Cam choice

[GMDAD]

Guys, Here is my current combo; 77 T/C
305+.30, stk H.O.305 heads 1.94/1.50, F/T pistons 9:1
Melling 443/465 214/224 112 1700-5200 range
Edelbrock 600, Edelbrock RPM, stk ex mani,dual 2 1/4"w/glasspacks,200r4 stk. conv (1240stall), 7.5 w/3.42's. 25.6" tire. 80mph@2000rpm. Not willing to change conv. or gears. 3100# pig! Everything else checks out carb/timing, jetting,vac adv, no vac leaks etc. My guess is that the cam was put in 4-6 degrees retarted (reads 12.5"vac. at idle)haven't confirmed this yet.Guy that put motor together no longer works at the shop where it was built. To compound the problem seems that the cam has some real "lazy" openings/closings:
int. open -10atdc closes 24abdc
ex. open 39bbdc closes -15btdc "old school" tech?? Shouls I try a more "agressive" lobe profile cam w/ less duration??? ANY SUGGESTIONS would be greatly appreciated. Thanks, G.

[ColinOpseth]

Well,
I won't give any specific advice. That part I'll leave to the experts.

If money is no object I would convert to link-bar roller lifters if I were you and use a roller camshaft. They have higher ramp angles and you can run a cam with more duration and lift with little or no appreciable loss in driveability.

As for cam selection, you may want to give Crane Cams a call. They grind all of the cams for GM Performance Parts.

Later,
Colin

[heinz057]

you should have plenty of vac. with that cam i would check the cam install.also make sure the valves are adj. correctly. i have about the same combo im using the comp cam xe256h-10 447/445 212 /218.i also used 1.6 rockers so the lift is now 477/484 i have installed straight up. also go to bowtie overdrive to there rpm callculator a double check your mph with that combo

[GMDAD]

Colin,
Unfortunatley I'm about out of funds for this project (house honey-do's next) so going roller is out of the equation.
Yeah that low vacuum reading has me to believe that it was installed retarted. Going to check the valve adj. next.Then open up the darn thing if needed. As far as the Comp Cam is concerned I'm thinking your opening/closing rates are more agressive and your centers are on 110? Isn't that XE ground w/4 degrees adv. when "straight up"? That would make it more responsive I'm sure. B.T.W. the specs are listed earlier are incorrect. Correct ones are they are as follows;
Int: 0 atdc open /34 abdc close
Ex: 49bbdc open/-5 btdc
I'll check into Crane, Comp, Crower etc. to see what they recommend. Thanks for the replies. Just frustrated and tired of scratching my head!! Again thanks, G

[Fastmax32168]

I cant determine from your original post exactly what the problem is with how the car runs. Is it simply the lack of vacum or is there a driveability or power problem?

[barebonesracecars]

See if you can find out if the cam was degreed when it was installed.

If not, and you tear it back down, I would borrow a degree wheel (and the related tools needed) from someone if you can. Well worth the effort (which isn't all that much...just time).

I agree...with those duration numbers, I'd think you ought to have around 17" of vacuum or so.

[GMDAD]

Guys,
I'm sure that the cam was installed "straight up" as per the non-performance stock build w/r.v.cam reman mentality. Now in retrospect I'm sure that a degree wheel for these folks is a mythical tool!!!
As to the performance of the car? Downright shamefull! No low end, slow to pick up rpm and when the cam does get into its "powerband"......well....no pull, surge of power, just steady as she goes, nap while waiting to reach 80,90, 100, 110 etc. No spitting, sputtering, jerking, high rpm cutout...................nothing.
I'm no mechanical wizard but there is something really wrong here! Going to check comp. and valve adj. sometime this weekend (time permitting) and if that turns to be alright?? Well.....I guess a teardown is in order. I just keep thinking the cam was put in 4-8 degrees retarted (probably wrong keyway) and to boot the specs. indicate to my out of state friend (GM mech) that there is no adv. ground into the cam therefore compounding the problem. Hell the tired 140,00 mile 305, Q-jet, Weiand 8004, single exhaust w metric 200 (higher geared) and orig. 2.29 one legger had more huevos!!! Again, thank you guys for the advise and therapy. (Keeps me from shooting my annoying neighbors Ford Ranger) *smiles* G.

