (professional hand held oil pressure gauge)

not running but cranking 60 psi cold

idle 1000 rpm (cold) 87 psi hot 75 psi
1500 rpm 92 psi fluctuating
2000 rpm 92 psi steady
2500 rpm 94 steady
3000 rmpm 100 psi steady


timing more of a mystery.

Using stock dampener with timing mark scribed on it.
I cant remember why but to set timing had to mark around dampener with white marks to check timing, stock timing mark is way below ) at rest . I forget why setting the timing with the mark on the dampener does not work at factory specs. I think it hads to due with the cam maybe. I has been to long and i forget. I am sure this is common though and someone can remind me why this is so.

ok from the timing mark on the dampener I had 3 painted white marks going clockwise. one about 3/4" one at 1 1/4", 1 at 1 3/4 " I do not remmber what advance these represent. I believe I marked them to check total adavnce at speed. I forget the conversion to get them to degrees could calc if had diameter of dampener. Ill try to get that.

timing light said idle was 1280 rpm after warmed up 0 btdc was about 2" from timing mark on dampener (degrees?) 1500 was about the same , 2000 was abt 2 1/4 ", seemed to be all in by 2500 was about 2.5" around from mark on dampener.

clearly I need a refresher on timing

any ideas what those marks convert to on degrees and any other comments on this information?

[screamingchief]

The cam specs being a bit of mystery here does'nt help thing much,neither are the things you're seeing with regards to the timing.

If it were my car,I'd probably plan on doing a "full on" degreeing of the cam just so I could find out exactly what cam is in there,with the secondary goal being to find out exactly when the intake valve is opening and closing,and to confirm the installed centerline for the cam.

I would also be 100% sure to check and confirm true TDC for the balancer during that process as well,and if I found that the timing mark was off on the balancer,I'd figure out why that was so,and possibly replace said balancer so that the timing mark was where it's supposed to be.

Then once you have true TDC for the balancer,you can then mark the balancer for total timing as well,as that makes timing the car a whole bunch easier to dial in later on.

Anyhow,if the cam were indeed smaller than the current Crower #60242 is supposed to be (say closes the intake @ 60° ABDC rather than 68° ABDC),and the CR is still roughly in the 10.0:1 range,it would explain why your cranking compression numbers are what they are (slightly higher than expected).

Couple that slightly smaller than expected cam with one that's been installed on an advanced CL and that will push those cranking compression numbers higher as well.

Though say thru the degreeing process you find that the cam is spot on and where it's supposed to be and the intake valve indeed closes @ 68° ABDC like the #60242 cam should when it's installed on a 108° ICL,then yeah it would be a fairly safe assumption that the static compression ratio is indeed a bit higher than that 10.0:1 CR assumption.

So,understand that the only way any of those cranking compression test results can really be put into a context in terms of figuring out what the static compression ratio may be,is when you already know for sure the info that degreeing the cam will tell you (intake closing ABDC at the seat).

Then it's not too hard to figure out appx. where things stand in that respect.

And as far as the plugs,again I'm not a fan of the AC rapid fires,especially the newer ones that use a platinum electrode.

And IMO an AC R46S is too hot a plug for this sorta combo.

For example I plan on using something like the Autolite no. 303 in my "hot" 400 combo with the 670 heads on it,and I've recommended the same to others here,and they run them with good results as well.

But an AC R43 or R43S should work too once the carb fuel curve tuning issues all get straightened out and it's not fouling plugs as SOP.

Also,I would ohm test all the plug wires per SOP.

I would be sure to get a good distributor in there too,nowadays there are so many decent choices for that item that I wont say to just do one thing or the other,but for sure I'd want a distributor that had a vacuum advance and a fairly "user friendly" mechanical advance mechanism,and if I were looking for an electronic distributor,I'd want one with a magnetic trigger myself,no optical or hall effect triggers.

Most here will just say to throw an HEI in there,as that's a pretty safe suggestion to make,though often they can be a pretty tight squeeze in a first gen (firewall),so I dunno if I would go that route myself,me I'd probably just use a plain old GM points distributor to minimize any clearance issues,that or one of the aftermarket small cap magnetic trigger distributors.

