engine timing dilema

[GREASEMONKEY72]

if it cant go any lower with backfiring through the carb then it sounds like the timing chain is off

[bhunt31]

Greasemonkey is probably 100% right. I'm sure we've all done it at least once...well, I have anyway...funny story...shows my lack of attention...not gonna tell it! hahahaha! Same thing happened to mine, check the timing chain...bet that's where you'll find your problem.

[cruiserman]

Originally Posted by 69chevyshort

well iguess the hole i drilled fixed it, i also BURPED the system a little more , and i got a few more air bubbles to come out. as far as the temp is concerned anyway.

I was going to suggest burping the system. I bet that was the problem. You shouldn't need to drill the t-stat.

[hotrod 80]

Check crank timing with a piston stop before tearing apart the motor . Verify #1 is at TDC and timing marks are lined up with the timing tab and valves on #1 are closed ( not 180 out ) . This will eliminate crank timing (slipped balancer ring ). Next verify the distributor is pointed to #1 . If this is in the correct position , then cam timing is the next check . If the motor ran good before the swap then distributor placement or cam timing should be the only variables .

[60ratrod]

an older dampener slipping wouldn't take much since there is a main steel body with a band of rubber sandwiched in between the outter ring and the main body. when i overhaul a motor that is one thing that i replace regardless.

[SCOTI]

Originally Posted by hotrod 80

Check crank timing with a piston stop before tearing apart the motor . Verify #1 is at TDC and timing marks are lined up with the timing tab and valves on #1 are closed ( not 180 out ) . This will eliminate crank timing (slipped balancer ring ). Next verify the distributor is pointed to #1 . If this is in the correct position , then cam timing is the next check . If the motor ran good before the swap then distributor placement or cam timing should be the only variables .

I agree w/this line of thinking. It ran before the top end swap so the balancer is most likely not the culprit. Checking TDC accurracy & working from there would be my approach . . .....

[Painter D]

if the cam or the timing chain was off from where its supposed to be, wouldnt it run really bad? because it runs really good the way it is now ,it just doesnt make sense mathmatically. also could the reason it backfires through the carb if i take it lower on the timing be something in the carb.

[bhunt31]

Originally Posted by 69chevyshort

if the cam or the timing chain was off from where its supposed to be, wouldnt it run really bad? because it runs really good the way it is now ,it just doesnt make sense mathmatically. also could the reason it backfires through the carb if i take it lower on the timing be something in the carb.

When I accidently installed my timing chain 4 teeth off on a single chain set(much wider than a double), it still ran, didn't run so good, had the distributor turned about 90* to where it was suppose to be. When you degree in a cam, that's what you do, you move the cam a tooth or 2 from the crank to retard or advance the cam. I run all my cams at 4-6* advanced, meaning the intake will be fully opened 4-6* before a normal cam. So, if you're familiar with cams, you know what the ICL is and on most SBC 106-108 is optimum, advancing the cam allows you to reduce the ICL by 4-6* and you can gain some pretty good HP out of the deal.

[Sport/Truck]

The new timing sets have different key sets on the crank gear to allow for more advance (& retard) of timing. If it was put on with advancement wouldn't you will need to add that into the number showing on the balancer?
s/t

[bhunt31]

Originally Posted by hotrod 80

Check crank timing with a piston stop before tearing apart the motor . Verify #1 is at TDC and timing marks are lined up with the timing tab and valves on #1 are closed ( not 180 out ) . This will eliminate crank timing (slipped balancer ring ). Next verify the distributor is pointed to #1 . If this is in the correct position , then cam timing is the next check . If the motor ran good before the swap then distributor placement or cam timing should be the only variables .

The only way he can check to make sure the cam is in right is to look at the rockers with #1 at TDC. The distributor is variable, it'll go in 30 some different ways.

