Double check my engine builder please 340 stroke

[yellow rose]

Ok...more info from the engine builder...I used the calculation tool he uses to verify the numbers. See attached photo

New info...
1) my block was tall and the deck height .018 above the piston
2) To keep the costs down for machining and due to the limited piston selection it drove the builder to select the Icon IC744 pistons are flat top that have 5cc eyebrows cut into the face. This minimized the amount of machining to the block and heads to achieve C.R. ratios and maintain rocker arm geometry.
3) the pistons have (8) .4 cubic inch or 6.44cc gap between the cylinder wall and piston that is .015 wide and .222 deep down to the first compression ring that adds cylinder Volume. (See pictures and the calculation tool allows for this measurement)
4) the cams advertised duration 253/266@20 deg or 276/294@6 deg. The intake closes at 76 degrees (actual zero). I used the 76 degree number in the calculator. Note: asked to install the cam with 4 degrees of advance.
5) the engine builder says the Static compression ratio will be 11.57:1 and the dynamic between 8.1 @ 1160 elevation or 8.4 at sea level.
6) I asked him about crank pressure. He said 225psi. I asked him if that was high. He said he has other engines out there with aluminum heads st 225psi and it is no problem. He said if my heads were iron he would have stopped at 180psi.

It helps when you have all of the answers. I hope these answers help everyone following the tread and who have contributed their thoughts and hands on experiences. I will get the motor assembled and let you know how it goes.

PS my builder said if I was shaky on setting the timing at first to run some 110 octane gas to get it dialed in to avoid detonation while I worked it out the initial timing.

View attachment 1715103145

View attachment 1715103146

View attachment 1715103147

1. Deck height is positive if the piston is down the hole. It is negative if the piston is out of the hole. So you have a negative deck if the piston is above the deck and a positive number if the piston is lower than the deck.
2. You can deck the block and head until you hit water and it won't affect rocker geometry if you have shaft rockers.
3. Crevice volume on modern Pistons is rarely more than .2 CR.
4. That's not much cam timing for the CR you have.
5. Tune up will be critical with that CR. I'm not sure I even like the cam you have, but all that money spent and you are going to handicap it with exhaust manifolds.
6. Aluminum and CI heads can run the same CR. That has been proven many times. If you can't run a CI head over 185 psi you'll have the same issue with aluminum heads.

 

[nm9stheham]

3) the pistons have (8) .4 cubic inch or 6.44cc gap between the cylinder wall and piston that is .015 wide and .222 deep down to the first compression ring that adds cylinder Volume. (See pictures and the calculation tool allows for this measurement)
4) the cams advertised duration 253/266@20 deg or 276/294@6 deg. The intake closes at 76 degrees (actual zero). I used the 76 degree number in the calculator. Note: asked to install the cam with 4 degrees of advance.
5) the engine builder says the Static compression ratio will be 11.57:1 and the dynamic between 8.1 @ 1160 elevation or 8.4 at sea level.
6) I asked him about crank pressure. He said 225psi. I asked him if that was high. He said he has other engines out there with aluminum heads st 225psi and it is no problem. He said if my heads were iron he would have stopped at 180psi.

Good for the added info. Good caliper pix!

Very real PROBLEMS that I found in your numbers:
1) The info that there is 6.44 cc in that gap is incorrect and is off by an order of magnitude. It is about 0.042 CI or about 0.64 CC.... I just computed it directly twice.
2) I used 278 as an estimation on the advertised already. Intake closing at .006" is 68 degrees, not 76 degrees, for 4 degrees of cam advance. It appears that you made a mistake in entering the cam advance and it has been entered as cam retard. With that mistake THEN the ICA will be 76 degrees. With that cam at 4 degrees advanced, there is no way that DCR will be low 8's.
3) In no way, shape or form will the cranking pressure will be 225 psi at sea level! You would need some sort to pressurized air to get there!

- Adding in the 0.64 cc's
- using a 278 advertised duration
- using a thicker head gasket than before at .051" thick
- 018" deck height
- 4 degrees of cam advance
.... then I get an SCR of 10.95 and DCR of 8.65. Those relative number compare as I expect; the builder's relative SCR and DCR number do not make sense with this cam. Cranking pressure is gonna by around 170 to 180 psi. That is not all that awful for 93 octane and AL heads. I suspect total timing will have to be limited some, but that is not any disaster IMHO.

