Here are the results from my very first dyno session with my LO3 91 rally sport. 159.4 hp and 244.2 torque on a chassis dyno. All three pulls were very similar to the one posted. The exhaust has been smelling a little rich since I did the intake and air cleaner, and the dyno result confirms this.

Here are my questions: What can I do to correct the rich condition? (fuel pressure regulator, chip or what?) Why might it be running rich? What do you guys think of the numbers? -Jake

PS I know I need full exhaust.

 

It's kind of hard to read your dyno graphs. If you could darken the lines and rescan it we could be of more help. You might also want to do the WINALDL thing and get some data logs that way as well. Check this out you'll find it interesting.winaldl

Steve

 

Man look at that torque plateau

It appears that you're putting out more than what the stock rating is at, even though you're only mods are the open element and the Edelbrock Performer intake. If you calculate for a 20% loss through the drivetrain, you're putting out some seriously high numbers for something that's damn near stock.

I don't know man, I don't think I would mess with the fuel pressure at the moment. Besides, when you do the full exhaust, it will probably lean you out some and you'll be more where you want to be.

 

Man my pc must be crapping out on me, I can't see any of the graph lines.

Gunny how'd you do that?

Steve

 

I have a REALLY, REALLY expensive gov't computer screen.

 

No fancy computer screen but I've got mad skilz with da paint shop yo yo, [grunt, cough, clear through]. Sorry about that, I don't know what happened. I fear ricers must be near by and the only way to get them to race is to speak like them. It's like going under cover, only with a domestic and faking ***** lingo.
Here is the above graph with a highlight for those that can't see it.

 

I've been trying to get WINALDL running, but I've run into some problems. I bought a $52 IBM thinkpad and installed WIN95, but WINALDL won't install right. Jonas sent me a patch, but it still isn't working. Whuz da dealy-yo? sorry, Prevost's mad skilz inspired me. Anyway, I'm waiting for a copy of WIN98, and as soon as I get some data logs I will post them here.

The peak numbers on my graph come from a little kick at about 3430 rpm. Is that normal for the LO3? I was expecting the peak hp at ~4000 rpm.

I was under the impression from reading some (possibly incorrect) posts that headers would richen me up even more. Not true?

How rich is 12.1 or 12.3:1? Not too bad? Am I probably fouling my plugs?

Thanks (especially for enhancing the graph) - Jake

 

Why does the graph stop so soon? I would have atleast taken her to 5,000. Your curve looks a little jumpy and seems that it was trying to climb still when youl et off.

 

I was curious about the kick in the graph as well. Generally, the peak hp of an lo3 is around 4k like you said. It is kinda hard to deturmine why yours is where it is. Maybe a flaw in the dyno run, or something like to much timing, and the ecm retards it at around 3,500rpm

 

That torque curve is flat as Oklahoma! Yeah man, pull higher, your horsepower just kept going up. I don't know what to tell you about that little bump in both curves, kinda wierd, I'd suggest another pull to at least 5000.

 

On the first pull, he went to 5K and the power dropped wicked after about 4K. Unfortunately, I don't think that he printed that one out for me. I guess it was like a test run. I will drive it next time.

Here's a different run that doesn't really have that weird kick in the middle. I traced over the lines for your viewing pleasure. It is kind of still climbing at 4200. Next time I'll take her to 5K always.

I have my base timing set at ~6* btdc. That should be okay, no? I've read a lot of posts about timing, and my Chilton's says to set it to 6. I really need to start logging data...

 

Well you deffinately have a great starting point. If you find out why you are so rich I bet your numbers will a bit higher. But they are great for damn near stock mods.

