Is high compression on the cheap possible on an A20? (pump gas)

I'd like to raise the compression on my motor but I don't want to spend $$$ on custom pistons. The car is cheap and so am I.

I've heard of shaving the head but I don't know if it's possible on this car with valve clearance and the timing belt length.
Anyone gone this route?

Maybe pistons can be used from another Honda, or crank/rods to make a stroker (stroking a motor raises the compression with the same pistons)

I've heard of people using Vitara pistons in Civics to drop the compression for high-boost applications, I'm trying to go the other way because the car is carbed

Interested as well. I want to do a full e85 build.

Longer rods is a good possibility. B18C1 rods are .7mm longer, which won't make a huge difference. You could always look into some custom rods, the next available OEM length is 141.5, which will probably be too long. Either way, you will either need a matching set of pistons, or have your OEM ones modified to accept the larger wrist pin.

I take that back, according to Zealautowerks calculator, a 137.7mm rod length would put us about .5:1 higher. Makes almost 0 difference in Rod/Stroke ratio, but definitely effects compression.

you can weld the combustion chamber so the head only has room for the valves. use fuel injected pistons as they are 9.3

How can longer rods change your compression?
I understand rod/stroke ratio but if your piston starts higher it will just travel the same distance down the cylinder with the same crank giving you the same compression but worse piston to valve clearance

As for welding the combustion chambers that sounds like something a very experienced machine shop would have to do but I'll keep it in mind

If I look up replacement pistons for this car they are all the same part number no matter the year or submodel. I guess I would have to get them out of a junkyard LXi/SEi

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Originally Posted by POS carb

How can longer rods change your compression?

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Seems obvious to me. If the pistons come up higher in the cylinder when they reach top dead center, that compresses the air/fuel mixture into a smaller space.

I'd say using the technique to increase compression carries some risk, such as greater chance of blowing a head gasket. I think I'd look for other ways to tweak performance. I can't give examples because this is not an area I've delved into. Some other members here may have some tips on this.

Using longer rods might work but I bet it won't be cheap. And adding 0.7mm to the rod length will only get you about 0.5 compression points.

By far the cheapest option is to mill the head. My experiments indicate that you should be able to mill up to 2mm off the head without running into problems with the coolant passages. It should still be safe with the valves too but so far this is just theoretical. I've never heard of anyone that actually tried more than about 1mm off. Milling the head will alter the cam timing a bit so you might want to get an adjustable pulley if you want to push it very far. You wouldn't have to though, it won't change a lot.

If you start with A20A1 pistons the stock compression ratio is about 8.8:1. Taking 1mm off the head will get you to 9.4:1. 2mm will get you 10.2:1.
If you start with A20A3 pistons the stock compression ratio is about 9.1:1. Taking 1mm off the head will get you to 9.9:1. 2mm will get you 10.8:1.


Welding up the combustion chambers is a decent way to go too as it doesn't affect cam timing or valve clearance. The question though, is how much difference can you make with this method. I only know of one instance where it was done on an A20 (the old Open Loop car had a welded up head. There may even still be pictures somewhere), but I don't recall there were ever any measurements taken. It would need to be done by a professional but it's not an especially exotic thing to do. The casting I'm planning to use for my big valve head (whenever I get around to finishing it) had some pitting corrosion around the coolant passages that had to be welded up. It wasn't any big deal for the shop that did it. Combustion chambers would be more difficult since you have to be careful of the valve seats, but it's not that big a deal. Probably the harder part will be grinding the chambers back down again to get them evened out to all the same volume.


Another option is to put in some domed B series pistons and rods. Not going to be very cheap though.


C|

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Originally Posted by cygnus x-1

Using longer rods might work but I bet it won't be cheap. And adding 0.7mm to the rod length will only get you about 0.5 compression points.

By far the cheapest option is to mill the head. My experiments indicate that you should be able to mill up to 2mm off the head without running into problems with the coolant passages. It should still be safe with the valves too but so far this is just theoretical. I've never heard of anyone that actually tried more than about 1mm off. Milling the head will alter the cam timing a bit so you might want to get an adjustable pulley if you want to push it very far. You wouldn't have to though, it won't change a lot.

If you start with A20A1 pistons the stock compression ratio is about 8.8:1. Taking 1mm off the head will get you to 9.4:1. 2mm will get you 10.2:1.
If you start with A20A3 pistons the stock compression ratio is about 9.1:1. Taking 1mm off the head will get you to 9.9:1. 2mm will get you 10.8:1.


