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Old 04-12-2009, 06:38 AM   #1 (permalink)
 
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Default Cam Lobe Height Differences, D15B and D15B7

I have a JDM D15B non-vtec installed in my 1993 Civic DX. It was formerly dual-carb'd, back when the engine was being used in a Honda Ferio MX driven in Japan. It was modified to have MPFI instead of the carburetors.

From studying a number of shop manuals, it seems the camshaft on this non-vtec D15B is different from the camshaft of a D15B7. The cam lobe heights and valve spring free lengths seem to be different for the D15B and D15B7. Best guess now for the cam lobe height specs is:
D15B intake and exhaust = 36.603 and 36.747, mm
D15B7 intake and exhaust = 36.957 and 36.996, mm

The other valve and cam specs for the two heads seem to be the same.

A stock USDM D15B7 is MPFI. I am wondering if mixing the MPFI modification with the formerly dual carburetor intake and head design features throws things off so my 93 Civic DX does not get optimal fuel economy. Is it possible to switch the camshaft from a D15B7 into my D15B's head?

Maybe splitting hairs. Please share your knowledge.

Last edited by honda.lioness; 04-12-2009 at 06:46 AM.
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Old 04-13-2009, 04:29 AM   #2 (permalink)
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It will be fine bro. Your over thinking things. It will run fine...
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Old 04-17-2009, 07:17 AM   #3 (permalink)
 
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It does run fine. I guess the differences are trivial and I should be seeing the same fuel mileage on this non-vtec D15B compared to a D15B7. Seems the valve durations are the same. For the archives, here is what I found honda.lioness - Non-VTEC D15B Engine Notes
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Old 04-17-2009, 09:11 AM   #4 (permalink)
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Could be attributed to wear on the cam...And, if i understand correctly, you're wondering if dpfi would get better mpg mpfi? MPFI should get better mileage, and I'd even go with the "bigger" cam
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Old 04-18-2009, 06:40 AM   #5 (permalink)
 
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Quote:
Originally Posted by xotic_crx View Post
Could be attributed to wear on the cam...And, if i understand correctly, you're wondering if dpfi would get better mpg mpfi? MPFI should get better mileage, and I'd even go with the "bigger" cam
Yes I was wondering about the wear on the cam. I searched the net and could not really find any discussions that kinda quantified cam lobe wear. (Though again, I am not sweating it at this point.) Both the stock D15B7 setup and my modified non-vtec D15B are MPFI. Thanks for the input on MPFI in general, though; that MPFI did better MPG, all other things equal, was my guess, but based only on crude comparisons at fueleconomy.gov and figuring direct delivery of the fuel to each cylinder tended to be more efficient. "Bigger" cam meaning larger lobes?
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Old 09-08-2009, 05:24 AM   #6 (permalink)
 
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Since March, I have filled up 24 times (1-3 gallons left in fuel tank each time) and averaged 42.5 MPG. My Civic is well-maintained; the gasoline has up to 10% ethanol where I live; I have been keeping the tires at about 40 psi since March; I do not use the air conditioning much. This MPG is consistent with or somewhat better than the individual reports at fueleconomy.gov for the D15B7 Civic manual transmission. Also from checking head codes on D15B7s at the junkyard, I have seen several PM3's and at least one PM3-8. My Civic's head code is PM3-8. I am now thinking that the difference between the non-vtec D15B and D15B7 is negligible to none.

One thing I did find is that the crankshaft pulley's center timing mark on the non-vtec D15B is set to 18 degrees (for the carb'd version). Whereas the MPFI D15B7 spec is 16 degrees. I adjusted the timing in April so that the TB cover pointer lines up with the red mark closest (= 16 degrees BTDC) to the white TDC mark.

I have been burning oil at the rate of about 1/2 quart every 600 miles since at least March and wonder whether this is boosting MPG. After examining all symptoms, my best bet is that the valve stem seals were worn. I replaced them last week. See writeup and photos at honda.lioness - Oil Leaks. I am hoping this fixes the oil burning problem.
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