[bhunt31]

Originally Posted by Sport/Truck

The new timing sets have different key sets on the crank gear to allow for more advance (& retard) of timing. If it was put on with advancement wouldn't you will need to add that into the number showing on the balancer?
s/t

Yeah, it will fire a little bit earlier since all cam events are happening sooner, but I'm running a 292H comp cam that's on 6* total advance and I'm still only running about 35* full advance.

[hotrod 80]

Originally Posted by 69chevyshort

if the cam or the timing chain was off from where its supposed to be, wouldnt it run really bad? because it runs really good the way it is now ,it just doesnt make sense mathmatically. also could the reason it backfires through the carb if i take it lower on the timing be something in the carb.

This is what leads me to believe it's only a tooth off . Mine ran really good a tooth off , but showed the funny readings you are describing . It ran a 12.20 1/4 mile a tooth off . I pulled the distributor in the pits and moved it a tooth and the timing readings made lined out and I timed it again and ran a 11.98 . I also don't run vacuum advance and have my advance springs just strong enough for timing not to fluctuate at idle . If you now have a low vacuum at idle situation they make a low vacuum advance pot to compensate for it .

Is the carb new to the combo ? I was thinking this was a running combo that you did a cam and head swap on . if it is a new motor or has more than a cam and head swap there my be more than a timing issue creating you situation .

[Billla]

I tried to read through the whole thread so I hope I'm not just restating the obvious

39 degrees total timing (w/vacuum advance) is definitely wrong; should be around 36 degrees mechanical advance by 3000 and then around 50 with vacuum advance.

So the question comes down to the references being wrong (TDC pointer) or the cam installation. If you've already VERIFIED TDC (the ONLY way to do this is in the car without pulling a head is with a piston stop) then IMHO it's time to pull the front cover and recheck the timing gear install. It's maybe 4 hours work...and you'll spend a lot more timing chasing ghosts until you do that. Once you KNOW those two are right then we can get back to timing and then finally carb.

I'll respectfully disagree that advancing a cam adds HP - it only changes where in the RPM range the HP is generated. Advancing the cam moves the power curves lower in the RPM range - about 500 RPM for each 4 degrees as a general rule of thumb. Also - this is something for an advanced engine builder, as it affects MANY other engine variables. Best to buy the right (or custom) cam than to "re-engineer" a cam by installing it any other way than "straight up".

[SCOTI]

Originally Posted by Billla

.....I'll respectfully disagree that advancing a cam adds HP - it only changes where in the RPM range the HP is generated. Advancing the cam moves the power curves lower in the RPM range - about 500 RPM for each 4 degrees as a general rule of thumb. Also - this is something for an advanced engine builder, as it affects MANY other engine variables. Best to buy the right (or custom) cam than to "re-engineer" a cam by installing it any other way than "straight up".

Too add to this..... most cam manufacturers build the 'off the shelf' type cam grinds w/the advance already figured into the design so it can be installed 'straight-up' which is where 99% of novice installers will need it.

[Painter D]

alright guys heres where im at,the temp problem is totally fixed. i put about 40 miles on the truck today and it ran great. i called trick flow and they told me sometimes timing sets are drilled wrong in other words the dots you are supposed to line up might be off. i said good thing you told me that, now that i am where i am, nice QC. but im not sure thats what happened. im starting to lean more towards the carb. it seems the more i mess with the carb the better the whole situation gets. its definately making some power, so much power i can hardly keep from spinning both back tires. but it also seems to be different each day, for some weird reason. any other tips?

[Painter D]

oh yeah when we did all this we checked all the TDC ,valve,balancer, stuff. and if it does come down to checking the timing set ,i have a 2 piece timing chain cover to make the job easier.

[bhunt31]

Originally Posted by SCOTI

Too add to this..... most cam manufacturers build the 'off the shelf' type cam grinds w/the advance already figured into the design so it can be installed 'straight-up' which is where 99% of novice installers will need it.

