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

  1. #26
    3Geez Veteran gfrg88's Avatar
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    Re: Is high compression on the cheap possible on an A20? (pump gas)

    What about destroking, using an a16 crank? Wouldn't that be a lot more rev happy without much problems? Has anyone tried that?
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    cygnus x-1's Avatar
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    Re: Is high compression on the cheap possible on an A20? (pump gas)

    Quote Originally Posted by gfrg88 View Post
    What about destroking, using an a16 crank? Wouldn't that be a lot more rev happy without much problems? Has anyone tried that?
    The idea has been brought up before, but I've never heard of anyone trying it. It would be interesting to try, but I'll keep my low end torque thank you.


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

    What chamber cc,s are you using for your compression calculation?
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    Re: Is high compression on the cheap possible on an A20? (pump gas)

    No replacement like displacement and at the end of the day the rod stroke ratio is way better than B20A it's also pretty similar to B18 which has no issues revving away! and we have extra 200cc to boot! Plus my engine definately has no issues with high revs and it picks up revs so quickly compared to modern engine with their heavy counterweighted cranks, double cams, and extra 4 valves plus vtec valve train. With a custom header I'd easily expect peak power to increase in the rev band as well as overall probably to something like 7800-8000 rpm and power to be at 210-215bhp. With a decent camshaft with more lift and little more duration I'd expect to see 220-230bhp at 8000-8200rpm with a still a decent torque figure of around 170-180lbft at 5750-6000rpm.

    Even as it is I have lots of low down power and with the car weight being so low it picks up really quickly from lower revs it's quite driveable on the road just in traffic it's tricky with lightweight flywheel so can hop around a bit.

    I think with a nice set of forged pistons oversize in 83.25mm with titanium wrist pins, possibly titanium rods from Eagle for B series, coupled with the header, camshaft and some better designed titanium valves and retainers this engine could potentially get near 250bhp mark. Although I'd still kill to find out what King motorsport did to get 340bhp!!

  5. #30
    DX User hatch88lxi's Avatar
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    Re: Is high compression on the cheap possible on an A20? (pump gas)

    Still a bit confused on the b18c1 rods! can we use them and still mill the head? can we use them at all without any mods? and will they bolt right up?

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    cygnus x-1's Avatar
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    Re: Is high compression on the cheap possible on an A20? (pump gas)

    Quote Originally Posted by Oldblueaccord View Post
    What chamber cc,s are you using for your compression calculation?
    I'm using 47cc. This was measured on an A20A1 head I rebuilt in 2006.



    Quote Originally Posted by hatch88lxi View Post
    Still a bit confused on the b18c1 rods! can we use them and still mill the head? can we use them at all without any mods? and will they bolt right up?
    Not directly because the wrist pin diameter is 1mm too big. You could is you used B18 pistons.


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

    sorry to thread jack, but is it possible to mill the head 2mm and use the b18c1 rods and pistons without have any interference or valve issues?

  8. #33

    cygnus x-1's Avatar
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    Re: Is high compression on the cheap possible on an A20? (pump gas)

    Quote Originally Posted by hatch88lxi View Post
    sorry to thread jack, but is it possible to mill the head 2mm and use the b18c1 rods and pistons without have any interference or valve issues?
    Umm, maybe? This is kind of getting into an area where no one has gone before. 2mm off the head will mean that the valves are protruding below the head surface at max lift, so piston shape and valve timing are going to matter a lot. What goal are you trying to achieve with this? There may be a better way to get there.


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

    You can't just drop B18 rods and pistons in it's not that simple, you need to make sure you have the engine bored to the size pistons your getting that you have the correct clearances for either stock cast pistons or aftermarket forged ones, forged pistons need more clearance as they expand more when hot. Also you need to check rod big ends clear the block castings especially if they're aftermarket as they'll be alot chunkier, and then also make sure that the bearings you use the correct size for your crank journals. You'll need to get rings that are preferably oversize and have them gapped to each bore size by hand, with 2mm off the head and B18 pistons your valve reliefs will be in different places to stock, with the pistons sticking out a tiny bit more than stock the valves are going to need to be clearing those, you may well have to machine a tiny bit off the valve relief pockets to make sure they clear, also you need to make sure that the chambers are bore matched as you could run risk that when engine gets very hot that the piston crown could hit the edge of the chamber walls. They'll be lot's of test fitting and using plastigauge to make sure things clear and there should allways be a little extra clearance nothing should just clear or it will end in disaster on a engine that's just run in and then warmed up fully. You'll also have to factor in what type of cam you'll be using, howmuch lift and duration, upgraded valve springs make sure the valve don't float at high rpm etc. Engines that are just chucked together tend to last minutes rather than years.

