Can we safely run our cars with 11.5 compression ratio?
05-24-2001, 01:41 PM
#21
UHH I hope not, because I am going to do it. Guess ill just have to see when I get the head back with a projected 11.8:1 compression ratio. BTW I went this much (mathmatical equation) because 12:1 is too much for me, but I think that 11.5 is not to the full potential. Oppinons?
05-24-2001, 02:07 PM
#22
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The best way, short of new pistons, is to go with a thinner head gasket. It's cheap and relatively easy. In fact, I'll bet the stock Honda gasket is a three layer riveted piece, so you could concievably just drill out the rivets and remove a layer.
On this engine, if you were to reduce the gasket thickness by 0.010" (10 thousandths), you'd see a compression increase to about 11.4:1. Coincidentally, a single layer on a stock Honda 3 layer gasket is about 0.010 compressed! (the typical 3 layer ends up being 0.025-0.030" compressed, but I haven't seen an F20C piece yet, so you'll have to take a look yourself). Sounds like the Spoon piece would provide a similar boost to a USDM engine.
Now, in terms of cam timing, I belive the way the tensioner is setup, you will get advance with a thinner gasket (not sure). However, we're talking about a timing gear which has an outer circumference of about 8-10 inches. Or, every degree of crank rotation corresponds to about 0.022" of chain movement. This means that we'd see less than 2 degrees timing alteration in the worst case scenario, and less than 1 degree if my estimates are accurate.
Oh, and BTW, there are adjustable gears coming to the market. I've had a chance to take a look and might even be an early tester on my car. Unfortunately, they are far more complex than past DOHC sprockets, so the expense will be higher.
UL
Oh, mdgrippa, I assume since you're going for 11.8:1 you shaved about 0.020" off the head? If so, that will cost you 2-3 degrees of timing change. Might actually help power, but you won't know without adjustable sprockets.
[Edited by ultimate lurker on 05-24-2001 at 03:09 PM]
On this engine, if you were to reduce the gasket thickness by 0.010" (10 thousandths), you'd see a compression increase to about 11.4:1. Coincidentally, a single layer on a stock Honda 3 layer gasket is about 0.010 compressed! (the typical 3 layer ends up being 0.025-0.030" compressed, but I haven't seen an F20C piece yet, so you'll have to take a look yourself). Sounds like the Spoon piece would provide a similar boost to a USDM engine.
Now, in terms of cam timing, I belive the way the tensioner is setup, you will get advance with a thinner gasket (not sure). However, we're talking about a timing gear which has an outer circumference of about 8-10 inches. Or, every degree of crank rotation corresponds to about 0.022" of chain movement. This means that we'd see less than 2 degrees timing alteration in the worst case scenario, and less than 1 degree if my estimates are accurate.
Oh, and BTW, there are adjustable gears coming to the market. I've had a chance to take a look and might even be an early tester on my car. Unfortunately, they are far more complex than past DOHC sprockets, so the expense will be higher.
UL
Oh, mdgrippa, I assume since you're going for 11.8:1 you shaved about 0.020" off the head? If so, that will cost you 2-3 degrees of timing change. Might actually help power, but you won't know without adjustable sprockets.
[Edited by ultimate lurker on 05-24-2001 at 03:09 PM]
05-24-2001, 02:36 PM
#23
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ultimate tuner said ;-)
I'll bet the stock Honda gasket is a three layer riveted piece, so you could concievably just drill out the rivets and remove a layer.
I'll bet the stock Honda gasket is a three layer riveted piece, so you could concievably just drill out the rivets and remove a layer.
- Except the fire ring [tech term escapes me]. Wrapping around the layers, it would sit higher than the gasket with one layer removed.
ultimate tuner then said
Now, in terms of cam timing, I belive the way the tensioner is setup, you will get advance with a thinner gasket.
Now, in terms of cam timing, I belive the way the tensioner is setup, you will get advance with a thinner gasket.
Close - you had a 50/50 chance. When the distance from the cams to the crank is reduced, the difference in chain link or belt distance gets shorter and the cam timing retards. Adjustable timing gears to advance both cams 2.5 degrees to restore the correct cam timing on our heads shortened .030in. Which is a lot, but a good baseline.
05-24-2001, 05:00 PM
#25
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I haven't seen an F20C gasket yet, but on the B18C gaskets, you could use either the top layer alone or the top and bottom layer together (essentially removing the flat steel segment in the middle that didn't have any corrugations - that's what Spoon's gasket looked like too). Did it on several engines running high compression without issue.
Does the F20C use a different gasket design where the pieces are integral as opposed to individual stampings?
And of course you're right on the cam timing. It shouldn't matter where the tensioner is. The damn clockwise rotation, to a single gear back to individual gears has me thinking in circles (pun intended) :-)
Oh, and 2.5 degrees for 0.030"? Damn, I was close, that's a little over 0.8 degrees per 0.010". Gotta love back of the envelope calculations :-)
So, tell us a little about your engine...
UL
Does the F20C use a different gasket design where the pieces are integral as opposed to individual stampings?
And of course you're right on the cam timing. It shouldn't matter where the tensioner is. The damn clockwise rotation, to a single gear back to individual gears has me thinking in circles (pun intended) :-)
Oh, and 2.5 degrees for 0.030"? Damn, I was close, that's a little over 0.8 degrees per 0.010". Gotta love back of the envelope calculations :-)
So, tell us a little about your engine...
UL
05-24-2001, 05:39 PM
#26
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ultimate lurker said
Does the F20C use a different gasket design where the pieces are integral as opposed to individual stampings?
Does the F20C use a different gasket design where the pieces are integral as opposed to individual stampings?
So, tell us a little about your engine...
05-24-2001, 09:14 PM
#28
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0.040" means a lot more compression. On the order of 12.5:1 or so. 0.020" would get you about 11.8:1. Going to a Spoon headgasket would get you around 11.4-11.5:1 depending on the exact thickness. This is probably the best bet because it is reversible. Oh, and 0.020" is going to retard your cams about 1-2 degrees. The Spoon headgasket will have about half that effect.
UL
UL
05-25-2001, 02:12 AM
#29
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Originally posted by ultimate lurker
Going to a Spoon headgasket would get you around 11.4-11.5:1 depending on the exact thickness
Going to a Spoon headgasket would get you around 11.4-11.5:1 depending on the exact thickness
... and FYI, the Spoon headgasket is .46mm thick, the JDM .75mm and the ROW 1.2mm.
The resulting CR are, respectively, 12.19, 11.68 and 11.00.
