Getting worried-----

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DesertRat

DesertRat

Leading edge boomer
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I am getting ready to assemble my engine and after reading a couple threads on cam/TDC timing I am getting concerned. Below is the spec sheet on my Lunati Hydraulic for my 273/10.5:1 pistons, LD4B with Holley 4V and stock converter 904. This mild little cam should do fine with a stock converter and a proper A/F ratio shouldn't it? I am planning in dialing it in exactly per the spec sheet.
Thanks-DR:coffee2:
 

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I believe a 112 LSA is a mild cam. #1 find/confirm TDC on the dampener. read the degreeing articles from different sources (cam grinders/youtube etc). it does take awhile to grasp it but when you do you will find it is very simple (when you get "there" it will all click in your head. pretty much you are finding how many degrees away from TDC does does the top of the intake lobe "peak" & see if that matches what is on the cam card. IE 106 is less than 108 degrees so it (the cam) is peaking earlier in relation to the crank TDC therefore it is "more advanced" than if it was peaking later at 108 degrees away.
 
My precautions would be to:
- Make sure the cam is not advanced beyond the ICL spec'd
- Push the ignition timing forward with caution
- Make a check of your true compression ratio; if you have engine data on heads, combustion chamber size, any head milling, head gasket, and other factors that effect CR, list them here

My comments involve having a mild duration cam and high Static CR; your dynamic CR may be a bit high and it might be more prone to detonation. Keeping cam advance under control and keeping the ignition advance managed will manage that situation. And your true CR is likely not 10.5:1 anyway, if you are using stock parts and Egge pistons.

So this is mainly a 'be careful' comment. We went one step large on cam choice even with AL heads and a true 10:1 SCR just to stay comfortably away from 'detonation-land'.
 
nm9stheham said:
My precautions would be to:
- Make sure the cam is not advanced beyond the ICL spec'd
- Push the ignition timing forward with caution
- Make a check of your true compression ratio; if you have engine data on heads, combustion chamber size, any head milling, head gasket, and other factors that effect CR, list them here

My comments involve having a mild duration cam and high Static CR; your dynamic CR may be a bit high and it might be more prone to detonation. Keeping cam advance under control and keeping the ignition advance managed will manage that situation. And your true CR is likely not 10.5:1 anyway, if you are using stock parts and Egge pistons.

So this is mainly a 'be careful' comment. We went one step large on cam choice even with AL heads and a true 10:1 SCR just to stay comfortably away from 'detonation-land'.
Click to expand...

Thank you men! I have studied the degreeing/timing issue enough to understand it. I anticipate a dynamic CR of 9.6-10.0 based on everything I have studied on here and other sources. My takeaway here is to make sure the cam timing is no more that the card asks for and take it easy with the ignition advance until I see what I have. I will be running fuel additives and non-ethanol premium when available. There a few sources where I can get it.
Thanks and cheers!:prayer:
 
Don't you mean 9.6-10.0 Static CR? Not sure how you can get to the level of DCR with 10.5:1 273 pistons unless you have some heads shaved, etc. That level of DCR seems Ok for a large duration, high RPM cam. Others should comment, IMO.

That amount of DCR sounds quite high......OK on the additives. They may well be needed if your DCR is that high. Not sure you are out of the woods on this.....(why I asked for the details. If you are worried, then an open info flow should take place, IMO.)
 