  10. #35
    3Geez Veteran gfrg88's Avatar
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    Re: Is high compression on the cheap possible on an A20? (pump gas)

    Just to clear things up, it's LS(B18A/B1) rods that we use. Not GSR ones. They're too long I believe
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  11. #36
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    Re: Is high compression on the cheap possible on an A20? (pump gas)

    Quote Originally Posted by cygnus x-1 View Post
    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.


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    Pic of Open Loop head. 44cc
    Click image for larger version. 

Name:	welded A20a3 head (44cc).jpg 
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    Originally Posted by Justanothermike
    my A20 is not SLOW. ur A20 is slow.

  12. #37

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

    That's the one. ^^^^^

    I wonder what ever happened to that head?

    EDIT: Wait, is that 44cc the combustion chamber volume? If so that's only about 3cc less than stock, which is barely any difference at all. It has been reshaped though. Hmm.



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    Last edited by cygnus x-1; 04-15-2013 at 10:05 AM.

  13. #38
    SEi User Strugglebucket's Avatar
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    Re: Is high compression on the cheap possible on an A20? (pump gas)

    It's been a LONG time, but 44cc was the title I had saved the picture as.

    I think that adding the quench zones would be as much of an improvement, if not more, than the moderate increase in compression.
    Originally Posted by Justanothermike
    my A20 is not SLOW. ur A20 is slow.

  14. #39
    3Geez Veteran lostforawhile's Avatar
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    Re: Is high compression on the cheap possible on an A20? (pump gas)

    i like this thread, so basically shaving the head two mm would give you a decent bump in compression without too much trouble? Im going to be working on another engine eventually anyway

  15. #40

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

    Quote Originally Posted by Strugglebucket View Post
    It's been a LONG time, but 44cc was the title I had saved the picture as.

    I think that adding the quench zones would be as much of an improvement, if not more, than the moderate increase in compression.
    Yeah, that could be. I think I would still mill a bit off that head just because.


    Quote Originally Posted by lostforawhile View Post
    i like this thread, so basically shaving the head two mm would give you a decent bump in compression without too much trouble? Im going to be working on another engine eventually anyway
    Pretty much. The cam timing will (probably) have to be adjusted (it would be 4 degrees off). The valves should be ok but it would be a good idea to clay the chambers for confirmation. The only other potential issue is that the intake manifold might hit the coolant tube with the head 2mm lower. I mention this because the Manifold for my ITBs had really big bolt hole tabs on the under side, and would hit the coolant tube
    even with an un-milled head. It might just be that particular manifold but it's a good thing to check. Grinding down the tabs helped but I also ended up modifying the coolant tube to sit lower on the block.


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    3Geez Veteran lostforawhile's Avatar
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    Re: Is high compression on the cheap possible on an A20? (pump gas)

    Quote Originally Posted by cygnus x-1 View Post
    Yeah, that could be. I think I would still mill a bit off that head just because.




    Pretty much. The cam timing will (probably) have to be adjusted (it would be 4 degrees off). The valves should be ok but it would be a good idea to clay the chambers for confirmation. The only other potential issue is that the intake manifold might hit the coolant tube with the head 2mm lower. I mention this because the Manifold for my ITBs had really big bolt hole tabs on the under side, and would hit the coolant tube
    even with an un-milled head. It might just be that particular manifold but it's a good thing to check. Grinding down the tabs helped but I also ended up modifying the coolant tube to sit lower on the block.


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    the intake manifold is not an issue in my case lol , I know when I was doing the timing belt and valve springs, with the piston on TDC the valve would go all the way to the retainer before it hit the piston, it might be different on the BS vs the later A series though, so add an adjustable timing gear and you are in good shape, do you think the 2mm will affect the head bolt torque or will you need shorter head bolts? something to ponder
    Last edited by lostforawhile; 04-16-2013 at 09:55 AM.

  17. #42
    3Geez Veteran lostforawhile's Avatar
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    Re: Is high compression on the cheap possible on an A20? (pump gas)

    this brings up the methanol/water injection theory, normally you would use it on a boosted car, but this also would allow you to increase the octane rating of regular pump gas, and allow you to increase the compression without needing premium, I was looking at the technical setups in the snow kits, they have a stage one boost kit, which can also be triggered by any input, in non boosted applications, you can use an rpm switch, this would allow me to run 87 with high compression, and anything above about 4000 rpm,which is where they recommend spraying, no lower rpm, if it was setup to just above normal cruise rpm, it would prevent detonation when you were on the gas. it's a pretty simple setup, you can also adjust spray pressure up or down, it's not a power adder, it just cools the charge and effectively raises your octane rating. the tank can also be mounted at the rear of the car, the only issue I saw, and I will have to ask them, my intake splits into two Y runners after each carb, so i would need two nozzles one just after each carb. i dont mind running premium on a car that wont be driven every day, but the problem is, it's often not available here, when gas prices go up, a lot of the stations just dont order anything but 87
    Last edited by lostforawhile; 04-19-2013 at 08:20 PM.

