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DIY Turbo Discussion greddy on a 1.8? homebrew kit?

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Old 08-01-2009, 01:10 AM   #1
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Default Knock at 11 PSI

Got a bit of knock today at 11 PSI. Running 12.3 AFR, tapering to 12 though the range and 17* 4000 to 5500, 18* at 6000 and 16* from 6500+. Runs fine at 10 PSI. The thing is, it doesn't seem that fast. I have been running on 7 PSI wastegate until now. I was anticipating great things at 10. Kinda bummed. I can lay full on it in first and second and don't even get the tires to break loose.

I have full 2.5", big 3" magnaflow, FM high flow metal cat. What gives? Is my tune that bad?
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Old 08-01-2009, 01:18 AM   #2
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Post up your timing map, that should help. Richen it up too. Alot of us track guys run around in the low 11s.

Is this audible knock? Knocksense?

Get det cans, it might be false.
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Old 08-01-2009, 01:36 AM   #3
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Quote:
Originally Posted by thesnowboarder View Post
Post up your timing map, that should help. Richen it up too. Alot of us track guys run around in the low 11s.

Is this audible knock? Knocksense?

Get det cans, it might be false.
I don't think it was false. This wasn't the stock knock sensor. I heard it. Sounded like a diesel motor clattering. My WRX used to do this when I stood on it at low RPM's. I'm thinking it was knock. I'll log it tomorrow to be sure if it stops raining.

I can't post screen shots from homeso here is my 180 kPa line of the ignition map.


180kPa was

3000 13*
3500 17*
4000 17*
4500 17*
5000 17*
5500 17*
6000 18*
6500 16*
7000 16*
7500 16*

I have no problem going richer, especially if it will help me bump timing or run 11 PSI. I don't really want to go past 10-11 PSI on a stock 9.5 CR motor. That was my plan all along. I just couldn't believe that it wasn't faster than this.
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Old 08-01-2009, 01:39 AM   #4
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The only thing I can say is that you're not making power when you're detonating, so fix the detonation, and you might suddenly find yourself high on power. A friend of mines 92 miata with modified greddy was making 179 wheel horse with detonation. I took timing out until detonation was gone, and he hit over 200.

On the power note as well though, I have a 300zx t25 turbo on my 97 miata motor, and I didn't make really any huge power until I hit about 12 psi. Once I hit over 12, I can melt the tires in first and second.
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Old 08-01-2009, 01:40 AM   #5
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Advance should rise to redline. I ran 12 degrees at 14-15psi on the 2554 at 3500-5000rpm (torque peak), and 19+ degrees at 14-15psi at redline.

You're lean, too. Retune to 11.6:1 and try again.
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Old 08-01-2009, 01:42 AM   #6
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Originally Posted by dustinb View Post
On the power note as well though, I have a 300zx t25 turbo on my 97 miata motor, and I didn't make really any huge power until I hit about 12 psi. Once I hit over 12, I can melt the tires in first and second.

I need to log again. I could feel two surges in the power with a lag in between. I'm going to drop to 10 PSI and do some pulls hopefully tomorrow. I was travellign for business and didn't have my laptop. Did 350 miles today though.
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Old 08-01-2009, 01:46 AM   #7
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Advance should rise to redline. I ran 12 degrees at 14-15psi on the 2554 at 3500-5000rpm (torque peak), and 19+ degrees at 14-15psi at redline.

You're lean, too. Retune to 11.6:1 and try again.

So, richen by .5 AFR will be enough to offset the timing bump on top by 3*, right? That's pretty much what I see. I was scared to go more advanced but may have understimated the benefit of the additional fuel.
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Old 08-01-2009, 02:07 AM   #8
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you have no business running leaner than 12.0:1. Low comp is good.
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Old 08-01-2009, 07:12 AM   #9
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Way too lean IMO. Richen it up and start working on timing and you should definitely start making much more power.

When I first started using my current map it was at like 12-12.5 afr in the midrange/full boost. Car was slow as ***** and knocking. Richened it up and its great now. No knock (even in the dreaded 4300-5000 rpm) and it feels great. I'm at only 8psi.
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Old 08-01-2009, 07:24 AM   #10
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Quote:
Originally Posted by Stein View Post
So, richen by .5 AFR will be enough to offset the timing bump on top by 3*, right? That's pretty much what I see. I was scared to go more advanced but may have understimated the benefit of the additional fuel.
The additional fuel won't offset anything - you're too lean, period. Shove some more fuel at it and I bet the small amount of knock you're seeing will go away.

The 3* addition at top is probably something you can add right now without any ill effect; RPM is a natural detonation deterrent, and cylinder pressures will drop as torque decreases approaching redline. Adding timing in the 5700rpm+ cells is a great way to pick up quite a bit of power on the top end without sacrificing anything in the midrange.
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Old 08-01-2009, 11:29 AM   #11
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Sav didn't explain why timing should increase as RPM rises. It's because there is less propensity for detonation at higher RPM. in addition, you're heading away from the torque peak in most cases (especially on a stock long block) and cylinder pressures are going down.

But get a log of what's going on. It could be your closed loop ignition is sucking away all your timing.

That's what happened to mine... the base map had a knock retard of 1 to 1 degree and my timing went to zero and my torque went to ***. once I fixed that, the ************ pulls like a freight train at 10psi!
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Old 08-01-2009, 12:16 PM   #12
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You advance timing at higher revs, cos the piston is going up that much quicker you need to ignite the fuel a bit earlier.

