Hybrid compression

[tomahawk]

I have a 4g64 with 4g63 1g head I'm building but the compression ratio came out out of my particular specs. Here are my blueprints:

4g64 .020" over 87mm bore, custom pistons still retains stock dish
Swept volume inc overbore:
594.47cc

piston crown volume
17cc

Head milled .007"
Stock head: 47cc
With mill: 45.78cc

MLS .054" head gasket (with 86.5mm bore, i know a little will be hanging in)
Volume: 8.06cc

If I'm not mistaken, the ring lands are flush with the deck at TDC, so there's zero spec there

Total volume 665.31cc
Combustion volume 70.84cc

9.4:1 compression ratio. Awful.

Since it is expensive to mill the head, does anyone know where to buy a decompression or a thick head gasket? I'm at a loss here.

 

[sb7775]

call cometic or call Race Eng. in florida. also there is a compression ratio calculator at Ross piston.com if u need it, go here first and figure out the size u need hope this helps thanx steve

 

[tomahawk]

I'll try race eng. I called cometic yesterday and it's $200 for a custom gasket. Ouch.

I remember seeing "stackable" MLS gaskets somewhere for less

 

[Defiant]

If I'm not mistaken, the ring lands are flush with the deck at TDC, so there's zero spec there

You are. The piston tops may come up flush to the deck, but the ring is as far down as the first groove.

Since it is expensive to mill the head, does anyone know where to buy a decompression or a thick head gasket? I'm at a loss here.

So am I. Milling the head (which should be less than $100) removes metal and makes your combustion chamber smaller, while a thicker gasket goes the other way. Which one do you want?

 

[tomahawk]

You are. The piston tops may come up flush to the deck, but the ring is as far down as the first groove.So am I. Milling the head (which should be less than $100) removes metal and makes your combustion chamber smaller, while a thicker gasket goes the other way. Which one do you want?

What in the world are you talking about?? Remove metal to make it smaller? How can I cut something to make it smaller? And if there is more volume in my cylinder head that will effectively lower my compression ratio. Same with the volume with a thicker head gasket. More combustion volume : cylinder volume is a lower compression ratio. You must've typed that up wrong

Machine shop quoted me $300 to mill the head. No way less than $100 else I would jump on it.


BTW I DID find a stackable head gasket, but like most parts--Honda only :thumbdown


EDIT: I did type my first post up wrong, I meant to say the piston crown

 

[TimG]

I am at a loss here too. If you mill the head (deck the head) (remove material from the mating surface of the head), then you are raising the compression ratio. Defiant is right, I believe you are wrong.

Stackable headgaskets are fine for Hondas, but when you start giving the engine a higher combustion cylinder pressures like a turbo does, things leak and blow a lot easier.

I even don't understand what's wrong with 9.4:1 compression ratio either. That's a nice ratio to work with. Low boost applications will yield high power results. This will keep the turbo alive for a longer time. The only real downside is the lack of error which can be made with tuning. Just tell your buddy not be be a bucket-head when he's tuning and he'll like the mid to high compression engine with a turbo.

$300 is insane. I had my head rebuilt and the head decked for $199CDN.

 

[tomahawk]

no no no, not mill the head surface. I'm talking about milling the combustion chamber

Misunderstanding

My engine is a 2.4, and it's for road racing. Yeah it'd be nice to have low boost / high compression, but I can only see a use for that particular engine setup in slow, winding courses like canyon roads (or autocross) where there isnt much time to stay on the throttle. But unless you're crazy and like left foot braking and not letting off the gas as hard. I have a friend that does that in canyons, adjusted his suspension so the back is loose, and the car slides through all the corners. it's definately something to see if you got the balls to ride with that guy. Also, the turbo i'm using doesn't like to see low PR's. have to take that into account. I'll just cave in and get that custom gasket from cometic.

 

[CanadianTalon]

II even don't understand what's wrong with 9.4:1 compression ratio either. That's a nice ratio to work with. Low boost applications will yield high power results.

Ever see that post on a honda forum? 10:1 netted 10 WHP off boost vs. 9:1 on a motor at 300 WHP. On 9:1 you can run 6-7 more pounds of boost than you can on 10:1 on pump gas. I'm pretty sure that 9:1 motor is going to make a pinch more horsepower with 7 more pounds of boost than the 10:1 motor will. Same goes for the comparison of a 8.5:1 and a 9.5:1 motor. I can see making a case for a 9.5:1 Honda where you're horribly limited by traction, and with a light ass car you don't need a ton of horsepower anyways, but with a heavy AWD DSM I want as much pump gas horsepower as possible.

 

[hose101772]

My engine is a 2.4, and it's for road racing.

Soooo..this road racing class requires pump gas or something?I'm not following.

Or are you wanting to run pump fuel?

