Compression test results
 

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.

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.

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.

what mods?

Some good info on intake diameters/lengths.

[NA] 135whp with stock NA8 long block - MX-5 Miata Forum

Why?

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.

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?

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.

Virtual Dyno is great for before/after comparisons, but the absolute numbers aren't going to be accurate unless you get all of the input parameters right; weight, tire diameter, gear ratios...

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?

My MS3 base map came scaled to 240kPa from Rev and I haven't bothered to change it yet. As far as my cruise cell advance numbers, it's still a work in progress and I'm just not sure how high to go with light load timing. Anything done to your C5?

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

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.

?
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.

I meant 155-160 whp, not psi compression numbers. Perhaps I'm still wrong though, heck I don't know. Regardless I feel good about my 200ish psi results.

Worn seats. Long term, the #4 cylinder (runs hottest) has faster ring wear than the others. So usually its exhaust seat wear, some intake seat wear then ring wear.

your cold side intake needs to be longer. I vaguely remember 21" as the ideal length for us? someone can correct me if I am off there.

Also, for your mods, the expected power is 140-145whp.

Virtual Dyno is not a Real Dyno. :P

(man, I need to get off my ass and get a good tune on my car)

It's arguably no less real than a Dynojet. Both depend on accelerating inertia.

Truth. It operates off of Newtonian Physics and doesn't suffer from the calibration inaccuracies you would see with a "Real Dyno."

However, it is subject to variances from real world effects -- wind, slope, drag of the car (top up/down, windows open/closed), etc., etc.

As long as you keep the real-world variables under control, VD is repeatable and a great tuning tool. That's how you should use it (or any dyno for that matter). The absolute numbers should be ignored -- pay attention to comparative numbers as you tune.

Yeah, it's great for a comparison; however, a real dyno has less variables (such as traffic or bumps in the road) to deal with since it's in a controlled environment.

Blasting down a runway is more controlled that blasting down the freeway, but hey, anything to get an extra 5hp downhill with a tailwind. :v

Yeah thats the biggest however of it all. I've done runs back to back on the same road and can easily see windgusts fucking up my readings by 10hp.

I've got a flat, remote stretch that I do all my runs on. I always do several runs in both directions (usually 4 or 6 -- doesn't take long as I have good turn around points at both ends) and pick the run that seems to be the average. It is best to do it in calm conditions though. In N. TX, that can be tough. I've been trying to talk the Virtual Dyno developer into creating an averaging function -- no luck so far.

Yeah an average plot from all of the other plots would be very sweet.