Extrude honing is worth about 13 HP at the rear wheels on an 850CSi. When Jim Conforti did his E31 dyno session in Atlanta a few years ago, two 850CSi's were dyno'ed; one with EH intakes, and one bone stock. Everything else between the cars was identical. The EH equipped car pulled higher HP and torque figures throughout most of the RPM band and the consensus was that the improvement was totally attributable to the EH intakes.
BTW, do NOT pay Dinan for extrude honing. You can send your intakes directly to Extrude Hone Corp. and have them done for $800. Granted, Dinan powder coats them black, but if you like that look, you can have locally much cheaper than what Dinan is charging.
Good to see you here. For those of you who don't now Steve, he is a savant in the 8 series world, especially on the CSis
13 hp from extrude honing... Did the owner have a before and after of the engine? I know that BMW engines do differ quite a bit stock. The E39 M5 can vary 30hp...
I just think 13hp sounds a lot, but maybe not. I'm sure to stock 850CSi could differ 10-15 hp, that is only a 2% margin. That said, I'm a believer in honing and ceramic coating.
Carl
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"The E31, The father of all modern BMWs"
The extrude honing process involves the forced injection and passage of an abrasive sludge through the passages of the intake manifolds. EH estimates the result is an increase in airflow of 3% or more.
When we did the dyno runs, my former 850CSi was the one with the extrude honed intakes, the other was a "stock" 850CSi. I did have a "pre" dyno run, but unfortunately it was from a different dyno, so there was really an apples to apples comparison. We felt very confident that the measured gains were attributable to the EH'd intakes, and not production variations in the engine. Even in just driving them around, the EH car felt stronger.
And speaking of ceramic coating, I just got back my RD headers with their fresh Jet Hot coating. Hope to get them on within the next month or so.
Forgot to mention - yes, to do it right, the slightly enlarged openings on the intake runners should be matched to the intake gaskets, which need some transitioning in. Same for the headers.
There are two schools of thought on this. One says always replace them because they tend to eventually shrink with prolonged exposure to heat. The other school says that if they are visually okay, then they can be reused by applying a coat of hylomar to both sides. I also recommend using the hylomar even when you're installing new ones.
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