 

Chiltons or any service manual for that matter should tell you to set base timing to 0. That's the way most if not all TBI cars were set from the factory. You ought to set base at 0 for the base line run. Then progressively give it more timing until it just falls on it's face. At that time, take away 2 degrees. OR keep taking timing away if it isn't helping the performance of the vehicle, trust me, this is a big issue. I had my first tank of bad gas and it was so bad on the highway (3.73 gears stink) that the car was cutting out on me. I had to remove 2 degrees just to get it to run right without detonating. What I've noticed is that those 2 degrees EVERYWHERE, probably haven't hurt my performance. We'll find out with a chassis dyno although I'm itching to pull the motor and install it on our (C.A.R.'s) engine dyno.... believe this, it's already setup for a chevy v8 .
Where did they place the o2 sensor and do you have a cat?
If you don't have a cat then those AFRs look fine, installing headers will lean it out because your engine will be pumping more air and without a calibration change to tell the ecm that the engine is more efficient.... you'll get the same amount of fuel. More air, less fuel = lean .
Like I was saying earlier, go from 0 base to 4 to 8. Then when you get knock (performance pitfalls) take out some base timing. The biggest issue with stock calibrations and moding engines is that the emissions stuff is wacked. It doesn't help any that GM was in a rush to get these cars out the door that they just used what ran best at the time. You'll find tables in the stock calibrations that don't have anything to do with EGR BUT the certain cells that get used get "used" 90% of the time with EGR on, or vice versa. So a lot of overlap happens and you end up with a mess. When or if you ever do get into tuning your own eprom, you'll notice this within a few days of browsing. Some people say to leave it alone but take away some of the effect (divide most of the time) but others will tell you to just zero out the tables that doen't make sence and run with it, see if you can find any issues, etc.
Good luck with the dyno tuning. I would wait until you get headers on there and a performer intake. While you're doing the intake might as well do the lt1 cam swap . You'll have no problem pulling past 5000.

 

The dyno shop just stuck a metal tube up my tail pipe attached to a vacuum pump that ran to an oxygen sensor. I do still have the stock catalytic converter. I thought that the ECM was supposed to correct for rich mixture? Doesn't it sense that stuff and make adjustments?

As far as that lt1 cam, it would be cool, but I'm going to aim my sights on an engine swap. There's a smog legal crate 383 stroker TBI that I have my eye on.

I have a Performer TBI intake that I installed a couple months ago. There was an oil leak from the rear china wall the first time I installed it, and I had to do it over. Holy *** was I tired of scraping those gaskets off after I redid it the next weekend.

So, I'm hoping to build around the engine this winter (posi, gears, headers) in anticipation of an engine swap next year. I am going to get into eprom tuning as soon as I get my laptop situation figured out.

Would you recommend 3.42 gears rather than 3.73, Jon? So I should adjust the timing between pulls at the dyno and see what works best... makes sense. I'll probably hit the dyno again when I get headers.

Thanks for the advice and support - Jake

 

I realize I am not Jon, but my recommendation is to match the gears to the engine you plan on swapping in. For example, if the 383 you're looking at makes peak hp at 4,800rpm, then 3.42s would probably be better. However if it's peak hp is around 5,500rpm, then 3.73s would match it better.

Just outta curiousity, do you have a link or the specs on that 383?

 

The ONLY way to choose the right gear is to take where you will be trapping in the 1/4 give or take a couple mph and pick the gears that will put you slightly past your peak hp in 1:1 gear. BTW, bone stock, I gained .5 seconds shifting at 5,000 rather than 4400 where my tranny shifts at with my L03. Most near stock L03s wont even trap above low 80 mph. 4.10's would proplly be best for them even.

 

Here's a link to the stroker.
http://www.high-performance-engines.com/spc1.html

Anyone familiar with this company?

383 only makes 310 HP, but I would probably do some light mods before swapping it in. In particular, the cam. I would want to learn more about the specific details before throwing money at it. However, when I estimated the cost to build my own 383 from a used block, I would probably spend close to the cost of the new crate motor.

So, 25THRSS did your stock LO3 make peak horsepower at 5000 rpm? I have an automatic (4L60?); how can I change my shift point?

Do you think that the heavy duty Zexel Torsen posi would be worth the extra money (vs take-off) for a relatively mild daily driven 383? I am thinking Richmond 3.42s mainly for mileage.

 

I have never dynoed my car so I don't know where my actual peaks are. I do know from actual track times that 5,000 is where my stock L03 likes to be shifted at. Anything lower and you drop the rpm's way too low and out of my power band, and the track times prove it. The regular take off should be fine btw.