Welding up the combustion chambers is a decent way to go too as it doesn't affect cam timing or valve clearance. The question though, is how much difference can you make with this method. I only know of one instance where it was done on an A20 (the old Open Loop car had a welded up head. There may even still be pictures somewhere), but I don't recall there were ever any measurements taken. It would need to be done by a professional but it's not an especially exotic thing to do. The casting I'm planning to use for my big valve head (whenever I get around to finishing it) had some pitting corrosion around the coolant passages that had to be welded up. It wasn't any big deal for the shop that did it. Combustion chambers would be more difficult since you have to be careful of the valve seats, but it's not that big a deal. Probably the harder part will be grinding the chambers back down again to get them evened out to all the same volume.


Another option is to put in some domed B series pistons and rods. Not going to be very cheap though.


C|

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i really think welding the combustion chambers is the way to go. its the most cost effective. Changing pistons and rods is a total waste for a modest increase in compression ratio. Just how much more power do you guys think you are gonna make with this? The only way to realize any potential hp gain is to go obd1 and get a tune, and even that wont be much unless you add a intake, header/full exhaust and possibly cam...

Openloops LX-i coupe is a perfect example

I have the intake carb and full exhaust. I'd definitely put a cam in there, they're cheap. I just didn't want to run into a shitty weld job that causes hot spots in the combustion chamber, I figure any shop can mill a head easier/cheaper.
I just want to add some grunt the old fashioned way. This car is not worth the expense of a turbo or even an efi conversion
How much advance/retard can I get by just moving 1 tooth on the stock cam gear?

http://carphotos.cardomain.com/ride_...0055_large.jpg
It looks like there are 42 teeth... so 360 divided by 2 (cam spins at 1/2 speed) divided by 42 equals about 4.3 degrees???? sounds like too much
not sure how many degrees a mill would retard

Did someone say cam? :)
http://www.paeco.com/Honda%20Cams.htm

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Originally Posted by POS carb

I have the intake carb and full exhaust. I'd definitely put a cam in there, they're cheap. I just didn't want to run into a shitty weld job that causes hot spots in the combustion chamber, I figure any shop can mill a head easier/cheaper.
I just want to add some grunt the old fashioned way. This car is not worth the expense of a turbo or even an efi conversion
How much advance/retard can I get by just moving 1 tooth on the stock cam gear?

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1 complete tooth would be 360/42 ~= 8.5 deg. The crank spins twice the cam speed so that would be about 17 crank degrees. That's a lot, which explains why peoples engines run badly when the timing belt if off even 1 tooth.

I measured the cam pulley at ~4.75" diameter, so after converting to mm that's about 380mm circumference. 1mm off the head would be 1/380 * 360 = 0.95deg, which would be about 2 crank degrees. Not enough to matter a whole lot, although it might be measurable on a dyno if you took a bunch of runs.


After welding you would have to go after the chambers with a grinder to smooth everything out and equalize the volumes. Done correctly it can give a fair amount of improvement. But you're right, it takes more skill (and therefore cost) so milling will be cheaper.


Incidentally, if you wanted to build an engine for E85 only you would want to be in the 12-14:1 range. I was toying with the idea awhile back and figured out that you would need to weld up the chambers and mill about 2mm off the head to get into that range. Or use custom domed pistons. It would be an expensive project and now you're stuck running E85 or race gas only.


C|

Yes I'm thinking with Al heads 12.5 compression would be a start. it would be nice to flip back and forth between gas and e85 but be hard to do and have a nice e85 build.

Make it a true Flex-fuel car :)

http://proefi.com/info/applications/honda/

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Originally Posted by cygnus x-1

1 complete tooth would be 360/42 ~= 8.5 deg. The crank spins twice the cam speed so that would be about 17 crank degrees. That's a lot, which explains why peoples engines run badly when the timing belt if off even 1 tooth.

I measured the cam pulley at ~4.75" diameter, so after converting to mm that's about 380mm circumference. 1mm off the head would be 1/380 * 360 = 0.95deg, which would be about 2 crank degrees. Not enough to matter a whole lot, although it might be measurable on a dyno if you took a bunch of runs.


After welding you would have to go after the chambers with a grinder to smooth everything out and equalize the volumes. Done correctly it can give a fair amount of improvement. But you're right, it takes more skill (and therefore cost) so milling will be cheaper.


Incidentally, if you wanted to build an engine for E85 only you would want to be in the 12-14:1 range. I was toying with the idea awhile back and figured out that you would need to weld up the chambers and mill about 2mm off the head to get into that range. Or use custom domed pistons. It would be an expensive project and now you're stuck running E85 or race gas only.


C|

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Or you could get longer rods :)

141mm Rods would put you at about 14.5:1. Assuming we have room for rods that are 4mm longer

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Originally Posted by 2drSE-i

Or you could get longer rods :)

141mm Rods would put you at about 14.5:1. Assuming we have room for rods that are 4mm longer

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14.4:1 sounds like a valve smasher!

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Originally Posted by Legend_master

14.4:1 sounds like a valve smasher!