[barebonesracecars]

If they used an aftermarket 3-position (adv, str, and ret) timing gear set, it could easily be installed wrong. Some of those damn things are hard to see!

[GMDAD]

Reid,
I'm hoping that is all that is wrong with my motor (wrong keyway)
I should not assume anything. Short block was done locally, bored (probably not honed w/torque plates) cast f/t w/moly rings/ line bored (needed it) turned crank 10/10, block was NOT decked (I specified for this, didn't happen, wasn't charged, so.....) Hell they seemed suprised when I asked to "cam" that damn 305 and advised against it on a stock rebuild! Heads bought on Ebay (100% feedback); cut out for 1.94's, new springs,valves,guides,seals etc. typical 3 angle, milled .05, no port work. Motor was assembled minus tin. I should have double checked things but got in a hurry.
10 minutes into the cam break-in we had to shut her down (freeze plug leak...actually two of them... one on each side). Owner of the shop was gracefull enough to come out and remedy the problem. (stand up guy) Said he was going to have a "talk" with the kid who put it together. I hope I figure this out before I go crazy!!! One more time thanks for letting me vent! G.

[barebonesracecars]

Well, here's hoping it's something simple, and cheap.

Please let us know what you find out.

[Fastmax32168]

Heres a few random thoughts for you.
I think valve adjustment is a distinct possibility. I would definitely check that out.
If the cam was retarded it would have no low end at all, but would come on strong and pull like a bear up top.
Is the distributor lined up properly? Being off a tooth will cause exactly what you have.
Did you use the correct harmonic balancer for the timing cover? You know that some of the 305 motors had a different timing mark. You might want to check it against actual TDC.
I wouldnt be surprised if the heads are choking it off. There is a 350 in my monza with a stock set of 305 heads on it, it wont rev at all. The heads just wont flow enough to support any sort of reasonable power.

[Elfmagic]

I may be thinking about 2.02 heads but dont the 1.94 valves hit the cylinders on a 305 with a bigger lift cam like that ? Like i said i may be thinking of 2.02s please correct me if im wrong Kenny

[ColinOpseth]

Elfmagic,
I believe you have to eyebrow the top of the cylinders to use 2.02 heads. There's a tool you can buy to do that.

You should look into a set of AFRs. They're wicked, albeit a bit spendy. A great set of heads you shouldn't rule out are Vortecs. They've been called one the best GM production cylinder head designs of all time.

[GMDAD]

Guys,
Won't be able to get to the car this weekend so it will have to wait till the next one. I'll keep you posted. Unfortunatlley nothing has been cheap or easy on this car. She has fought me all the way.
B.T.W. the balancer/ timing cover are original, the outer ring hasn't slipped so I don't think the problems lie there. Going to double check everything, dist. location, weights etc.( motor only has 300 miles on it) including the valves and compression. 120# per cyl. sound right for this combo? I realize that the heads are flow deficient w/ 155cc runners and 198-204 @.500 lift (thereabouts) but I think they should be good up to 4800rpm. Roundy roundy guys use there same heads in certain classes. I figure it's making around 190-200 horse. Yeah it is the 2.02 that will cause problems on the blocks deck surface. Hey Elfmagic I agree with Colin, get a good set of heads and then you can smoke your hides in 4th!!! Thanks for all the suggestions/support everyone. Have a safe and happy weekend all. G

[mldeolde]

don't want to add to your frustration but another thing is that line bored engines some times need to use a special timing set because with out it they can be a little loose which can lead to erratic cam timing