I'll agree with you on the advance ground in, but most of Comp's single pattern cams aren't set up with advance ground in(straight from the Comp Tech's mouth)

The other thing about advancing the cam timing not increasing hp. I won't say you're wrong, I'll just say that I have published proof, in the form of professional testimony and dyno graphs, that it does, from David Vizard, one of the premier Chevrolet engine builders of the 20th century.

[Billla]

Originally Posted by bhunt31

I'll agree with you on the advance ground in, but most of Comp's single pattern cams aren't set up with advance ground in(straight from the Comp Tech's mouth)

The other thing about advancing the cam timing not increasing hp. I won't say you're wrong, I'll just say that I have published proof, in the form of professional testimony and dyno graphs, that it does, from David Vizard, one of the premier Chevrolet engine builders of the 20th century.

Every cam has some level of advance ground in - so the statement doesn't make sense.

Please, share the Vizard references - I have all of his books (and others) that state very clearly that advance is about WHERE the power is made vs. how much. Billy G from CompCams has also noted this in his tech talks, and both Car Craft and Hot Rod Engine Masters have done tests with cam advance and found little if any power increase (single digits) but significant differences on where in the RPM range peak power is made. I'm very comfortably saying that you're wrong (in a friendly way )

[UPDATE]
From the SA book "High-Performance Chevy Small-Block Cams & Valvetrains"

"Typically, advancing a camshaft...generally improves low-speed and mid-range power while hurting high RPM power. Establishing when the intake valve closes in relationship to TDC does more to shape the engine performance curve and the RPM point at which peak torque occurs than any other single cam factor."

[bhunt31]

Originally Posted by Billla

Every cam has some level of advance ground in - so the statement doesn't make sense.

Please, share the Vizard references - I have all of his books (and others) that state very clearly that advance is about WHERE the power is made vs. how much. Billy G from CompCams has also noted this in his tech talks, and both Car Craft and Hot Rod Engine Masters have done tests with cam advance and found little if any power increase (single digits) but significant differences on where in the RPM range peak power is made. I'm very comfortably saying that you're wrong (in a friendly way )

[UPDATE]
From the SA book "High-Performance Chevy Small-Block Cams & Valvetrains"

"Typically, advancing a camshaft...generally improves low-speed and mid-range power while hurting high RPM power. Establishing when the intake valve closes in relationship to TDC does more to shape the engine performance curve and the RPM point at which peak torque occurs than any other single cam factor."

"Typically, advancing a camshaft...generally improves low-speed and mid-range power while hurting high RPM power."

didn't have to, you did it yourself.

[bhunt31]

Originally Posted by bhunt31

"Typically, advancing a camshaft...generally improves low-speed and mid-range power while hurting high RPM power."

didn't have to, you did it yourself.

So, tell me where either of us were wrong, really. You said it changes where peak power comes in, and yeah, it does, but I said you can see some pretty good power out of doing it, which again, you can. Would you happen to have the books "How to build a Max Performance Small Block Chevy on a budget" and "How to build Big Inch Small Block Chevys"? In both of those books they go into how advancing a cam can help add power. Just about every one of his engines that he presents is set up with between a 4-6* advance on the cam. When you start dealing with long duration, tight LCAs degreeing and advancing take on a whole new level of performance tuning. I've built 406 stock car engines that if the cam wasn't advanced 4*, you'd lose 10hp on the high side. So putting it in straight up, would've given 650hp, 4* advance would've given you 660hp, so advancing can create horsepower.

[bhunt31]

Originally Posted by Billla

I'm very comfortably saying that you're wrong (in a friendly way )

absolutely, I'm not getting upset about it. We can have a civilized discussion without arguing. I have a feeling though, it's just a plain misunderstanding, and not so much differing views.

