[clm69z28]

I was analyzing my DZ engine build and found some interesting posts regarding DCR and cam profile relationships and so I thought I would post my build goals and assumptions for input/advice on how to improve the performance.

The car is a stock 69 Z28 with a four speed and 3:73'S and runs through the stock cast iron manifolds and dual pipe/single transverse muffler system. I also considered putting on the AIR system. The motor in the car is 11:1 and requires racing gas to boost the octane (I live in Calif. where the premium is not very good). I would like to consider the use of pump gas only for this build but it is not critical. The motor will be a "period correct" setup so that limits the modification options for the block (the block is an original DZ stamp so it can't be decked) and the use of the cast iron heads and intake manifold/carb setup. I am going to upgrade the internals of the engine and that's what I was trying to figure out when I came across this site.

The engine specs currently are:

-010 block with a 4.030 bore

-186 cast iron heads with 2.02/1.60 valves, screw in studs and guide plates. Three angle valve job with mild porting and valve unshrouding (heads were original 1.94/1.50)

-JE 202890 pistons with a 10.4 comp., with a 64 cc head, 1.8 comp. height and a 6.5 cc dome volume. This piston is meant to be used with a deck height of 9.00" which is less than the standard 9.025" factory deck height.

-Crower Sportsman 5.7" rods

-Head gasket is open at this point but the assumption is a .041" thickness with a 4.166 hole.

-Duntov 30-30 Camshaft with the following specs:

Intake opens BTDC 60:50
Intake closes ABDC 105:23
Intake Duration 346:13
Intake Lobe Center (112)
Intake Lift .485"
Exhaust open BBDC 108:50
Exhaust close ATDC 57:23
Exhaust Duration 346:13
Exhaust Lobe Center (64)
Exhaust lift .485"
Distance between centers (132)
Overlap 118:13

I used Pat Kelley's DCR and compression calculators and with this setup the DCR seemed very low at 7.05, probably due to the lower dome height of the JE piston, the higher factory deck height and the head gasket thickness ( I believe that I have calced it correctly but I have never done this before so all caveats apply).

I started to research how to get the DCR up to around 8:1 and if this cam would still work, and if not what would be as close to the sound and characteristic of that sweet revving 302. I don't believe that I can go to a thinner head gasket due to one of the pistions only being about .024" in the hole so the next thinner gasket I found was .015" which would be below the threshhold of .040" for piston/valve clearance. I found that advancing this cam at least 4 degrees would help the situation, but there seems to be more to it than that. That's when I decided to post my build. If I have left anything out let me know, otherwise thanks in advance for the feedback.

[DoubleVision]

Mr. Gasket carries a head gasket thru Summit racing that is .028 thickness.

[cobalt327]

Originally Posted by clm69z28

I was analyzing my DZ engine build and found some interesting posts regarding DCR and cam profile relationships and so I thought I would post my build goals and assumptions for input/advice on how to improve the performance.

The car is a stock 69 Z28 with a four speed and 3:73'S and runs through the stock cast iron manifolds and dual pipe/single transverse muffler system. I also considered putting on the AIR system. The motor in the car is 11:1 and requires racing gas to boost the octane (I live in Calif. where the premium is not very good). I would like to consider the use of pump gas only for this build but it is not critical. The motor will be a "period correct" setup so that limits the modification options for the block (the block is an original DZ stamp so it can't be decked) and the use of the cast iron heads and intake manifold/carb setup. I am going to upgrade the internals of the engine and that's what I was trying to figure out when I came across this site.

The engine specs currently are:

-010 block with a 4.030 bore

-186 cast iron heads with 2.02/1.60 valves, screw in studs and guide plates. Three angle valve job with mild porting and valve unshrouding (heads were original 1.94/1.50)

-JE 202890 pistons with a 10.4 comp., with a 64 cc head, 1.8 comp. height and a 6.5 cc dome volume. This piston is meant to be used with a deck height of 9.00" which is less than the standard 9.025" factory deck height.

-Crower Sportsman 5.7" rods

-Head gasket is open at this point but the assumption is a .041" thickness with a 4.166 hole.

