Can you tell me my compression ratio?

[garner7555]

I pulled my heads off today getting ready to go back up with aluminum Sidewinder heads.  I have the 2355 pistons, and today I measured to see about piston to deck height.  My piston measures to be about 0.018 down in the hole.  This is a stock stroke 440 that has a 0.030 over bore.  The heads I will be using advertise a 84cc chamber.  The head gaskets are 0.040. 

Thanks to everyone and a special thanks to Firefighter (Ron) for advising me on all of my parts selection and providing me with Fire Core ignition system!

Heads
http://www.mopartsracing.com/parts/Sidewinder.html

Head Gaskets
http://www.summitracing.com/parts/fel-8519pt1/overview/make/chrysler

[BSB67]

9.7:1

Go with a 0.020" gasket and have 10.2:1 and good quench.  

[c00nhunterjoe]

9.7:1

Go with a 0.020" gasket and have 10.2:1 and good quench.  

X2. The good quench on aluminum heads will let you run 93 fuel and max timing for the engine.

[garner7555]

Well darn.  I already bought those head gaskets.  Will it make enough difference to be worth ordering the thinner gaskets?  And do the thinner ones hold up as well?   Thanks.     

[c00nhunterjoe]

Yes, order the thinner ones.

[myk]

I think going up a half point in compression is worth ordering the gaskets again...

[c00nhunterjoe]

I think the quench is more important then the 1/2 point, but they are both cheap improvements.

[b5blue]

  Eat the 40 bucks and take full advantage, I'd chuck my set in the trash if I had to, just to get things right!     The 83-4 CC head chambers puts you right at the edge of ideal just by changing gaskets. From what the guys here showed me, it's worth it. (I have a small pile of should not have bought stuff here, worth hundreds.)

[garner7555]

Ok,  I'm willing to buy other gaskets if it's worth while.      Do you guys have a recommendation on a gasket that is 0.020 thickness?   Also do you think my valves will get close to the piston?  (I will put my specs below)


2355 pistons
0.018 down in the hole
Stoke stroke
These heads - http://www.mopartsracing.com/parts/Sidewinder.html
This cam  -   http://www.summitracing.com/parts/lun-10230703
I am planning to run factory stamped rocker arms.
Heads have not been shaved and block deck height hasn't been machined either.

Thanks for the help and advise guys!   

[garner7555]

  Eat the 40 bucks and take full advantage, I'd chuck my set in the trash if I had to, just to get things right!     The 83-4 CC head chambers puts you right at the edge of ideal just by changing gaskets. From what the guys here showed me, it's worth it. (I have a small pile of should not have bought stuff here, worth hundreds.)

I feel your pain, I am removing a mopar purple shaft cam with basically no miles on it, sold the tunnel ram with duel 4 barrel carbs that i bought when I was a teenager, ect. ect. ect.       

Now I seek help from Firefighter Ron and all the other experts here on this forum.  Thanks for all the help guys!

[firefighter3931]

Personally, I'm not a fan of the steel shim head gaskets on aluminum heads. The different expansion rates between the cast iron block and the alloy cylinder head is a concern. The composite head gasket is a better choice, inmo. 

With regards to power output ; how much do you think a 1/2 point of compression is worth in a mild street build ?  Maybe 5 hp at this power level ?  Would you even be able to feel a seat of the pants difference ?

If You absolutely had to have the increased static comp....then milling the heads .030 would be a better option, inmho. 

I know if this was my engine....I'd be using the composite head gasket and calling it good. 



Ron

[Brass]

Cometic offers a .027 Multi-layer steel gasket that can be used with aluminum heads and iron blocks.  Here is their website:

http://www.cometic.com/automotive-gaskets.aspx

I did a quick search and Jegs carries Cometic head gaskets:

http://www.jegs.com/p/Cometic-Gaskets/Cometic-Big-Block-Mopar-383-440-Cylinder-Head-Gaskets/2849549/10002/-1

They are not cheap, and if you go this route, make sure you get the right one for your application. 

[firefighter3931]

Cometic gaskets are excellent quality but do require a special finish on the block and head surface in order to seal. This has to be specified to the machine shop during the build process. If you don't do the proper machinework & prep..... they will not seal properly. 


Ron

[Brass]

Good to know, Ron - thanks. 

Also, based on the information provided, Summit's compression calculator is saying the static compression should be 10.3:1 using the .040 Felpro gaskets:

http://www.summitracing.com/expertadviceandnews/calcsandtools/Compression-Calculator/

Am I missing something?

[b5blue]

Well I thought composition gaskets could be had at the thinner thickness, yea you don't want an all steel gasket. Now it's a can of worms? 

[garner7555]

Good to know, Ron - thanks. 

Also, based on the information provided, Summit's compression calculator is saying the static compression should be 10.3:1 using the .040 Felpro gaskets:

http://www.summitracing.com/expertadviceandnews/calcsandtools/Compression-Calculator/

Am I missing something?

My pistons have valve reliefs, which amount to about 7cc dish I believe.   Also, Did you include that the pistons are 0.018 down in the hole?

[Brass]

That's it!  I did not account for the dished pistons - so that would be the difference.  Sorry if I contributed to any confusion.

