Here is a scan of a recent dyno run on my 388 engine. The current mods are in my signature.

Don't take the actual values of the air fuel ratio too seriously. The wideband O2 reading was taken at the tail pipe so the cats are throwing off the real reading. Notice the rather drastic change in air fuel from one run to the next. The higher one (13.2) is the second run. I suspect its higher because the cats heated up during the first run. An SS Camaro had showed the a similar kind of change from one run to the next.

I had a loose coil wire which I did not discover until I got home which caused a sneeze during the second run.

I don't think there is any problem with fuel delivery since there is no dramatic drop off at any point and the reading is not way lean. The only places I can think of where the problem might be is spark knock, bad wires (which I am changing) or plugged cats.

Any suggestions would be appreciated.






[Modified by AquaMetallic94LT1, 11:16 PM 10/19/2002]

 

What's the fuel pressure set at?

 

Spark knock would make a much more erratic curve than that so I don't think that's it.

In any case, what are you running for exhaust? If those are stock cats on stock manifolds that is probably your trouble. A friend of mine just dyno'd yesterday. He has a 383 with what I'm pretty sure is an identical cam, 383, pocket ported stock heads, etc. The major difference would be that he runs long tubes and no cats into a set of very high flow mufflers. He made 369 hp and 379 torque.

Looks like you made 345 hp, 331 torque. When I added long tubes and mufflers to my car I picked up 23 hp and 32 pounds of torque (on stock heads), that would put you at 368 and 363, if you consider that a stroker with better than stock heads would see more benefit than a 350 with stock heads, that should put your numbers right up there with that of my friend.

So if you're running through stock exhaust, that's your whole trouble. The engine is an air pump and you've got to be able to get the air out of it just as well as you get it in. If you've already got some long tubes then I don't know what to tell you. Cat's alone shouldn't cost you that much hp.

:cheers:

 

Thing looks pretty strong to me. Looks also like you could have taken the RPMs up a bit more to maybe get a better HP reading. Usually they roll over pretty drastically when they are out of juice. Yours is still climbing pretty good. It looks like its starting to bend, but it may have a large radius which will get you over 350 HP.

Also if that wire was causing you to have a weak spark, it could be accounting for some power too.
:cheers:

 

I agree with nathan, if you're running anything but long tube headers, hi-flow cats and good cat back exhaust, you're robbing a lot of hp. For a good example, look at JConforti's recent posts when he changed exhaust. I wouldn't be surprised to see another 40hp.

I also agree with ski, you gotta take that motor up to at least 6500rpm to find the top of your hp curve.

 

Sooo... ~420 HP at the crank isn't good for that engine? :confused: What were you expecting? Honestly, it doesn't look that bad.

 

345rwhp and 331rwq is very low for 383ci LT1. Well ported heads and cam can produced better number than that. Obviously something not working properly that caused him the hp.

Bruce
93LT1 Conv w/ZF6
Blown D1-SC/N2O
ARE built 383ci/Stage II heads

 

Thanks for the replies. I am contemplating the long tube headers very seriously. I have a Corsa cat back in the car right now with the stock cats. I am thinking about putting on high flow aftermarket cats as well.

89vette is getting 430 hp at the crank from his stepup. He's got a superram so his power peak power is in the upper 5K range. He's got long tubes also.

I thought lingenfelter was getting about 440 from his 219 cam superram LT1s with stock LT1 exhaust.

I was expecting about 450 - 470 peak crank hp with this setup. I have the right heads and cam specs for the job. I can't figure out what is missing other than exhuast. The fuel air is set at 12.5:1 at WOT above 3500 and the spark is set at 38 deg at full throttle. Some of the tuners like more are advertising a lot more hp with similar setups.

I am limiting the upper rpm to 6300 because the block has 2 bolt mains.

I desktop dynoed this setup and it predicts 487 hp with headers and full exhaust.


:confused:


[Modified by AquaMetallic94LT1, 2:51 PM 10/20/2002]

 

With headers and full exhaust you want to be sure you have SOME type of restriction; you can't go and slap on some huge, longtube, ceramic coated, equal length headers and have the exhaust ports made a little bigger and then put on 3" pipes all the way back. Not enough restriction, and some is needed for proper ignition. Get rid of the cats and precats and move the O2 sensors further down the exhaust. Use a high performance muffler. Run some longtube equal length ceramic coated headers back into an X-pipe and down some 2 3/4"-3" pipe to the mufflers. It's your best bet. :yesnod:

BTW, that is where your horsepower went. :cheers:

 

I changed the wires this afternoon and found some of the problem. The lead inside the side that went into the distributor side had slipped all the way into the boot and was not clicking securely on to the distributor.

Based on the torque curve I think I have too much cam. I'd like to advance the cam but can't do it with an LT1 distributor.

 

Join the club dude. I dyno'd 340 rwhp and 350 rwtq with a 383, 10:1, ported AFR 190's, 230-236 .604-.608 comp cam, SLP 1 3/4, LT1 intake, and the SLP y-pipe with 2 stock cats going into the 3" SLP cat back.