You are right, some of the stuff I do not know. I can tell you this, The heads are the stock 273 closed chamber heads with stock valves, new and set up to the lunati cam specs with seat pressure, open pressure and installed height using comp dual valve springs. Lunati cam and matched lunati lifters. Heads machined to straighten at .010 off with new seats and guides installed, I do not know the head chamber CC. I am using the Egge pistons 10.5:1 at
.040 over with Mr Gasket 11216 .028 compressed thickness. Stock 273 shaft adjustable rockers with 340 TA pushrods for the hydraulic lifters by Comp. I have no idea what the static or dynamic CR will be but maybe you can divine something close from the attached information. It is not too late to change the cam with something having more duration but up to now I did not think it was neccessary. Please understand, I appreciate all the advice and help and am not trying to blow anyone off. I asked for the advice. If this is a bad combination I can change it, it is not too late. BTW, I am the guy with four (count em) four master cylinders so a wrong cam choice would not me a new experience to me. I just got to reading some of the cam/timing problem threads on here and got to thinking about my own build. Thanks for asking, if I can give more information I will be happy to but this is about all I can tell you until I can run a compression reading on the engine.
TIA----DR:burnout:
 
The Wallace calculator says a true 9.7 Scr will come in around 8.2 Dcr.(EDITThat is to say, if you build it to a true 9.7Scr) This should run on pump-gas easy. This is with an ICA of 56*, which is your cam, in at 106*. So with careful measurement, as mentioned, this looks doable.
But. You said you're not quite married to that cam, so why not wait to see what the exact Scr dials in at? Then reassess the cam possibilities. If the Scr really comes in at over 10, then worry about Dcr. JMO

EDIT And this is to say, wait til after you get it all measured up. Then if the Scr is too high for your cam, you have 2 choices 1) a later closing intake, or 2) a lil more chamber volume. But if the Scr comes a lil low for your cam choice, you have the opposite choices; an earlier closing intake valve., or a lil less chamber volume.

To change the chamber volume, you can play with gasket thicknesses, or shave the pistons, or swap to the later 60cc heads.
I think it all hinges on just where your Scr can be adjusted to.It looks like you have a fair amount of choices to play with.
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FWIW, I like to run on the ragged edge of very nearly too much compression. That way I can run 91 on the weekend, when I'm likely to stand on it, but run 87 the rest of the time, letting the compression really work for me.
 
I see you are following the TMM 273 build thread and he has an SCR check in there. If that is right, then you should be OK. What is not listed there are the 2 actual head gasket thicknesses that he tried; he lists one as 'thin' (SCR in the upper 9 range, and the other as Felpro Perma torque, which could be .039" or .051". He had the heads shaved .020" more than your heads, so that helps you.

But, since this is somewhat SCR critical, I would encourage you to CC the heads, check the deck height, and then CC the piston volume below the deck; you can do all of this since it is not yet assembled (no excuses! LOL). Then the SCR can be worked out. I did it, but come out with a much higher SCR then A/J, but the dome volume is always difficult on these Egge pistons, with their limited specs, and I don't trust my numbers at this point. I'll dig some more.

If it does end up in the low-mid 9 range, then all is good and it's gonna be a perky lil' motor.
 
Well I re-read TMM's build thread and printed out the E-4 spec sheet to compare with my Lunati spec sheet. I can't see a lot of difference in the cams, mine has a little more lift and almost the same duration @ .050 lift. The only change that jumped out at me is the Isky looks to be timed @ 0 advance and I can control that on my degree setup. I do wish I had a little more duration as that seems to be the critical issue with the advice I have been getting. I can check static CR but I am confident it will be less than Mike's 9.7 SCR. Thanks to all for the input, it looks like I am going to learn to CC head chambers. Also, I need to buy a degree wheel if anyone has any reccommendations.
Thanks---Douglas:coffee2:
 
I just printed on off from here and pasted to thick poster board, and used the crank snout bolt and washer to hold it on. You have to place and cut the center hole very precisely to retain accuracy.

http://www.machinerycleanery.com/DWUniversal.htm

Cc'ing the below deck volume of a cylinder with piston at TDC would be good too, due to the vague info on the Egge piston volumes. Pretty easy to do if you can cc the heads. Or use TMM's method. (I have never done that one....)

And if you don't put in maximum ignition timing, that can help as a stopgap or permanent fix for a bit too much DCR. Or change cams. It is not a disaster at that level, just a revision.
 
