Ignition Module Failure....???"

[Tim81]

There has been a lot written about the ideal quench of .040, with that said I would seriously consider what the car is being used for? Here is a engine with zero deck clearance that his already kissed a valve. I doubt if anyone would notice the difference between .040 and .050 quench and with alum heads you shouldn't have to worry about detonation. not trying to disagree with anybody here the tighter the quench the better to a certain point...Good Luck with putting it back together...Tim

 

[LannyL81]

Peer81

To ge honest, the CR gives you a good indication. But with the program Gerry has you have to look at the DR! Your 280 cam with 1.6 rockers will bleed off so much air (or compression) that I think you can get away with the 64cc's

Yes it does.....way too much overlap.....I have the wrong cam!!
​

 

[GerryLP]

To ge honest, the CR gives you a good indication. But with the program Gerry has you have to look at the DR! Your 280 cam with 1.6 rockers will bleed off so much air (or compression) that I think you can get away with the 64cc's.

When I look at Gerry's compression a CR of 9.5 is nice but the DR is 7.0 and 8.25 is about the max you can have with iron heads. So still a full piont of compression to squeeuze out/improve.

Greetings Peter

Peter,

I was trying to figure out what I may have done wrong, and when I compared the XE268 cam data, I noticed that that I had entered exhaust valve opeing (74 deg) in place of intake valve closing, which is 60 degrees @ 0.006".

So thank you for alerting me about my numbers. Thanks!

Here is what it reads when I corrected the intake valve closing value...

Dynamic CR really illustrates how well the combination of parts in the engine come together to arrive at one goal.

 

[GerryLP]

Gerry,
I do not know what the distance is between top of piston when at BDC and the block deck is....is that supposed to be 9.000cm?

3.48"/2 (stroke) + 5.7" (rod lenght) + 1.56 (compression height) = 9.000" or zero deck

At TDC the distance is zero to slighty negative by a few 0.001's....will have to measure again.

If the piston is lower than the deck, then it is called "in the hole", and therefore however thousands of an inch that comes out to be, then you add that to your deck (for example 0.005" in the hole = 9.005" deck.

The head gaskets I have found have a compressed thickness of 0.040"....but I do not have the bore dimension in front of me...4.066 to 4.125....or so.

Use these to fine tune the quench and/or CR. On a zero deck block, you definetely DO NOT want to be less than 0.040" quench (if accurately measured; if eyeballing it, then add 0.005" to avoid harmful errors).

With the 882 heads I had a static CR of 9.1 something and that was with 75cc heads. If I went with a 64cc head the CR would be well over 11:1 and would require higher octane than pump gas. Now with aluminum I could go with 70cc or 64cc....more likely 70cc and still get by with 91 octane pump gas.....64cc may be pushing that a little due to the hot air temps of summer in Tucson.

Remember that advertised values will yield advertised "lies". When I cc'ed my Vette's original heads, they were coming in at nearly 78 cc's (not the advertised 74 cc's). Measuring pays off later on when you are trying to figure out why your engine comes out a limp noodle or why it is popping at 4K RPM.

The cam is only the Comp Cam 280H and I am using 1.6 roller tip rockers. The E-Street heads from Edelbrock will go for over 0.500 lift where I am about 0.480. Not changing cams as I have the CCC and this is supposed to be the largest cam I can use and still use the CCC....at least that is what Comp Cams told me.

Remember that the cam data for the CS268H is based on 1.52 rockers, so if the cam has 0.315" lobe lift when multiplied by 1.52", the gross lift is 0.480", but when multiplied by 1.6", the gross lift is .505". Also, the valve stays open longer, so your valve timing changes. A degree wheel will help you come up with your own customized valve timing numbers.

Also I really do not want to pull the cam out. I do need to check the lobes and need a good method for doing that.....know one?

What do you mean with "check" the lobes???:confused Are you thinking a lobe may have gone flat?

GerryLP:cool

 

[LannyL81]

Gerry:
Can you explain the first equation; 3.48/2....and the compression height? Why is the stroke divided by 2...and what is the compression height a measure of?

I will still need to actually make a measurement, but the piston at TDC is zero or slightly above the deck.

