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Author Topic: Timing question
Reggie Verified Driver
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I'm running 14 deg. BTDC on my SM, but someone has suggested it would run better at the higher speeds with only 10-12 degrees BTDC. The larger number of degrees helps with torque at low speeds, but allegedly kill the top end. What say you guys? any experience on this stuff? Thanks. R

Cajun Miata Man Verified Driver
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It's all trade offs. Ideally, you would want the flamefront to start "pushing" on the top of the cylinder at something like 10-15 degrees after ATDC if memory serves. So, depending on fuel type (burn rate) and rpm the exact best BTDC number moves. Computer advance tries to make up the the rpm variable.

13-15 BTDC is a "normal" range for "in the dark" tuning. Unless you are going to tune on the dyno to see how the timing affects your specific motor, probably best to leave it at 14 BTDC.

--------------------
James York


sponsored by:
Stan's Auto Center, Lafayette LA
powered by:
East Street Racing, Memphis TN
set up guru:
Gilfus Racing, Austin TX

TillerTech
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Also, the timing marks are just an approximation.
I had one here that ran like stink with 18 indicated and didn't detonate.

John

--------------------
Miata Race glass and CF from Legacy Molds. 4 1/2# CF Hood
http://www.jnent.net

Reggie Verified Driver
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I do well at low rpms, good torque, but at highest speeds a couple of cars pull away from me very slowly. I would rather pull away from THEM. So, should I lower the timing a couple of degrees to see what happens? Or just leave it alone? [Smile]

Teamfour Verified Driver Made Donation to Website
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Reggie, call Bob Thornton at Race Engineering. He will give you the low down and is glad to help always. You will also find that timing will not by itself help you pull away.

--------------------
Lee Tilton
1993 Meowta #04
Brimtek Motorsports/ Team Four Racing
Team Four Racing

Keith in WA Verified Driver Made Donation to Website
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quote:
Originally posted by TillerTech:
Also, the timing marks are just an approximation.
I had one here that ran like stink with 18 indicated and didn't detonate.

John

The timing marks can be off quite a bit. Not sure why but much more than you'd expect just with variations in the plastic cover. You really have to actually find TDC, see where the marks line up, and use that as a reference point.

Put some kind of depth gauge (like a long socket extension) down the #1 spark plug hole, and see how little the piston moves when you rock the crank a few degrees off TDC.

--------------------
Keith Novak
(Will work for tires)

Cajun Miata Man Verified Driver
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quote:
Originally posted by Reggie:
I do well at low rpms, good torque, but at highest speeds a couple of cars pull away from me very slowly. I would rather pull away from THEM. So, should I lower the timing a couple of degrees to see what happens? Or just leave it alone? [Smile]

I would say timing won't turn that around in itself. You are probably just being out motored or have too much drag.

--------------------
James York


sponsored by:
Stan's Auto Center, Lafayette LA
powered by:
East Street Racing, Memphis TN
set up guru:
Gilfus Racing, Austin TX

Reggie Verified Driver
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We're only talking about a very little difference in speed, 1 or 2 mph on the straight. I'm faster in most corners. Is the timing immaterial, then? Or do I need to advance or retard to gain mph? Staying the same doesn't seem like an option, so which should I try-since the timing marks are not right?

TillerTech
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The correct way to find tdc is the positive stop method. I took one form the Rotax Max motor, lengthened the wrench end and it works just fine.

I would suspect the issue of top end ponies at this point is more AFR and not timing. A good dyno can help identify this. What vintage car?

John

--------------------
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quote:
Originally posted by TillerTech:
The correct way to find tdc is the positive stop method. I took one form the Rotax Max motor, lengthened the wrench end and it works just fine.

Not having a degree wheel or any idea what the positive stop method is, I turned mine about 20* one way, measured the depth of the piston, made a mark, turned the crank until I found the same piston depth the other side of TDC, made another mark, then found the midpoint between the two marks.

--------------------
Keith Novak
(Will work for tires)

Reggie Verified Driver
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My car is a '90 model, 1.6L. Thanks, guys.

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quote:
Originally posted by Reggie:
We're only talking about a very little difference in speed, 1 or 2 mph on the straight. I'm faster in most corners. Is the timing immaterial, then? Or do I need to advance or retard to gain mph? Staying the same doesn't seem like an option, so which should I try-since the timing marks are not right?

The timing is not immaterial, but there are many more variables involved than a simple turn of the CAS. Besides, if there is a magic formula to solving the annoying 1-2 mph on the straight problem, *I* wouldn't broadcast it here. I'd keep that dirty little secret tucked away in a safe and be the guy going 1-2 mph faster at the end of the straight unless cash is changing hands.

(BTW- If someone tells you there is a secret and what it is...please PM me!) [Wink]

--------------------
Keith Novak
(Will work for tires)

pat slattery Verified Driver Made Donation to Website
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Your probably just racing against some 99 cars Reggie [Smile]

--------------------
keeping the faith for the 1.6

Arrow Karts

soupy
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Reggie, not trying to be a smart$$$ here but just because you think you are faster in the corners doesn't mean you are faster OUT of them. It's not always the motor. Just saying don't be shocked if you get the timing where "everyone" runs it and it doesn't fix you're problem.