BTW, if you tune it with 110 octane, then it'll run good with a lot of timing but you had better pull back total timing before putting in 93 octane Premium.

And I have to question the deck being as tall as .018 over those pistons. ICON's and SCAT rods and such decks are not usally that far off. So be careful; as R. Reagan said: "Trust but verify"....

 

[MObarracuda]

8.1 is friendly.


What is your elevation?

If it's 3000 plus ft, now the picture is clearer.
But something about this entire post is suspicious...

Why are you hiding the cam specs?

I posted a picture of the cam card that came in the box with the cam. It was not complete with the all the usual data. I called the cam grinder and posted more info today at 1:48pm in a previous post. Here is the cam card that they sent me

 

[MObarracuda]

I posted a picture of the cam card that came in the box with the cam. It was not complete with the all the usual data. I called the cam grinder and posted more info today at 1:48pm in a previous post. Here is the cam card that they sent me

View attachment 1715103313

The data from my call from the cam builder“....the cams advertised duration 253/266@20 deg or 276/294@6 deg. The intake closes at 76 degrees (actual zero). I used the 76 degree number in the calculator. Note: asked to install the cam with 4 degrees of advance.”

 

[MObarracuda]

Good for the added info. Good caliper pix!

Very real PROBLEMS that I found in your numbers:
1) The info that there is 6.44 cc in that gap is incorrect and is off by an order of magnitude. It is about 0.042 CI or about 0.64 CC.... I just computed it directly twice.
2) I used 278 as an estimation on the advertised already. Intake closing at .006" is 68 degrees, not 76 degrees, for 4 degrees of cam advance. It appears that you made a mistake in entering the cam advance and it has been entered as cam retard. With that mistake THEN the ICA will be 76 degrees. With that cam at 4 degrees advanced, there is no way that DCR will be low 8's.
3) In no way, shape or form will the cranking pressure will be 225 psi at sea level! You would need some sort to pressurized air to get there!

- Adding in the 0.64 cc's
- using a 278 advertised duration
- using a thicker head gasket than before at .051" thick
- 018" deck height
- 4 degrees of cam advance
.... then I get an SCR of 10.95 and DCR of 8.65. Those relative number compare as I expect; the builder's relative SCR and DCR number do not make sense with this cam. Cranking pressure is gonna by around 170 to 180 psi. That is not all that awful for 93 octane and AL heads. I suspect total timing will have to be limited some, but that is not any disaster IMHO.

BTW, if you tune it with 110 octane, then it'll run good with a lot of timing but you had better pull back total timing before putting in 93 octane Premium.

And I have to question the deck being as tall as .018 over those pistons. ICON's and SCAT rods and such decks are not usally that far off. So be careful; as R. Reagan said: "Trust but verify"....

Thank you for taking the time to review my application. As you can see I have no clue what I’m doing. I’m still learning and I’d like to reproduce the simulation and get confident numbers before assembling the motor just in case anything has to change. I will measure the piston to block height. The engine builder said he would come over to my house to help me any time since he provided the spec.

 

[MObarracuda]

Wrong piston for what you want to do. Price is not an issue as the -20 dish are the same price from multiple vendors.

Doing the dance about elevation helping is folly at best. At 1000-1500 above sea level is not even worth the effort to try and sneak in under the wire.

Putting them down in the hole and running a.039 gasket you are just close enough for quench, but, that is getting iffy if the piston is more than .010 down. IMO, you'd want a .030 gasket to make quench work for you.

Cold days and high atmos pressure are going to be your enemy...

Thanks for the advise...the engine builder will come to my home and measure the assembled block. I have noted your observation in my build book.

 

[CPMotorworks]

I'd suggest not using that incorrect calculator on the KB site, that has really caused a lot of bad information on this site.
Can anyone here tell me what RPM you use to figure DCR, and do you understand what DYNAMIC means, and why it's called DYNAMIC compression?
I would suggest you buy PIPEMAX, it gives correct numbers and is very useful.
OP, I come up with 11.88:1 Static, 10.834 DCR, 195psi cranking @ 150rpm starter speed, and 103-106 octane requirement. 87 octane in your combination will not be pleasant.
EDIT: The top of the pistons are small to allow growth from the heat, as they are in a dynamic situation.

