00Vette04GTO

Ok... So always worked on cars as a hobby. Have assembled a few engines and taken many more apart. I've put on about every part that exists on a car and stripped them completely. But it's time I learn more about what I am doing. I am working with a great platform here, so why just throw parts together from off the shelf.

This is my first adventure down this road and I thought it might be useful to share and also get your thoughts on my way. This should come full circle in the next 1-2 weeks max so stay tuned as the math and decisions progress.

Working with a machine shop for the machine work, my dyno guy to lead me down the right path, and my hands to do the work.

Long story short, I purchased a new engine from the internet - and this guy did what I would have done. Threw a bunch of parts together and called it an engine. The specs he told me the engine were do not even closely match reality. After some issues I have decided to bite the bullet and do this engine right.

So while my heads are at the shop getting repaired from my builders mistakes I am taking some measurements to decide how to optimize this engine's performance. Measuring is simple and done with a $20-$50 dollar digital caliper from your local parts store.

(Measurements in standard US)

Bore size: 3.903
Stroke: 3.650 (supposed to be 3.633 so I am going to talk to dyno guy and remeasure)
Head gasket: .050
Valve recesses in pistons (flat top): .155
Squench: -.017

Head Specs:
trickflow generation X
FAST AS CAST 220 cylinder heads for LS2
205.5 intake valve
1.570 exhaust valve
65cc

Comp 1.72 Roller Rockers (which is why my heads are at the shop - to machine down the guides so the valve stem seals dont bottom out)


We are going to work to optimize my compression and cam to take advantage of these heads. We are a little worried about the large valves for the LS2 heads bottoming out on the LS1 bore - so waiting to hear from dyno guy to give him these specs to see what he thinks. I want to shave the heads down for compression but we need to be careful.


More to come... Stay tuned!

00Vette04GTO

RonSSNova

Seems like you have a good foundation assuming the machine work is good.
You will need to see how many CC those valve reliefs are when calculating compression ratio. I would think most aftermarket peestons would accomodate the larger valves in your heads.

I have the AFR heads, 2.02 and 1.60 valves and have stock pistons. My PTV is close at .075", but no issues. You won't have a problem there.

You can use more cam, just depends on what idle quality you want to live with and how good your tuner is at making it idle well. The converter will play a role as well. 114 lobe sep will be easier to make idle well, as opposed to 112.

Fun project, I'm glad you are slowing down and doing it right!

Ron

00Vette04GTO

Ok... Dyno guy is happy with the numbers I gave him.

He had a car on the dyno at the time, so he will call me back in a while with more detailed info.

Dyno guy is happy with that but wouldn't mind seeing 3ccs shaved off the heads.

So just waiting on a call back from him to tell the machine shop how much to take off the heads, and then we are going to discuss cams.

So after talking to him I decided to do my own math to learn what's going on here. I want to know what compression ratio I am at now.

First My Numbers (couple of small corrections)

Bore size: 3.903
Stroke: 3.633
Head gasket: .050
Head gasket bore: 3.998
Valve recesses in pistons (flat top): .155
Valve Recess (cc): -3cc
Squench: -.017

Head Specs:
trickflow generation X
FAST AS CAST 220 cylinder heads for LS2
205.5 intake valve
1.570 exhaust valve
65cc chamber volume





First we need to break some things down.

Cylinder volume = 0.7853982 x bore2 (squared) x stroke

so
Cylinder volume = 0.7853982 x 15.233409 x 3.633
Cylinder volume = 43.46627286674899


Clearance volume = 0.7853982 x bore2 x squench
Clearance volume = 0.7853982 x 15.233409 x .017
Clearance volume = -0.2033929641438846

Piston dome or dish (valve recess) in cubic inches = cc's x 0.0610237
Piston Volume = 3 x 0.0610237
Piston Volume = 0.1830711

Head-gasket volume = 0.7853982 x gasket bore2 (squared) x compressed thickness
Head-gasket volume = 0.7853982 x 15.984004 x .050
Head-gasket volume = 0.62769039851964

Chamber volume in inches = cc's x 0.0610237
Chamber volume in inches = 65 x 0.0610237
Chamber volume in inches = 3.9665405

Then we take this formula:
Compression Ratio =
Cylinder vol. + clearance vol. + piston Comp. vol. + gasket vol. + chamber vol. divided by Clearance vol. + piston vol. + gasket vol. + chamber vol.

So:
Compression Ratio = (43.46627286674899 + (-0.2033929641438846) + 0.1830711 + 0.62769039851964 + 3.9665405) / ((-0.2033929641438846) + 0.1830711 + 0.62769039851964 + 3.9665405)

Compression Ratio = 48.0401819011248 / 4.57390903437576
Compression Ratio = 10.503090800467

Compression Ratio = 10.5:1

RonSSNova

What measurement is squench?

Here is a handy online calculator.

http://www.kb-silvolite.com/calc.php?action=comp

Assuming your squench measurement is how far out of the hole the pistons are (my stockers are .008 out), this calculator says you are at 10.45:1

Which kind of makes sense given the large head volume and the 3cc valve reliefs.

