NC with Cosworth making only 150 hp????

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morrisg
Posts: 128
Joined: Mon Nov 15, 2010 12:02 am

Re: NC with Cosworth making only 150 hp????

Post by morrisg »

The air/fuel ratios look good, 11:1 to 12:1, so rich enough to prevent detonation but not horrible. Back pressure measured at the O2 bung is only 2 lbs, so it isn't a blocked exhaust or cat. So that points me to an air blockage elsewhere. The oscillations in the power output might be explained by a blockage that is flapping open and closed in the intake tract. After all, we control the power of an engine by using a throttle plate to restrict air entry, so any other intake restriction would also reduce power. A shot in the dark: take a look inside everything in the intake chain and look for loose or flapping items. Also, since you are running higher boost, check the throttle plate return spring. If this isn't strong enough to withstand the added pressure of the intake, it might be flapping around causing the power oscillations. An even longer shot: maybe the intake gasket didn't match the ports exactly and you have a gasket piece flapping around causing intake air velocity turbulence? Or maybe the gasket is just sitting in the airstream and the power oscillations are due to poor intake air flows?

This is interesting; keep us informed of your progress.
OM-ARC
Posts: 47
Joined: Wed Sep 19, 2007 10:20 am
Location: Miami

Re: NC with Cosworth making only 150 hp????

Post by OM-ARC »

Seriously... reach out to Jay. He knows his stuff and is working with some Cosworth owners and their troubles... You can find him here and in miata.net as blackone....
fredmuggs
Posts: 41
Joined: Sun Mar 13, 2011 6:40 pm
Location: Sheldon SC

Re: NC with Cosworth making only 150 hp????

Post by fredmuggs »

Ted928 wrote:I know a few people have asked you to check to make sure the bypass is not getting stuck and you verified that it is clear of hoses. On some models the mechanism will get caught on the brake lines when the engine rocks. I had to bend my lines out of the way.

You can check to see if boost is developing using scangauge, ultragauge, dashdyno.

Good luck.
Thanks for the response. I also had to move my brake lines. The external mechanism is clear to operate. Cosworth just advised I could remove (and block) the vacuum line to leave the bypass closed. That would allow me a manual check for operation of the compressor and to see if the bypass might be leaking or staying partially open.

I've used a manual gauge and the dynos to confirm I have pressure from the blower at the existing sensor on the blower housing. But there is no way to check at the intake ports. That's something you can bet I'll fix, if I have to pull the blower off the head.

Car is at a shop, now. And we will try the vacuum line trick next week.

Thanks for your interest,
Fred
Ted928
Posts: 2
Joined: Sun Mar 11, 2012 4:17 am

Re: NC with Cosworth making only 150 hp????

Post by Ted928 »

I went back and looked at your original post where it says you have an automatic tranny. Maybe that is not able to transmit all the new torque. Since the engine has boost and rich fuel, the engine must be making high power.

i am just guessing as I am not experienced in SC or automatic trannys.

Keep us informed.
jboemler
Posts: 304
Joined: Fri Oct 10, 2008 6:15 pm
Location: Mukilteo WA

Re: NC with Cosworth making only 150 hp????

Post by jboemler »

fredmuggs wrote: Measuring back pressure at the O2 Sensor shows 2 lbs.
OK, let me ask the stupid question. I've never seen a back pressure measurement quoted before -- how is it done? What are the test conditions, and the measuring device? What values are considered "good" or "bad"?
fredmuggs
Posts: 41
Joined: Sun Mar 13, 2011 6:40 pm
Location: Sheldon SC

Re: NC with Cosworth making only 150 hp????

Post by fredmuggs »

Ted928 wrote:I went back and looked at your original post where it says you have an automatic tranny. Maybe that is not able to transmit all the new torque. Since the engine has boost and rich fuel, the engine must be making high power.

i am just guessing as I am not experienced in SC or automatic trannys.