-Duntov 30-30 Camshaft with the following specs:

Intake opens BTDC 60:50
Intake closes ABDC 105:23
Intake Duration 346:13
Intake Lobe Center (112)
Intake Lift .485"
Exhaust open BBDC 108:50
Exhaust close ATDC 57:23
Exhaust Duration 346:13
Exhaust Lobe Center (64)
Exhaust lift .485"
Distance between centers (132)
Overlap 118:13

I used Pat Kelley's DCR and compression calculators and with this setup the DCR seemed very low at 7.05, probably due to the lower dome height of the JE piston, the higher factory deck height and the head gasket thickness ( I believe that I have calced it correctly but I have never done this before so all caveats apply).

I started to research how to get the DCR up to around 8:1 and if this cam would still work, and if not what would be as close to the sound and characteristic of that sweet revving 302. I don't believe that I can go to a thinner head gasket due to one of the pistions only being about .024" in the hole so the next thinner gasket I found was .015" which would be below the threshhold of .040" for piston/valve clearance. I found that advancing this cam at least 4 degrees would help the situation, but there seems to be more to it than that. That's when I decided to post my build. If I have left anything out let me know, otherwise thanks in advance for the feedback.

Given the figures:
• 4.030" bore x 3" stroke
• head gasket 0.041" thick x 4.1" bore diameter (you need not use a HG w/ 4.166" bore)
• deck 0.025" in the hole
• 64cc chambers (you have to verify this! Often undecked heads will be larger than 64cc)
• dome of 6.5cc,

I get 9.76:1 compression ratio. But this runs the quench out to an unacceptable 0.066". To get the CR up and quench distance down, a thinner HG is needed. There are various high quality gaskets available that are composite construction (composite gaskets makes sealing to an uncut deck more positive) that might work well for you, like:

• Victor Reinz Nitroseal p/n 5746- Compressed thickness is 0.025", 4.1” bore. NAPA carries Victor.
• GM 10105117- Multi-layered stainless steel gasket with a 4.1 bore, .028" thick, will handle some surface irregularities of the deck and head surfaces (supposed to be the “revised” gasket, better seal- Post #23 ). $21/ea. @ Summit.
• GM 14096405- Stainless steel layers over a graphite core (or graphite on one side, SS on the other), is .028" thick, 4.1” bore.

Shim type gaskets w/the rubber coating are a bit more forgiving than the uncoated gaskets. You can sometimes take an ever-so-light skim off the block and retain the suffix, or have the decking done in such a way that that area is left untouched. This will allow the use of a shim HG w/a lot better chance of no sealing problems.

So, using a 0.015" shim HG puts you at 10.5:1 w/quench at an "ideal" 0.040".
Using a 0.025" HG, the CR becomes 10.2:1 and the quench would be 0.050". The 0.028 gasket will give you 10.1:1 CR and a quench of 0.052".

I'll leave the DCR calculations up to you. But I do have to say there are other solid lifter flat tappet camshafts that I believe would be a better choice unless authenticity takes precedence over more efficient power production.

Heck, you could run a stout hydraulic cam w/Rhodes hydraulic lifters and have better power and still the tickety-tick of solids. Blasphemy, I know. Just saying'.

[clm69z28]

Originally Posted by cobalt327

Given the figures:
� 4.030" bore x 3" stroke
� head gasket 0.041" thick x 4.1" bore diameter (you need not use a HG w/ 4.166" bore)
� deck 0.025" in the hole
� 64cc chambers (you have to verify this! Often undecked heads will be larger than 64cc)
� dome of 6.5cc,

I get 9.76:1 compression ratio. But this runs the quench out to an unacceptable 0.066". To get the CR up and quench distance down, a thinner HG is needed. There are various high quality gaskets available that are composite construction (composite gaskets makes sealing to an uncut deck more positive) that might work well for you, like:

� Victor Reinz Nitroseal p/n 5746- Compressed thickness is 0.025", 4.1� bore. NAPA carries Victor.
� GM 10105117- Multi-layered stainless steel gasket with a 4.1 bore, .028" thick, will handle some surface irregularities of the deck and head surfaces (supposed to be the �revised� gasket, better seal- Post #23 ). $21/ea. @ Summit.
� GM 14096405- Stainless steel layers over a graphite core (or graphite on one side, SS on the other), is .028" thick, 4.1� bore.

