Car Making Peak Power Under 4500RPM, Things To Check? - Ford Mustang Forums : Corral.net Mustang Forum
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post #1 of 54 Old 05-13-2009, 02:26 PM Thread Starter
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Car Making Peak Power Under 4500RPM, Things To Check?

Guys I'm having an issue with my car making peak power real low, like 4300rpm low. Here is a picture of my last dyno, this was rich and low timing but you can see how it made peak power at 4300ish RPM and just fell off after. I've since got a new tune from Bob Kurgan with a leaner AFR and more timing and it still "FEELS" like it's making peak power early then falling off after. I'm going to get to the dyno again by next weekend but it still "feels" the same as it did before so I'm making this thread to see what I can check in case I'm looking over something simple. I was going to add more boost to get it faster but it should be making peak power a lot later than it is so I need to fix the problem first. Here is the combo:

Stock block/bottom end
TFS TW heads
1.72 Roller Rockers
Stock Cam
Exploder Intake
Stock TB
Hellion Turbo kit with a Master Power T70(.68 exhaust housing) making 10psi
Timing now is at 21* total but I have a 22,23,24* total timing tunes I've yet to try(waiting till dyno day)

Plugs are new and there is no check engine lights and no mechanical issues/problems that I know of. Anyone have any suggestions? Thanks in advance.

Last Dyno Graph(hard to read, sorry but you can figure it out if you look at it for a sec):



-Dave
1992 Mustang GT
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post #2 of 54 Old 05-13-2009, 09:23 PM
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i would start by putting it on another dyno..


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post #3 of 54 Old 05-13-2009, 10:45 PM
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I dont know ,but that stock cam with tw heads cant be helping the problem to well.

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best time-11.67
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post #4 of 54 Old 05-13-2009, 10:50 PM Thread Starter
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Quote:
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i would start by putting it on another dyno..
Hmm, I'll see if I can find another one in the area to slap it on. It just feels like it doesn't pull up top on the street either.

Quote:
I dont know ,but that stock cam with tw heads cant be helping the problem to well.
Most stock cam cars pull up top pretty good, if I knew that would of been an issue I would of put a F cam in it, everyone said it doesn't really need a cam change being a stock block.

-Dave
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post #5 of 54 Old 05-13-2009, 11:22 PM
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With heads I think the f-cam would have been a lot better than that stocker.Not saying that is the problem,but most stock cam cars I've been in are turds above 5000.

89 coupe- some parts

best time-11.67
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post #6 of 54 Old 05-13-2009, 11:23 PM
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maybe the air filter is too small

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post #7 of 54 Old 05-14-2009, 08:17 AM Thread Starter
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Car doesn't have an air filter on it, just a single layer screen. I don't think it's the cam, at least everything I've saw in the past would show that it's not the cam at all because the stock cam is considered a "decently good" turbo cam.

Any other suggestions, there is something causing it not to pull up top and I want it fixed!!!!

-Dave
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post #8 of 54 Old 05-14-2009, 08:34 AM
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I'll start.. I think its the tune LOL

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post #9 of 54 Old 05-14-2009, 01:15 PM Thread Starter
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Quote:
Originally Posted by flyin_hawaiin View Post
I'll start.. I think its the tune LOL
Don't start with me Bob! Hahahahaha, the poor tuner always gets blamed but not from this person, it's something though. The car may be going a little rich, I plan on pulling a lb or two of fuel pressure out on the dyno if need be but it shouldn't stop pulling like that with a 11.5ish AFR should it? It's 11.6-11.8 throughout the curve for the most part but could go a little richer right before a shift.

The exhaust housing on the turbo shouldn't be an issue either should it? I'd like to try a .96 housing on it just to see how much it actually does affect it. Anyone have any feedback, need to get this thing fixed so it pulls like it should!

