343 rwhp, 352 rwtq.

383, 10.3:1, AFR 195 heads, Stealth Ram, 52mm throttle body, de-screened MAF, 32 lb Bosch gen III injectors, Howards Max Torque roller 234 242 .569" .585", SLP 1.75" ceramic coated headers, Magnaflow cat, Magnaflow cat-back.

Air/Fuel Ratio was 13.5:1 +/- .2 for the duration of the dyno pull.

We did one pull with the air cleaner lid removed (to rule out the air cleaner as the restriction) and it picked up nothing. I know that the single 3" exhaust is a restriction, but 40 to 60 hp? This motor should make at least 380 hp to the wheels.

It has a 700r4, Midwest 9.5" 3400 rpm stall, 4.10 gears.

Any ideas?

 

Huh, it should be making more than that, I'm not sure why it's not tho

 

maybe needs the tune setup tweaked

 

tune if its not done already but check for valve float it will make if feel good till about 3500 then feel like its droping off coud just need a spring upgrade with that size cam I would have 987s

 

We made several pulls changing timing and fuel until we found what the motor liked best. While tuning, the runs started at 313 rwhp (very lean up top, slightly rich down low). We next tuned to achieve an optimal a/fr, followed by adjusting the timing advance.

The engine runs well, and sounds good, datalogs all look good. It just seems to be getting choked by something, which prompted us to remove the air lid and allow the motor to draw air straight through the MAF. Again, we picked up a few hp in the midrange but nothing on top. This is what leads us to suspect the exhaust as the restriction, but could it really be 50 to 60 hp?

 

sounds exactly like valve float what springs do you have

 

These numbers were the result of the custom tune.

I'm running Beehive springs with tool steel retainers. They are 135# seated (1.750" height) and 367# at 1.150" (353# @ 1.165, my open height).

I should have enough spring, but maybe not?

 

Comp Cams 26918-16 - Comp Cams Beehive Valve Springs Details
Chevy LS1/LS2/LS6

Specs

OD: Top 1.075" Bottom 1.310"
ID: Top .650" Bottom .885"
Seat Pressure: 125 lbs @ 1.800''
Open Pressure: 367 lbs @ 1.150''
Coil Bind: 1.100"
Spring Rate: 372 lbs/in

 

unbolt it from the collector see what it puts out then.youll probably gain 10+hp with true dual but not 50hp.

 

What was the rpm at which you made peak hp, and after the peak what does the hp curve do. With your setup you should be making way more hp and torque than that!

 

Torque peak is at 4550. The curve goes up slowly, has a dip at 5100 (305 hp @ 5000, 295 hp @ 5075, 305 hp @ 5150) and then slowly goes up again. Peak hp is at 5900.

 

Can you post the dyno graph? It sounds like you are ok as far as valve float but I would need to see the graph and would like to see more spring for that cam also. Have you been to the track with it since the dyno? If so what was your trap mph? If your motor is sound and needs more exhaust then you could be loosing quite a bit from it. Need more data tho.

 

could also be a bad valve ajustment and maybe a vacume leak

 

I have dual cutouts on my exhaust with nowhere close to the goodies you have.
gain 3 tenths and 3mph with them open. exhaust is 3 inch flowmaster with no cats.
my guess it's the exhaust.

 

the magnaflow cat maybe

 

I had the cat installed on Saturday (before the dynotune) because the hollow factory cat sounded terrible, and I was hoping to quiet the car down a bit (Lots of kids in my neighborhood, including my 2 yr old, and I leave for work at 6:00 am). The turbulent reverb sound is gone, but the car is not really any quieter, and the power loss was noticeable. I think that maybe the cat needs to be replaced with a straight pipe since it didn't quiet my car down anyway, but then I'm still dealing with a 3" catback.

 

it has to be your exhaust. I don't have any dyno number difference. But once at the strip I left the cutout closed and ran a 12.20 and the very next run, I opened the cutout and ran a 11.72. Huge difference. I had a 3 inch catback just like you. I would look into getting a cutout

 

You could run a free flowing exhaust system that is quiet. Dual 3" into a terminator box back into dual 3" mufflers (magnaflows or pypes) all tucked in and won't kill your HP.

 

This is precisely why I'm looking to setup some time with you before winter, lol!

 

Well that may have to wait till the spring because I am going to be moving the shop to a new location that will start construction a few months. Until then I am finishing up some long term projects to clear the current shop out.

 

Put a vacuum gauge on it, if you don't see the needle go to zero at WOT then your throttle body is too small.
Have you tried advancing the timing any?