Shim type gaskets w/the rubber coating are a bit more forgiving than the uncoated gaskets. You can sometimes take an ever-so-light skim off the block and retain the suffix, or have the decking done in such a way that that area is left untouched. This will allow the use of a shim HG w/a lot better chance of no sealing problems.

So, using a 0.015" shim HG puts you at 10.5:1 w/quench at an "ideal" 0.040".
Using a 0.025" HG, the CR becomes 10.2:1 and the quench would be 0.050". The 0.028 gasket will give you 10.1:1 CR and a quench of 0.052".

I'll leave the DCR calculations up to you. But I do have to say there are other solid lifter flat tappet camshafts that I believe would be a better choice unless authenticity takes precedence over more efficient power production.

Heck, you could run a stout hydraulic cam w/Rhodes hydraulic lifters and have better power and still the tickety-tick of solids. Blasphemy, I know. Just saying'.

Thanks Cobalt327 for the great information. Given that the originality of the block is a big limiting factor, the head gasket seems to be of even more importance given it's impact on quench, clearance, etc. The issue with the block is the fact that the drivers side bank all measures about .026" in the hole. The pass side starts at about .024" and grows to .030" in the back. The engine builder wants to use the Fel Pro 1103 head gasket given that the block surface won't be perfect. I found a Mr. Gasket head gasket that might work and keep me in the safe zone for clearance and a good quench, but it is a metal shim construction: 1130G NEW 4.100" .020" Embossed Steel Shim, Elastomer Coated(Not For Use w/Lightweight Head). I will also check into the ones that you listed.

It appears from the product information that this gasket might squish down to a .018" thickness (is that possible?). If so, this would translate to a .044-.048" clearance and quench. Are you familiar with these type gaskets?

With an advance of about 8 degrees with the 30/30 cam, it calcs. at a DCR of 7.63 and an SCR of 10.38. What is the effect of this much advance: does it take away the idle quality, have large impacts on the top end, and is it a problem?

[cobalt327]

I have no experience w/the p/n 1130G HG, but if the compressed thickness comes from Mr.G, I would have to assume it's correct.

When you are calculating the DCR are you using a "correction factor" of any kind? Some calculators (it is claimed) are more accurate if the intake closing point is fudged some amount, and this is different between the different calculators. Maybe someone will read this who knows what's up w/ the Pat Kelly calculator and can assist you in getting a correct DCR- not that you are incorrect, it's just that I don't know if you're correct or not w/the calculator you're using.

[clm69z28]

The calculator I used (Pat Kelley) doesn't have a fudge factor, it requires the use of absolute valve duration, not the durations at some lift e.g. .050". Other than that, I am not aware of any other fudge factor. Maybe it is built into the program?

Do you have any opioion of the type of material between the two gaskets that I mentioned? The composition of the Fel Pro and the Mr. G gaskets are different; do you see any issue substituting one for the other?

And does the cam advance of 8 degrees seem to be problematic? Thanks.

[cobalt327]

Originally Posted by clm69z28

The calculator I used (Pat Kelley) doesn't have a fudge factor, it requires the use of absolute valve duration, not the durations at some lift e.g. .050". Other than that, I am not aware of any other fudge factor. Maybe it is built into the program?

Do you have any opioion of the type of material between the two gaskets that I mentioned? The composition of the Fel Pro and the Mr. G gaskets are different; do you see any issue substituting one for the other?

And does the cam advance of 8 degrees seem to be problematic? Thanks.

Advancing the cam will put the intake c/l at 104º. Not a deal killer, although it also will decrease the valve to piston clearance of the intake valve. As I said earlier, I would spec a cam that did what I needed it to do w/o needing anything even close to a 8 change- but that's me. If you are committed to this cam you have to do what you have to do.

So that said, you still have to degree the cam in to know where you are starting from, in order to to know how much advance you actually need to get some theoretical DCR, so start w/degreeing the cam in.

HERE is a list of valve train points to check.