-Dave
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post #10 of 54 Old 05-14-2009, 02:40 PM
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.96 would definately move the power band UP


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post #11 of 54 Old 05-14-2009, 06:52 PM Thread Starter
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There are people on Turbomustangs with h/c/i and turbo cars like mine running 130+mph with the .68 housing, that's the only reason I haven't really changed it out.

Anyone have any ideas?

-Dave
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post #12 of 54 Old 05-17-2009, 03:00 AM Thread Starter
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Took the car to the dyno again, with the air fuel around 11.8 the entire pull the car still falls on its face at 3800-4000rpm. Turned the boost up to 13psi and the car made 449hp at 3900rpm. I won't be keeping the boost this high once I figure out why it's not pulling up top like it should but I want it to make around that hp number on 10lbs and I don't think it'll have a problem doing so.

Thinking I will do a exhaust housing swap though, maybe that is actually what is killing it up top. For the money I have to try it, buddy has one I can use but I'll probably just order one to try and see how that helps the car.

-Dave
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post #13 of 54 Old 05-17-2009, 08:19 AM
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question is.... do you have a log of your boost?? does it hit 13psi at 3800 and fall to 10psi by 6000? might be your wastegate..

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post #14 of 54 Old 05-17-2009, 09:31 AM Thread Starter
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Quote:
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question is.... do you have a log of your boost?? does it hit 13psi at 3800 and fall to 10psi by 6000? might be your wastegate..
I don't have a log of the boost gauge but it was holding steady on all boost settings based on my gauge. Everyone seems to think it's the housing and I've been wanting to try the bigger housing for awhile because it'll work better with what I have planned in the future anyways, I think I'll be getting one just to try it out.

-Dave
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post #15 of 54 Old 05-17-2009, 03:53 PM
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I cant see the dyno here at work but "usually" big down low and nothing up top is turbo running out of breath, turbo housing too small, exhaust restriction, intake restriction.... something along those lines.

Personally I like running an AFR close to 10.8-11.2 I dont like going much higher just from a safety standpoint.

Nothing but slow chebby's right now.....
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post #16 of 54 Old 05-17-2009, 08:18 PM Thread Starter
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We unhooked the catback from the car on the dyno last night and it didn't gain any horsepower but it did make peak power a few hundred rpm higher. We know the turbo isn't too small, exhaust isn't a problem either or it would of gained a lot of power when we unhooked the mufflers. Intake restriction, nothing there really to cause a restriction, sure it might not flow as good as a bigger intake/bigger TB would allow it but it's not hurting it TOO much I don't think, def nothing to cause it to drop power like that.

Turbo housing will be bought tomorrow, everyone seems to think that's it.

-Dave
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post #17 of 54 Old 05-19-2009, 10:47 PM Thread Starter
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Changed the turbo over to a turbonetics T76 with a .96 exhaust housing on it, took it back to the dyno to see how it done. Same ####, different day pretty much. Car made peak power at 4000rpm and then the power went bye bye.

Did find three boost leaks though, one HUGE one where the throttle body shaft comes through the throttle body. I have another stocker TB laying around that I'm going to put on it but it may be time to order one. The other one is where my boost gauge connects, gonig to redo it...it's very small but I want it taken care of. The third one is where the MAF electronics mount to the actual MAF housing. What would be the best way to fix this one, use RTV or gasket paper?

-Dave
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post #18 of 54 Old 05-19-2009, 11:14 PM
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if the boost leak is as big as you say, then im sure thats a huge issue.. i would also look into the rocker lash.... possible valve float??

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post #19 of 54 Old 05-20-2009, 07:06 AM
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What kind of ignition are you running and what do you have your plugs gapped at? Even though it may not be blowing the spark out, a weak ignition could contribute to your problem.
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post #20 of 54 Old 05-20-2009, 08:06 AM Thread Starter
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Well here is a way to put the boost leak in prospective, using a boost leak tester and a air compressor that powers a shop it took 5-6 seconds for the pressure to go from 5psi to 20psi in the piping.