[BSB67]

I have done this very test on a 400 hp ish 440. It will be more than 5 hp, and track performance will indicate that it is quite a bit more. The reason, and the beauty of maximizing CR, is that it is about the only change that increases power everywhere in the power curve.  The entire power curve moves up.  Other changes usually move it around (i.e add some here, but lose a little there).  So not only will it add 10 or more hp at peak power, it will add power at 3000 rpm, and sharpen the cruise throttle response just a little too. It is a winner everywhere.  Second, acquiring the good quench has additional value as well.  

Finally, I've heard the theory dozens of times on how the shim gasket cannot compensate for the different expansion rates of the aluminum head and iron block.  This actually seems very logical and make sense to me as well.  However, there are way too many success stories out there with folks using the standard shim gasket in this application to ignore.  I know a lot of guys using the shim gasket without issue.  And I have not heard of a failure because of the gasket.  Maybe they are out there, but I would be a little surprised that I have not heard of it if they were at all common.

Ideally, you would have a set up that would allow the use of a typical 0.040" composite gasket and have a 0.40" quench too i.e. a zero deck block.  But, where you are at, that is not an option without decking the block.  And that I would not do.  Nor would I mill the heads to get more compression because that will cost more $ and you still won't have the right quench.

But I would try the shim gasket, it will likely work, and you'll have your cake and eat it too.  If there is a sealing problem due to the gasket, pull the heads and put on the composite gaskets that you already own.

No matter which head gasket you use, you should make sure that the head is not constrained (for expansion) by the dowel pins that align the head to the block.  That could cause a problem, and some have claimed that it has.  Undersize pins are available.

In my opinion, there is no bad choice here. I personally would not leave the power on the table for the cost of some gaskets.  

[BSB67]

hit the wrong key, I guess. How do you delete a mistaken post?

[garner7555]

That's it!  I did not account for the dished pistons - so that would be the difference.  Sorry if I contributed to any confusion.

No confusion.      I should have looked up that calculator instead of post this I suppose.      

[c00nhunterjoe]

Ive seen every combination from steel to steel, steel to aluminum, and all aluminum with each option gaskets, some without "perfect" machining. Some of the wildest ones that we all swore would never seal, ran the best, others that were done perfect by the book leaked. On a 400 hp big block, the raise in compression discussed in this case would be more like 15hp in my opinion across the entire rpm range as stated above by bsb67 PLUS the better quench which comes down to more free hp and less chance for detonation. I would say try the steel shims.better yet, if this were my engine, i would use the steel shim.

[b5blue]

  When I talked to Todd he said use composite, in my case at .060 over with my pistons the standard gasket hits the sweet spot. There are 2 mindsets at play here. One is it's no big deal to tear down the top of your 440 several times to possibly experiment test/tune to tweak out every bit of power/performance before settling in and calling it done.
  The other mindset is do it one time and do it as good as possible and move on to the 100's of other aspects the car needs. Even 20-30 more horsepower does not matter if the engine runs nice and is reliable.  Back in the day I thought nothing of spending each weekend doing the first, I'd cut heads down and change stuff so much the parts house and machinist knew my parts and car. It was how I had fun. Nowadays I'm a bit more like the second mindset, I really don't care if more power could be had I want to work on other parts of the car. 

[garner7555]

  When I talked to Todd he said use composite, in my case at .060 over with my pistons the standard gasket hits the sweet spot. There are 2 mindsets at play here. One is it's no big deal to tear down the top of your 440 several times to possibly experiment test/tune to tweak out every bit of power/performance before settling in and calling it done.
  The other mindset is do it one time and do it as good as possible and move on to the 100's of other aspects the car needs. Even 20-30 more horsepower does not matter if the engine runs nice and is reliable.  Back in the day I thought nothing of spending each weekend doing the first, I'd cut heads down and change stuff so much the parts house and machinist knew my parts and car. It was how I had fun. Nowadays I'm a bit more like the second mindset, I really don't care if more power could be had I want to work on other parts of the car. 

Well said!      I fall in the 2nd mindset in this situation, my car is freshly painted and wiggling the 440 with headers up into position without scratching up my engine bay isn't something that I care to do on a regular basis.       If it wasn't for that I would be more willing to try I suppose but for my current situation it's just not worth the risk.  I am putting it back together with the 0.040 composite gaskets in hopes that I won't have to tear back into it anytime soon. 
I still appreciate everyone's advice and comments!  If my car was still a wearing old paint and I had more free time then I might chance it, but for my current situation I'm gonna go the route of composite.  Thanks again guys for all the advice and comments.   

[firefighter3931]

Using the RBR calculator I come up with 9.96:1 static compression. The 2355 speedpro pistons are 4cc for the valve reliefs....not 7cc   

Quench will still be there because the ideal range falls between .040-.060 and this one will be at .057 

The other thing to consider is the resulting cylinder pressure ; the VooDoo cam with it's shorter seat to seat timing and quick lobes will trap more air and increase dynamic compression vs a slower ramped profile. While the static comp is slightly less than ideal....the cam will more than make up for it. 

It's all about the "combination" and this one will work great for it's intended purpose. This combo will yield nice street manners, strong throttle response and lots of tire frying torque. The car will have no problem lighting up the tires from a dead stop ! 



Ron

[BSB67]

Certainly you you need to decide what is right for you.  But i will leave this go, but with two last comments:
1) If you believe what you read, 0.060" piston to head distance is about the worst for ping.  That said, I don't think ping itself will be an issue for you.  It is an efficiency thing.
2) You will not have a head sealing issue.  I'll bet money on it.