I did cc a chamber on each head when installed some years ago and of course I have lost the numbers. The 74cc is an estimate...since they were "supposed" to be 75cc and they were shaved a bit to make them flat.

Checking my cam card I have slightly different numbers: lobe lift is 0.3020 with 1.50 ratio, yielding gross valve lift of .454. With 1.6 ratio rockers I get 0.483. The springs I have on my GM 882 heads were supposed to be good for over .500.....key word here is "supposed".

As far a the cam lobes...I just want to check the lobes and make sure none have gone flat. I was thinking of using a dial indicator and measure the distance the lifter raises as I rotate the crank.

What does your DCR calculator show for my engine?

Thanks for all the help.....I think I need it.

 

[GerryLP]

Gerry:
Can you explain the first equation; 3.48/2....and the compression height? Why is the stroke divided by 2...and what is the compression height a measure of?

I will still need to actually make a measurement, but the piston at TDC is zero or slightly above the deck.

The 3.48" stroke is the total distance that the piston's pushrods (with a typical length of 5.7" on 350 CID applications) travel while mechanically attached to the crank journals. The deck is measured from the imaginary centerline of the crankshaft. So you divide the total stroke by two.

Compression height is the distance between the wrist pin and the top of the piston. Different manufacturers offer many variations of this measurement to accommodate different applications. The link below explains further.
Compression Height - Lunati Power

I did cc a chamber on each head when installed some years ago and of course I have lost the numbers. The 74cc is an estimate...since they were "supposed" to be 75cc and they were shaved a bit to make them flat. Checking my cam card I have slightly different numbers: lobe lift is 0.3020 with 1.50 ratio, yielding gross valve lift of .454. With 1.6 ratio rockers I get 0.483. The springs I have on my GM 882 heads were supposed to be good for over .500.....key word here is "supposed".

I think I still have your data, or at least the one we began back in 2007. If the valve springs are actuated beyond what they are designed for, they'll often experience binding.

The duration timing on your engine's intake and exhaust valves change from modifications to the valve train. Let's pretend that the intake closes on your engine's cam at 60 deg BBDC IAW the cam card. But that is with a gross lift of 0.410 (for example). Now, let's pretend that you installed 1.6" rockers, and so by the time the engine reaches 60 crankshaft degrees of rotation, the valve still has approximately 0.021" of travel to close, yet the crankshaft degrees keep ticking another 3 or 5 degrees until the valve closes. Therefore, your new valve closing BBDC is 65 degrees, and this affects the Dynamic Compression Ratio or DCR. This can also cause problems, for "who" else is moving right along with the crankshaft degrees??? That's right! Pistons!

What does your DCR calculator show for my engine?

Thanks for all the help.....I think I need it.

I'll post an image of the 2007 data on your engine.

 

[GerryLP]

Lanny,

This is the only file I have on your engine. I am not sure at what stage of your buildup these numbers were input. I am not sure if this is what you were trying to attain with your engine, or if it was something with which you were trying to experiment. Also, there may be errors on data entered, but you are the only one who can recognize which data point is trust worthy or consistent with your engine's details.

Let me know which entries you need changed, and then I'll show you the result in this thread.

p.s. the date on this file is 12 Feb, 2007

 

[LannyL81]

Understand compression height...1.56" is correct
Understand the change in duration due to changing rocker ratio.
Looking at the data in the chart, the intake valve closing, it should be 60 ABDC.
Do not know the piston distance from top of piston to first ring, pistons are H631CP30..
Deck clearance height....I recall making that measurement but just do not have those numbers...I do not think it is -0.006 though...time to get the calipers or dial indicator out again.

When I was looking at the cam data card.....and getting re-educated on cam specs....I think I bought this cam as I was going to do a 383....then I changed my plans due to budget constraints at the time....this cam is for a 383....not a 350. It has an LCA of 106.....no wonder I have no compression pressure when I did the measurements.....

So new cam it will be. In fact all new top end. But this time since computer applications are readily available....I will be able to match the cam to the heads and finally have a proper working engine.