Ron

00Vette04GTO

Space that my pistons stick above or below the deck of the block (he gave me the terminology - so correct me if i am wrong) at TDC

In my case it is above the block (negative)

RonSSNova

The calculator calls it deck clearance, negative number if above.
Give it a whirl!

Ron

00Vette04GTO

Will do... Thanks Ron!

Still wanna try to figure out where I went wrong in my math there... Hopefully I will figure it out in a few and will revise if I do. (I have a curious mind)

PhysicsDude55

I get 10.5 : 1 compression ratio with the numbers you gave.

I think what's tripping you up is the piston dish volume ADDS to the umcompressed and compressed volumes, not subtracts.

I get an uncompressed volume of 48.04017 C.I.
and a compressed volume of 4.57387 C.I.

00Vette04GTO

That was it... You are tha man!

Updating math in above post now.

00Vette04GTO

So doing some further math my builder seems to be dead on. If I take 3ccs off of the heads:

Chamber volume in inches = cc's x 0.0610237
Chamber volume in inches = 62 x 0.0610237
Chamber volume in inches = 3.7834694

Compression Ratio = (43.46627286674899 + (-0.2033929641438846) + 0.1830711 + 0.62769039851964 + 3.7834694) / ((-0.2033929641438846) + 0.1830711 + 0.62769039851964 + 3.7834694)

Compression Ratio = 47.8571108011248 / 4.39083793437575
Compression Ratio = 10.8993115929998

Compression Ratio = 10.90:1



Now I just need to make sure that I don't bottom the valves out on the pistons... But that can be done with a little less lift on the cam (if necessary) so I should be ok, right?

RonSSNova

With those valve reliefs, you won't have an issue. The TFS heads also roll the valves to 12 deg instead of the stock 15, which helps some more.

Lift isn't the determining factor, duration and cam timing are.

Ron

00Vette04GTO

Ahh... Gotya. You are correct. It is going to come down to where my valve is at when the piston is TDC - which is more of a cam duration/timing deal.

So out of curiosity... Doing a little more math if you multiply my uncompressed volume times 8 you get 384ci... Does that basically mean with these heads I have a 384ci motor? (I know people generally stroke/bore to get the extra ci) or does a motor's ci only refer to engine block?

I apologize if this is a stupid question... But as I said I'm a "former" parts swapper that's been trying to learn more and more as I go. Pretty good on diagnostics but fall short on the actual mechanical engineering aspect of it.

RonSSNova

Just the bore, stroke and # of cylinders determines the CID.

Not a dumb question!

Ron

00Vette04GTO

Ok guys... Heads are rebuilt! Heading out to pick them up from the machine shop now. He actually took 1 more cc off the heads than I wanted but I think I'll be ok.

Chamber volume in inches = cc's x 0.0610237
Chamber volume in inches = 61 x 0.0610237
Chamber volume in inches = 3.7224457

Compression Ratio = (43.46627286674899 + (-0.2033929641438846) + 0.1830711 + 0.62769039851964 + 3.7224457) / ((-0.2033929641438846) + 0.1830711 + 0.62769039851964 + 3.7224457)

Compression Ratio = 47.7960871011248 / 4.32981423437576
Compression Ratio = 11.0388308860128

Compression Ratio = 11.04:1

Now we get down to which cam... Any suggestions or ideas as to how to correctly spec this? I want max power but as decent idle as possible. (camming is good, but I do want to drive this on the road). I have a 3000 stall converter.

My dyno guy's pretty slow in responding - and a lot of times I have to keep calling... So no recommendation from him yet.

Will post pics of the freshened heads in a little while, when I get back.

-Mike

00Vette04GTO

Just talked to my dyno guy... He is recommending roughly these cam specs:
236-238 intake
234-235 exhuast
110-112 lsa
.600 lift

Any opinions? He says this will be the best cam for bottom end power, while maximizing horsepower/torque. He says we could definitely get more horsepower with a bigger cam, but it's a tradeoff of low end power. So he wouldnt go any bigger. Do you guys agree?

00Vette04GTO

00Vette04GTO

I personally would like to go with a bigger cam, but am inclined to listen to my dyno guy...

Can you guys give me some thoughts on the cam? I have these good heads - I'd like to put them to use.

RonSSNova

Have you asked over on LS1TECH?
Way more cam guys over there.
Tick performance can set you up as can EPS (Engine Power Systems)
Both offer custom grinds. Tick would have some really good shelf grinds.

Ron

00Vette04GTO

Actually did post over there - after here - as I had the same thought that they might be more into that aspect of theses engines. They referred me to Brian Tooley, Tick Performance, and Ed Curits (FlowTech Induction). Have contacted all 3 and am awaiting a response from them. The guys at LS1Tech seem to think any of them will have a field day with me having all my numbers together for them... I'll keep ya updated on what I find out and how the build goes.

-Mike