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Discussion Starter #1 (Edited)
All cylinders came back with 180-185! Motors in good condition. No smoke (not seemingly burning oil). This compression should be good for around 10:1 rating (not exact but rough estimate).

Haven't been able to really test it. Car has a misfire (please read my other thread and help me!). I expect it to be strong though!

Anyone think this should be stickied (or at least the info added to a current sticky)? I think people would like to know this info...


EDIT:

Ok, I originally did this test the same way I originally did the test on my H22. I didn't pull the gas pump fuse and I didn't have the throttle open. I just redid my H22 doing it this way and the compression jumped from 190ish across to the following:
1. 215
2. 210
3. 220
4. 220

So with these new numbers comparing to the old numbers w/o changing anything, I'd expect doing the B21 bottom end with B20 top end to change similarly (like 205-210ish across).

Sorry for the mix up. When we originally did both tests, we just wanted to make sure that each cylinder was close to the other. As long as the technique was the same for each cylinder (which it was), you can verify that there are no issues with the engine (which we did).

Refer to Con's post right below. He did the same thing the first time and after doing it correctly the second time, he got about the same percentage jump in compression...
 

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cool........... I did another compression test on my car, this time removing the fuel pump fuse and depressing the gas pedal

180 across the board

I know I have an el-cheapo compression tester, but should it be that much difference. Johnathan said it wasn't necessary to remove the fuse and press the gas with his :shrugs: results from his was 155psi on all 4 cylinders
 

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Discussion Starter #3
You haven't done anything to raise compression, have you? Stock B20a w/ no mods to raise compression?

If so, that seems pretty high.

Maybe you want the TB open to get more air to create more pressure. I wonder if that would help with Jonathans tester...
 

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academyracer said:
would there be any loss in compression due to altitude?
yes. Same reason why motors make less power at altitude, and NA cars are slower.
 

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slipknot95758 said:
on my fresh rebuild on a b20a5 that was bored 10 over with the only mod being headers, i am getting 210 in all cylanders
what did you do to bump the compression ratio? that's extremely high for the b20a5...
 

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hey daily im thinking about doin this, with that high of compression did you get any gains? I have a B20 sitting in the garage with a good head (as far as I know) and the head on my car now (b21) has a crack on the top where the lifters sit, right next to the PS pump. did you have to do any special fabing to make it fit or anything?
 

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b20 heads are a direct bolt on to a b21 block. it will bring your stock b21 compression up from 9.4:1 to ~9.94:1. i suggest using the b21 cams though, or at least the b21 exhaust cam. and make sure you readjust the valve-train
 

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is there any gains to raising the compression that much? or is there any problems raising it that much? because i would really like to stop that oil leak its startin to get worse I think. It drips down and hits the exhaust mani and smokes like a bitch
 

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yes, there will be some minor gains, im estimating about 8-12hp. the downside to raising the compression to 9.94:1 is that you have to use a minumum of 89 octane gas instead of 87.
 

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89 octane wont be to bad its only what 10 cents a gallon more. how much work is it to swap the head anyway? will I have much problems doing it while its in the car? And what prep should I do to the other head before I put it on (keep in mind I dont have much money to blow, so no out to shop stuff) I do however know ppl that might have like the tools to grind valves and stuff
 

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its very easy to do still in the car. very easy, just takes a lil time. usually takes me about 3 hours to get the head off, and 1-2 to get it back on (not including adjusting the valvetrain). you will need a head gasket and an intake manifold gasket in the least, which will be about $50-$60 for both. exhaust gasket you can usually reuse, and valve cover gasket you can usually reuse.

you may want to have a shop install new valve seals for you though, and if its a high mileage motor, you'll want new valve guides as well. and it never hurts to have valve seats grinded and lapped along with the valves for perfect seating/sealing.

theres a million different things you can do when changing the head, it all depends on how much you can afford, what condition the "new" head is in, how long you want to be able to drive it before having any issues, and what you dont mind the motor doing. personally i like to keep my motors in as perfect of condition as possible, so i always invest the extra money and have everything replaced with the proper parts and in the proper way.

in the least figure at least $75.00 just to drop the head on. this covers the required gaskets, and anti-freeze. and you should usually do an oil change very shortly after putting the new head on, as when you have it off, you may get some dust/dirt in the oil passages, and maybe the new head will have some dust/dirt up top that will get washed away as the motor runs and get into the oil filter. anytime i have the head off, i always change the oil less then 100 miles of driving after its back together.
 

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maybe ill pull the head off my spare motor tommorow, is there anyway to check the valve guides and the valve seals, etc? Because I cant afford to just send it off to the machine shop right now so if it needs it the head im using now will have to do for a lil while
 

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no, theres really now way to check the guides and seals. only way to really tell is by how many miles are on it. if you take off the valve springs, sometimes you can tell if the seals are bad just by looking at them, but the only way to tell by sight is if they are REALLY bad. be forwarned though, putting a b21 head on a b20 block will drop your compression from 9.0:1 to ~8.55:1 and you'll lose a bit of power.

i'd say just pull the head thats on there now, and give it to a shop to just replace the bad valves and thats it. and buy the valves yourself from autozone or advanced auto parts and bring them to the shop with the head. otherwise the shop will charge you retail price for the valves.
 

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im doin the opposite man B20 head on my B21 you said that would raise compression.
I have a B21 in my car and a spare B20 in the garage. and valves arnt the problem with the current head its the outside of it is cracked and leaking oil
 

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my bad, its 5am here lol, and im still awake. yeah, like i said at the top of this page it will bump compression from 9.4:1 to approx 9.94:1. sorry for the confusion, i was looking at a different thread earlier bout a guy that broke his timing belt and was asking a lot of the same questions as you bout changing the head, and checking/changing the valves lol. forgot i was posting to this one and not that one. i wonder if i put my reply to this thread in his thread? oh well
 

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bump

i am thinking about grabing a cheep b21 block at the junk yard and doing this with my b20a head, would i still need a new manifold? i dont see why i would...... but anyways.... is it a proven fact that it will raise compresson? and should i expect an actual gain of 8-12 hp? because if so .... thats worth it to me


edit

from what i have read about the b21 block the FRM sleeves dont crack and cause the oil burn they actualy tear the rings wich causes the oil burn.... in which case it would take awile for it to happen after an engine re-build

is this true, or have others found cracked sleeves?
 
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