 

[RustyRatRod]

Run it. If it doesn't run on 87 like the builder says, make him make it good.

 

[BrianT]

3) Builder recommended 750cfm carb. I like Edelbrock’s AVS carb...is he 650cfm too small or 800cfm to large for a street driver?

I can't help with cam and compression, but there seems to plenty of help for that. I can tell you that I run an 800 cfm Edelbrock on my 408 street driven with no problems. We ran it on a chasis dyno and the A/F ratio was great straight out of the box. Sent the jet kit back to Summit unopened. I think there's one for sale here on FABO right now.

 

[MObarracuda]

I can't help with cam and compression, but there seems to plenty of help for that. I can tell you that I run an 800 cfm Edelbrock on my 408 street driven with no problems. We ran it on a chasis dyno and the A/F ratio was great straight out of the box. Sent the jet kit back to Summit unopened. I think there's one for sale here on FABO right now.

Thanks for the reply...appreciate that

 

[nm9stheham]

I would suggest you buy PIPEMAX, it gives correct numbers and is very useful.
OP, I come up with 11.88:1 Static, 10.834 DCR,

Unfortunately, this program calculates DCR in a very different way, one that looks to be totally unrealistic and unusable. It computes the effective stroke as if the intake valve is completely closed at .050" lobe lift; that is OK for anyone thinks the valve is effectively sealed at a valve lift of .075". (If so, we won't ever have to worry about valve leaks again LOL.) This program also computes a 'DCR at valve lash' which is closer to the numbers that normally get discussed as DCR.

That is always a squishy aspect of DCR computations... at what angle is the intake valve effectively closed and the cylinder pressure starts to build. IMHO this Pipemax program gives an unusable DCR answer; it works the DCR at an intake closing of 43* ABDC. Others use 15 degrees after the .050" point on the intake lobe, or 58* in this case. And then the one I use takes it at the 'advertised' closing point, or 76* in this case.

 

[MObarracuda]

Good for the added info. Good caliper pix!

Very real PROBLEMS that I found in your numbers:
1) The info that there is 6.44 cc in that gap is incorrect and is off by an order of magnitude. It is about 0.042 CI or about 0.64 CC.... I just computed it directly twice.
2) I used 278 as an estimation on the advertised already. Intake closing at .006" is 68 degrees, not 76 degrees, for 4 degrees of cam advance. It appears that you made a mistake in entering the cam advance and it has been entered as cam retard. With that mistake THEN the ICA will be 76 degrees. With that cam at 4 degrees advanced, there is no way that DCR will be low 8's.
3) In no way, shape or form will the cranking pressure will be 225 psi at sea level! You would need some sort to pressurized air to get there!

- Adding in the 0.64 cc's
- using a 278 advertised duration
- using a thicker head gasket than before at .051" thick
- 018" deck height
- 4 degrees of cam advance
.... then I get an SCR of 10.95 and DCR of 8.65. Those relative number compare as I expect; the builder's relative SCR and DCR number do not make sense with this cam. Cranking pressure is gonna by around 170 to 180 psi. That is not all that awful for 93 octane and AL heads. I suspect total timing will have to be limited some, but that is not any disaster IMHO.

BTW, if you tune it with 110 octane, then it'll run good with a lot of timing but you had better pull back total timing before putting in 93 octane Premium.

And I have to question the deck being as tall as .018 over those pistons. ICON's and SCAT rods and such decks are not usally that far off. So be careful; as R. Reagan said: "Trust but verify"....

Cylinder head gasket thickness is important...I will measure the deck height tonight to gauge where the piston will land. Thanks.

 

[69_340_GTS]

Piston to bore clearance ".015 inches"? That's like 10X what it should be.

