Total timing, high CR, High altitude, street car.
I have posted many forums here, but i did not have the correct engine specs. To those who read this and see that there are a lot of the same questions i am sorry, but i was ignorant when buying a car and i am now left with these problems. I am on a low budget, and do all the work myself. I am 19, living with my parents, and on my way to be an engineer. I do my best to do everything using proper protocol, use the right torque settings, and make sure everything goes together smooth. so...
I bought a 1989 camaro with a rebuilt 350, not knowing anything about timing, carbs, intake, CR, and cam specs. Had all sorts of trouble, but the motor blew up anyhow and i tore it apart to see that it was build like crap.
So i got a 1988 rs, took out the non-running 305 tbi, and put in a motor that my dad had in his garage. It was the only option because of very limited budget.
sbc 350, casting code 3970010
Heads: 462 camel hump, redone with 2.02/1.06 stainless, ported
1.5 roller rockers, dual valve springs
I FINALLY found the cam card after all the other posted saying it was .510 lift with XXX duration.
cam specs: (shocking, but a good explanation for my timing problems)
here we go...
Crane cams 111411, mechanical flat tappet
lift w/1.5 rockers .545" int/.563" ex.
adv. duration 292/300
@ .050 tappet lift 256/264
lsa 105, IC 102, calculated valve overlap to be 86*
valve lash set at .026" while motor is hot.
operating range 4200-7200, oval track cam
I basically have everything set up to match, other than the fact is it my daily driver. I will not lie, i LOVE the top end when i merge on the highway, but stop-go traffic during the day is a pain in the butt!!!
weiand single plane with raise plenum
edelbrock 750cfm, mallory 140 gph fuel pump
short tube headers, dual 2.5" exhaust, goes from headers, to magnaflow mufflers under the driver and passenger seats, and dumps right out
rebuilt rear end with 4.10's and new posi
t-5 5 speed (i'm surprised it has lasted this long )
I have a procomp billet aluminum distributor, adjusted my timing to 24 at idle, 38 total.
SO here are my questions:
With these pistons and the 64cc cambers on the heads, what is my static CR? (at the time, i didn't think to take the picture at tdc, so the picture is with the #1 at about 30* ADC)
At 5000ft, (1) will 91 octane be alright??? no pinging at all, and will stay below 190* on the highway. compression test shows 165-170 psi while the engine is warm.
(2) Is pre-ignition audible??? Is it very noticeable???? What are the symptoms???
I was running with no vacuum advance, but it seamed to get a little warm (my collector gaskets have failed twice) I drove for 40 miles on the highway, and at the end of the journey i could hear exhaust leaks from the collectors
(3) What should i limit my vacuum advance to??? (at 3000rpm: 24 initial+ 14 mech+ ???? vacuum= ????) my current vacuum can has 20*, less??? should my total timing be less if my cr is to high??
(4) What should i do about the aftermarket timing tab??? ive heard they can be inaccurate.
Currently i have the idle purposely set at 1200, and still get only 4-5" of vacuum (no leaks... really, have idle mixture screws adjusted)
(5) For the sake of saneness, should i change the manifold??? Ive heard the torker II is good, but i really would like some good input. I know that most people would suggest changing the cam to something sane, but that would be costly, and i really only drive 100 miles a week anyhow (very soon going to get a second car)
please tell if there is something obviously wrong in the above discription, if this motor goes out, i will be left with nothing, and have wasted tons of $$$.
Thanks for the help!!!
Last edited by Biscuit6447; 08-06-2009 at 01:22 AM.
I love the cam you have, it's spec'ed pretty good for the attempt at running pump gas with the compression you may have, even if that wasn't the original intention.
Without and actual piston to deck height measurement at TDC, it will be impossible for anyone to accurately tell you what compression ratio you have, it could be anywhere from 10.8-1 to 12.5-1+. You're 38 degree total timing spec is really pushing it, I'd lower it to 32-34 for a safety factor(hot day, high underhood temps, bad batch of gas), you will need to physically limit the advance curve to 8-10° so that you can keep the 24 initial, and probably only add 15-16° vacuum at cruise using the full time vacuum source. If it surges at cruise it's too much vacuum advance, the rest you will have to play by ear(literally) for spark knock - sounds like marbles inside a hubcap......
Cold outside air ducted to the carb instead of hot underhood air will help a good amount. Run a 160 thermostat too. Put some 3/4"-1" spacers between the hood and the hinges at the hood bolts to let hot air out of the back of the engine bay(Racer trick).
Be conservative on the timing and look at a plug regularly (daily) until you feel comfortable with it, you are looking for bubbled or blistered porcelain, black flyspecks on the porcelain, bone white coloring, all signs of pre-ignition or detonation. If it shows up, retard the timing some more to keep the engine alive, and live with the loss of performance and mileage
Your collector gasket issue has nothing to do with engine temp, either the flanges aren't flat or are too thin or you didn't retighten the bolts after a short heat cycle following installation.
You can't do much about the timing tab unless you find true top dead center with a piston stop, otherwise it is just a guess. I would expect to only see 4-5 inches of vacuum from that cam. Torker II would be a big step in the wrong direction, as would going to a smaller cam. You need the big cam duration and late intake valve closing point to bleed off cylinder pressure below peak torque for it to survive the high comp ratio and pump gas.
You are basically going to have to be eyes, ears, and hands on until you get to know the engine, the only other way to fix this is to change either the heads or the pistons to lower the compression ratio and that means $$$. Your 5000' elevation and cam size(duration) works in your favor, and I think you can do this if you pay attention to it, it is not outside the realm of possibility. I've run an 11-1 Iron headed 406 at 800' elevation on 92 octane with no problems set up the same way, cam and all.