  18. #43
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    Re: Is high compression on the cheap possible on an A20? (pump gas)

    Quote Originally Posted by lostforawhile View Post
    the intake manifold is not an issue in my case lol , I know when I was doing the timing belt and valve springs, with the piston on TDC the valve would go all the way to the retainer before it hit the piston, it might be different on the BS vs the later A series though, so add an adjustable timing gear and you are in good shape, do you think the 2mm will affect the head bolt torque or will you need shorter head bolts? something to ponder
    should be negligible and require the same torque. Nitro guys swap in / out different thickness head gaskets all the time to raise or lower the compression ratio. 2mm would affect the valve / piston clearance and timing as mentioned before.

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  19. #44
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    Re: Is high compression on the cheap possible on an A20? (pump gas)

    Quote Originally Posted by lostforawhile View Post
    this brings up the methanol/water injection theory, normally you would use it on a boosted car, but this also would allow you to increase the octane rating of regular pump gas, and allow you to increase the compression without needing premium, I was looking at the technical setups in the snow kits, they have a stage one boost kit, which can also be triggered by any input, in non boosted applications, you can use an rpm switch, this would allow me to run 87 with high compression, and anything above about 4000 rpm,which is where they recommend spraying, no lower rpm, if it was setup to just above normal cruise rpm, it would prevent detonation when you were on the gas. it's a pretty simple setup, you can also adjust spray pressure up or down, it's not a power adder, it just cools the charge and effectively raises your octane rating. the tank can also be mounted at the rear of the car, the only issue I saw, and I will have to ask them, my intake splits into two Y runners after each carb, so i would need two nozzles one just after each carb. i dont mind running premium on a car that wont be driven every day, but the problem is, it's often not available here, when gas prices go up, a lot of the stations just dont order anything but 87

    there is always debate in this area. People have the common misconception that a water / methanol injection kit is a power adder like N2O. To me it does not increase the octane rating. if anything it has a similar effect as a inter-cooler with compressed CO2 passing through it. You are putting combustion byproduct (water aka H20) in addition to a low / "cooler" burning alcohol. The reason this works is a thermodynamic and enthalpy characteristic. The water mainly serves as a anti-knock agent, the transition from a liquid state to a gaseous state can "absorb" a bit of thermal energy, allowing higher compression ratio's and / or boost. The alcohol mainly serves as a carrier for the water and anti corrosion agent to the injection system internals and helps atomize the water better to produce a uniform charge ( note injection nozzle style and spray pattern are other considerations). In our A20s with a 9:1 something compression ratio, i would say benefits of this are minimal if anything, unless the compression ratio is bumped to 10:1 or greater.

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  20. #45
    3Geez Veteran lostforawhile's Avatar
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    Re: Is high compression on the cheap possible on an A20? (pump gas)

    thats my plan, one of the ways to build power is to increase compression, the reason for me wanting to add a system like this is if premium wasnt available, I could still run 87 with the system at higher RPM and not have to worry about knock, octane is nothing but knock resistance, and a system like this increases the effective octane of whatever is in the tank

  21. #46
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    Re: Is high compression on the cheap possible on an A20? (pump gas)

    yes in that sense lost, octane rating is related to the knock characteristic, specifically the how well controlled the burn is. Hence why they add ethanol to most gasoline blends around 10-15% are common now. The ethanol does raise the octane rating, however it decreases the energy per unit significantly. At 20% ethanol the energy is nearly cut in half from pure Iso octane. So say an average of 12.5% ethanol is now used is roughly a 29% reduction in energy per unit. In your case Lost, you may have access from the
    aviation field to chemicals such as MTBE (methy-tert butyl ether) which has been phased out and replaced with methanol / ethanol and was a really good anti-knock agent but it caused environmental issues. So going back to the water / methanol and or ethanol injection system. You are starting out with a fuel with 10-15% ethanol as it is, adding more ethanol and or methanol to the cylinder will effectively help with knock, but ultimately reduce the effective energy. I think that de shrouding the valves, properly gaping and indexing the spark plugs, welding up the combustion chamber, shaving the head, and domed pistons ( as other have mentioned to check valve clearance at TDC) should give a really good bump in compression , however this doesn't resolve the knock issue. Timing adjustment was always one way GM addressed the knock issue with their 80's cars.

    In my honest opinion, i think the injection is more of a hassle than it is worth, you might as well just add ethanol to your gasoline or run E85, Or jsut keep adding toluene to your tank.

    you also have to think of the compression ratio, you are mainly discussing about a static compression ratio not the dynamic ratio which is very different and always lower than the static compression due to a full air / fuel charge in the cylinder

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