Deck Height Question

[h8my408]

I've been tossing an idea around with deck height clearance in relation to compression ratio. If I were to piece my own stroker kit together, and have the piston sitting in the hole, is there a negative effect other than lowering the compression? To give an idea, here is the math I am looking at. All of the numbers are calculated using standard engine math and specifications of the parts I would use.


Deck Height - 9.503
Stroke - 4.0
Rod Length - 6.125
Piston Compression Height - 1.17

Deck Height Clearance - 0.208
Compression - 7.57

My reasoning for this, compression only bumps horsepower 2% or so per FULL POINT. However, the detonation is raised or lowered significantly. With a turbo 351, I should be able to make large numbers on large boost with pump gas. Also I would be able to put rediculously large valves with lots of lift, with the extra clearance.

Am I missing something?

Jonathan

 

[347HO]

Yes, you're missing something important.
STATIC compression has almost no significants on a running engine.
I say this because the valve events actually control your cylinder psi, as well as ignition timing, spark plug protrusion and heat range.

When you deal with boost, boost is determined by the greatest restriction before entering the cylinder.
What I'm saying is you can have massive amounts of boost with little affect on cylinder psi, while on the other spectrum you may have a small amount of boost and a huge cylinder psi numbers.

 

[h8my408]

347 I understand what you're talking about, but that answer tells me nothing either way of what I am asking. Maybe I should ask this SPECIFIC QUESTION...

What is wrong with having a .208 deck height clearance?

 

[347HO]

My answer to your specific question would be "detonation" will occur with too much quench.

Because I haven't experienced this first hand, you should probably ask someone who builds engines for a living and/or has experience with what you're attempting to do.

In almost all cases at "our" level of engine building... .035" to .045" of quench is desireable.
This means your piston to deck height plus crushed gasket thickness = quench.

 

[rbonella]

pros

I've been tossing an idea around with deck height clearance in relation to compression ratio. If I were to piece my own stroker kit together, and have the piston sitting in the hole, is there a negative effect other than lowering the compression? To give an idea, here is the math I am looking at. All of the numbers are calculated using standard engine math and specifications of the parts I would use.


Deck Height - 9.503
Stroke - 4.0
Rod Length - 6.125
Piston Compression Height - 1.17

Deck Height Clearance - 0.208
Compression - 7.57

My reasoning for this, compression only bumps horsepower 2% or so per FULL POINT. However, the detonation is raised or lowered significantly. With a turbo 351, I should be able to make large numbers on large boost with pump gas. Also I would be able to put rediculously large valves with lots of lift, with the extra clearance.

Am I missing something?

Jonathan

I've been doing this for a while now. If I were you, the best way to do things is doing them correct once! Instead of getting opinions from the opinionated, call a couple well known engine builders locally or nationally and asked them your specific questions and tell them what you want out of the motor. They are the pros. Compare all the info and make an EDUCATED decision. What cam, what intake blah blah blah can be discussed here with not too much worry, but when you're deelin with expensive motor work....just ask the pros!

 

[h8my408]

Thanks for both of your responses. I have just the guy to call, I haven't thought about him until just now. Helped me out with a wicked 2.3T motor in a XR4TI.

 

[347HO]

Thanks for both of your responses. I have just the guy to call, I haven't thought about him until just now. Helped me out with a wicked 2.3T motor in a XR4TI.

This is good!
Post up what is said and what results would occur concerning your question. It will be interesting to read.

 

[vristang]

Yeah, let us know what this guys says...

By the way, I am planning out a 2.3t build right now... Can you send me a pm with this guys name? Or just post if he wouldn't mind...

The one local guy I know of that has experience with 2.3's is working on retiring... last time I tried he was tough to contact.

good luck,
jason

 

[h8my408]

So here's the laymens terms on quench as it was laymened out to me ...

The larger the quench, the more prone to detonation. The quench area is small because it creates velocity in the combustion chamber, which does a few things at once.

It forces the mixture to the center of the chamber so the sparkplug can get a more complete and even burn. While this is happening, it is cooling the chamber by creating velocity to cool any hot spots. With the quench as far away as I wanted it. There would be hardly any quench, and the hotspots would cause prefire and detonation.

I'm not sure if he wants me to state his name, with him being retired and all. The only reason I have any contact with him is because of my former roommate's dad and him were racing buddies in the days of the big cars and big blocks.

As for the 2.3 build, he didnt actually touch anything. Just pointers here and there. He offered to port my head, but because he was retired, I knew his work ethic. My roommate has an engine sitting with him, waiting for machine work. Its been 7 years. LOL.

Sadly, the motor didnt last long. I made a critical mistake when plumbing up the wastegate actuator (Completely closed the thing). I hit 27 psi untuned and no intercooler. Boom. Used 5.7 chevy length rods, wiseco pistons, and a crank out of a 2.5l ranger.

 

[rd]

Not sure I follow this.

.028 is a lot of deck clearance for a 5.0. I had my last on machined to nearly 0 deck height as part of blueprinting and raising the compression. This was a NA motor with iron GT 40 heads.

Add a gasket thickness and you are giving up some compression.

If you are setting this up for the specific purpose of lowering compression to work with a blower or turbo, this is certainly a good way to do it.

Theres nothing really wrong with it otherwise.

 

[347HO]

So here's the laymens terms on quench as it was laymened out to me ...

The larger the quench, the more prone to detonation. The quench area is small because it creates velocity in the combustion chamber, which does a few things at once.

I'm not sure if he wants me to state his name, with him being retired and all.

On the quench, keeping with layman's terms... I agree.
If "he" went further into it, using your boosted application, I'm pretty sure a flat top piston and quench is not the same as a dished piston and quench.

Your engine builder/machinist reminds me of someone I know down in the south Tacoma area.

 

[h8my408]

He didnt get much into it, and I didnt press. He was laughing pretty hard at the idea though. Liked my enthusiasm for an idea of a 35psi pump gas car.

Rd, I was not making a typo when I said ".208" piston to deck height. I was talking about some seriously large quench.

I've since come with another idea, and now have a 351 longblock that will be coming up for sale soon. I'll post that in the classifieds when the time is right.