 

why not test the exhaust back pressure, to see if its over 2-3 psi at high rpms , indicating a restriction or temporarily disconnect the exhaust system to see if the change in restriction makes a difference in your results?

whats your ignition advance curve look like?
can you post CLEAR LABELED pictures of the spark plugs?

theres always a reason and a logical, test, & verify ,step, bye, step approach rather than random parts swapping and wild guesses will locate the problem

 

I will check the vaccuum reading.

We set the timing where the engine made maximum power. When we lost power, we re-burnt the chip with the last timing values.

 

The back pressure test is also something that I've considered doing. I need to drill a hole and get a back pressure probe from my old shop.

I do not know the exact advance curve because I was not the one burning the chip. I just know that my tuner added timing at various points until we lost power or encountered spark retard, and then backed up to the last good value.

 

I should add.... While we were trying to richen the a/fr up high (it would go to 16:1 a/fr when the rpms went over 4000) I watched the fuel pressure gauge to make sure it wasn't due to fuel pressure loss. The fuel pressure actually climbed above its set point.

It is set to 44 psi with the vacuum port open, and idles at 39-40 psi at idle with the vacuum reference line in place. While making the dyno runs, my pressure would linearly increase with the rpm's of my motor up to 46 psi or a bit more.

How is this possible with out positive pressure being present at the regulator diaphragm?

 

You might have some bad injectors. Read the plugs to see if any are showing signs of going lean.

 

your potential peak power is almost always found with a 383 having a similar cam, compression etc between 5600rpm-6400rpm and at about 12.6:1-12.8:1 f/a ratio with about 34-36 degrees ignition advance, now you might be a bit off , but thats normal and should be a starting point in the tune,as usual knowing exactly what your currently dealing with and calculating what you need to get to your goal is key here
it could easily be a case of the injector being to small to keep up with demand,,your 32lb injector will max out at about 420hp,read the links use the calculator links provided,[/color][/b]

http://www.witchhunter.com/injectorcalc1.php4

http://forum.grumpysperformance.com/...hp?f=55&t=1200

 

 

 

The photos didn't come out as well as I expected.. All of the plug insulators are rose colored.

I tested the cylinder pressures in this order: 1, 3, 5, 7, 8, 6, 4, 2, 1

The compression (engine cold, throttle closed) is as follows:

Cylinder:
1. 200, 180 (first cylinder tested was at 200, I checked it again after the other 7 cylinders and it was 180)
2. 175
3. 187
4. 175
5. 180
6. 176
7. 175
8. 176

 

my guess is still the exhaust....joeblue picked up .048 with his exhaust uncapped. that's approx. 45 to 50 ponies which would put easily at 380+.

 

Hey gixx I think you may need more injector. you say you ran the fuel press at 49 psi with 32s. Well on a 355 I had 35s jacked up to 60psi and was maxed out at 410 rwhp. Your combo should do that with ease. Could be exhaust and fuel. Grumpy is right, 16 to1 is too lean for power.

 

It would hit 16:1 wide open before the custom tune. It is now 13.0:1 +/- .2 throughout the powerband (I was thinking it was closer to 13.5:1, but I verified it is actually a little richer).

I saw the injector calculators, but was told that these 32 lb would actually flow enough for 475+ flywheel hp.

 

I saw the injector calculators, but was told that these 32 lb would actually flow enough for 475+ flywheel hp.[/quote]


Yeah that's straight flow with no bends or G-forces to overcome. I always size my injectors 1 step higher than what I calculate and sometimes I still may run out. At 430 chp you may be going static. That would put you at about 360 rwhp. Also a dyno is good for getting a good idea of what the car is doing but having a wideband on the car while going down the track can really dial a car in. 13.5 afr is a little lean for wide open throttle all the time. 12.8 to 1 is better and if you get some good air you won't go lean.

 

Does this have anything to do with the torque converter ?

 

your plugs indicate a very lean condition, in the upper rpm range

Id try the calculator again, it suggests 410 -420hp is max with a 32 lb injector

http://www.witchhunter.com/injectorcalc1.php4

 

The converter may be too loose or flashing too high on the dyno to get the reading you want. Burnout91 made 397whp with the same combo but the converter was stock. He went to a 3500 stall and the whp dropped to 375whp. Make sure your base timing is set at 6*-8*. What headers are you using? Check my sig. You don't need duals.

 

here's my 2 cents. On the 70s chevelles swapping from stock manifolds to headers was worth 90 hp easy. www.mufflex-performance.com should have what you need. i think last time I was poking around I saw a 4 1/2" catback. I know 4 inch for sure.