If you leave the timing static you're effectively retarding the timing as revs increase, if that makes any sense :lol:
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Old 08-01-2009, 01:21 PM   #13
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Quote:
Originally Posted by y8s View Post
Sav didn't explain why timing should increase as RPM rises. It's because there is less propensity for detonation at higher RPM.
Actually, it's mostly a function of the angular velocity of the crankshaft.

At 3,000 RPM (or 50 RPS) it takes the crankshaft .02 seconds to rotate a full turn, or 5.6e-5 (.000056) seconds to rotate one degree.

At 6,000 RPM (100 RPS) it takes only .01 seconds to complete a full turn, or 2.8e-5 (.000028) seconds per degree.

So let's say that at 3,000 RPM your ignition timing is 15BTDC. Thus, the spark event occurs .00083 seconds before TDC. If you leave the timing at 15BTDC at 6,000 RPM, then the spark will be occurring .00042 seconds before TDC- it has essentially been retarded by 50%!

To appreciate why this matters, understand that the velocity of propagation of the flame front (and therefore the rate of burn of the mixture) is more or less independent of RPM. In a perfect world, we want the burn to progress at a rate such that peak combustion pressure occurs at somewhere in the 15-18 ATDC range in order for the crank to be in the best position for the rod to exert leverage upon it. (I'm paraphrasing Corky here.)

So let's posit that for a given manifold pressure and AFR, peak pressure occurs .00168 seconds after ignition. (I'm pulling this number out of my ***, but it will serve the purposes of this example.) At 3,000 RPM, if we light off the spark at 15BTDC and then wait .00166 seconds, the crank (which is travelling at .000056 seconds per degree) will have gone exactly 30 degrees and will be at 15ATDC when peak pressure occurs. (ain't that special.) By contrast, at 6,000 RPM we'd need to light the fire at 60BTDC to achieve the same result.

Now obviously there are some variables at play here that I'm not accounting for, such as the fact that the "ideal" peak pressure point moves around with RPM as well, and that if we really did ignite the mixture at 60BTDC it would have developed a fair measure of peak pressure while the piston was still travelling upward on its way to TDC, and this is a good way to break things. So by necessity, we have to slow things down a tad as the RPMs rise, or we'll be getting a good look at our connecting rods (through the hole in the side of the block) before too long.

But you get the general idea.

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Old 08-01-2009, 01:32 PM   #14
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Basic forced induction theory claims engines make best power between 13.2 and 12.5 AFR (A. Graham Bell) so although a complete burn is not happening running richer than this is to help chamber cooling. Although the benefit of how low AFRs is good ranges from 9 to 11 by most experienced engine builders you can be safer this way.
Personally I would suggest WI over running these richer AFRs as it will produce better power that way and is not exactly an expensive investment now (yes I know properly controlled systems with 3d mapping are but bodge isnt and does 80% of expensive stuff).

Edit: Just read Joe Perez post above. The man is spot on (as were his references ). His point also adds to my WI suggestion as although water is a flame retardant, W/A injection setup will raise octance helping knocking, speed flame front travel as well as retard it meth and water effects, as well as producing cooler charge for greater density and atomisation. All these effects combine (if taken on face value and perfect timing) to produce a far superior burn and greater peak pressure (= more power). Devils Own kits are good value and basic stuff (yes even the controller based ones) but I you have 5th injector ability they are usually mapable properly so all you need a PWM valve (if you find a cheap PWM valve link me it as I been looking for yonks)

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Old 08-01-2009, 01:35 PM   #15
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Yeah, these some of these proposed AFRs are reminding me a bit of e-cool.
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Old 08-01-2009, 06:53 PM   #16
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OK, bumped the 5500+ timing from 16* to 19* and added some fuel. It's running between 11.7 and 12 now. No knock. I did cut it back to 10 PSI at the same time so not sure if it was a combination of the three or not. Knock readings 5000+ are 13, tapering to 8. This is compared to one log from yesterday that I found that was 25 tapering to 18 so it is better.

No more knock. It will be good enough for the autocross tomorrow. Still wouldn't break loose in first (not launched or floored) nor in second (floored after 1-2 shift.

Did a couple of full pulls to the top of 4th. It will pull 60-110 (at shift 2-3 to the top of 4th) in 9.6 sec per the log.

y8s, the closed loop timing isn't pulling any timing. I checked the logs and they are following my map. I have disabled the auto timing retard feature for the moment until I set up the knock base map.
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Old 08-01-2009, 07:03 PM   #17
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Quote:
Originally Posted by Joe Perez View Post
Yeah, these some of these proposed AFRs are reminding me a bit of e-cool.
All I know is that every time my car strays over the 12:1 point, it knocks. Feed it fuel to 11.6:1, and the knock goes away.

I don't like to see anything leaner than 11.2:1 on the track. 11.6:1 makes me nervous. I shut it down at 12:1.
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Old 08-01-2009, 08:26 PM   #18
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Quote:
Originally Posted by Joe Perez View Post
Yeah, these some of these proposed AFRs are reminding me a bit of e-cool.
No idea who/what e-cool is but I guess who did see who I referenced those AFRs from. He is a top engineering consultant to many F1, NHRA, NASCAR teams so has a great deal of experience in this field so why should any of us normal job folk disagree with him. Admittedly achieving his wonder figures require race team money but he knows race team engineering not bodge shop.
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