Frustration "dialing in a SR 383" Opinions please
 

My high hopes were dashed this past saturday at the GMHTP shootout. My best run was my first, I ran a 12.93 @ 106 mph. I'm not concerned about the et since it's dependent on a lot of factors, but my mph is probably 10 mph low. I had it dyno'd at the event and it cam out a disappointing 261 hp and 323 tq at the rear wheels. Unfortunately I can't scan the graph, but according to the dyno operator , it started detonating at about 3700 rpm. The graph then looks like a rollercoaster to about 4200 and gradully climbs to about 4500 where it stays relatively flat till about 5600. Another guy there seemed to think the dipswere due to a lean condition. The dyno operator felt I should be seeing another 80 hp and I agree.
Question- I've suspected a vacuum leak. When I start the motor cold, the motor races up to about 1400 rpm and settles around 1100. Then it chops around from 800-1100 ( Chip is set to idle @875 rpm.) The motor is throwing no codes. When I've hooked it up to a snap on scanner, both the blm and the int are right around 128. Could my problems be related to a vacum leak? I checked the fuel pressure and it seemed steady at aroung 40 psi wth the vacuum hose connected.

Any ideas would be very much appreciated.

Thanks,
Glenn



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Neptune, NJ
White '87 Vette - 383 Superram ported and matched to TPIS big mouth intake, Eagle cast crank, 6"eagle forged rods, srp/je forged pistons, LPE 219 cam, ported heads(2"x1.56" ferrea valves), Comp cams pro-magnum 1.6 rr's, double springs, titanium retainers,Hypertech power coil and cap, 4 bolt block, TPIS headers, auto(trans kit,shift kit),Pro Torque 2600 stall converter, k&N filter, 3.07 rear diff., Silver ZR-1 wheels 17x9 and 17X11

maybe ignition, how long has it ran like this? What ignition do you have? I would think it would have to do something with that. If not maybe fuel, spark plugs, vacum leak. Just from you info to my head that is what i think.
Bobby

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89 red iroc-z
386 strocker
ross pistons 10.5.1
eagle h-beam rods
miniram
slp cam 224 230 535 544
1.6rr
edelbrock performers p+p
ford 9', 4.11, 31 spline
baer rear brakes
line lock
all the bolt ons
200 shot on the way

A couple of thoughts here: first of all, I think you can rule out a vacuum leak because if you had a leak, your block learn would be much higher due to a permanent lean condition. 128 block learn is perfect. Almost too perfect... are you sure the car was in closed loop when you read the blm and integrator? If the car is in open loop some scanners will show a standard 128 for both numbers.
My second thought was that if you aren't running a custom prom, and I didn't see it in your sig, then you should be. Seriously, it will make a world of difference. That could be all your problem is. Your stock prom for a 350 has no idea about the fuel and timing needs of a stoker motor.

Thanks for the responses.
I'm running a brand new hypertech coil and cap, new ngk plugs and new moroso spiral max wires. I kind of doubt it's an ignition issue but I guess it's possible.

When I hooked it up, I'm almost certian it was in closed loop. The Int and blm were both hovering around 128. I have a custom chip from Ed Wright ( Fastchips)

OK, maybe it's not your prom. If the numbers were fluctuating then you were in closed loop. I was just making sure. As for the possible vacuum leak, check the IAC number on the scanner if you still have access to it. 20-30 is what it should be at, but if you have a vacuum leak it will be really close to zero. You probably ought to check it the old fashioned way with a vacuum gage too. If you have the scanner there are a lot of things you can check. Like check the total timing advance, especially when you are getting detonation. See if there is any knock retard. Also look at the injector pulse width or duty cycle. If your injector duty cycle is maxed then this would cause a lean condition. What lb injectors are you using?

I'm using 24lb injectors. Next time I have a chance to hook up the scanner I will look at the other things.

It is NOT a vacuum leak.
it could very likely be a lean condition.

OBD-
I assumed that a vacuum leak (false air) could create a lean condition, is that true?
What are some other causes of a lean condition?

Do you by chance know the WOT 02 sensor Mv.s??

I wouldnt be to upset with that mph. Im sure you were setting your expectations higher, we all do. If you read lingenfelters book you think wow he made those numbers with that cam?? When First got my 383 all together I expected better numbers also and didnt get them. If the car is running into detonation that could be a real hp killer. You need to use some sort of scan tool to see if your timing is eratic during detonation. The distributor itself coud be worn or the timing chain could be bad. The timing could also cause your eratic idle. The cam you are runing is a very mild cam and shouldnt be causing any real computer problems.

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87z 383,afr 190's, comp hyd roller(242/248-.540/.562,114 sep),Ported and polished mini ram, 30lb inj, 3.42 gears, tremec 5spd, , 1,3/4" slp headers, speed pro bank to bank-wb02.
"Just remember children, no man can beat you once youv'e found the cliterous." 'chef'

I would do several WOT runs while getting the O2 sensor output voltage with a scanner.

Also, check to see that during normal highway driving that the ECM is in closed loop mode.

40psi for fuel pressure seems low to me. I expect that you are running lean and detonating because of it along with alot of spark retard.

Get a good scanner and do some investigation.

If you dont have a scanner, increase your fuel pressure to 45psi and make more runs at the dragstrip. If your times drop and the speed increases, then I think that that would prove that you have a lean condition at WOT.