 

[furrystump]

The ICON 20cc dish piston is 10 grams heavier than the 5cc flat top. Shouldn't have any issues with balancing it. I would go the dished piston. Trying to think outside the box is fine if you really need to and you have the time/money/inclination to, but this isn't that type of effort. If the dish pulls out to much scr go with thinner gasket a .027 cometic for example. Carb is small, I run 800 thunder series AVS

 

[CPMotorworks]

Unfortunately, this program calculates DCR in a very different way, one that looks to be totally unrealistic and unusable. It computes the effective stroke as if the intake valve is completely closed at .050" lobe lift; that is OK for anyone thinks the valve is effectively sealed at a valve lift of .075". (If so, we won't ever have to worry about valve leaks again LOL.) This program also computes a 'DCR at valve lash' which is closer to the numbers that normally get discussed as DCR.

That is always a squishy aspect of DCR computations... at what angle is the intake valve effectively closed and the cylinder pressure starts to build. IMHO this Pipemax program gives an unusable DCR answer; it works the DCR at an intake closing of 43* ABDC. Others use 15 degrees after the .050" point on the intake lobe, or 58* in this case. And then the one I use takes it at the 'advertised' closing point, or 76* in this case.

I'm sure Larry Meaux would be interested to hear how it's incorrect, not to mention all the professional builders that use it for reference.
The problem with basing your whole cam selection on DCR is what I see as "squishy". I've seen more than a few threads talking about how people are adjusting cam timing for this magical 76° closing point, regardless of the combination.
Again I ask @ what RPM are you calculating DCR? Does the induction system operate at the same VE throughout the RPM range? Does cylinder pressure remain constant from 800-6000 rpm? There is a reason it's called Dynamic Compression.

 

[nm9stheham]

I've seen more than a few threads talking about how people are adjusting cam timing for this magical 76° closing point, regardless of the combination.

Uh ... what magic 76 degree closing point? All of these computed/assumed closing angles vary from cam to cam, regardless of program.

I just Googled 'Pipemax DCR'; there are tons of threads questioning the DCR results. What I am trying to explain is that the program is computing DCR in a way that is not the 'normal' way; it gives much higher results than what the vast, vast majority of people refer to as DCR , and that is because it computes quite a different angle. If it's computing something that does not relate to what most people use, then it is pretty useless.

BTW, DCR is a simple computed value. (Well, simple if everyone uses the same angle reference!) All the thoughts of how it varies with RPM, VE and such, is more commonly referred to as 'effective CR'. That term has been around since at least the 60's.

 

[nm9stheham]

Piston to bore clearance ".015 inches"? That's like 10X what it should be.

He is only looking at the very top of the piston, above the top ring land, where a bigger clearance is not uncommon. This was for figuring out the volume in that crevice.

 

[69_340_GTS]

He is only looking at the very top of the piston, above the top ring land, where a bigger clearance is not uncommon. This was for figuring out the volume in that crevice.

Got it. It just seemed excessive. But you're right.

 

[nm9stheham]

It WOULD be excessive for the skirt clearance! Just a wee bit of noise and oil consumption and smoke.... LOL

 

[moper]

You NEED to listen to YR and CP. Pipemax is as close to reality as one will find, and blessed by many higher end professionals in all forms of performance building.
Honestly I can't see why you're using this builder.
"Milling will change rocker geometry." BS. Deck height and cylinder head thickness has nothing to do with rocker geometry on a Mopar with shaft rockers.
That static ratio never changes, and dynamic takes into account the valve timing to calculate the compression ratio. Neither ratio will change as they are mechanical parts that don't change. But - cylinder pressure goes up with volumetric efficiency. Your suggested static is way too high and the camshaft as said is too small. 225psi is nuts for pump fuel. Add to that the cylinder pressure ramping up as the cam and heads start to work (assuming they do) and you are asking, imploring, in fact yelling for detonation problems.
You need a new builder.

 

[MObarracuda]

Thanks you

Wrong piston for what you want to do. Price is not an issue as the -20 dish are the same price from multiple vendors.

Doing the dance about elevation helping is folly at best. At 1000-1500 above sea level is not even worth the effort to try and sneak in under the wire.

Putting them down in the hole and running a.039 gasket you are just close enough for quench, but, that is getting iffy if the piston is more than .010 down. IMO, you'd want a .030 gasket to make quench work for you.

Cold days and high atmos pressure are going to be your enemy...

Thanks you for weighing in...I always appreciate your comments