Your cr is at least 11.5:1. probabily closer to 12:1+ with those pistons.
That cam wants as much inital timing at idle as you can throw at it.
With cams like that I routinely lock out the mechanical advance and set the now fixed timing at 34-36deg (SBC). But because of the excessive cr you will want to dial back that timing to around 29-31deg. Try it. It will "drive" much better.
Then, vacuum advance should be used if at all possible. But needs to be custom tuned to your car. i suggest a adjustable vac housing set for around 10-12deg of vacuum advance (limit). The rate in/out needs to be optimized by drive testing. A "stock" vac can won't well work becasue of the lower manifold vacuum (big camshaft).
The weiand manifold is a good high rpm manifold. A dual plane manifold, any dual plane manifold will run much better at low rpm overall. You'll like it a lot better on the street. A Edelbrock Performer RPM manifold (or simular dual plane hi rise) is what you want. Do not bother with the Torker II.
What were the numbers stamped on the tops of the pistons?
A water/methanol injection system will allow you to run full power timing (34-36deg) without detonation on pump gas with the high cr.
You are right on about the header gasket failure. Not enough or too much spark timing at cruise and or excessive lean or rich AFR at cruise create excessive exhaust port temps and late fuel burn (spark advance) in the exhaust.
Fine tuning the edlebrock carb using a AFR meter will help fuel mileage and driveability. Remember this is a "universal" calibrated carb that needs to be tuning to your car for best results.
Last edited by F-BIRD'88; 08-06-2009 at 09:26 AM.
In short you want a lot of initial (I think locked is a bit much but it may be okay) and about 34 total. I would start with about 28 initial and go from there. Low RPM is where your detonation is most likely to occur and taking out a few degrees there may help it run safely on pump gas. With better gas you could use more total with domed pistons, BUT you don't want to push it on pump gas- best to save that for the track.
If the racey Crane cam is getting you down and you drive your car more than race it:
For vastly improved streetability consider changing the cam.
The OEM cam from a 71-72 350 LT-1 Corvette would be a good one.
A lot, lot less overlap, yet designed for high compression, high performance street use with a late intake valve closing event.
Elgin Cams #E904P Available in a affordable cam+mech lifter set for $114 from Competition Products #E904M
Very easy street manors, best with a dual plane hi rise.
A good match to your shorty headers/dual exhaust system tuning.
Adjust the valve lash tight (.020"in .024 ex) and you'll have to listen hard to tell its a solid cam at idle. idles easy at 700-750rpm.
242-254@.050" .459"-.485" 116 LSA install on 110 intake C/L
Last edited by F-BIRD'88; 08-06-2009 at 12:35 PM.
Thanks for the input guys!
here is some more info:
I do have the 160* thermostat, but i have the stock radiator. On hot days, even with the dual radiator fans i have, it will get really hot around town, but 190 on the highway. I took the a/c condenser out to increase flow. What would be a good aluminum radiator to get??? I was looking at summit's race radiator because it is cheap, and has no heater ports or anything (I really don't want to get a $400 be cool custom fit radiator )
Here are the heads
The #'s stamped on the piston are: ".030 7000p"
the #3 plug:
The oil is from the pcv. Even with the baffle in the valve cover, oil still splashes and finds it way into the intake. I just recently make a catch can for the pvc, and after 200 miles there was about 1/2 a cup in the can, and still some residue in the hoses and the carb. any suggestions??? is some sort of filter a possibility???
I haven't had any pinging and no detonation that i know of even with 38 total degrees, but i did lower it 3 deg today; so i have 21 at idle and 35 total. Really didn't seam to run any better and/or hotter or colder. Since the collector gasket blew, i hooked up the vacuum advance, and it took the advance to 58* @ 3000 no pinging but still a lot?!?!?! would 40-48
at cruise be better??
I have the carb jetted 1 stage leaner on all modes (power mode, cruise mode, and secondaries) and have stronger step up springs. If i wanted to run race gas once, just to see the difference, would i have to modify to carb settings???
Would a bolt on cowl induction hood be a good way to get cool air??? ( i really don't care how it looks, i just want functionality)
What is a surge??? currently, i have to grind the clutch some to get it to move without it stalling. and sometimes it will feel like some sort of boost from 1200-2000 of the line. I also have underdrive pulleys on the crank and alternator. I have an aftermarket wieand aluminum water pump also. the water pump change helped the cooling, but the pulleys made no difference.
Basically whenever i need to make a big chance, i save up for two weeks and get the part. I.e. the exhaust only cost $200. I only make $7-$9/hour.
Thanks for the input, again!!!
The Summit rads work fine, just have to be fitted to the car, they aren't direct fit and will need custom mounting fabbed up. You can move the heator hose to the intake next to the thermostat housing, 60's and 70's stuff was that way. The under drive pulleys are a step in the wrong direction for cooling.
Is the vacuum advance can adjustable in through the nipple?? 58° seems too much 48-53 seems more reasonable, but at altitude I don't know.
The cowl hood would help, but only if it is sealed to the air cleaner; and it is a big expense, fiberglass is not cheap. Look here for help last.
Surge due to too much vacuum advance is the car ever so slightly speeding up and slowing down at a steady highway cruise speed, feels like a ship rolling on the ocean and is only slightly noticable.
I would expect to have to slip the clutch some to get rolling with a cam that big, or it will buck.
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