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As mentioned in the OP, we hope to be able to run Enduros with this car. That means low enough compression to stay on pump gas for the much greater fuel economy. We will still run E85 for Sprint and TT.
With an almost identical set up and a Mazda crate motor we made 125 whp a few years ago. So this output is anomalous. I feel is either a different cam spec or the intake manifold design on the NB6. We will find out
If you're healthy NA6 motor is making less than 110 with the exact same setup, you need to rebuild the damn thing.
I'v been wondering if the NB6 intake man. design has much of an improvement over the older NA6 version. Have not been able to find out much about this, and am interested, as I am also running a NB6 in my '93. So, in addition to a slight compression ratio bump, the solid lifters, slight intake cam lift increase, the NB6 also has a different intake manifold, and TB, correct? Mine is a street car, running MSM2 ECU.
I have not seen any documentation that indicates a compression ratio bump or Cam lift increase for the NB6. Can you share your sources?
Will have to do some digging; I recall the guy I bought the car it's in saying that was the difference between the 1990-93 NA6 and the NB6, so I have nothing official to offer, but do seem to remember in my search for differences that I had read about a slightly higher Comp. ratio, and more aggressive intake cam timing (as in a very slight amount). I'll post back if I find anything definite. Have you discovered any differences in the intake manifold?
We don't have any B6 parts in the shop. Had to source them, the IM is inbound. Purpose of this thread is to document and share findings so, we will. Compression test indicates same CR as USDM NA6 although that's not scientific.
I started to think that maybe the used motor we bough had received a water pump or timing belt service and could have had its cams mistimed. B6's make peak around 7000. Ours made peak at 6200 which is pretty wack. Indicates mistimed cams more than a bad engine.
So we're pulling the valve cover to check cam timing. While we're in there we'll measure cam lobes and see if they have part numbers.
All the google searching I'v done has threads containing guy's saying the cam lift is higher on intake, but that's all it is: guy's saying, so at this point it's unknown, until Emilio has time to measure the lobes, or someone else who has had one apart can offer up the definite info.
I have a low-mileage 1.6 that I've been slowly modifying, and so I'm really curious how this engine build goes. The "we don't modify 1.6s we swap 1.8s in" line makes sense for most people, but not those of us who are unreasonably stubborn about keeping ours! So it's nice to see there are some reasons to use a 1.6 (a bit shorter for better weight dist, a bit lighter overall), and it'll be interesting to see how much you get from it. I know you'll have to tune your car to 132 HP to make the lb/hp ratio specified by the rules, but I also wonder what the not-detuned HP limit will be on this engine when it's complete. And also how you'll modify the tune for endurance racing (if I'm reading into that correctly), is that just a change in redline, or timing or what?
It's super cool that you started with a NB, not many people could or would do it that way. Which makes me wonder if you had started with a 90-93 body, would you have used an airdam or still gone with BTM bodywork? Or maybe that would be track dependent?
Miata Engine History and Interchangability Guide This guy seems to know quite a bit about the engine's development over the years. He states that the JDM 1.6 shares the same cam specs as the US 1.6, but advances the intake timing a few degrees, in addition to the solid lifters. Cam # is: BP5A12420. Compression ratio is the same as well.
Checked cam timing, lift on cams. Different P/N's than USDM, Difficult to get a solid answer from interweb on just which version we have. Starting to think that we have the "90bhp" version sold from 94 on outside of the US. Wiki page states that the NB6 was bumped to 110bhp from 99 on.
JDM NB6 cams in it have .5mm les intake but .35mm more exhaust lift than USDM manual NA6 cams. Small change. Whichever cams we have, the Kelfords, 9mm In & Ex are going in along with adjustable cam gears. We're so far down on power that just swapping OEM cams isn't going to get us there.
Glad I ordered the Kelfords 4 months ago (just arrived). Was hoping we would make the power with a junkyard JDM motor. Didn't.
So far at least, it appears starting with a freshly rebuilt NA6 motor is probably a better choice. While you are rebuilding, shave block to bring CR to about 10.0:1 while retaining squish. If you have budget leftover, deshroud and bowl blend. That should, base don our past experience, get you to about 135whp on corn.
Meanwhile, we'll swap cams and start A/B testing intake manifolds. Also ordered a JR header (4:2:1) to A/B against the RB (4:1). For science.
NB6 cam lobe measurement and NA6/NB6 intake manifold comparisons
We measured the lobes and checked the casting marks on the camshaft today.
NB6 intake (B6KP): 7.25 mm
NB6 exhaust (B6MC): 8.25 mm
For reference,
USDM NA6 intake: 7.86 mm
USDM NA6 exhaust: 7.9 mm
Checked the timing belt for misalignment, but the timing looks good.
USDM NA6 manifold and auto trans TB showed up last week and visually compared it to the NB6 manifold. Looks like the TB on the NA6 manifold mounts further back than the NB6. Also noted is the downward angle the NA6 manifold has compared to the more parallel to the ground angle shown with the NB6.
Last edited by VagaXt; 03-25-2019 at 10:41 PM.
Reason: Adding title
Race 2 is up. The lack of power is annoying, but made the racing epic. However, it is not as annoying as the racecraft I had to deal with starting at 17:00. After all of that while trying to keep calm, the race for P3 ended in a dead heat with timing showing a tie to the 1/1000th second, but I lose the tiebreaker.
Last edited by VagaXt; 03-26-2019 at 01:32 PM.
Reason: Adding title
Not sure what the deal is over there, but here in Australia you are allowed to move the car once to cover your line, but you cannot then swerve back across to block another line. The other driver was a bit of a poor sport in my view, there were times I counted him swerving up to 3 times to block you - that's not cricket sir!
Not sure what the deal is over there, but here in Australia you are allowed to move the car once to cover your line, but you cannot then swerve back across to block another line. The other driver was a bit of a poor sport in my view, there were times I counted him swerving up to 3 times to block you - that's not cricket sir!
Same rules here. One move is pretty much the norm across the globe. That driver, on his provisional (learners permit) license no less, had the audacity to tell Sonny (pro coach, 3x national champ, multi lap record holder) "That's what racing is, get used to it" or some such malarkey.
Said driver has been contacted nad "talked to" by racing organization after chief steward saw the video. I believe the race directors comment to Sonny after viewing the video was.. well, lets just say the RD might not have been so patient had he been in Sonny's seat.
03-20-2019, 03:32 PM
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