Thanks for the link to krazykuda's lesson (wonderfully written BTW!) on checking compression Bad Sport. I have studied it at length and I will be making all those checks on my motor to arrive at an accurate SCR. Once I know SCR, it will be easy to decide whether to keep the cam I have or get a bigger one with more duration. I am looking forward to doing the work.
Thanks all-DR:coffee2:
 
For what it's worth, I have a Lunati 60404 in the 340 in my Duster. The compression on my 340 works out to be 9.8:1 (static), which I came to after cc'ing the heads, calculating the head gasket volume, and talking to KB about the piston volume on the KB243's because of my early 340 putting the pistons .018" proud of the deck. According to the calculator the dynamic effective compression ratio is 8.195, and the cranking compression even with the 60404 is about 180 psi on my gauge.

The 60404 is quite a bit more cam than the 60401, I posted the cam card below for it's specs. With my iron 308 heads (ported, 2.02/1.60) I run 91 octane, and run the timing at 20* advanced at idle and 34* all in to prevent detonation. It pulls 9-10" vacuum at idle. I had to pull the timing back a couple degrees to keep it from detonating with the advance all in to run it with the less than great 91 octane here in California.

So, I would definitely calculate out the C/R and consider what the dynamic compression will be before I went with a 60401. More than likely the "10.5:1" pistons won't put you anywhere near 10.5:1 for your actual static compression ratio, but I would definitely check.



Lunati60404camcard.jpg
 
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DesertRat said:
Thanks to all for the input, it looks like I am going to learn to CC head chambers. Also, I need to buy a degree wheel if anyone has any recommendations.
Thanks---Douglas
Click to expand...

I bought these:

http://www.summitracing.com/parts/sum-g1057/overview/

Pointer can be made from a piece of wire or wire coat hanger.

http://www.summitracing.com/parts/sum-980180/overview/

You can get this ^^ separately and then come up with a piece of plexiglass, cut it to size and drill a hole.

I just found it easier to buy the kit. You will need a funnel with a very small spout to fit the hole. I also picked up a syringe and put a small piece of heat shrink tube on the end to suck some of the liquid up through the hole so I could put it back in the bottle before pulling the plexiglass off, that way you don't keep losing it all over. I use rubbing alcohol with green food coloring in it, it helps to be able to see it better to be sure all of the bubbles are out.

I also bought a piston stop:

http://www.summitracing.com/parts/cca-4933/overview/


You will probably want a dial indicator as well, ifn you don't have one.

When cc'ing the heads I just use grease around the hole and work the plexiglass onto it, it was sufficient to hold it in place. Be sure to use enough so you get a good seal.
 
Dudes! We are rolling now! The DesertRat CC kit from downtown, 2 EA 60 CC vet syringes with needles, $3.50. One piece 18" X 24" X .220 lexan plexiglass from Lowes with 4 ea. 5 1/2" X 5 1/2" squares cut from piece. (bought whole piece) $22.00. Have plenty for spares. I have the dial indicator for TDC in the block. I will use the alcohol/food coloring method. Don't need piston stop as we will degree the cam in with the heads off the motor. The head gasket volume is just a math calculation. Have heat shrink in my kit already. Can't get the below deck reading until we get the pistons installed, in a week or two. Got my *** chewed by the Doctor for not taking it easy enough on my shoulder surgery so I am going to have to cool it for a while. Thanks to all for once again saving my *** from another big mistake.
The one armed DR:)
 
Careful drilling the hole in the PG, it loves to spider if the bit catches. :D

What I do is take a bit and shave off the sharp points right at the outer edge of the cutting edge, voila, nothing to catch now.

How do you plan to stop the piston in the exact same spot when going the opposite way? I suppose a fella could make one easy enough. The stop I posted is designed to be used with the heads off.
 