 

[Defiant]

What in the world are you talking about?? Remove metal to make it smaller? How can I cut something to make it smaller? And if there is more volume in my cylinder head that will effectively lower my compression ratio. Same with the volume with a thicker head gasket. More combustion volume : cylinder volume is a lower compression ratio. You must've typed that up wrong

Machine shop quoted me $300 to mill the head. No way less than $100 else I would jump on it.

What do you think "milling a head" is? It's a flycut of the mating surface of the bottom of the head- the part that sits on the block. The part that sandwiches the head gasket between the block and the head. It's just a flat cut. Because it's removing the metal between the bottom face of the head and the top of the combustion chamber, it increases compression ratio. It takes away from the volume in your head.
Are you referring to porting, or unshrouding valves, or just what?

 

[blue1]

With the head gasket sitting in the bores is going to leave a hot spot! knocking is going to be your biggest issue. i have Cometic HO765 .051 with 87mm bore size! for my 4g64 hybrid.

 

[GTM]

What do you think "milling a head" is? It's a flycut of the mating surface of the bottom of the head- the part that sits on the block.
...
It takes away from the volume in your head.

Is that anything like a lobotomy...

No wonder they wanted to charge him $300 when the rest of us pay $50.

I don't know where he got all those numbers but they should be suspect for he may have inverted something there too. Hopefully he will get it right before he bolts anything together.

Cheers,
GTM

 

[gsx951]

What do you think "milling a head" is?

I'm thinking maybe he's a two-stroke guy. Recutting combustion chambers is very common there (but then they have no valves in their heads.)

 

[slvrstingray]

if your looking for a thicker head gasket... call up mitsubishi and find the head gasket that they use for all their reman engines. it is a multilayer metal headgasket that is very thick.

 

[tomahawk]

What do you think "milling a head" is? It's a flycut of the mating surface of the bottom of the head- the part that sits on the block. The part that sandwiches the head gasket between the block and the head. It's just a flat cut. Because it's removing the metal between the bottom face of the head and the top of the combustion chamber, it increases compression ratio. It takes away from the volume in your head.
Are you referring to porting, or unshrouding valves, or just what?

I'm thinking maybe he's a two-stroke guy. Recutting combustion chambers is very common there (but then they have no valves in their heads.)

Thank you. He understands; I'm not completely nuts.
Yes I am a bike guy at that too

 

[suicidal2af]

Ever see that post on a honda forum? 10:1 netted 10 WHP off boost vs. 9:1 on a motor at 300 WHP. On 9:1 you can run 6-7 more pounds of boost than you can on 10:1 on pump gas. I'm pretty sure that 9:1 motor is going to make a pinch more horsepower with 7 more pounds of boost than the 10:1 motor will. Same goes for the comparison of a 8.5:1 and a 9.5:1 motor. I can see making a case for a 9.5:1 Honda where you're horribly limited by traction, and with a light ass car you don't need a ton of horsepower anyways, but with a heavy AWD DSM I want as much pump gas horsepower as possible.

The key word there is off boost. You need to look at the effect it has on torque -- if it makes a 10 ft/lb difference across the rev range, you're going to be looking at some serious HP differences up top.

Higher CR will spool a turbo faster and make more power on equal levels of boost. End of story. You just need to do a better job tuning, or things go boom easier.

 

[FireyIce01]

I think your best bet is going to be to get new pistons or shorter rods.... though I doubt that's what you want to hear.... you might be able to take a die grinder and increase the size of your combustion chambers, but if you're going to do that, I would CC the chambers while you're increasing the size of them, make sure they're smooth, and that they all will hold the same volume (in CC's) of water... best done with a buret (I believe that's what it's called, long glass tube, with CC markings and a tee knob that allows you to drip measured amounts of water) which can be had from chemistry supply places... there was a good writeup on it in Hot Rod magazine a couplefew years back, but I'm sure you can find some info on it online

 

[GTM]

The key word there is off boost. You need to look at the effect it has on torque -- if it makes a 10 ft/lb difference across the rev range, you're going to be looking at some serious HP differences up top.

Higher CR will spool a turbo faster and make more power on equal levels of boost. End of story. You just need to do a better job tuning, or things go boom easier.

I would like to know how he got his numbers in his first post or who did them? I'm not confident in them until he indicates they are real and not something someone told him or some urban legend of the blind leading the blind.

Where does the 17cc dish in the piston come from, did he take modeling clay and then drop it in a graduate ... I seriously doubt it. Did he cc the head, does he know it's never been cut before?? Is it warped, what he going to do then. He wants a trick motor but is just going to ruin all the parts and labor it if he can't answer some basic questions.

Cheers,
GTM

 

[tt281gt]

I would like to know how he got his numbers in his first post or who did them? I'm not confident in them until he indicates they are real and not something someone told him or some urban legend of the blind leading the blind.