[Billla]

Originally Posted by bhunt31

So, tell me where either of us were wrong, really. You said it changes where peak power comes in, and yeah, it does, but I said you can see some pretty good power out of doing it, which again, you can. Would you happen to have the books "How to build a Max Performance Small Block Chevy on a budget" and "How to build Big Inch Small Block Chevys"? In both of those books they go into how advancing a cam can help add power. Just about every one of his engines that he presents is set up with between a 4-6* advance on the cam. When you start dealing with long duration, tight LCAs degreeing and advancing take on a whole new level of performance tuning. I've built 406 stock car engines that if the cam wasn't advanced 4*, you'd lose 10hp on the high side. So putting it in straight up, would've given 650hp, 4* advance would've given you 660hp, so advancing can create horsepower.

I have both of those books, and neither support your position. Your position, if I understand it, indicates that MORE power is possible - my position is that this is not the case and that changing the timing of the cam only impacts where in the RPM range peak power is made.

I don't think a stock car engine is what the original poster was building, and I question your math that advancing the cam ADDED top-end power. This is counter to every cam theory (and practice) I'm aware of. You even note in your response that advancing changes where the power comes in...so how do you reconcile a 10HP gain at 6000 RPM? And, of course, talking about peak power without noting the RPM it occurs at means nothing

In "budget" book, he advances the GM "929" cam and the CompCams 268H cam 4 degrees in his first 3 engines and the #8 engine (4 out of 10 installed advanced) specifically because he wanted the power lower in the RPM range as they were a street engine with street gearing. For the 929, he was working to take an already "torqy" cam and move it down into the most commonly used range (#2 was for his 1974 pickup ) For the CompCams 268, the goal was the same - to make more torque lower in the RPM range. He's specifically giving up high-RPM HP to make low/mid-range torque.

Making a statement like "pretty good power" suggests that people take this approach without fully understanding what they're doing - as you note, Vizard is a very experienced builder and so is doing the right checks and balances to ensure issues like decreased valve clearance, etc. are taken into account. Other factors such as the heads used (All the Vizard engines had heavily modified "camel hump" heads with big valves) gearing, etc. all come into play.

What I say is "wrong" is that you're advocating installing a cam advanced without any knowledge of the engine, gearing, etc. Making a decision to do this is part of the overall build process and requires an engine builder that knows what they're doing....and one that can't find the advance they want in a stock cam.

I'm building a '95 LT1 383 right now with the GM "HOTCAM"....installed 4 degrees advanced. This is because the cam was designed to produce peak power at 6000 RPM (and has validated this with many dyno runs) and I have a self-imposed 5500 RPM redline due to a 2-bolt main block and cast crank. I expect the same power, about 500 RPM lower...and many published dyno runs show that's exactly what I'll get.

[hotrod 80]

69chevyshort , any update on your problem?

[Painter D]

well the truck runs great, the total timing is still at 39 deg. (i think) i tuned a little more on the carb and got it to run perfect , i was starting to lean towards the carb on the backfire issue anyway. i think it was dumping too much fuel all at once and thats why it backfired through the carb. (if that makes sense) either way if it aint broke, i dont fix. ive put about 100 miles on it since , the only problem i have to figure out now is this traction thing,LOL when i give it the gas both back tires go up in smoke.

[bhunt31]

Originally Posted by Billla

I have both of those books, and neither support your position. Your position, if I understand it, indicates that MORE power is possible - my position is that this is not the case and that changing the timing of the cam only impacts where in the RPM range peak power is made.

Do you see where he said that a cam too retarded will hurt performance? A cam can be installed straight up and be too retarded for the engine...that's what I'm getting at. A cam installed 4-6* advanced won't hurt anything for a street engine when it comes to power, but a cam 4-6* retarded will drop power, throughout the band. I do also remember reading him say that "SBC engines run best with between 4-6* advance in the cam" and that's where I run every one of mine and have never had an issue with expected power. It depends a lot on the LCA of the cam. A cam with a 112 LCA will benefit from having 4* advance to bring the LCA back down to 108* where 383 cubes and under run best at. It varies from cam to cam. The cam I bought had a 112 LCA, so I advanced it to put it back down where it needs to be. If you bought a cam with 106-108 LCA, it wouldn't need advancement, it'd be good straight up.