An embossed, coated shim HG will not be as forgiving as a full composite HG on an unmilled deck surface. I have no idea what a p/n 1103 Felpro fits. Are you talking about a 1003? If so it's a composite 0.041" thick w/a (too large IMO) 4.166" bore diameter. I've said above where a 0.041" compressed thickness HG puts the quench and CR (CR will be a bit lower due to the HG diameter- I computed it using a 4.100" dia.). Personally I would use one of the thinner composite HG's. Why give away CR and quench- when you need more CR and less quench?

Distance between centers (132)

What is the LSA really?

[techinspector1]

Originally Posted by cobalt327

What is the LSA really?

Some of the numbers don't prove out in math, but if we use the intake opening and closing figures of 60.5 degrees/105.23 degrees, adding 180 for getting from TDC to BDC, we find an intake duration of 345.73 degrees. On the exhaust side, adding 108.50 degrees/57.23 degrees, adding 180 for getting from BDC to TDC, we find an exhaust duration of 345.73 degrees, same as the intake duration. More than likely, these figures were taken using the old S.A.E. J604d spec. I seem to remember it as 0.004" on the intake and 0.006" on the exhaust. The ramps on these cams were very long. Not having a 0.050" figure in the published data and not having access to the rate of lift, I cannot determine the 0.050" duration. The intake centerline is given as 112, the exhaust centerline as 64. Adding these figures together and dividing by 2, we find a lobe separation angle of 88 degrees.

You also have to take into consideration that the cam was a solid flat tappet, so there is the factor of valve lash to consider.

Personally, I'd wrap the motor/trans up in moisture-proof stuff and build a 383 5-spd for it. Mark hit it right on the money with the Rhodes lifters.

[6426yy]

Personally, I'd wrap the motor/trans up in moisture-proof stuff and build a 383 5-spd for it. Mark hit it right on the money with the Rhodes lifters.

X2 The value of that engine is IMO too high to risk driving around with. 010 blocks are everyware, then if you have to have one milled just tell everyone that it's the original block when it's really a 350 ot 383 like tech said, or find a 283 crank if you wana stick with a 302.

[clm69z28]

The actual LSA for this cam is 114 degrees. If the cam is advanced 8 degrees, and the piston deck clearance and the gasket are in excess of .042", does the advance reduce that clearance amount? And if so, what would the loss of clearance be or does it reduce it by some undetermined amount that has to be physically measured?

As to the cam, I am hoping that I can make the 30-30 cam work given the goal of using the factory parts as much as possible. All of the comments on using a different motor are certainly valid and I probably should have considered that more seriously before I started. I don't drive the car that much-about 3K miles in 9 years-so the risks are low on the original stuff.

I wish that I had done all of this upfront and not after the bottom end was pretty far along and the components weren't totally analyzed. Thanks for all of the good input. I certainly enjoy the learning curve.

[cobalt327]

Originally Posted by clm69z28

The actual LSA for this cam is 114 degrees.

Thank you, sir.

If the cam is advanced 8 degrees, and the piston deck clearance and the gasket are in excess of .042", does the advance reduce that clearance amount? And if so, what would the loss of clearance be or does it reduce it by some undetermined amount that has to be physically measured?

The deck clearance with the gasket thickness, etc. is describing what makes up the quench distance- the distance between the flat part of the piston deck and the deck of the head. The quench isn't affected by advancing or retarding the cam. In the diagram below, the quench distance is labeled the "Squish Band". Different name, same measurement:



Advancing the cam reduces the intake valve to piston clearance, and this, along w/the exhaust valve to piston clearance would be physically measured during the mock up phase of the build. The closest the valves get to the pistons doesn't happen at TDC like one might expect. Look for the minimum intake valve to piston clearance to be somewhere around 5° to 20° ATDC during valve overlap. The minimum exhaust valve to piston clearance is around 20° to 5° BTDC during valve overlap. The clearance you are looking for with steel rods is generally said to be 0.080" for the intake and 0.100" on the exhaust unless there is some reason to use a different clearance. Add 0.030" for aluminum rods.

HERE is a short page on using the "clay method" for determining the P to V clearance.

[clm69z28]

Thanks for the excellent info. Learn something new every day. I will dig around some more to see if anybody has info on this cam/advace issue.

[clm69z28]

Thanks for the excellent info. Learn something new every day. I will dig around some more to see if anybody has info on this cam/advace issue.

[cobalt327]

You're quite welcome. Let us know what you find.