4g61t.org

As the title stated, I got the head machined what I figure is 6 thousandths because I had 3 thousandths warp.

So, I know that I have never been able to find the combustion chamber volume here or the theory concerning what I have ended up with...

Compression ratio = volumes + distance relationship
Cylinder head combustion chamber CC's or equivalent

Does anyone know what the stock figures might be?
I can pull up the bore, stroke and original Compression ratio but unless someone has spec'd this whole process I fear that I won't get a really accurate answer. That aside any speculation is welcome.

Tim

Is the head still off of the engine? The simple method would be to see how much water the CC holds, which is kind of hard to do when the engine is assembled.

_________________
Witty Signature Goes Here!

You're right. The head is off the engine and it is tucked away in the basement where it won't get dirty. What would be the most appropriate CC measuring tool; ie water dropper thingy with CC markings? drugstore item? I'm going to stop by the drugstore and see what they say.

All I need now is some clear acrylic stuff, drill a hole and some grease to block the water from draining.

And for those who are reading this, make sure the valves are installed (preferably after a valve resurface/new otherwise you may encounter a leak )

Thanks for the reply Kyle! Now it's time to pick up my rod bearings.... the last part I've been waiting for.

drumroll please budabudabudabudabudabubuda boom (my engine should be in soon...) The APC Glo-Pedals got installed last night, way rice but holy SChnikies are they ever cool to look at!!!!

Got the syringe from the drugstore and got the plastic drilled and greased, but as luck would have it my valves with the cam lined up from reassembly were letting water past them! I just had them resurfaced so I figure they are a little too tight on clearance ... yet another little thing I'll have to check after priming the engine just before she kicks over.

Well, that dashed my hopes of making that easy; I could lightly grease the valve faces and seat to get this pig to seal but I REALLY don't want to have to disassemble the head again to clean it. I just don't have any money left before she goes back together.

Sorry if I got anyones hopes up on finding out these specs, as they make for great coffee table chatter.

I know we'll get the specs someday.

I have been thinking of putting the CR from 9.2 upto about 10.2 maybe 10.5. I guess it would need to be about 0.010, best if someone can measure the combustion chamber though. Theres calculations out there to work out the CR from the combustion chamber cc.

As for comb. chamber measurements, wasn't it Archimedes who came up w/ that water displacement idea? Maybe filling the cc w/ some plastic stuff and throwing that into a scaled pot w/ water will do it.

_________________
Got rabies?

Jeepers Jimminy Crickets Batman, Eth how do you come up with this stuff?
Do you have too munich err much time on your hands?
More to the point, I like the sound of that idea as long as the plasticene comes back out with no issues.... now all I would need is plasticene and a measuring device large enough to fit a cylinder head into.

*edit*
I'm a nunce, just pull the plasticene out and measure it's volume, duh!
alright you may keep reading.
*edit*

I'm putting the head on tomorrow so I don't think that I would have time to do this though. oh well maybe someone will pick up where this conversation leaves off.

pumaproton,
Do you have the 12V head on your 4g15 or g15b? I can't remember your ride right now.
If you have the 12v valve head like me, the service limit on decking the head is .008" max, or so my dealer manual tells me.
I guess the only way of upping things is with taller pistons with proper reliefs or the valves and stuff ala hyundai x?? (I know the 4g15 tech has this stuff..) pistons or custom popups?
I'm starting to get 427 Super Cobra Jet flashbacks
*eyes roll back, falls over, body riddled with spasms*

I'd only worry about decking the head fully, then installing Hyundai pistons and having something meet, unless the hyundai pistons already had this margin of user error (of sorts ) dialed in. hmmmmm

Why not just use a compression guage after the head is installed?

_________________
Had a:
1991 Eagle Summit ES Hatchback - 4g15 12v 5spd
1991 Dodge Colt -4g15 12v 4spd
Have a:
1978 Oldsmobile Cutlass - 468BBO TH350
Round 3:
1990 Dodge Colt-4G63T 5spd

Well for one if you run better rings and they are a tighter fit or hold compression better than the original were disigned to, you might not have an accurate base for comparison

I have a 4G15, same as the EFI block/head but just has a carb on it.

Compression gauge doesn't give you a Compresiion Ratio, and you can't tell easily from it.

