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 Post subject: New owner question
PostPosted: April 1, 2024, 10:54 am 
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Joined: March 11, 2024, 11:18 pm
Posts: 5
Hi! I just picked up a 1957 Super 7 replica with a 1990 1.6 naturally aspirated engine and a 1999 6 speed gearbox. I love this little thing! She handles great, fun from 14-45 mph. BUT! I went to take it on the highway to drive to work and she STRUGGLED to get over 60mph and no matter what I did, it wouldn't go anything over 71. I assume that these cars should be able to go quicker? (especially because the motor in a factory Miata MX-5 would bring that car to 116mph)? If 71 is all I can get because that's the normal for these vehicles, then ok, but if it can get up there, I'll tear down the engine and go through all the workings and see if there's something not right.

The short, how quick can we get these cars to go with a 1.6L Miata engine?

Thanks!

Chris


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 Post subject: Re: New owner question
PostPosted: April 3, 2024, 3:16 am 
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Joined: July 29, 2006, 9:10 pm
Posts: 3163
Location: Oregon, usually
Hi Chris, you are right, something is not right with this car.

I had a Miata-powered Locost about a dozen years ago, and despite the lack of streamlining, I recall it broke the ton (or "passed me in excess of 100 miles per hour," as the officer explained it) with ease. I can also tell you how much horsepower it takes to go 71 in a Locost (long story) and it's less than 32. Tell us more about where you're located and maybe someone in this group can swing by and solve your mystery...and it is a mystery; I think your car's lack of performance has a cause more interesting than, say, worn rings or burned valves, but I can't guess what that cause might be.

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 Post subject: Re: New owner question
PostPosted: April 3, 2024, 7:42 am 
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Joined: September 22, 2005, 8:12 am
Posts: 1880
Location: 4AGE in S.E. Michigan
Welcome Chris
Sounds like you are dragging around a couple dead cylinders :ack:
Start trouble shooting by doing a compression test. Have you pulled the plugs to see what they look like?


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 Post subject: Re: New owner question
PostPosted: April 3, 2024, 9:27 am 
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Joined: July 7, 2011, 12:17 am
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Location: Oregon City, OR
Congratulations and welcome to the forum! The aero is unquestionably terrible on these cars, but still, you should effortlessly be able to cruise at 70. I agree with everyone else, start with a compression or leak-down test.

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 Post subject: Re: New owner question
PostPosted: April 3, 2024, 9:52 am 
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Joined: March 3, 2006, 10:48 pm
Posts: 1592
Location: Shawnee, Ks
Welcome. Fantastic looking car. Please put in your avatar where you are located. Someone that is local to you and is on this forum may be able to help. If you're not motor savvy look for an import speed shop that specializes in Miatas. I doubt a Mazda dealer would even look at it. Russ

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 Post subject: Re: New owner question
PostPosted: April 3, 2024, 10:29 pm 
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Joined: March 11, 2024, 11:18 pm
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I'm in Sarasota Florida. I wanted to compression test today, but our horses had other things in mind. That's a task for the weekend. It was really odd the other night. I was driving to pick up one of my kids from soccer practice and 1st through 4th gears felt good and got up to like 60. But whenI went into 5th and 6th eventually, the car actually slowed down. In 5th it kept at 58 and when I hit 6th, 53. It was the oddest feeling, so back to 4th and at 4000 rpm, 60 mph, nothing more. My engine tuner said "that's strange. May need a full tear down".

::shrug:: but, we will start basics. Compression, spark plugs, ignition.

Thanks everyone! I'll update my profile (since I just joined) to reflect more information. :-)

Chris


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 Post subject: Re: New owner question
PostPosted: April 3, 2024, 11:21 pm 
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Joined: September 30, 2005, 1:28 am
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Location: Sunny-Okanagan, Canada, eh?!
And fuel pressure; check that.

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 Post subject: Re: New owner question
PostPosted: April 4, 2024, 2:18 pm 
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I suspect one of the cams is off one tooth in the timing belt. One cam has to be held rotated a few degrees in order for the timing mark to align for the belt to be installed and the belt tight on the driver's side away from the tensioner. After correcting (if needed), rotate the crank a couple turns to recheck the timing mark alignment.

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 Post subject: Re: New owner question
PostPosted: April 10, 2024, 10:26 am 
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Joined: March 11, 2024, 11:18 pm
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Compression test was normal. 110 in all cylinders. replace the spark plugs. spark test was showing normal spark but low fuel. I'm replacing the fuel pump now. (once it arrives...which should be tomorrow).

Thanks everyone!


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 Post subject: Re: New owner question
PostPosted: April 10, 2024, 11:32 am 
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Joined: April 1, 2010, 10:26 am
Posts: 569
I would not say 110psi is normal, did you have the throttle fully open when running the test?

"Spec compression for your engine is 192 psi, with 135 psi the low limit and max allowable difference between cylinders of 28 psi."

Graham


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 Post subject: Re: New owner question
PostPosted: April 10, 2024, 1:59 pm 
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Agreed.

"I suspect one of the cams is off one tooth in the timing belt. One cam has to be held rotated a few degrees in order for the timing mark to align for the belt to be installed and the belt tight on the driver's side away from the tensioner. After correcting (if needed), rotate the crank a couple turns to recheck the timing mark alignment."

Being a tooth off, it will start and run ok but will exhibit the same behavior you've described.

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Miata UBJ: ES-2074R('70s maz pickup)
Ford IFS viewtopic.php?f=5&t=13225&p=134742
Simple Spring select viewtopic.php?f=5&t=11815
LxWxHt
360LA 442E: 134.5x46x15
Lotus7:115x39x7.25
Tiger Avon:114x40x13.3-12.6
Champion/Book:114x42x11
Gibbs/Haynes:122x42x14
VoDou:113x44x14
McSorley 442:122x46x14
Collins 241:127x46x12


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 Post subject: Re: New owner question
PostPosted: April 10, 2024, 7:36 pm 
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Joined: July 7, 2011, 12:17 am
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Location: Oregon City, OR
I’m with the rest of the tribe, your compression test is quite low. I wouldn’t be surprised if MiataV8 nailed the problem, there are many reports of Miata owners not getting the cam timing correct. It’s not difficult to do, but does require being meticulous and double-checking your work. There are a number of YouTube videos that cover how do it it. I would start by getting comfortable with the process and verifying that it has been done correctly.

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 Post subject: Re: New owner question
PostPosted: April 13, 2024, 7:54 pm 
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Joined: March 11, 2024, 11:18 pm
Posts: 5
I didn’t even think about the absolute value of compression. I was only looking at the real values and consistency between cylinders. ::facepalm::

I’ll check the cam tomorrow. Being off a tooth would be a nice easy fix. If not - I will try a compression test again when warm and with WOT and also try it wet to see if the piston rings are fried. And then maybe have to tear down and do a head gasket.

Thanks again for everything!!

Chris


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