 

damn 90hp really?thats more then a cam and intake swap probably.

 

When I get back on the dyno, hopefully in a couple of weeks, I will do a run with the Magnaflow cat removed (I have a MAC flanged cat delete on the way, and will be installing a cut out in that delete). Next I will do a run with the cut out open. Maybe then I should crank the fuel pressure up to 58 psi (my LS injectors flow 36 lbs at 58 psi) and do a run to see what happens. That should tell me if the motor wants more injector, right?

vincentZ28... My headers are SLP 1.75" w/o A.I.R. ceramic coated.

 

It's not all the exhaust is holding you back. Look at the WHP my car made with the full Exhaust system hooked up. You may have other issues. Don't believe that BS. What cam do you have? Tune you car with the full exhaust intact.

 

Lol, funny. You would make more hp with a better exhaust system on your car and so would he. Not saying you can't make X amount or there is a max that you will hit with X size pipe but once you meet the max hp that a system can support without being a restriction then the more hp you make past that point the greater amount of hp you are giving up. I have been there and done that. Hell I have a 3" single on my BMW and it's just a lil 2.5 ltr 6. That 3" system is one of the things holding back some power. Just put a psi gauge on it and see for yourself.

 

I started this thread looking for advice on what to look at because I know something is amiss. My engine components are all in the first post. I just had a full custom tune done at the dyno last Sunday, with full exhaust in tact, and a new cat installed. I lost a noticeable amount of power after the cat was installed on last Saturday.

As noticeable as the loss of power was, it has to be at least 20 hp in the cat alone... The car would blaze the tires, and instantly redline, at any speed in first gear before the new cat. After the new cat, it would still spin from a roll, but not completely overcome the tires... It was more like a scratching, squawking spin (again, from a roll). Matting it from a stand would still annihilate the tires after the cat, but when I hit third it would just scratch (it would continue to spin until I let off, or hit OD, before the cat). Definate loss of torque and power. It worsens as the revs climb.

However, even with the power loss from the cat, there is still something else wrong here.

I appreciate all of the insight and advice from everyone, thank you!

 

Yup, been there done that. Back in the day when my Z28 had just a bolt on 350 and was my daily driver I had to worry about the smog testing so I ran dual cats with a 3" Dynomax catback and lost some of my torque and topend. I later put a 2.5" dual system on it retuned it (carb) and it was a big diff. Just look at all the guys that are fast NA, and you will see a trend. That 350 was running 11.70s back then (95').

 

Ok! Well I have a dual cat set up and he has a single cat set up. That will make a difference in power but he still have other issues besides the exhaust. Proper timing, Valve springs, Cam not degreed properly, Wrong plugs, Weak fuel pump.

This is a long shot but did you disconnect the EST wire before you set the timing? Some people forget to do that.

 

I agree, there are other things that isn't right. He should right down all the things that could be holding him back then go through the checklist. Start with the free/low buck stuff first.

 

Base timing is set at 10 BTDC (with EST unplugged), the motor did not like 6 BTDC at all. The total timing is around 38 to 40 degrees (when we tuned, we added timing until power was lost due to ECM pulling timing and then backed it down to the last known maximum advance). My valve springs are not the heaviest, but they are more than capable of handling my moderate cam (see posts 7 and 8). Cam was degreed to manufacturer spec (I can't remember what the number was, but my builder degreed to spec). Plugs are AC 41-629 (the new FR3LS) gapped at .035". My fuel pump is a brand new Walbro 255 LPH which came in the Racetronix kit (with wiring kit to maintain maximum voltage). While on the dyno, my fuel pressure actually increased to more than the set value (see post 25). This fuel pump will supply enough fuel to support over 600hp NA.

Thanks for all of the advice! I don't need my hair to fall out any faster than it already is!

 

One more thing. Did you port the HSR? From what I understand they are not that good if you don't port them. You need to change the Throttle Body to a 58mm. 383cu+ likes it and your set up should be over 500 fwhp. Mine is right at 480fwhp with a smaller cam and heads that yours.

 

Interesting, I have not ported the HSR. I've considered purchasing a 58mm TB, but have not as of yet.

 

Was this a mustang dyno?

Was the converter locked on the dyno?

Did it not make any more power with richer mixture? IE 12.5-13.0 to 1 range Timing seems high with AFR 195 heads. What plugs you using? .750 reach? What gap?

Did you datalog the dyno run? Whats your injector pulsewidths?