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milling will work fine, yes. But you can forget going E85 with the stock carb type setup. Youd need a seriously modded carb to account for the e85. To support the same hp level on 85 youll need about 40% more fuel than gasoline (richer mixture) to make the same hp. So if you just want a little added kick, get a reground cam, and have the head milled to up the compression, then set the timing back to stock and rock it as is with the exhaust/setup you already have. I wouldnt even bother for e85 plus itd prolly corrode the carb badly.

Even if you had a totally flat top piston and ran it all the way up to the head surface you would still only get around 11.5:1 compression. The combustion chamber is just too big. You would need some big carbs to support it too (if you want to stay low tech).

Somewhere around 10.5:1 is probably a good target for regular pump gas.


C|

Other option is my route, A20A3/4 pistons oversized to 83mm, then skim the head 1mm (1.5mm is fine too I've gone that far), deck the block .5mm then look around for a rare A18 head in good condition (that's the hard part!) this should get you easily to 11-11.5:1 higher if you go further on the head skimming to 1.5 - 2mm off. If your not running huge lift this should be fine my engine has 33mm inlet and 37mm exhaust valves currently and the pistons are stock A20A3/4 without pockets increased in size run a 285 degree cam with 10mm lift and I've had no issues what so ever with valve contact happily revs to 8500rpm all day long! :) But you do need to check clearance with what ever you go with using plastigauge or similar because every engine is different and so are the parts depending on when they were made etc.
Instead of wasting good money on aftermarket rods I'd say just make up some custom pistons for the stock rods with flat tops and only 3 valve reliefs per piston this combined with bit of head skim and deck skim should get you high enough CR ration I don't like domed pistons as they don't put a nice even spread of combustion on the piston and also added stress on our already weak choice of head gaskets.

BTW having longer rod means you'll have to chamber match the head to the bores and make sure it's perfect because anything sticking out will get clouted by pistons coming up, I know the head gasket is thick but .7mm with a deck to the block to flatten it square for rebuild could be a close call. Although when cold the difference is ok when the engine has heated up and at maximum revs you could end up a lot closer than you think! Plus all the aftermarket rods are much heavier, if your using as N/A engine better off with stock rods, have them balanced, polished and stress relieved new lighter wrist pins and re torque the stock bolts to 35lbft instead of 25lbft and use loctite. I've only had one instance of rods failing and that was due to a mate of mine that missed 5th gear and planted it into 3rd gear at 140mph the rods or bolts stretched and after a few hundred miles two of them failed and went straight through the side of the block :( Other than that every other stock rod I've used and have been many have been fine on a N/A engine and all revved happily to 7500-8000rpm.

you will need a head to flow really good to get the motor to spin up got 8.5k. also he has carb trans so the gears are long. i had teg gears in my trans and the motor used the powerband much better. personally i would not rev the a20 more than 7500rpm

Quote:

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Originally Posted by cygnus x-1

1 complete tooth would be 360/42 ~= 8.5 deg. The crank spins twice the cam speed so that would be about 17 crank degrees. That's a lot, which explains why peoples engines run badly when the timing belt if off even 1 tooth.

I measured the cam pulley at ~4.75" diameter, so after converting to mm that's about 380mm circumference. 1mm off the head would be 1/380 * 360 = 0.95deg, which would be about 2 crank degrees. Not enough to matter a whole lot, although it might be measurable on a dyno if you took a bunch of runs.


After welding you would have to go after the chambers with a grinder to smooth everything out and equalize the volumes. Done correctly it can give a fair amount of improvement. But you're right, it takes more skill (and therefore cost) so milling will be cheaper.


Incidentally, if you wanted to build an engine for E85 only you would want to be in the 12-14:1 range. I was toying with the idea awhile back and figured out that you would need to weld up the chambers and mill about 2mm off the head to get into that range. Or use custom domed pistons. It would be an expensive project and now you're stuck running E85 or race gas only.


C|

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Was thinking if you used a reground cam you could tell them you wanted it reground 2 degrees advanced.

You can easily modify the stock cam gear to cover that if you wish but a ally one would be better as you can easily adjust the range and find the sweet spot of the cam for the most power.

Accord gears aren't that bad 1-4 are ok just 5th is pretty tall always splash a bit of NOS on! :)

A20 that's blueprinted can handle 8500rpm easy mine kinda proves that! But we weren't talking about revs was just using mine as example of what you can achieve on a ghetto build. As all my engines use stock OEM parts just everything is hand assembled and blueprinted. Only thing that isn't stock is the inlet manifold, carbs and a few custom valves you can use old exhaust valves as inlets and have 4 new custom stainless big valves done.

I suppose if your increasing valve size this will decrease chamber volume size so you can't rule it out! lol! especially if you have no dish in the valve heads so they're nice and flat.