3.4 tdc pistons in rwd 3.4

[robertisaar]

That's what my setup is.. 3400/3500 3.4 RWD pistons...

probably the best hybrid combo possible without dabbling into custom parts...

[60dgrzbelow0]

ohhhh really!
Thank you for the explanation.. me dummy

wouldn't Quad Cam have been a Better name
Rolls off the tongue

Every time I see the Glamor Shot of Uncle Rico in your Avatar Box... I can't help laughing my ass off and wondering whether I'll live long enough to eventually cast my "Vote for Pedro". Thanks for having such a great SOH... Ooooops.... Sorry about that...I forgot you had a little problem with TLAs.... SOH = "Sense of Humor"....

[blownarrow]

[jschmieding]

Opposite side, if you put 3.4 RWD pistons in a 3400, you'd get like 12.xxx:1 compression. If you drop 3500 heads onto the block, which have bigger chambers, the compression works out to 11.5:1.. That's what my setup is.. 3400/3500 3.4 RWD pistons...

I have a 3400 block with 3500 heads and 3.4 pistons for a 93-95 camaro and using all this I am still coming up with 12.xx:1 compression on the calc. what pistons are you using to get to 11.5:1? and can 11.5:1 run on pump gas?

[IsaacHayes]

Bore				3.622"
Stroke				3.310"
Head Gasket Bore		3.80"
Head Gasket Thickness		0.060"
Combustion Chamber Volume	32.4cc
Piston Dome Volume		 8.0cc
Piston Deck Clearance		.0095"


Final Displacement		3352 cc
Calculated Compression Ratio	11.51:1
Quench 				0.07"

That is with 3500 headgaskets. If you use 3400 headgaskets, the gasket bore is 3.75 and the compression becomes 11.56:1.

You can run that setup on 93 octane for sure with a cam with an intake close event of 33* ABDC. I'm going to try to run that on 91 though since I only have 91 around here. A larger cam will bleed off more compression so that the actual (or dynamic as it's called) compression is much lower.

Using the calculators online which just take with a grain of salt, the dynamic or actual compression of the above setup with 33 IVC ABDC is 10.75:1. For what it's worth....

[ForcedFirebird]

Well then Issac, you would have to follow that "one line calculator's" recommendations and stay under that 9.x:1 DCR for pump gas .

Can't go by that!

The "DCR" - any way that you can gather - will only tell you your approximate cranking pressure which means squat in a running motor. How can one determine "dynamic compression" when it IS just that: dynamic. It is constantly changing dependant on engine load, cam specs, RPM, and even octane rating.

[robertisaar]

How can one determine "dynamic compression" when it IS just that: dynamic. It is constantly changing dependant on engine load, cam specs, RPM, and even octane rating.

LOTS of EPIC TRUTH in that statement.

[blownarrow]

So whats thinkness should used when running the TDC pistons in an iron head? I'll also be running an Engel cam with a .489lift and a .277dur
So using WOT (ben) rule of thumb below, What would be my best bet for Compression / and Quench on my build?

Taking the stock 3400 for an example, we have a piston that has a flat area around the outside, and a heart shaped combustion chamber on the head with lots of flat area around the outside. This is a great design to put the mixture into the center of the cylinder. The stock piston sticks out of the block .020" and the head gasket is .060" thick. This leave .040" between the top of the piston and the surface of the head. .035-.045 is considered optimal quench distance, depending on the RPM you intend to run. For 5000 RPM on stock forged connecting rods, .035" is enough space. For 6000-7000, .040" is enough. Past that and .045" should be used. The reason being that connecting rods stretch at higher RPM. You must account for the stretch or there will be a greater possibility for piston to head contact.

For custom pistons, the piston height can be adjusted easily and either the gasket or head can be changed from a stock spec to give the beste quench. For stock engines, the following should help you choose your MLS gasket thickness

3100 - Piston sticks out .020". Head Gasket should be .060" thick (Stock)

3400 - Piston sticks out .020". Head Gasket should be .060" thick (Stock)

3500 - Piston sticks out .010". Head Gasket should be .050" thick (Stock is .060")

3.4 Iron Head - Piston sits .010" below deck. Head Gasket should be .030" thick. Compression will be increased but no problem on iron heads. Compression will be in the 13:1 range using 3400 heads.

[98goldZ]

Well then Issac, you would have to follow that "one line calculator's" recommendations and stay under that 9.x:1 DCR for pump gas .