 

5000 on a LO3 , no but seriously are you sure your tach isnt off, For a long time i thought mine made peak power near 5, till i put an autometer tach in the other day, come to find out it was a little over a 1000 rpms off. Peak power is about 4200 or so for me, well at least by seat of the pants feel. It feels like it takes forever to get to 4500 let alone 5000. But I guess it can happen.

Kevin

 

I'm pretty sure. I just did a little math with my gears, tire size, speed, etc. My tach is correct.

EDIT: just to clarify, I'm not saying I make peak power at 5,000, just that in the 1/4 shifting at 5,000 gives me the best times. It doesnt really feel like it's dying off until after 4800 or so though. I've taken it up to 5500 before but it felt like a dog that high.

 

Well hmm.... i take it you have 2.73's, if so i can see how it would drop outa the rpm range, i had those darn things, hated them except for the mileage. Then i got me some 3.42s, much better.

 

lol yeap, 2.73 peg leg. Soon to be 3.42 posi though. I would go much steeper, but with my future plans I will be trapping way too high and run out of gear, so 3.42's it is.

 

yeah i still have a peg let tho, my orig rear had a warped axle, so i got another rear out of a 86. I had planned on the slp take out posi, but i cant find a 28 spline axle around here.

 

I'm not sure but I think S10 axles are the same length. Maybe someone will correct me or confirm me on this.

Steve

 

I'm running with the SLP take-off posi in a 10 bolt that has over 180k miles BUT I replaced all seals and bearings about 20k miles ago. It's happy with the easy 2.03 60' times on street tread. I don't know how much further I'd push it but I will run slicks at least ONCE at the track, who knows what'll happen, crossing fingers.
The issue with crossing the 1/4 mile at peak hp is that it's incorrect. In reality you do need to cross just over peak hp for your best time in MOST cases. The reason is just like somebody else said, shifting drops rpms a LOT. You shouldn't shift at peak hp but instead look at the integral of your hp curve and then figure out the rpm drops. If you don't know an integral is as simple as figuring out the area under the curve. Do an excel spreedsheet to figure out the rpm drops after a shift and then look at your hp curve. You will need to go beyond your peak hp to "land" in a nice high hp rpm. This goes WAY back and isn't anything new. It's a big reason why some engine builders for high rev small blocks swear their lives to the hydra-rev kits (extra springs on the lifters to supress valve float). If you shifted at peak hp you're going to be slower than if you shifted after, not too much after but definatly after!
Whiz, get those headers on there and next time you go to the dyno tell them you still have a functional cat and that you would like the wideband installed in place of the factory o2 sensor. After that cat you never know what the actual AFR was because the cat does some amazing things to hydrocarbons but needs oxygen... what happens one might ask. Well know this, stock AFRs are extra rich under WOT to put the cat out. By putting out the cat they were making certain the cat didn't turn into a multen ball of toxic junk. All in all, just look at applications of the wideband o2 sensors in REAL research and OEM applications. All use an o2 sensor PRE cat, only post cat o2 sensors are for checking how well the cat converters are working. This can be found in every OBD-II vehicle.

 

I think we need a sticky on gears. Too many people make it out to be a lot harder than it really is. It's not a guessing game like some would have you believe, nor is it a science people. It's very simple as I explained before. The ONLY way to choose the right gear is to take where you will be trapping in the 1/4 give or take a couple mph and pick the gears that will put you slightly past your peak hp in 1:1 gear.

 

Just so you guys don't think that I was making it up when I said,

 

My LO3 knocked pretty good with premium fuel and 6* base. I had to back it off to 4* to keep her happy. However I have also seen some LO3's go as high as 8* advaced. I geuss it is whatever your car likes.

 

Wow, that stupid little V6 needs 10*!? What the crap!?

 

just looks under your hood at the sticker. It will say 0.

 

One more question:
Do you guys think that the sharp HP drop at ~4025 might be a knock and subsequent timing retard? --I remember hearing it hesitate near the end of the pull. I was running on 1/2 tank 87 and 1/2 tank 92 octane.

