[leejoy]

Help

I just got my BB Chevy 454 engine rebuilt. Has a .060 overbore. Installed a new Comp Cams Extreme Energy Hydraulic Cam Part # 11-250-3 (.575/.578 lift) (284/296 duration at .006 lift). New lifters & springs. Also installed new MSD 6A Ignition & Billet Distributor. Have dual plane intake manifold, stock iron rectangular port heads (ported and valve job) (approximately 10.5:1 comp ratio) roller rockers, vacuum secondary 650 holley carb, headers, mech fuel pump, etc.

I got the motor running - made some adustments, ran the engine at 1500 RPM for 15 minutes to break in the cam. the only way I got the engine to idle and stay running at like 600 rpm was advance the timing a lot. when I put the timing light on the #1 cylinder, it showed a timing of about 35 deg BTDC. Is that right? If I go any less like 15-25 deg the engine stalls. If I go more like 45-50 deg BTDC it nearly stalls. I was told approximately 10-20 deg BTDC at idle (vacuum advance disconnected and plugged ) is about right for initial timing advance. But I have that huge lift and duration cam. Is that why this is happening?

Also I should add that I don't know if I have the carb and vacuum lines correct. For example, I removed the PCV valve (because I have new aluminum valve covers) and plugged the PCV vacuum line sticking out of the Holley carb - thereby reducing the intake of air and raising manifold vacuum I think and also making the engine run rich perhaps. Might that be a problem? I thought at Idle, typically the manifold vacuum is high and the PCV valve is closed anyway right? But with this extreme cam there is very little manifold vacuum anyway right? I'll hook up my vacuum gauge next time I run it and check.

Any suggestions? I took the car for a ride and it ran good but I am concerned about the initial timing at 35 Deg BTDC at idle and not sure if my timing marks are off or if that is actually the case.

[Bumpstick]

What kind of balancer...? Factory...? It could be off (slipped)...? But might also just need some tuning...? That little 650 Holley is a might small for that setup... Also if I`m not mistaken it just has the front half for idle and mixture adjustment... With that large of cam you are most likely uncovering your idle circuts and thats why it wants so much timing... A good four corner idle type carb would fix the problem... Otherwise you`ll have to modify your current carb (drill holes in the front throttle plates on the bottom)... That 454 should work good with 750`s to 950`s in cfm... Those square port heads will breath but might be somewhat soggy on the bottom but really hustle from 3000rpm and up...

[leejoy]

I learned during this rebuilt that I have a internally balanced 454 crank. I guess 454 cranks are typically externally balanced. I noticed slugs of tungsten drilled into the counterweights of the crank - so internally balanced. I check the flywheel - no weights. I checked the balancer on the front of the crank - no weights - no drilling into it. It had a keyway that matched up with the keyway on the crank so I couldnt screw it up.

With regard to the carb....yes I know the 650 is to small. It will be replaced with a 800 or 850 doulble pumper within the next year. I already spent this years budget (about $2000) under the hood on the rebuild, etc. I'm broke. I expect a carb to cost me about $300 to $450. anyway, you are right, there are idle adjusting screws only on the primary bores, not the secondaries. and yes you are right about drilling holes in the throttle plates to give it more air so that I can close the primary throttle down to a position that it still uses the idle circuits. However instead of drilling holes in the throttle plates I did something different.... I adjusted the screw for the secondariy throttle plates such that they are always cracked open even in idle giving the motor more air. it seemed to help but that was done before the rebuild....Does it matter if my vacuum line to the PVC valve is plugged or is that normal? And getting back to the original question, is 30-40 deg BTDC unusual for this type o motor setup to keep it idling?

[Bumpstick]

Yes it is very unusual for it to take that much timing...? Also by opening the rear throttle valves with no idle circut on them or any way to adjust a mixture coming out of them you may be leaning the idle to much...? (this sounds like more of the issue with the carb)The PCV valve port being plugged is ok...

Still have to ask on the balancer is it a factory style balancer with a rubber ring...?

[poncho62]

Check for top dead centre and see if the timing mark lines up. If its now internally balanced, its not the original balancer.

[leejoy]

dear bumpstick

thanks for your help thus far. Can I send you a picture of the balancer? that will tell you what type it is. It is definitely not a stock balancer because it does not look stock. and yes I know what you mean about the carb with respect to opening the secondary throttle plates and making the mixture lean but I have no choice so far. it was the only thing that allowed me to idle the motor. would drilling holes in the primary throttle plates be a better idea?

Originally Posted by Bumpstick

Yes it is very unusual for it to take that much timing...? Also by opening the rear throttle valves with no idle circut on them or any way to adjust a mixture coming out of them you may be leaning the idle to much...? (this sounds like more of the issue with the carb)The PCV valve port being plugged is ok...

Still have to ask on the balancer is it a factory style balancer with a rubber ring...?

[leejoy]

Originally Posted by poncho62

Check for top dead centre and see if the timing mark lines up. If its now internally balanced, its not the original balancer.

whats the best easiets way to check for TDC when the motor is fully assembled and installed? I agree with you. maybe it just appears that the timing is very advanced when in actuality the timing marks on the balancer and the timing tab bracket are off. Can I send you a pic of the balancer? would that help?

[poncho62]

Originally Posted by leejoy

whats the best easiets way to check for TDC when the motor is fully assembled and installed?

Use a piston stop. I made one by hollowing out a spark plug and welding a bolt into it so it extends down and contacts the piston. Thread that into the #1 spark plug hole. Turn the engine by hand so that the piston contacts the stop. Make a mark on the balancer at "0" on the timing tab. Rotate the engine the other way until it contacts the stop again....make a mark. Half way between these marks is true TDC.

Wouldn't hurt to loosen the rockers on this cylinder so the valves doesn't touch the stop.

[leejoy]

hey poncho buddy

thanks for the tips. That really helps a lot. What is your opinion on the timing being approx 35-40 deg BTDC at idle with my setup (big cam). Is that considered normal or is something definitely wrong?

[curtis73]

This whole scenario is not shocking to me at all. Initial timing (especially with a hairy cam) is best when advanced very far at idle. Mine is locked at 36, but I can get away with that partly due to 8.6:1 CR.

Where the timing actually is at idle is pretty inconsequential. In real life you'll probably have to back it off to the mid 20s to get an acceptable curve under low RPM load, but don't worry about where it runs "right" at idle. Mine will run smooth as silk at 40 BTDC at idle with my low CR and old-school open chamber heads.

[leejoy]

hey buddy

thanks for your help. I need it. can you come over an help me with it? Just kidding. I'm in chicago area. How bout you? Anyway I am in the process of testing and tuning the motor after the rebuild and learning how to do this. first time for me. I know how engines work but tuning and troubleshooting them is another story. I have to mess around with the centrifugal spring weights also once the engine is running good. I've got the MSD distributor with interchangeable springs for the weights. I've got carb issues too I think. I'm running a holley 650 (I know it's small) vacuum secondary carb with adjusting needles only on the primaries. in order to keep it running I had to crack open the secondaries a bit (with adjusting screw) and back off the primarys such that fuel would be drawn from the idle circuit ports and not the transfer ports if you know what i mean.

[curtis73]

Look around the last couple days of posts. There was another poster who had BBC timing issues of a similar nature. There is really good stuff in that thread.

I'm in Los Angeles. I'll come help you... be there in about a week. Just kidding.

[leejoy]

thanks buddy

yes LA is to far away. I will search that thread like you said. thanks again for your help - I really need it.

Lee

[curtis73]

Sure thing. Shoot me a PM if you have more questions after you read that thread.