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Old 07-17-2005, 12:44 AM
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which engine to build up? m20b23 or m20b27

i've currently got an m20b27 in my car that some of you probably know about, but i've recently acquired an m20b23 and a seperate high(er) compression i head.

i would like to hear opinions as to which engine would be the best candidate for building up in order to get good reliable power and torque. car is still going to be a street car but can be a touch on the angry side as i've got another car to drive. i take the car to the race track about once a month and gets driven pretty hard so i'm not looking for a peaky dyno queen, more something that has a nice spread of power and torque.

both engines are in good condition and i'm prepared to throw a fair chunk of money at the project.

my ideas at the moment are to:
a) put the high comp i head on the b27 along with the usual things that go with that (forgies, better engine management, port&polish, etc)
b) put the high comp i head on the b23 and take it out to a 2.8 or there abouts along with the other goodies mentioned above

anyone got any other ideas or opinions as to what would work best out of those 2?

*edit* car is in australia as well so it will be run on 98 RON fuel all the time

Last edited by the afro guy; 07-17-2005 at 01:01 AM.
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Old 07-17-2005, 10:10 AM
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What do you mean seperate higher compression head? unless it has had a lot of material added to the combustion chamber that isnt happening. I personally would be very suspect of a head which has had the chamber modified (thats the only explaination for it being a higher comp ratio), chambers are funny things, you can mess up squish zones very easily which leads to poor combustion and actually looses horsepower instead of generating more.

put the 323i head on the eta bottom end. That will give you a good engine with good compression ratio of somewhere around 9.0:1-9.3:1 (compared to using the 325i head). Your problem is though you have an eta to begin with, you are going to need to do something about your ecu, injectors (should go up to 19lb) and intake manifold in order to take advantage of the engine setup. You can get a chip for your existing eta unit, swap to 325i ecu or go aftermarket, it's up to you. A good set of extractors, some cleaning up of the head and a good exhaust system and you should go close to pushing 200hp from the engine. If you want more power, look towards going for larger valves, some porting and polishing and a larger cam to squeeze a few more out of the M20.

Alternatively you could sell your complete 323i engine and "higher compression" head, along with your eta head (if you can sell it that is), get the larger 325i head, a new set of pistons (in order to bring up the compression ratio of the stroker) and drop them all into your eta block.

Either way you go you are going to achieve similar power outputs, people just use the 323i head to increase the compression ratio of the stroker because the eta block and 325i head result in low compression ratio using stock components (namely eta pistons).

Last edited by MaDhAtTeR; 07-17-2005 at 10:14 AM.
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Old 07-17-2005, 12:52 PM
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the head... well.. i'm not exactly sure. i picked it up for free from a friend of a friend who told me it was low comp, no reason given, wasn't exaclty sure what'd been done to it but upon closer inspection it looks like every other head i've looked at. anyway. i'm going to get someone who knows more than me to have a look at it and see what the verdict is. i'd say its just a normal 323i head.

so from what you guys are saying, the b27 block and b23 head is going to be the better option? my plans for that involved, aftermarket ecu, port and polish, better cam, extractors and all that exhaust gear, and forged pistons for a better comp ratio.

what are the benefits of the b25 head over the b23 head? i know the combustion chamber is a slightly different shape and the compression ratio will be lower on the b27 block. so whats the advantage of getting one of those? sounds like that will be a much more expensive option for not a lot of difference in performance.

with the injectors, what needs to be done there? i don't know all that much about injectors in general, let alone whats going to work on this sort of setup.

what is the effect of the larger valves? or is that all just part and parcel with the port and polish?

Last edited by the afro guy; 07-17-2005 at 01:00 PM.
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Old 07-17-2005, 02:23 PM
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What Madhatter says is correct.

The Madhatter knows his stuff about m20 engines.
Basically I would forget about the 2.3 liter block used in the 323i e21.

First look at the casting # on the head.. What numbers are there?
Is it a 200 head or an 887 one?

Assuming its the 200 head found on the eta, or perhaps a 323i, your best bet would be to match this with a 2.7 ETA liter bottom. This is a "stroker" and an excellent performance upgrade that totally transforms the car.

Now the 325i e30 887 head flows better and lends itself to more performance due to the design of both the intake manifold and the "I" head. If you have this head, then you should either grab a supereta block or get some custom pistons and got to work on the 2.5 liter bottom end. You can increase the bottom end too 2.8 liters using 85 mm pistons, but its some money in both the pistons and the boring out.

My engine is the 2.8 liter m20 1990 887 head with metric mechanic pistons and the 524td crank. Metric Mechanic sells both the 2.9 liter m20 engines, and the 3.0 liter which puts out over 230HP using the e36 m3 crank.

The e36 crank in the m20 is a powerful NA stroker engine, but it costs some money.

later,
J

Last edited by JJG323; 07-17-2005 at 02:26 PM.
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Old 07-17-2005, 02:39 PM
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thanks for the responses guys.
the head that i've got is a 1264200 from a 323i.

i think i'm now set on dropping that onto my eta block.

does anyone have any responses to my other questions about injectors and larger valves?

cheers
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Old 07-17-2005, 09:36 PM
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The difference is the chamber is more of a wedge shape and it was designed for a smaller bore engine. The actual chamber is smaller in diameter which is where the big compression ratio increase comes from when you use a 323i head on the eta block. When you use the 323i head on the eta block it results in a higher compression ratio than if you used the 325i head on the eta block.

The only real reason to use the 323i head is if you want to use the existing eta pistons, it is a way to bump up the compression ratio without having to swap pistons. But because you are going to replace the pistons you could probably do the 325i head swap (ie bolt that on to your eta bottom end instead of the 323i head) if you can find one cheap enough. Probably looking upwards of $700 for a 325i head here, so it is really one of cost. The 325i head flows better than the 323i head because of the larger port and valve sizes, but IMHO it doesnt really warrant spending an extra $1000 to purchase the head.

