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Old 01-30-2012, 02:51 AM   #1
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Default "exhintake" mod on NB head

I have been searching about the exhintake mod for a couple of hours and I notice people have done this mod on 94-97 heads. The mazdaspeed intake camshaft seems to add some power on a 99-00 head but it looks like the exhaust cam has even more lift and duration. Would it be beneficial to use the exhaust cam on the intake side too? (I know I have the modify the cam gear or get an adjustable one) any issues with valves getting to close to the pistons?
Last question is, can I use 94-97 adjustable cam gears on a 99 head/95block since I will have the CAS in the back of the head?
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Old 02-08-2012, 09:29 AM   #2
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the lift is same
bp5a cam
349 lift 251 degrees duration
exintake mode
350 lift 272 degrees duration

with 272 duration you will need ecu . You canot use 94-97 adjustable cam gears.because 99 cam sensor is on the intake cam gear you can buy toda adjustable cam gears for 99. if you dont have a header mid ex. and catback ex. and ecu . you dont get any hp on high end but you will on mid range maybe 5 hp maybe less . I drive
jdm 2000 miata . I have bp5a cam from the factory. same hp with the usa car .maybe bit more on mid range .
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Old 02-08-2012, 10:12 AM   #3
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You can use a CAS on a '99 head, and it goes in the back of the exhaust cam.
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Old 02-08-2012, 11:30 AM   #4
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i wish i knew more about this as i have one in my car - 99 engine - but the previous owner installed it and has most of the info on it.
cas is in the rear
idk what he had to do with the cam gear. there's a little bit of info from sideshow (previous owner) in my build thread on cr
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Old 02-08-2012, 09:35 PM   #5
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nb exhaust cam has higher duration, but you shouldn't need aftermarket ecu, and a few posts that I've read about guys who have done it, said the same thing. At 1mm or .050" lift, there's no overlap running 2 exhaust cams, so it's not crazy aggressive or anything. But the extra duration and lift would help for sure I think, especially turbo app. I'm going to do this, just because it will be cheap horsepower, probably won't do much else to the head.

http://www.solomiata.com/cams.html
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Old 02-08-2012, 11:32 PM   #6
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Quote:
Originally Posted by aaronc7 View Post
nb exhaust cam has higher duration, but you shouldn't need aftermarket ecu, and a few posts that I've read about guys who have done it, said the same thing. At 1mm or .050" lift, there's no overlap running 2 exhaust cams, so it's not crazy aggressive or anything. But the extra duration and lift would help for sure I think, especially turbo app. I'm going to do this, just because it will be cheap horsepower, probably won't do much else to the head.

http://www.solomiata.com/cams.html
You could get the cam timed so there is no overlap, but typically when you increase duration, the overlap increases. That extra duration timing has to go somewhere. Doesn't matter if both cams are exhaust or intake or you swap the intake and exhaust, virtually all NA Miatas will end up with overlap unless you open the intake very early. If I wanted to reduce overlap, I wouldn't be using a cam with more duration.
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Old 02-09-2012, 04:58 AM   #7
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i said at .04 or .05 lift, theres no overlap. less lift, yeah there's some, but probably not enough to matter/make a difference it seems based on what i've researched.
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Old 02-09-2012, 10:40 AM   #8
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I can't say with certainty that you are incorrect, but I can suggest that maybe you are. I can say finding any consistent data on Miata cams is rather frustrating. It seems that everyone has different data, so it is very difficult to determine exactly what is going on.

OK, having said that, I'm basing this on the cam data listed in the NASA Spec Miata rules, posted here: http://www.nasaproracing.com/rules/spec_miata_rules.pdf
I'm also using the cam calculators here: http://www.wallaceracing.com/Calculators.htm

I know that Solo Miata list very different timing figures than NASA does, but the timing figures at Solo really don't match up to the duration numbers, so I chose to go with the NASA Spec numbers. I'll also say the NASA numbers seem to open the intake valve very early, but without any credible evidence to the contrary, I have to go with them. One more thing, it sure seems to me that Mazda chose to add about 4-7 degrees to the closing ramps, so I think that the factory cams are asymmetric; that is the raw duration numbers may be a little misleading compared to a symmetric profile. Now I'm not saying asymmetric lobes are a bad thing, actually just the opposite. But when I studied the data, I came to the conclusion max lift was not in the middle of the duration numbers, it's slightly advanced. If you subtract about 4-7 degrees from the closing numbers, the max lift numbers center up. Another way is to use duration at .050” lift to run the numbers, which is what I usually do.

OK, so looking at the data, using the stock 99 cam, we have the intake .010” open at 23.43 degrees BTDC. At just degree after TDC, the intake is .060” open. The exhaust is closing, but is still open .070” at .85 degrees ATDC. That is a fair amount of overlap, my calculation say about 7.25 degrees at .050 lift. That is, about 7 degrees of crank rotation near TDC when both valves are open at least .050.

When you substitute another exhaust cam for the intake, it is even more. Still trying to verify this, but it looks to me that the factory cams have 100 degrees center line (intake fully open at 100 ATDC). Again, according to my calculations, if you time the exhaust cam at full inlet lift at 100 degrees, you wind up with about 10.86 degrees overlap at .050. That might not seem like much, but it's about 50% more. The original intake has timing of roughly 2/22 at .050” lift, the exhaust cam on the intake is about 5.5/25. The first number is degrees BTDC/the second ABDC.

The stock timing (according to NASA) is 23/51 56/43. These are .010 lift numbers, so you could maybe add a few degrees to them. I have found timing figures from Schrick, a European cam company. They list a cam with 22/62 62/22 timing. So maybe that intake opening is not so far off, but way different to 8 listed at Solo Miata. The Schrick cams work out to full inlet lift at 110, which seems a bit more realistic to me, but I really can't speak to that. I'm not saying any of these numbers are correct. I would really like to know if anyone has a different take or has measured their cam timing to see how they line up.
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Old 02-09-2012, 11:34 PM   #9
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good info, I had not seen the NASA data, all of my stuff was based off of the solo miata info. Yeah i noticed their valve timing numbers did not match up to their duration specs @.01". I'll plug the nasa numbers into my cam excel sheet I made when I get back to my personal computer and see what kinda stuff I come up with.
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Old 02-10-2012, 12:15 AM   #10
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Yeah, I'm getting the same numbers as you now iwth the NASA figures. Kind of annoying there's such a big variance going on out there. Solo miata shows lobe centerlines for intake/exhaust as 110/112, whole NASA is 100/100, that's where the big difference is, it seems. 110/112 with LSA of 111 seems more 'likely' but who knows. I think at this point I'm just going to go roll with it and not worry about it... at least I'll have more lift, haha
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