Keep us informed.
Thanks for your interest:
Back in March '11, I did some research and it appears the AT in the Miata is the same as that used in the RX8. Here's that info

Found from four (unvalidated) sources that the AT in my '07 Miata should be SJ6A-EL (Miata '06 - '08) which is also used in the RX8 ('06-'09).
First source Level 10, which offers value body rebuild for $600 to sharpen shifts. Level10 says the trans is not controlled by the ECU, but by a separate trans controller which they can reflash or supersede for DOLLARS.
Second source: http://www.transtec.com/selector_guide/Mazda.htm
Third: http://www.autotransparts.com/MazdaTransmissions.html
Fourth: http://amtrans.nl/mazda.pdf
If the SJ6A-EL is, in fact, the correct trans, and is also used in the RX8, it should take a lot of power right out of the box. With a very little tricking, it should take a lot of really hard use.

Seems to me, to "lose" 50 HP in the drivetrain would require that the HP/torque must be going one of three places
(1) burned off in slippage -- but the trans isn't slipping: sound tach, etc.
(2) "detuning" through timing and/or fuel to reduce output. When we look at the fuel and timing logs, this is not apparent. The numbers go where the calibrator tells them to go.
(3) burned off in the torque converter. I can't think right off how to check that.

Thanks, Ted928 for the input. I'll see what I can find out about the converter issue.

PS:
Brian -- you know a Mazda Rep who might be willing to give some input on the trans?
fredmuggs
Posts: 41
Joined: Sun Mar 13, 2011 6:40 pm
Location: Sheldon SC

Re: NC with Cosworth making only 150 hp????

Post by fredmuggs »

jboemler wrote:
fredmuggs wrote: Measuring back pressure at the O2 Sensor shows 2 lbs.
OK, let me ask the stupid question. I've never seen a back pressure measurement quoted before -- how is it done? What are the test conditions, and the measuring device? What values are considered "good" or "bad"?
Hi, jboemier:

Thanks for your interest.
I asked, and the shop put a pressure gauge on the bung for the O2 sensor, which is located between the two converters (both still in place).

I think you may be onto something. Seems to me, measuring pressure between the converters might tell us about the rear converter, but not the front. I'll follow up with the shop and have them pull down the exhaust at the manifold. They should be able to visually inspect the front converter from there. I've also come up with an idea for the rear converter. Kind of a "standard fix," if you know what I mean.

Good question.
Thanks,
Fred
fredmuggs
Posts: 41
Joined: Sun Mar 13, 2011 6:40 pm
Location: Sheldon SC

Re: NC with Cosworth making only 150 hp????

Post by fredmuggs »

Hi, Brian:

At one time, there was a recall of this Cosworth kit. Do you know what that was about? Do you know anyone over at Cosworth who might lend some insight?

Thanks,
Fred
fredmuggs
Posts: 41
Joined: Sun Mar 13, 2011 6:40 pm
Location: Sheldon SC

Re: NC with Cosworth making only 150 hp????

Post by fredmuggs »

OM-ARC wrote:Seriously... reach out to Jay. He knows his stuff and is working with some Cosworth owners and their troubles... You can find him here and in miata.net as blackone....
Hi ON-ARC"

I must be in the wrong fourm or something over at miata.net. Couldn't find a "Jay" or "blackone."

Just before I email the Moderator over there, do you have any additional contact info for Jay?

Thanks,
Fred
jboemler
Posts: 304
Joined: Fri Oct 10, 2008 6:15 pm
Location: Mukilteo WA

Re: NC with Cosworth making only 150 hp????

Post by jboemler »

By "pressure gauge", do you mean the same fixture that's used for leak-down testing? I somehow doubt that's a valid test, since it's intended to measure something that's almost fully sealed, using very small flow numbers. With the rest of the exhaust very open by comparison, the flow required for any meaningful value would have to be much larger than the leak-down fixture can provide. I also wonder how much the potentially open valves in the head would distort the readings.

Basically, I'm just not sure your 2-pound number means anything at all, but willing to be convinced.
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