Gerry....would like your help and your program. I will send you the block measurements as soon as I can. Will also send the cam specs from what Comp Cams recommends using Cam Quest......need to determine if the 1.6 rockers need to be replaced...what chamber size heads to get, 64 or 70 cc.


Thanks for the help.

 

[GerryLP]

looking at the data in the chart, the intake valve closing, it should be 60 ABDC.

Yes. It is. I should have made my example consistent with an actual cam. :ugh

Do not know the piston distance from top of piston to first ring, pistons are H631CP30..

I tried to find it on line, but could not find it. But the sample data that came with the software uses 0.3" height. I measured my with the Sealed Power H618CP20 piston in my Vette's engine, and those are 0.282. The difference between the two is a mere 0.01 in the CR. So can split the difference if you like and go with 0.291" if you like, but we're probably splitting hairs.

The 0.3" value is reflected on the chart as of now and the 60 deg ABDC value.

...So new cam it will be. In fact all new top end. But this time since computer applications are readily available....I will be able to match the cam to the heads and finally have a proper working engine.

Gerry....would like your help and your program. I will send you the block measurements as soon as I can. Will also send the cam specs from what Comp Cams recommends using Cam Quest......need to determine if the 1.6 rockers need to be replaced...what chamber size heads to get, 64 or 70 cc.

Lanny,

I will help you with whatever I can, bro.:L

You were saying earlier that your dampener has a 90 degrees scale on it. When you measure your TDC height of the piston in comparison with the deck, take the time to see if TDC is where the dampener says it is...just to make sure. Get that TDC tool at the local speed shop. Get the one used when the heads are off. You are gonna have to back it off TDC in the compression stroke and once the tool is installed, let the set screw to protrude just a few thousands of an inch. When you rotate the dampener towards TDC again, gently push it until it hits the tool above the piston. mark on the scale with a grease pencil the degrees. Then rotate the dampener in the opposite direction until the piston gently touches the tool again, and mark the scale on the dampener with a grease pencil as well. the exact middle between the two marks is TDC.

That gives you true TDC. It may come to be a degree off in either direction of the "0" mark on the dampener. The true deck height measurement can only be made with the true position of the piston at its true TDC.

On another subject, consider going back to 1.52 rockers and keeping the cam (if you want to save money). If you want to mimic a dual pattern cam (different lift/duration between intake and exhaust), you can opt to use the 1.6 rockers on the exhaust valves.

 

[LannyL81]

The numbers you have for the piston is close enough.

The trouble with the cam I have is the LCA...106 is just too much overlap. So I have been using Comp Cams Cam Quest and I like either the XE256 or XE262 grinds. The XE256 I could use the 1.6 rockers...the XE262...maybe not. Need to figure out which head chamber size to use as well.

I will find exact TDC using the method you described next week.

Thanks for the support. Like I said I want to get this correct this time.

Okay....I confused two numbers above.....the LCA or lobe separation angle of my cam is 110, not 106...that is the intake center line from TDC intake stroke. The overlap on this cam is 48 degrees...with 1.5 rockers...and just a bit more with the 1.6 rockers....just where I wanted it. So I will probably keep this cam afterall.

 

[GerryLP]

I found a couple of articles on lobe separation or lobe cam angles if you feel like reading...

http://www.hotrod.com on cam_lobe_centerline_angle_tech

http://www.chevyhiperformance.com on camshaft_lobe_separation_angle_-A performance_test

 

[Tim81]

Lanny, You might want to look into a Melling MTC1 cam. I'm using this cam in my motor which is very similar to yours. I am very happy with it but you may be looking for more power. I am also using 1.6 ratio rockers with this cam and the computer seem to be happy with it as well. The duration @50 is 204/214 with a LSA of 112, maybe too mild for you I don't know. Lift with 1.6 rocker arms is .448/.472. I can tell you that the idle is very smooth and the response is very good from off idle to about 5K rpms. My Static compression is just under 9:1 and total FWHP is around 310. Not a monster but a lot better then stock. I am using a older Weiand 8000 Action-Plus intake with stock Chevy 487X heads...Tim

 

[LannyL81]

Tim...what is the chamber size of those heads? What octane do you have to run?