As for injectors, as long as they are the usual bosch type, pretty much any high impedence injectors is what you want to look for. If you get them from ebay.com mustang 5.0L injectors is what a lot of the E30 guys use. You will need 19lb injectors (of which the mustang injectors are) for the stroker.

Personally, is there any reason you want to replace the pistons? if you have money to spend on a custom set, then fair enough go out and buy them, otherwise i wouldnt bother. I would use your existing eta block, rods and pistons, replace the bearings and rings (plus other stuff) to freshen up the engine, then bolt the 323i head onto it. That will give you a good stroker (better than the eta + 325i combo when you use the standard pistons), a nice horsepower increase, and as already stated, around 200hp.

Increasing the compression ratio past the low 9's that the above 323i head + eta block combination yields is only going to result in about a 4% power increase, so like i said, it really comes down to cost vs output.

Larger valves in the 323i head will see it flowing larger volumes of air, the 323i head has smaller valves (40mm inlet, 34mm exhaust) than the 325i head (42mm inlet, 36mm exhaust), thats why i said, if you want to squeeze a few extra horsepower out of the motor you can look at larger valve sets. They are usually called alpina valve sets, they increase your valve sizes 1 or 2mm which will get it flowing similar figures as the 325i head. Keep in mind the best 323i head to use is the one from the E30 with the 731 casting (the last 3 numbers in the cast number above the inlet ports on the head), the earlier 200 head has smaller inlet ports (32mm for the 200 head vs 36.5mm for the 731 head).

If you choose to go with the 323i head and go for larger valves you will need to have the seats replaced to compensate for the larger valves. Any cylinder head service can do it for you though and it isnt terribly expensive.
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Old 07-17-2005, 09:45 PM
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Quote:
Originally Posted by the afro guy
thanks for the responses guys.
the head that i've got is a 1264200 from a 323i.

i think i'm now set on dropping that onto my eta block.

does anyone have any responses to my other questions about injectors and larger valves?

cheers
Ahh, then what you have is an E21 323i engine (or the head), or very unlucky and have a pre-update E30 engine which produces like 138hp.

See the comment above about the differences between the 731 and 200 casting heads.

because you have the earlier head with the smaller ports, i still would consider selling what you have (ie the engine complete, plus the other parts) and look at getting either a later E30 "731" head or the later still 325i "885" head. You can use the earlier 323i head and it will increase the compression ratio as per the later model head, but out of the lot the 200 head is really at the bottom of the barrel. The head you have there is exactly the same head that is on your eta, the only difference being that your eta motor doesnt use 7 cam bearings (only uses 4), there is no point in using it really. See if you can do a part exchange with the wreckers or a cylinder head place, maybe swap the 200 head you have there plus the one off your eta block for the later 731 head or 885 head from a 325i. You might have to sweeten the deal with a little cash, but it would be cheaper than buying the head outright.
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Old 07-17-2005, 09:58 PM
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Quote:
Originally Posted by AustinE30
What do you mean "higher compression i head"

The combustion chamber cc's of the eta and 323i heads is significantly less.

If you slap a 325i head on your 323i block you will loose compression, alot. Same is true with eta bottom end.

Heads do not have compression ratios. Pistons do.
As far as i know there is no such thing as a high compression i head, thats why i was asking if they modified the head to add something to the combustion chamber. It isnt just the smaller chamber volume of the 323i heads which increases the compression though, it is also because it was designed for an engine with a smaller bore so you end up with a bit of overlap.

And thats incorrect. Putting a 323i head on an eta block actually increases the compression slightly (the eta is 8.8:1 standard). Compression ratios are altered by changes in combustion chamber size, it isnt just pistons which have an effect. Actually, for that matter rods will have an effect on compression ratio too, so really it is a combination of chamber, plus pistons plus rod length (which is effectively stroke) which is going to alter compression ratios. Thats before you even calculate the volume of the gasket of piston to bore clearence.
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Old 07-19-2005, 12:52 AM
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i thought that might happen with the 200 head. i did read somewhere that it had smaller ports.

looks like i'm off to play swapsies with someone. hunting for a 731 starts now. i think i know someone that has one gathering dust.

so with the pistons, a custom set probably won't have that much of an effect? it is a fair chunk of money that can be spent elsewhere if its not really worth while.
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Old 07-19-2005, 11:59 PM
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i'd rebuild the 2.7 litre and make a 2.8i stroker motor.
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Old 07-20-2005, 01:29 AM
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Did you read what he said stumpy?

As for pistons, yeah, well if you use the eta setup and put a 323i head onto it, that gives you a decent compression ratio anyway. It isnt high, like i said, around 9.0-9.3:1, but adding pistons to increase the compression ratio wont result in a large increase in power. Like i said, say if you were to increase it a full point, so say you run a 10:1 comp ratio, now you have an engine that has to run on nothing but the best fuels (otherwise it will ping, and you know what fuels are like down here), you have spent anywhere from $700-$1200 for pistons, and all you have got out of it might be an extra 3-4% power increase.

Did you read the big thread about it on eurocca? not your thread i mean, im talking about the other stroker thread. It was like 3 pages long and goes through pretty much every senario possible.
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Old 07-20-2005, 01:37 PM
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Quote:
Originally Posted by MaDhAtTeR
Did you read the big thread about it on eurocca? not your thread i mean, im talking about the other stroker thread. It was like 3 pages long and goes through pretty much every senario possible.
nope, never even came across that one. i'll go have a squizz for that now

cheers for all the info and opinions guys. can never have too much information on things like this
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