--------------------
Charlie Campbell
Race Engineering
carbotech brakes

Reggie Verified Driver
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The other car is a 1.6 junk yard motor. My car, also a 1.6, while in ownership of the previous owner won every race entered the year before i bought the car. It had been a crate engine before John Phillips Racing worked on it for the previous owner. Don't know what he did, but the car was fast. When I pull ahead of the competitor and then pull away, passing in side by side racing in 3rd gear,then quickly shifting to 4th, his car slowly overtakes mine on the straight, while running side by side (no drafting by either of us). Someone suggested that I should reduce the timing to 10-12 degrees BTDC(from a reading of about 13-14 degrees BTDC) to help with top speeds, though higher timing would help in lower rpms. I have new NGK racing plugs, balanced injectors, and a high-revving, well-maintained engine. Unless my competitor's car is lighter than mine (mine is 25 lbs over the weight limit), there must be something amiss for a junker to outpull in this manner a tried and proven crate engine with great compression (now). I shift quick, at optimum rpms. Yes, in the corner at issue, I'm faster both INTO and OUT of it. I have momentum and I pull ahead in 3rd, but in upper 3rd gear and then in 4th at higher speeds, I lose the lead. If not timing, What are your thoughts? Call Bob T? [Good idea;I plan to do that, too.]

Apex to Apex
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Also depends upon octane too, does it not? 87 vs. 93 or racing fuel?

--------------------
"Driving is a serious business" - John Milner, 'American Graffiti'

Reggie Verified Driver
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93 ethanol laced fuel. I'm thinking of buying the unadulterated fuel at the track next time. What do you prefer: 87 or 93?

Cajun Miata Man Verified Driver
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What's your AFR across the rev band? What's your engine leakdown? What's the fish scale say?

--------------------
James York


sponsored by:
Stan's Auto Center, Lafayette LA
powered by:
East Street Racing, Memphis TN
set up guru:
Gilfus Racing, Austin TX

Reggie Verified Driver
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I need to install an a/f meter, but have not done so yet. The AFM has been set by ART in Dec. 2008 while KB had it. It is a fixed setting. Dyno testing at Hoyt's last year revealed 14 to 1 at 3,500 and 13.5 or so from 5,000 rpms and higher , up to 6,500. HP is about 10 below the 1.6 Pro engines. If you believe what I need is more hp I'll send you a PM about that. Scales are about 2315 with one gallon of fuel (with me and gear aboard). Stan did leak down-it was good; compression is excellent. Air filter is clean; 5w30 Mobil one oil. New front hubs to be installed asap. Royal Purple rear lube. Synthetic tranny fluid.

Cajun Miata Man Verified Driver
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If your AFR is still flat at 13.5 from 5000 up, that's pretty darn good. An AFR is good to have though, especially for a 1.6. Really almost required to keep it on its tune.

In regards to scales, I meant the rolling resistance of your car. You can use a fish scale to measure how much force it takes to move it. Parasitic losses can easily amount to more than what you are hoping to get by timing. This is real important the faster you go.

If you are 10 hp down from Pro, that sounds pretty weak to me. Years ago, a racer I knew had a 150,000 mile street motor with just an AFM adjustment get nearly the same.

If you want to get every last bit, we can make up a list to check.

--------------------
James York


sponsored by:
Stan's Auto Center, Lafayette LA
powered by:
East Street Racing, Memphis TN
set up guru:
Gilfus Racing, Austin TX

Reggie Verified Driver
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I've lost your address. Can you pm me at sim5mons@gmail.com? Thanks, jim.

Willie the Tard Verified Driver
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quote:
Originally posted by Reggie:
The other car is a 1.6 junk yard motor.

some people say that have a junk yard motor and don't never believe a racer (or anyone involved in racing).

--------------------
William Keeling a.k.a. Willie the Tard

Cajun Miata Man Verified Driver
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quote:
Originally posted by Willie the Tard:
quote:
Originally posted by Reggie:
The other car is a 1.6 junk yard motor.

some people say that have a junk yard motor and don't – never believe a racer (or anyone involved in racing).
Straight from the horses mouth... [Smash]

--------------------
James York


sponsored by:
Stan's Auto Center, Lafayette LA
powered by:
East Street Racing, Memphis TN
set up guru:
Gilfus Racing, Austin TX

Willie the Tard Verified Driver
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quote:
Originally posted by Cajun Miata Man:
quote:
Originally posted by Willie the Tard:
quote:
Originally posted by Reggie:
The other car is a 1.6 junk yard motor.

some people say that have a junk yard motor and don't – never believe a racer (or anyone involved in racing).
Straight from the horses mouth... [Smash]
yes I am sure I am one of many [Smile]

--------------------
William Keeling a.k.a. Willie the Tard

Sacslider
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The "oh ya, thats just a junk yard motor..." works until your motor builder makes you agree to disclose who built your motor before he rebuilds it. [duck]

--------------------
Craig Evans
#27 Spec Miata
San Francisco Region
Life, Liberty, and pursuit of another checkered flag.
SpecMiataSuperstore.com

   

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