Compression test results
1 Attachment(s)
I did a compression test on my 00 today and got the following 200,196,200,202 on a warm engine. From online reading these seem to be nice consistent numbers. I was concerned about my virtual dyno numbers of 140/124. I'm thinking I need to ditch my RL header for an RB and possibly my Monster flow intake for a coldside set-up.
https://www.miataturbo.net/attachmen...ine=1382895784 |
Those are awfully low dyno numbers for a turbo car.
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Compression looks great. From your sig, you're normally aspirated. Those are decent numbers in that case. Remember, it's wheel HP/TQ, after drivetrain losses. Add 15-20% to get HP/TQ at the crank.
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The car is n/a, not forced induction. I was hoping for closer to 150whp. I experimented with a short coldside intake today. As the experts have said many times, I lost torque and, in my case, topend as well. I'm going to keep tinkering and see what I get.
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what mods?
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Some good info on intake diameters/lengths.
[NA] 135whp with stock NA8 long block - MX-5 Miata Forum |
Originally Posted by 6speed
(Post 1067207)
I was hoping for closer to 150whp
The dyno chart you have posted is excellent for what, based on your signature, I assume to be a mostly stock 2000 engine with a few bolt-ons. For what it's worth, I would not expect a significant improvement from replacing the riceland exhaust manifold with a racingbeat unit. The materials quality will be a bit better, but there's not a significant difference between the two in terms of design. |
Emilio from 949 racing typically quotes about 155-160 for a healthy 01+ block with a fresh 99/00 head with the bolt-on's I have . I was thinking with a .5 less compression I would see maybe 145-150. Since my shortblock seems ok, I may invest in a set of cams from somewhere. Any Idea's or input is appreciated. I know this is "Turbo Miata" but this site is much more tech. oriented than m.net.
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Tune might be a bit suspect. Get rid of those lean bumps. Have you tuned the spark timing and decided on a target afr on the dyno?
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2 Attachment(s)
I have tuned the timing tables. I'm running roughly 33-34 degree's total timing under WOT in the upper rpm's. I have also played with AFR's between @ 12.4 -13.4 on the chance my AEM wideband was off. The AFR changes netted me nothing really +- 1-2 whp, while more timing just set my knock sensor off. The spike around 5500 corresponds to a drop in map readings that I think is from an intake resonance. I have adjusted my target AFR in that region to try to counter the spike.
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Originally Posted by 6speed
(Post 1067161)
I was concerned about my virtual dyno numbers of 140/124.
Even wheel dynos can vary by more than the 5 or 10 whp that you're talking about. |
All dyno's will vary all the time. Stressing over anything sub-5hp is a waste of time IMO.
That said, I've so far had great luck with VD with over 5 runs all showing within 1-2hp of each other. IF that plot of yours is accurate, that's pretty impressive for what it is. I have a mint 01 engine with a 3" midpipe and e85 that I made 122/117 with repeatedly, your 140/124 sounds about right for the mods. I run little bit less timing though, just because 10:1 *edit: kinda curious about your spark map: why run 30* in the cruise cells and 33 at wot? Also why are your maps scaled to 240kpa? Planning for boost soon? |
Originally Posted by 18psi
(Post 1067932)
*edit: kinda curious about your spark map: why run 30* in the cruise cells and 33 at wot? Also why are your maps scaled to 240kpa? Planning for boost soon?
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Bone stock and recently sold lol. Gotta update the sig.
What I'm saying is: if you safely ran 33* at 100kpa you should be able to run AT LEAST that much in the cruise cells. Both your tables need cleaning up and re-scaling, but that stuff is fairly straightforward so no biggie |
5 Attachment(s)
Look any better? I'm thinking it still needs some timing advance in the 40-55 load 3-4k range. I Don't know why I hadn't rescaled sooner, so I could use the full resolution. Thanks so much for pointing that out.
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Originally Posted by 6speed
(Post 1067220)
Emilio from 949 racing typically quotes about 155-160 for a healthy 01+ block with a fresh 99/00 head with the bolt-on's I have .
Not my quote, perhaps someone elses. Consult the FSM for compression numbers. USDM NB2 should be around 205psi when new, broken in and warm. Leakdown under 2% for new motors. Most used NB's we see are in the 140-170psi range. They'll still run OK but make less power. Most compression loss from normal wear is from exhaust valve seats. Often times a <100k motor with medium compression can get most of it back with just a valve job. Sorry for jumping in the thread out of nowhere. As you were. |
So, a valve job nets a decent ROI in most cases? Are the exhaust valves bad at the seat or bent at the stem typically? I ask because I heard they bend easily.
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Originally Posted by emilio700
(Post 1069467)
?
Not my quote, perhaps someone elses. Consult the FSM for compression numbers. USDM NB2 should be around 205psi when new, broken in and warm. Leakdown under 2% for new motors. Most used NB's we see are in the 140-170psi range. They'll still run OK but make less power. Most compression loss from normal wear is from exhaust valve seats. Often times a <100k motor with medium compression can get most of it back with just a valve job. Sorry for jumping in the thread out of nowhere. As you were. |
Originally Posted by sixshooter
(Post 1069471)
So, a valve job nets a decent ROI in most cases? Are the exhaust valves bad at the seat or bent at the stem typically? I ask because I heard they bend easily.
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Originally Posted by 6speed
(Post 1067207)
The car is n/a, not forced induction. I was hoping for closer to 150whp. I experimented with a short coldside intake today. As the experts have said many times, I lost torque and, in my case, topend as well. I'm going to keep tinkering and see what I get.
Also, for your mods, the expected power is 140-145whp. |
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