I've since had the exhaust redone to get rid of both cats, one is gutted, and I have 3" all the way back, and it feels much faster now, also louder. I also found a vacuum hose that wasn't hooked up, and 1 burned plug wire.

Just this weekend, a guy with a LT1 350, 11:1 comp, 232-242 hydraulic cam, cnc ported LT1 heads and hooker longtubes going all the way back with 3" pipe on both sides dynoed 399 rwhp.

I'm thinking about switching to the longtubes also. I'm off about 80 rwhp than I think I should be right now. Don't think I'll pick up that much power with the exhaust change, but when I go back to dyno, I'll uncap the exhaust at the headers to see what it's robbing from me.

Keep us posted on what you find out.

 

His name is Jessie Coulter, and you guys were at TEA. Actually I hate to let you down, but it wasn't quite 399 hp. The dyno was displaying STD corrected numbers rather than the more common SAE numbers. Either is fine and it doesn't affect anything, so long as you compare apples to apples. He actually made 391 hp.

I also happen to know that nobody got a printout from the dyno. If you would like your printout or the run files, I'll send them to you, I've got them all. I got to salvage our dyno information before the dyno was sold. :cheers:

Hmm, I was looking and I don't see your numbers. You didn't dyno Saturday did you? In any case I'll throw out Jessie's graph, looks like this



He's got a nasty mid RPM thing going on that he needs to figure out, but other than that it looks really healthy. Here's by cheap shot BTW, those are TEA lT1 heads with stock valves he's running, they actually flowed a little less than mine because of the stock valves. I feel confident he'd be over 400 with my heads, or if I had his cam. We may tune it to over 400 yet, his A/F is a little lean on the top end.

And just wait until he gets that nitrous system working!


[Modified by Nathan Plemons, 6:59 PM 10/21/2002]

 

I know Jessie, I just bought a bottle from him on Sat. Those figures were for comparison's sake. I didn't dyno Sat.

The point is, even with 33 cubes less, and 30 cfm less on airflow, he made 50 more rwhp than my 383. I'm going back to the dyno today to uncork the exhaust to see if that is what's holding me back. The y-pipe is 2.5 inch outside diameter, so I'm guessing that it's 2.25 inch inside. Jessie has 3" all the way back with no bends, and I'm wondering if that's my problem.

 

Hmm, hope you're not planning on coming to the TEA dyno, it's kinda gone.

I do know that when he had "Riggs Racing" heads he dyno'd fairly poorly and he picked up 15 hp by opening up his cut out. Do you happen to know if these numbers were through his muffler or using his cut out?

Is that on your heads you mean? Could be a velocity issue. All the airflow in the world doesn't do much good if it's not moving, could also be a peak numbers vs. area under the curve thing too. Who knows, some people just have bad luck too. I'm sure you'll figure it out in any case :cheers:

 

I'm dynoing at PG in Nashvegas. TEA ported the heads, and they flow 295 intake at .600 and 235 exhaust at .600, and that's where my cam peaks in lift.

I hope it's the exhaust, and nothing else.

 

Well I wish you luck! Let me know how it turns out, and if you don't mind get the dyno run files on a disk and e-mail them to me. I like to collect them, never know when a discussion such as this comes up.

If exhaust alone fixes your problem than that would be a great asset to be able to throw up both numbers for comparison sake. That sort of thing tends to really drive the point home for some people who just refuse to accept it otherwise.

 

Nathan, where do you get the software to read the dyno files? I have the file on disk with a .DGJ extension. I didn't find anything on the dynojet website, help!

 

The stock manifolds and cats are quite a major restriction, I dont have dyno results but I picked up a solid 2-3 tenths and 2-3MPH going to long tubes and losing my cats......you will never pass emissions with that cam so why even keep the cats. You also need to spin the motor up more than that, with that cam you should see your peak HP closer to the 6500rpm mark. Check your valve adjustment also, make sure that your rockers arent a tad bit too tight or misadjusted. Good luck :) :cry

 

Thanks for the suggestions. Your right on the peak power being at 6500. I figure its around 360 or more. I need to dyno it again to see what change there is with the new wires.

Your correct about the car failing emissions. Just for grins, I took it through the Oregon DEQ testing a couple days ago. It passed the NOX part but failed the HC (what a shock) and just barely failed the CO. The relevant numbers were:

2.3 g/mile HC (1.2 g/mile is the limit) and 30.8 g/mile CO (30.0) is the limit for that one.

We have full IM240 emissions inspections here so getting rid of the Cats is not an option. I suspected the cam wasn't going to pass so my plan for that has been to put on 1.3:1 break in rockers from comp cams for inspection purposes. I have been debating between those and a smaller cam since the peak power is so far up in the rpm. I was expecting the peak to be around 6000.

 

Since you have a 6 speed you will be able to run long tubes with cats (Random Tech) without clearance issues that the Auto cars are plagued with. You wont regret going to long tubes/high flow cats.

Do they offer a show car emissions waiver in your area????