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'87 L98 TPI IROCZ, AFR190 heads, 3.70 gears, ZZ9 cam, 2400 Art Carr TC, SLP 1 3/4" headers, SLP cat-back, no cat, no AC, no MAF screens, Accel manifold base & SuperRam, 24#/hr SVO injectors, Edelbrock double roller timing chain, MSD ext coil & distributor, trans cooler, 52mm TB with airfoil, TB coolant bypass, AFPR(58psi), K&N filters, Hotchkis lowering springs, my custom chip, Lay Ind. ram air kit, SS Brakes 1LE upgrade 12" rotors dual piston calipers, 265/45R16 Kumho V700 tires.
ET 13.39sec @ 107.21mph
'90 Eagle Talon AWD, no rust thru 9 winters
'99 Camaro SS, red, 6-spd, T-tops, Mcleod clutch, Pro 5.0 shifter, MAF processor, Direct Flow airlid, K&N filter, next mod: 4.10 rear gears
313.7Hp & 320.6ft-lbf, ET 13.55sec @ 105.1mph

Nope..

your fuel map may not be anywhere near right.

87Z, I get good MPH with an LPE cam.




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*I do custom performance mods on Edlebrock Performer carburetors (dualplane intake mods in the works),
White 1986 Irocz, 305 with iron #416 heads,
383 with aluminum TFS heads,
Edlebrock Performer-RPM intake and Performer #1407 carburetor, +110hp shot of crack, 700R-4 tranny, Vigilante 2400 lockup converter, 3.25:1 Ford 9" rear, Mcreary Road-Stars, SLP-stainless 1.75" shortie headers & Y-pipe, single 3" Borla exhaust, Linginfelter-TPI camshaft part number 74216 pulls 17" vacuum solid. Cam specs 213/219 @.050 114-LSA, sometimes advertised at 216/219 @.050 112-LSA .462/.470 lift @1.5:1 ratio. Using Harland Sharp 1.65:1 roller rockers. MSD-6AL, billet distributor, multi-retard, blaster-3 coil, and RPM switch. SouthSide machine subframe connectors, SSM lift-bars, Moroso 4" underdrive crank pulley.

N/A runs 10.9 @124,
Crack-runs 10.3 @135
haven't run at track since Oct-99
* vizit miy homepayge * http://www.geocities.com/trailerparkpage/

I'm in the same club. 13.06 @ 105 is all I can muster with almost the same set-up as Glenn. I just ordered a pushrod length checker and will do a compression test this weekend to try and find the problem.

Good luck.

Goin' fast ain't as easy as it looks in the magazines.

Odb i guess your one of those rare cases. There just are not to many cars with that cam running those kind of numbers. Props to you for doing it, but you are a minority. I run my car the same way I drive it everyday. Nitto drag radials, power everything, and weight with me in the car of 3654lbs. Best mph before speed pro w small cam was around 108.

87 z-ya,
The motor should be putting out around 330-350 to the rear wheels. When I had it dyno'd It put out approx 260 rwhp (Ed Wright Fastchip) and I was getting (at least I was told) lean spikes above 3700rpm. The Dyno graph looked like a roller coaster. I had it dyno'd initially using an a chip made from 89vets.bin that is downloadable from various sites. With that chip, it was putting out 270 rwhp but it idled very poorly and when hooked up to a wideband O2 sensor, it showed WOT AF ratio of 17-1! From what I've been told, given I wasn't experiencing any detonation on that run, an AF that lean is impossible. I suspect this dyno shops O2 sensor needed replacing.
As far as speeds and times. At the GMHTP shootout recently, I met a guy with an 87Vette set up similarly (frankly, even cheaper components) that was running 12.5's at 111 mph and that was in crummy air. I know of a few others with similar setups that are running 11.8's at 117 mph with drag radials. Keep in mind this is a vette and I suppose it's lighter than the F-car. For what it's worth, the race weight with me in it was 3480 lbs at the GMHTP shootout. (I'm not exactly small 6'3", 290 lbs and I had 3/4's tank of gas)

ODB,

You have to have had your heads fully ported to get those kinds of mph numbers with that cam. What are your flow specs?

87,

The whole point of this post is to try and find areas of improvement in our combos. Maybe we have a common factor that is limiting performance, I don't know. That's what I am trying to find out.

Your mph at 108 doesn't look that high either, was that with the factory computer and a custom chip? Did you pick anything up by going to the Speed-Pro system?

I agree that if you read all the books and magazines you think you should be going faster. And yes there is always going to be someone with a setup "similar" to yours running better numbers. I think my car should be putting out #'s of around 350hp at the rear wheels, but I know its not. If in fact your a/f was 17-1 at wot under the load of a dyno I think it would be burning holes in the pistons. My previous times were with the stock Ecm and stock gm 350 chip. Im taking it to the track tonight to see how it does with the speed pro, but to tell you the truth it doesnt feel much faster. I have a crane cam in it now (224/230@.050, .509/.528lift, 112 sep). And its way to small a cam for my combo. Comp made me a much better one that I am waiting to put in once I get used to tuning the speed pro. Glen, do you have a way to check fuel pressure at wot under load? My car ran terrible and slow for a long time. I had the stock intank pump and a external add on pump. I hooked up a fuel pressure gauge inside and found out the press. would die under wot. The intank pump had come apart and the brushes were barely making contact. What a hazzard that was. Keep us posted on progress

[This message has been edited by 87Z-ya (edited April 06, 2001).]

87,
I'll be checking WOT fuel presurenext week whn I get home from vacation. I'm also going to bring it to a dyno shop that has a scanner and a wideband o2. Fastchips told me that once I get that data, they will be able to modify the chip appropriately.

your A/F ratio at WOT should be around 13:1

I've never had my heads flowed. I got them in 1995 from Summit for $800.

the cam or heads alone don't determine performance potential. It's always a combination of the entire vehicle plus tuning.