Get a big enough degree wheel so that you can read it but not so big that it wont fit on engine when in the car.... I have both of those now...lol

12" should be good...
And get a crank turning socket that has a provision for the wheel. Dont use the crank bolt
to hold the wheel on
 
Bad Sport said:
Careful drilling the hole in the PG, it loves to spider if the bit catches. :D

What I do is take a bit and shave off the sharp points right at the outer edge of the cutting edge, voila, nothing to catch now.

How do you plan to stop the piston in the exact same spot when going the opposite way? I suppose a fella could make one easy enough. The stop I posted is designed to be used with the heads off.
Click to expand...
Did not catch the piston stop first look. I will order it as well so we are set up properly! Thanks for the catch BadSport!
 
mbaird said:
Get a big enough degree wheel so that you can read it but not so big that it wont fit on engine when in the car.... I have both of those now...lol

12" should be good...
And get a crank turning socket that has a provision for the wheel. Dont use the crank bolt
to hold the wheel on
Click to expand...
Can you put me on to where I can get one of these?
 
For comparison, I am running this Crower hydraulic on my 273 Commando. It was rebuilt with TRW hypereutetic .030 over domed pistons. It runs on CA 92 octane 10% Ethanol premium timed at 12º BTDC without knocking.

Crower Cam Spec

Part No. 31914
Application 340 Dodge
Grind No: B.T.
Rocker Ratio 1.5:1

Adv. Duration In. 264
Adv. Duration Ex. 264

In. Lift .427 Clearance (hot) .000
Ex. Lift .427 Clearance (hot) .000

Info for degreeing @ .050 tappet lift:

Intake Opens -2 BTDC
Closes 30 ABDC

Exhaust Opens 38 BBDC
Closes -10 ATDC

Duration @ .050
Intake 208
Exhaust 208

Lobe Center 110
In. Lobe Lift 284
Ex. Lobe Lift 284

______________

http://www.wallaceracing.com/camcalc.php

Your cam has an Overlap of -12.00 degrees 
Intake Duration of 208.00 degrees. 
The Exhaust Duration is 208.00 degrees.
The Inlet Cam has an Installed Centerline of 106.00 degrees ATDC.
The exhaust cam has an Installed Centerline of 114.00 degrees BTDC.
 
mvh said:
For comparison, I am running this Crower hydraulic on my 273 Commando. It was rebuilt with TRW hypereutetic .030 over domed pistons. It runs on CA 92 octane 10% Ethanol premium timed at 12º BTDC without knocking.

Crower Cam Spec

Part No. 31914
Application 340 Dodge
Grind No: B.T.
Rocker Ratio 1.5:1

Adv. Duration In. 264
Adv. Duration Ex. 264

In. Lift .427 Clearance (hot) .000
Ex. Lift .427 Clearance (hot) .000

Info for degreeing @ .050 tappet lift:

Intake Opens -2 BTDC
Closes 30 ABDC

Exhaust Opens 38 BBDC
Closes -10 ATDC

Duration @ .050
Intake 208
Exhaust 208

Lobe Center 110
In. Lobe Lift 284
Ex. Lobe Lift 284

______________

http://www.wallaceracing.com/camcalc.php

Your cam has an Overlap of -12.00 degrees 
Intake Duration of 208.00 degrees. 
The Exhaust Duration is 208.00 degrees.
The Inlet Cam has an Installed Centerline of 106.00 degrees ATDC.
The exhaust cam has an Installed Centerline of 114.00 degrees BTDC.
Click to expand...

If I understand what I am reading, this setup is a little milder than the one I have planned. But you don't state your SCR.
 
Comp Cams #4799 $43.49 at summit

don't go cheap and get the Proform aluminum one. I read bad reviews.

These make it SO MUCH EASIER!!
 
If you seal the plexiglass to the head surface for cc'ing, keep the sealing RTV as a skim coat. A layer .006" thick will add about a CC to the measurement by itself.

Would like to see your results.
 
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