What does valve float sound like or do when it happens? I've never been around that before so I can't say for sure on that one. The rockers are quiet, they don't make a peep but I guess that doesn't mean they are right, I'm up for anything.

Ignition is stock right now, I had a Mallory Hyfire box and it went out. Need to send that thing back for repairs, running 3923 autolites gapped at .032 I think it was.

-Dave
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post #21 of 54 Old 05-20-2009, 08:08 AM
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i would say the boost leak and stock ignition.. ive never had luck over 6psi with stock ignition gapped as low as .018..

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post #22 of 54 Old 05-20-2009, 10:41 AM
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If your running stock ignition its definatly a problem. ESPECIALLY with a .032 gap
My car breaks up horribly over 4k without the ignition hooked up..
Pick up a 6a and I bet it makes a different

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post #23 of 54 Old 05-20-2009, 05:49 PM Thread Starter
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Maybe that's it, not sure. It's funny because my Mallory box died a day or two literally in front of my first dyno date. Things always work out for the best don't they. I'm going to send this box back to Mallory and get a quote on fixing it. They want an invoice and I bought it new from Ebay awhile back so I'm going to have to dig to find it. Not sure why they want an invoice if it's not covered under warranty anyways, oh wells.

I'm going to fix the boost leaks and get the ignition box fixed and try it again. Even though it's a stock cam, it should still make power at least to 5200-5400 shouldn't it? I was wanting to shift the car around the 5400-5500 rpm range, hence the reason I went with the stock cam and 1.72 rockers.

-Dave
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post #24 of 54 Old 05-21-2009, 02:19 PM
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Bob, if the engine was having that much trouble moving air don't you think the MAF curve would be flatish?

I am with you on another dyno, will the engine make it to 6000?Backpressure? Is the turbine housing free of debris? I had a turbo a while back come out of the box with a piece of tubing in the scroll and it was "shy on power"...

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post #25 of 54 Old 05-21-2009, 04:49 PM
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My guess is the boost leaks. The wastegate will hold closed to make up the difference and keep the boost steady BUT the turbo will be spinning faster to do so and perhaps you are getting out of the efficiency range of the turbo which means hotter air and less power.
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post #26 of 54 Old 05-22-2009, 02:39 AM
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My guess is valve float or it's blowing out the spark.

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I also think its valve float or spark blow out
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Valve float by 4500 would make an engine that would never make it to 6000


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post #29 of 54 Old 05-22-2009, 04:01 PM Thread Starter
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Valve float by 4500 would make an engine that would never make it to 6000


Jay Meagher
So you're saying if it was valve float and it was doing it that bad then it wouldn't be able to rev as high as it does? That gives me some hope, haha. I sent the ignition box out for repair and am currently looking to buy a TB. Redoing my boost gauge tonight because it was a tiny little leak where it connected. Also waiting on a buddy to find the T20 bit to take my MAF apart so I can put a gasket/RTV under it to hopefully seal it. That will take care of the ignition and the boost leaks.

Is .032 too big of a gap for the plugs even with a good ignition box and coil?

-Dave
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post #30 of 54 Old 05-22-2009, 04:27 PM
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If you were getting into spark blow out your graph wouldn't be so smooth.

How many #'s per hour of air was it eating? Do those numbers jive with your dyno numbers?

Jay Meagher


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post #31 of 54 Old 05-22-2009, 08:47 PM Thread Starter
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Quote:
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If you were getting into spark blow out your graph wouldn't be so smooth.

How many #'s per hour of air was it eating? Do those numbers jive with your dyno numbers?

Jay Meagher
Jay,

That's what I've said all along about the ignition not being the issue because the power curve is still smooth. I guess having the ignition box fixed and put back on def isn't going to hurt anything though.

Not sure how you figure out "pound per hour" of air but the car is making 10psi. We turned it up to 13psi and it made 449rwhp at 3900 or 4000rpm. Obviously I want it running right because it'll make that much power at 10psi no problem. I want around 460ish rwhp to be happy I think, just looking to get this thing going. Would valve float cause the power to fall off like that and still have such a smooth graph? What are some signs of valve float?