I can't believe you can only take off 0.008, that seems like a small margin. I have 0.008" listed as the Gasket Face Distortion service limit.

See this useful page: http://www.knology.net/~jediklc/D.htm

pumaproton,

I think that we just might be saying the same thing about the .008" limit. The manual shows this spec when referring to how much the head can be shaved to correct warpage.....hmmm maybe I should check the manual

1991 Dodge Colt 200 Chrysler Service Manual
Quote from ^

Chapter 9-59
Cylinder Block grinding limit = .008
Note
When the cylinder head is assembled, 0.2mm (.008 in.) or less of grinding is permissable.

Chapter 9-42
Cylinder Head
Standard Value: 0.05mm (0.0020 in.)
Limit: 0.2mm (.008 in.)

If the measured flatness exceeds the limit, grind and repair the surface to gain the flatness of standard value or less

Grinding limit: 0.2mm (.008 in.)
Note
When the cylinder block is assembled, 0.2mm (.008 in.) or less of grinding is permissable.

End Quote

So, I guess that only .008" total from the block deck height and the cylinder head cumulative is allowed in the case of the 4G15 as listed in ye' old manuel. I would have figured that there would have been a little more room too but when you consider the higher compression ratio that it already started with, it doesn't surprise me that much.

Good idea! Fill the chamber with something like modeling clay and smooth it flush with the head surface with a straight edge. Fill a graduated or marked cylinder to a predetermined level and then drop in the clay and measure the difference in displacement! I need to do this as well since i have a 4g15 head that ive ported and polished and was wondering how much i'll need to shave the head.
As for the manuals clearence reccomendations, they are maximum warpage limits that can be corrected. Remember if the head is warped too much, the cam will bind and eat theier journals. (Seen it in Hondas)Thats what those figures represent. Your only really limited by valve clearence issues and compression ratios.

_________________
http://members.cardomain.com/socrateez
04' Olds Alero
91' Colt GL hatchback
4g15 12valve 5spd.
4g37 TB, MAF & Injectors. 4g37 ECU
Ported & polished & custom CAI w/K&N filter
5* Cam retard, 7*Ignition advance
2-1/4" catback w/flowmaster muffler
89 GT brake and suspension swap
Lots of little s#@t

pheww I knew that sounded a little tight...... Thanks Socrateez

*bumpity bump bump bump*

Does anyone think that RPW or somebody like them will give me the time of day if I was to ask them what the stock 4g15 12V combustion chamber volume was, and what it would have maybe changed to, after decking the head .006"?

I really want to finish off this thread so maybe it can be used for good reference for everyone else. If I can get the specs or something very close then we can derive the compression ratio and use these figures to run a dyno sim on the Desktop Dyno stuff (my copy has been misplaced but somebody else I AM SURE has this lying around to plug in the relevant numbers to check power returns and stuff)

sigh.....

Sent an email to RPW today concerning the above post I made.

quote
Salutations from Ottawa, Ontario, Canada. Spring is just upon us here in the North and as a result the cars have been degreased, and opened up following their long winter romp. I have just had the pleasure (I use the term loosely!) of fully disassembling my 4g15 12V engine following a large oil consumption problem; engine scored 170-180 psi across the board but consumed it's crankcase oil entirely in under 1000 Km's. I took the head to a machine shop and had the valves resurfaced and the head apparently needed some material shaved to correct .003" inch for warping. I was told that the head was shaved .006" inch total. My main question concerns the original combustion chamber volume that a 12V head of this vintage would have, and secondly, what would the new combustion chamber volume be following the .006" shaving. Have I realised maybe a .1 compression ratio bump per .001" taken off the head? I have posed this question while entered in a discussion on the forums at www.4g61t.com but no one at the time had the tooling and means to perform this procedure. I myself ran dry of funding to fill the chamber (while it was off the head) with a putty or the like, to measure in a water/graduated chamber once removed. These numbers will give us some very useful archival info once realised. Full credit to you guys/gals will be posted following any assistance you may have in this regard.
Thank you in advance for your time and patience for reading my letter.
Tim Eagles
Member www.4g61t.com
end quote

Well, I've tried to start something here.... just crossing fingers now....