| MayanArch |
Posted
Wednesday, Oct 11th 12:37am [Edit] [Quote] [IMS] [View car] |
Member
Post nr. 1174
Florida, USA
Baur E21 2.7 1982, Baur E30 318i 1985, 323i 1978 |
OK, I have had the chance to see an "is" head side by side with that of an E21 323i. The difference is HUGE.
I am posting this because I dont even see where there is room for porting in the "is" head. I mean, those ports are huge......and their outer rim is already very close to the bolts that hold onto the intake and exhaust.
About the most I can see doing in one of these is gasket matching.
I am no expert.....but I just dont see where there is room to move.
The E21 head has about 3/8ths to a half an inch between the threaded studs and the intake and exhaust ports. The "is" at most has about 1/4" and 1/8" in the ones that are closer.
The E21 intake ports take about a 15 degree turn to get to the dome. The "is" is a straight wide shot. I would say that the port opening into the dome is about twice as large as the E21 intake ports.....or close to it in area.
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| bmw_m_320i |
Posted
Wednesday, Oct 11th 6:28am [Edit] [Quote] [IMS] [View car] |
Member
Post nr. 723
Helena, Montana
none right now :( |
thats why the 885 head is about is good as it gets! But port size isnt everything, efficiency, and gas velocity play a big role in how a head performs, bigger ports can flow worse than smaller ports if it isnt done correctly. |
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| redmist |
Posted
Wednesday, Oct 11th 7:02pm [Edit] [Quote] [IMS] [View car] |
Member
Post nr. 983
NY USA
357i , 325i e30 turbo |
Exactly, that's why I'm using the "e" engine to turbo versus the "i". The "i" breathes better in high rpms but not down low because of the big runners and ports. I can overcome the restrictive "e" items with boost past 4K. The power won't be as great as the "i" of course in the 4k and above range but I think it more enjoyable where I drive most, the 0 to 4k range. |
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| imaradiostar |
Posted
Wednesday, Oct 11th 8:18pm [Edit] [Quote] [IMS] [View car] |
Member
Post nr. 893
Nashville, TN
81 323i, 82 525i, 85 524td, 90 535i |
That being said...a stock 325i engine can easily make over 300 horsepower with the correct turbo in a very reliable form. I think you'd be hard pressed to call the stock M20B25 an unbalanced engine! Sure, it doesn't pull as hard at low rpm as an eta but it still feels pretty decent.
I'm thinking about building a mild stroker using a 2.3 crank in combination with 84mm bore size and a welded up M20B25 head. This way I can use cheap pistons (dished forged ones are around 400 a set) and standard rods. The welding on the head would be to reduce the volume and create a squish area that will match the piston shape. It's even possible to use eta pistons and mill them at the top for a similar design.
Mayan- all the M20B25 heads are the same except the supereta head. All the 87-90 325i and 525i cars used them. Eta engines need not apply...just look for an 885 casting and dual valve springs.
jamie |
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| myersport |
Posted
Thursday, Oct 12th 3:28am [Edit] [Quote] [IMS] [View car] |
Member
Post nr. 184
east tennessee
'82 320iS. '91 327iC |
Even the supereta has the exact same casting, just a different cam and minus the inner valve springs.
--Dennis |
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| imaradiostar |
Posted
Thursday, Oct 12th 7:39am [Edit] [Quote] [IMS] [View car] |
Member
Post nr. 896
Nashville, TN
81 323i, 82 525i, 85 524td, 90 535i |
| myersport wrote: | Even the supereta has the exact same casting, just a different cam and minus the inner valve springs.
--Dennis |
of course...but I was trying to keep it simple.
But, the supereta head makes sense in the long run. He really ought to go with a bigger cam than stock if he's going to have a bigger bottom end. With 2.7 or more liters of displacement and a long stroke you won't be hurting for low speed torque, or at least that's my experience from driving stroker M20 engines. I think anything that can be done to optimize mid and high rpm power is ideal.
jamie |
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