-Dave
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post #32 of 54 Old 05-23-2009, 11:35 PM
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If your on a stock PCM log the MAF voltage and see how the voltage increases. If the voltage stays flat and the AFR doesn't over rich we could be on to something.

Check backpressure.

I can't really get on board with valve float as your issue. If the valvetrain lost control at 4000 rpms it wouldn't make it to redline.

How are the rockers adjusted?

Can you get to a dynojet?

You can also log fuel PW into the dyno and see how much fuel it's eating that way.

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post #33 of 54 Old 05-24-2009, 09:41 AM Thread Starter
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If your on a stock PCM log the MAF voltage and see how the voltage increases. If the voltage stays flat and the AFR doesn't over rich we could be on to something.

Check backpressure.

I can't really get on board with valve float as your issue. If the valvetrain lost control at 4000 rpms it wouldn't make it to redline.

How are the rockers adjusted?

Can you get to a dynojet?

You can also log fuel PW into the dyno and see how much fuel it's eating that way.

Jay Meagher
Jay,

1. I can probe the MAF and check voltage on the street on a pull. I got another TB from a friend and redone my boost gauge, so the big boost leak and one small one is fixed now. The only boost leak I have left is where the MAF electronics connects to the actual MAF housing.

2. There is a dynojet in my area that I can use, I'm going to get the boost leaks and ignition box back first because the guy is pretty pricey on using his dyno. There is also a mustang dyno in my area, which would be better to use?

3. That's good to hear, I was dreading replacing valvesprings. With me having a stock cam, this is basically the lowest lift setup you can possibly put on those springs, surely the supplied TFS springs can handle a stock cam with 1.72 rockers...eek.

4. The rockers were adjusted like this:
1. Remove the valve covers, and pick a cylinder you are going to set the preload on.

2. Hand rotate the engine in its normal direction of rotation and watch the exhaust valve on that particular cylinder. When the exhaust valve begins to open, stop and adjust that cylinder's intake rocker arm.

3. Back off the intake rocker arm adjuster and remove any tension from the pushrod. Wait a minute or two for that hydraulic lifter to return to a neutral position. The spring inside the lifter will move the pushrod seat up against the retaining lock if you give it time to do so.

4. Now spin the intake pushrod with your fingers while tightening down the rocker arm. When you feel a slight resistance to the turning of the pushrod, you are at "Zero Lash". Turn the adjusting nut down one half to one full turn from that point. Lock the adjuster into position. The intake is now adjusted properly.

5. Continue to hand turn the engine, watching that same intake. It will go to full open and then begin to close. When it is almost closed, stop and adjust the exhaust rocker arm on that particular cylinder. Loosen the exhaust rocker arm and follow the same procedure described before in steps 3 and 4 to adjust this rocker arm.

6. Both valves on this cylinder are now adjusted, and you can move on to your next cylinder and follow the same procedure again.



5. I don't think backpressure is it because it didn't pick up any power with the T-76 on it with the bigger .96 housing. Actually it made less because the turbo wasn't in its range yet. Power fell off at the same RPM, even with the mufflers unhooked(making sure the exhaust wasn't a restriction)

6. Not sure about logging pulsewidth, have to check into that.

Thanks for your time Jay.

-Dave
1992 Mustang GT
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post #34 of 54 Old 05-24-2009, 09:17 PM
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definitely get it on a dynojet and report back.

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Bought a tamper proof torx bit set yesterday, so I can remove the MAF electronics today and put some gasket paper/rtv combo on it to hopefully seal that little leak. After that is fixed that'll be all the boost leaks fixed. Waiting on Mallory to give me a call on how much it'll be to fix my ignition box. As soon as that comes back I'll make a pull on the street and watch the MAF voltage, if that checks out I'll be taking it to the dyno and see what we come up with.

-Dave
1992 Mustang GT
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