And to give any fuel curve tuning advice,we would need to know where you are now with that 650 DP holley,that includes the jetting,the squirters,the pump cams,the PV rating,as well IFR,PVCR,IAB,HSAB all that sorta stuff.

And if you opt to stay with the performer intake,be sure to check for vacuum leaks around the baseplate of the carb,Edelbrock also makes a thin "plate" #2732 (w/a better gasket) that helps prevent that from happening,so I would suggest using one of those as well.

Once you get it to stop fouling the plugs as SOP,then you gotta work on trying to clear out some of that carbon build-up,understand that there are several ways to do that,so maybe plan to cross that bridge when the time comes.

Like I said,there is a process of sorts to work thru,if after all that leg work the primary problems persist,then you maybe try and make a plan to address any percieved short-comings or such.

The cooling system stuff is a whole other can of worms,tons of things to consider in dealing with that,so spend some time digging thru the cooling system forums for more ideas how to approach those problems.

Good luck with it,and I'm sure everyone here will try to help walk you thru all this stuff.

Bret P.

[PontGuy]

I usually don't jump in on these "cam selection for 400/455" posts because there is a lot of good knowledge on this topic, and those with more experience than I have are usually quick to respond. But I did notice the listed cam specs were odd, so took the dive.

Bret, I am right there with you on everything that you are saying.

170/180 on the compression test is higher than I would want to see, but not beyond reason. So I wouldn't throw out the cam just yet. Degreeing it to see what you really have would be a good idea.

But top priority for me would be the distributor. You are going to need good spark control to make the engine work right for a street application, and no/little centr and no vacuum advance are a problem. I like factory points, most here prefer HEI's, but however you go make sure it has a centr curve that is appropriate for a pretty hot Pontiac engine.

[screamingchief]

Pretty much that's what I'm getting at,I would wanna know for sure where I stand before making any bigger changes like swapping out cams or such.

Dealing with all that little stuff needs to be done anyways,even if he's gonna swap out cams or such later on,so doing that stuff now is'nt going to be much different than it would be dealing with that later on.

FWIW

Bret P.

[cscottfergus]

Thanks again.

I will see about replacing the distributor with a vacuum advance unit.

quote"Then once you have true TDC for the balancer,you can then mark the balancer for total timing as well,as that makes timing the car a whole bunch easier to dial in later on. I think that is what I did years ago and hence marks on balancer, Ill check it out.


I will need to do some reading or visiting with experienced people to learn how to degree the cam or check its specs as mentioned. Do I need to take everything off the front of the engine to do this? I am familiar with concept but have not done this.

I'll check for vacuum leaks and will need to disassemble carburetor or study it to get the carb specs documented.

I think I would like to switch back to the stock intake and Q jet eventually.

at idle the last mark I had made on the balancer is lined up with zero. Can't remember significance of that.

I'm reading and rereading your suggestions and going to figure out what steps to do in what order and learn how to do them or hire someone.

Know any Pontiac Guys who work North of New Orleans? One of my mechanics is a drag racer and shop owner so I suspect he can help me. I would rather learn and do it myself though.

possible diagnosis order...
pull carb and document specs.
ck for vacuum leaks.
Degree cam to ck specs , confirm tdc
replace distributor with rebuilt original points distrib. ( there was a Pontiac gentleman rebuilding these in TX several years ago, believe he was a member of these forums, I forget his name,

[cscottfergus]

I didnt have a chance to make any changes but gave some though to the timing.

anyone know stock diameter/circumfrence for 67 pontiac 400 balancer?, I measured 17.5 circumference, is this correct? calculated to 5.57" diameter,

used this to make sense of the timing i noted earlier. If I am off on my circumfrence meas. then degrees will be off too

Have not checked tdc recently on car.

Idle at 1300 calc to 41 degrees advanced. 2500 calc to 46 degrees. sounds too high must have circumfrence wrong.

[cscottfergus]

67Drake your problem here

http://forums.maxperformanceinc.com/...t=400+dampener

looks similar to mine, how did yours turn out?

[cscottfergus]

Found this great post that shed light on the timing mark issue and reminded me why and how I marked dampener earlier. Should I replace dampener to head off any potential fatigue failure? It has about 195,000 miles on it. Brand recommendation?

http://forums.maxperformanceinc.com/...pener+diameter