Bad Valve Guides?

[folkenheath]

For dynamic compression I just calculate the remaining stroke left after the intake valve closes, so lower stroke, but compressed down to the same combustion chamber. The main factor in the difference is the intake valve closing point, but the connecting rod length also plays a small role in the dynamic as it can change the motion of the piston slightly with the same stroke.

For a SBC or BBC I usually shoot for around 8:1 or so, I have my 489 at 8.2. For a LS I would say 8.5 is good. You don't want to be much higher than those numbers for premium pump gas.

This lets you push the compression more to real world results. For example, my 489 has 10.2:1 static compression and an 8.2:1 dynamic. However, the BBC in my regal has 11:1 static compression, and only 7:1 dynamic. The major difference is the camshaft is much larger on the regal BBC, and the intake valve remains open for at least another 20 degrees or more of crank rotation. I would of gone higher compression on the regal but I stayed with an off the shelf piston.

But this is one of the tools I use to optimize the camshaft and compression ratio to work together. The larger the cam, the more static compression you can get away with.

 

[folkenheath]

Figuring dynamic compression, is not something I have a lot experience with. What would be an acceptable dcr for reg pump gas and street performance

Well I just wrote a whole response, clicked post, and two of them showed up, so I deleted one and now they are both gone... Can you restore what I deleted?

I'll type it again later..

 

[Wes Harden]

Well I just wrote a whole response, clicked post, and two of them showed up, so I deleted one and now they are both gone... Can you restore what I deleted?

I'll type it again later..

I saved it for you.

Good info, I am learning.
The intake on most cams closes after top dead center, to increase dynamic comp would you want it to close sooner or later ?

 

[folkenheath]

I saved it for you.

Good info, I am learning.
The intake on most cams closes after top dead center, to increase dynamic comp would you want it to close sooner or later ?

Thank you, you are good! It wasn't that long, I just don't like typing, especially twice.

The intake typically opens before top dead center (BTDC), but doesn't usually close until after bottom dead center (ABDC). It's a balance of flow and cylinder pressure, because the longer the valve stays open, the more air has time to flow in, but the lower the dynamic compression ratio will be, so you may end up with lower cylinder pressure if you hold it open too long for the RPM targeted. Wider duration is better for high RPM power, and lower duration is better for low RPM torque, for more than one reason.

The intake valve closing is dependent upon the intake duration and the intake centerline (ICL). The higher the number ABDC, the later it closes, this would be associated with a larger intake duration or retarded camshaft timing. Advancing the cam closes the valves sooner for more cylinder pressure at lower RPM but less flow at higher RPM.

 

[Wes Harden]

ahh, that make sense to me. I had confused atdc with abdc. This is helping push me toward advancing my cam. I wish I take better measurements and written them down when I built my engine 20+ years ago.

 

[folkenheath]

ahh, that make sense to me. I had confused atdc with abdc. This is helping push me toward advancing my cam. I wish I take better measurements and written them down when I built my engine 20+ years ago.

Many cams are ground 4 degrees advanced from the factory, but the only way to know exactly where you are for your engine combo is to degree it in. Often I don't need to move it, but I have had to move several, and one time I caught an error of 12 degrees! It was a used timing set and I replaced it and the problem went away.

 

[Wes Harden]

While I have the tool and ability to degree this cam, it is an assembled running engine in the truck.
I am judging the possibility of advancing the cam on the rpm where it starts to pull well. That is @2700, I would like that to happen at say 2400-2500 rpm.
Nothing on this engine is designed for hi rpm performance

 

[tarussell]

While I have the tool and ability to degree this cam, it is an assembled running engine in the truck.
I am judging the possibility of advancing the cam on the rpm where it starts to pull well. That is @2700, I would like that to happen at say 2400-2500 rpm.
Nothing on this engine is designed for hi rpm performance

Wes, if you’re gonna go through the effort to validate and degree the cam in your motor ya’ might as well just go ahead and put one of them big-ole motors in it - a proper 454 will cure damn near any power curve cravings.
Ya’ know you want to - just do it.
Small blocks are measured in cubic inches and big blocks are measured in cubic feet ( I have to give credit to NVRENUF for that calculation - he pulled that one on me back in 1990 and that’s when I converted over to the big motors ).

You’ll never lack for power again at any RPM.

 

[Operator238]

Can I get a cam spec’s that would manipulate a higher DCR?

Before I pull the trigger on an LS or LT, is this motor worth saving or move on? If I move on, I’m worried about my 700R4 behind it. If I need to swap to a different transmission, which? Then the transfer case adaptability comes into question.

 

[Wes Harden]

if you ls swap with a 5.3 or mild 6.0 they came with 4l60e's, which is newer model number for the 700r4. Your 700r4 will live behind them, TV cable correct and kept cool.

 

[folkenheath]

Can I get a cam spec’s that would manipulate a higher DCR?

Before I pull the trigger on an LS or LT, is this motor worth saving or move on? If I move on, I’m worried about my 700R4 behind it. If I need to swap to a different transmission, which? Then the transfer case adaptability comes into question.

You can, but it will be a compromise toward more bottom end and less midrange/top end.

if you ls swap with a 5.3 or mild 6.0 they came with 4l60e's, which is newer model number for the 700r4. Your 700r4 will live behind them, TV cable correct and kept cool.

I agree, SBC or LS, leave the 700R4, it has a larger gear range, if he finds a big block, then ditch it for a TH400 or 4L80E.

 

[Operator238]

So can I pull the trans, engine and transfer case out together ….or do I need to remove the transfer case where it mates to the transmission?

 

[folkenheath]

You can pull it out all together but it's a little more cumbersome.

I would probably disconnect the trans from the engine and leave the trans/tcase in the rig.

 

[Operator238]

Alright well I picked up this Gen 4 6.0 (LY6). Has some great cross hatching. Trying to figure out what cam to put in. It’s got the big dog 823 heads

 

[folkenheath]

Nice! That will surely wake up with a cam and headers!

It looks like they used the cathedral rocker arms on the rectangular port heads, we will need to fix that.

Are you using a factory computer or going aftermarket?

You just need some motor swap plates and some swap headers.

You may also need an adaptor flexplate to reuse the 700R4 trans.

 

[Operator238]

Nice! That will surely wake up with a cam and headers!

It looks like they used the cathedral rocker arms on the rectangular port heads, we will need to fix that.

Are you using a factory computer or going aftermarket?

You just need some motor swap plates and some swap headers.

You may also need an adaptor flexplate to reuse the 700R4 trans.

I wondered why the rocker tips were not square on the stem! I don’t see any tab coming off the head gasket. Should I do a leak down test? I have all the equipment to do it.

 

[folkenheath]

It can't hurt to get a baseline because they obviously did some work to it.

Did they reuse the head bolts? That's a big no go on those torque to yield bolts.

 

[Chickntrk]

It’s concerning to me that someone was in there already…..do you know history on this engine? I’ve seen LSs go 300,000 without being torn down so I’m curious as to why someone was into this one

 

[Operator238]

What do these numbers mean?

 

[Operator238]