Can't go by that!

The "DCR" - any way that you can gather - will only tell you your approximate cranking pressure which means squat in a running motor. How can one determine "dynamic compression" when it IS just that: dynamic. It is constantly changing dependant on engine load, cam specs, RPM, and even octane rating.

DCR will bleed off compression at low engine loads and rpm's. it can help a high compression engine run on lower octane with a big donkey dick cam. BUT under high engine load and higher rpm's when the engine starts to scavenge and gets really effiecent, you can thro the DCR out the window and the "REAL" compression (SCR) takes over. so if your gonna cruise around with a big donkey dick cam, high SCR engine and never get in it ass then fine. but under a load, forget it

[blownarrow]

BUMP on my Question?


blownarrow; So whats thinkness should used when running the TDC pistons in an iron head? I'll also be running an Engel cam with a .489lift and a .277dur
So using WOT (ben) rule of thumb below, What would be my best bet for Compression / and Quench on my build?
Taking the stock 3400 for an example, we have a piston that has a flat area around the outside, and a heart shaped combustion chamber on the head with lots of flat area around the outside. This is a great design to put the mixture into the center of the cylinder. The stock piston sticks out of the block .020" and the head gasket is .060" thick. This leave .040" between the top of the piston and the surface of the head. .035-.045 is considered optimal quench distance, depending on the RPM you intend to run. For 5000 RPM on stock forged connecting rods, .035" is enough space. For 6000-7000, .040" is enough. Past that and .045" should be used. The reason being that connecting rods stretch at higher RPM. You must account for the stretch or there will be a greater possibility for piston to head contact.

For custom pistons, the piston height can be adjusted easily and either the gasket or head can be changed from a stock spec to give the beste quench. For stock engines, the following should help you choose your MLS gasket thickness

3100 - Piston sticks out .020". Head Gasket should be .060" thick (Stock)

3400 - Piston sticks out .020". Head Gasket should be .060" thick (Stock)

3500 - Piston sticks out .010". Head Gasket should be .050" thick (Stock is .060")

3.4 Iron Head - Piston sits .010" below deck. Head Gasket should be .030" thick. Compression will be increased but no problem on iron heads. Compression will be in the 13:1 range using 3400 heads.

[SappySE107]

I was hoping someone else would take a stab at this, but here goes.

91-95, .040 or .045 thick
96-97, good guess. .040 dome in the middle, so .040 and .045 might work, or it might cause a problem. I don't have that setup here to compare unfortunately.

[ForcedFirebird]

DCR will bleed off compression at low engine loads and rpm's. it can help a high compression engine run on lower octane with a big donkey dick cam. BUT under high engine load and higher rpm's when the engine starts to scavenge and gets really effiecent, you can thro the DCR out the window and the "REAL" compression (SCR) takes over. so if your gonna cruise around with a big donkey dick cam, high SCR engine and never get in it ass then fine. but under a load, forget it

Yes, it will bleed off compression according to a compression guage during cranking - but in a real running engine, those DCR calculators are way off. That was thinking from 40yrs ago, way before we had the kind of knowledge and technology to actually monitor an engine more closely. Hell, if you go back far enough, there was no such thing as overlap on a cam because if the intake and exhaust gasses were to mix, then that would decrease the efficiency of the internal combustion. Well, we later discovred that the intake gasses would help the exhaust gasses escape all that much better if they were to meet.

Fast forward to modern times.

As soon as people started modifying engines for speed (this came from outlaws wanting to outrun authorities ) we realized that overlap is a good thing since the piston actually stops it's vertical movement for a brief period and the intake charge being at full speed won't allow the exhaust to "revert" back into the intake tract, and since the exhaust gasses are still in it's expansion, will actually help "suck" the intake charge in.

With the current advancements in technology, science, physics, chemistry etc - we now know that if we take car in directing the flame in combustion cycle we can capture a lot more if the intake charge and can even achieve over 100% efficiency. Modern engines rune diesel-like compression ratios, get better gas mileage and use even more conservative cam specs (assuming your "BIG" cam is a long duration).

Maybe Ben will chime in with the specs of the cam in the 12.6:1 3400 with 3.4DOHC pistons and relatively early intake valve closing specifications - unless you can prove the theorem of the ever elusive DCR calculator, I beg to differ.

Spot on timing and fuel curves can make some pretty impressive outcomes.

[98goldZ]

maybe you misread or i mistyped something? what exactly are you begging to differ?