Where does the 17cc dish in the piston come from, did he take modeling clay and then drop it in a graduate ... I seriously doubt it. Did he cc the head, does he know it's never been cut before?? Is it warped, what he going to do then. He wants a trick motor but is just going to ruin all the parts and labor it if he can't answer some basic questions.

Cheers,
GTM

Yeah, tomahawk is an idiot! My gst ownz your car queer! .




























MODS: he is my buddy im kidding.

GTM: I beleive he had everything blueprinted by a machine shop.

 

[GTM]

Yeah, tomahawk is an idiot! My gst ownz your car queer! .

MODS: he is my buddy im kidding.

GTM: I beleive he had everything blueprinted by a machine shop.

Who is advising him on this project? If he doesn't understand basics of how machining a head will affect the head CC and CR how is he going to make this run?

You guys wouldn't be putting us on because you are board?

GTM

 

[CanadianTalon]

The key word there is off boost. You need to look at the effect it has on torque -- if it makes a 10 ft/lb difference across the rev range, you're going to be looking at some serious HP differences up top.

Higher CR will spool a turbo faster and make more power on equal levels of boost. End of story. You just need to do a better job tuning, or things go boom easier.

http://www.boosted-hybrid.com/viewtopic.php?t=1612

Tested a 10:1 motor then 9:1 compression. Spool up was exactly the same. 1-2 WHP off boost, 10 WHP on boost.

Hard factual data > your assumptions

 

[tmizer]

0.062 --> 9.16
0.080 --> 8.86
0.093 --> 8.67

That got me thinking as well as I just bought a SCE copper gasket to use with an o-ringed 4G64 block... I probably should've done the calculations beforehand, but thought the 0.062 gasket (9.02 on standard bore vs 9.16 on 0.020 overbore) would be fine....

 

[tomahawk]

Who is advising him on this project? If he doesn't understand basics of how machining a head will affect the head CC and CR how is he going to make this run?

You guys wouldn't be putting us on because you are board?

GTM

So you are telling me I don't know what I am doing. You shouldn't be replying if you don't know what you are talking about. My calculation for the compression ratio was correct and checked by a machinist who builds winston cup engines for 2 NASCAR teams. That comment was completely unwelcome. I didn't appreciate that one bit.

 

[tmizer]

87mm Cometic MLS gaskets are available for the 4G63.

0.074 and then 0.120 are the 2 largest sizes available. Consequently for your overbore:

gasket --> compression ratio
0.054 --> 9.38
0.074 --> 9.04
0.120 --> 8.35

The problem I think lies in the fact that there is volume above the top ring, and if the volume of the valve cutouts is not taken into account, all those will conspire to a BETTER compression ratio. One cc of extra volume in the head or maybe the valve cutouts, for example, will decrease CR by 0.1

 

[GTM]

So you are telling me I don't know what I am doing. You shouldn't be replying if you don't know what you are talking about. My calculation for the compression ratio was correct and checked by a machinist who builds winston cup engines for 2 NASCAR teams. That comment was completely unwelcome. I didn't appreciate that one bit.

My apologies, it wasn't clear that the intent was to _increase_ the combustion chamber volume by milling.

If you really want to know the cc rather than doing some rather complex angle, decreasing radius, tapers, etc. which may not provide the accuracy desired there is a quick and dirty method which will actually provide more reliable results.

Use a spray wax or anti-stick cooking spray such as "Pam" which will act as a mold release. Take some good quality modeling clay (artist supply store) and press it into the combustion chamber. You can use different size portions as you build up the "mold" just avoid trapped air pockets as you work it in. You will have it stand a little proud, you then trim this off with a stout bladed knife or a solid violin string which you can saw back and forth to trim level. Now you have the exact shape you pull the clay out hopefully all in one piece but may not happen, so you dig everything and add to the mass. With a "graduate" you fill partly to some measure mark that is enough to cover the clay. Remembering this number you drop the clay into the graduate, read the new number and subtract the the original. You can do same for pistons. Presto, there is your cc volume.

It took longer to write than it takes to actually do the job. Yes you can use a pipett but there are issues such as making the head level so it doesn't spill over the top edge. You can do this for each cylr so you can balance them exactly, make any modifications by welding or die grinding, changing valves etc. If you ever get "torn down" by the racing governing body (yes I did this for several years with SCCA) they will use either of these two methods. Usually they don't cc pistons for they will already have known set of tables for their displacement by manufacturer but if you tamper with them and your cc is found to be out of spec. you get disq.

If you want to have the machine shop rough them in and you do the final rework with a die grinder including polish you can save yourself some money. Of course the worst case is if you take too much out you then must heliarc it back in and rework.

Looks like others have given you gasket thicknesses so you know what to play with.

Cheers,
GTM