 

[GerryLP]

Lanny,

Here is the calculation on your engine with 70 cc's chamber heads and a 0.051" gasket....check out that CR and that quench!

The 64 cc heads will bump CR to 9.7 and change.

p.s. See page 4 on this GM catalog, and you'll find that 0.051" gasket
see page 60 (page 4 of document) for 12557236 — Composition Head Gasket

 

[Tim81]

Tim...what is the chamber size of those heads? What octane do you have to run?

The heads have a chamber size of 75cc 1.96 intake and 1.5 exhaust. These are stock open chamber heads used on early 70's LT-1 motors. I couldn't afford new heads and there was no way I was putting the stock 624 heads back on. For stock GM Iron heads these are pretty good heavy cast heads that flow well, not as good as after market heads or vortec heads but for me they work just fine....Tim

Car will runs good on 89 Octane better on 92 Octane with my timing set at 12BTDC. Quench is .055 a little too much but so far no signs of detonation.

 

[LannyL81]

Lanny,

Here is the calculation on your engine with 70 cc's chamber heads and a 0.051" gasket....check out that CR and that quench!

The 64 cc heads will bump CR to 9.7 and change.

p.s. See page 4 on this GM catalog, and you'll find that 0.051" gasket
see page 60 (page 4 of document) for 12557236 — Composition Head Gasket

Gerry,
I checked #1 piston and at TDC it is 0.010 out of the block. I am going to check #7 as well, just to see if the block was milled flat or not. I will also check the even cylinder bank as well. If I find the block was not milled flat....oh boy....wife will really be after me to sell the car and I will probably try.

Stay tuned.

 

[GerryLP]

Gerry,
I checked #1 piston and at TDC it is 0.010 out of the block. I am going to check #7 as well, just to see if the block was milled flat or not. I will also check the even cylinder bank as well. If I find the block was not milled flat....oh boy....wife will really be after me to sell the car and I will probably try.

Stay tuned.

Scott Edwards, from Edward's Engines (in Albuquerque), was the one who I spoke about the machine work for my L81, and I had him check the block's flatness of my block, and he found 0.002" difference, and although he told me that he could machine the block to 0.0002", I would risk my original engine's stamping, and I told him forget it! He also said that 2/1000" was about average flatness from production lines, and that it would not hurt anything.

So your engine's deck is at 8.990". This will penalize your engine's quench even more. If you put everything back the way it was, you'll have to use a thicker gasket. Your quench should not be less than 0.040", for many engine operating variables could bring a piston and valve on a colision course.

But you know what?...easily solved. That 0.051" gasket will bring you to a quench of 0.041"

 

[LannyL81]

Had a slight error in my deck measurement...piston was pushing against the magnetic base....did not see it.
Remeasured and I was more correct the first time: I measured at the piston center of #1 and #8 and ranged from 0.005 to 0.007.

Yes the 0.051 gasket is the one for me, but the GM one has a bore size of 4.000...that will not work. FelPro also makes one as well. Came across Flatout Gaskets, they have one on sale at Summit...4.175 bore, 0.050 compressed thickness...quench of 0.045...not bad.

Could you run your program with both 70 and 64 cc heads? Your statment that the CR would only be 9.7 with 64cc heads does not seem correct.

Back to being undecided about the cam though. The 110 LSA bothers me. Would probably be better-off with a 112 LSA for how the car is used. The Melling MTC-1 cam that Tim mentioned sure seems like the way to go...and then I could re-use my 1.6 rockers.

 

[GerryLP]

In one of the web-based article link I posted, they were talking about CompCam's,"Thumper", series which handsomely produced some nice torque figures in their test series. I am liking it as well. .

 

[LannyL81]

In one of the web-based article link I posted, they were talking about CompCam's,"Thumper", series which handsomely produced some nice torque figures in their test series. I am liking it as well. .

Yeah they are going to thump alright. Did you see how much overlap they have???....Going to need some higher compression with any of those cams. And I thought my little 12-210-2 grind had too much overlap.....compared to those my cam has "none". Do not see how they would produce low end torque...the RPM's are way up there.