25TH - Yeah, more stickies would be good. From a novice's perspective, searching through 1000's of posts to find good information can be frustrating. Plus, there's a lot of BS out there. I used your your advice on gears, and I now think that maybe 3.23s would be good. 12in tire radius, 4400 rpm, 97mph in third gear(with a new 320 hp engine). Good stuff.

 

the knock retart is a possibility. You need to hook it up to winaldl to find out for sure if it's knocking or not and then you can set your timing accordingly.

 

I think the 6* of base timing that is listed is what the computer advances it. When you set timing unplugging the EST(?) wire you set timing to 0* for stock and then I believe when its plugged back in the computer advances timing to 6*. This is kind of going off of vague recollection though.

 

I think BronYrAur nailed it on the timing. Maybe somebody with the stock .bin data can confirm?

A couple things to take into consideration on this though, which may lead to choosing different gearing or not:

1) 320hp should be able to pull off better traps than 97 mph. Just as an example, Jon is using the 350 H.O. motor rated at 330hp/ 380lbs/tq. He is trapping in at 103mph+. Granted he has done a lot of tuning and other mods, but you will probably do the same over time. Of course his peak hp is at a higher rpm as well.

2) If you change out the camshaft like you mentioned, that will also change the characteristics of the engine a lot, depending what you go with. The cam in there right now looks to be very mild.
I don't know how credible the power numbers are on that 383, but they lead you to believe they are accomplished with the stock tbi (seeing as how it uses the edelbrock tbi performer w/ stock bore sizes). Boring the tbi manifold to 2" and going with a larger tbi would also make for a good amount of potential power.

3) Tire radius. make sure you are positive this is the size you want to go with. For example, simply changing to 12.5" radius leads to a 4mph difference, bringing the speed up to 101.3mph at 4,400rpm.

These are just some things to take into consideration, but it is why I said to match the gears to the engine you plan on swapping in. There are some assumptions to be made, like assuming the 383 is good for traps of 100mph in stock form, in which case 3.23s would work good, as you would pass just past peak hp in your 1:1 ratio gear.

However, a cam swap will change that. Say you swap cams and maybe intake and bring your peak hp to 340hp at 4,900rpm. *Assuming* 340hp is good for 104mph+ in the traps, then 3.42s would probably work better (using equation on tech page), as you would be at 5,000rpm at 104.4mph.

Kinda like 25THRSS said, the best way to deturmine what rear end to go with is from trap speeds.
But because you are building around your future engine G_whiz, it makes things a little more complicated, especially if you plan on swapping cams and what not. Just something to take into consideration.

 

That Chiltons says 6 base, that's what they say to advance the timing too with the plug undone. The computer advances it more than that. Keep in mind that even if the manual says to put it at 6, it's wrong. Our cars came with 0 as the base timing setting AND it's coded in the eprom as such. Under "initial timing" there is a 0. 0 * 90/256 is still 0 .
3.42 gears should be an all around great gear. I think the 3.73's are a little too much for my car. I should have gone with 3.42's. I'll cross the mark at redline and in 3rd BUT my 60' times suffer from having a 2800 stall converter, those 3.73's, and the 4L60's high 1st gear! If there were slicks on my car I wouldn't be complaining. In any case, the 1st to 2nd shift ALWAYS breaks the tires loose under WOT no matter how much traction compound is put down. Depending on the tires you use and the cars main objective I would look closely at 3.42's

 

these cars run rich from the factory. Make your stock regulator adjustable and drop the FP.

as far as rear end gearing goes it all depends on your end goals. Any reasonbly healthy motor is going to want 3.73s or higher, that is unless you are building it to be a tow truck and not a performance car which is something I sadly see all too often.


Im in the big horsepower camp, low end torque is for motorhomes. Big cam, high flowing heads, single plane, high compression, proper gearing (and stall converter if you are unfortunate enough to have an auto) and you cant go wrong

 

yeah, pablo, high horsepower is nice if you dont mind spending all your time above 3500 rpms and prostituting yourself to pay for the gas bill. I prefer somewhere in the middle. Good high end capabilities but still responsive and fun below 3500 rpms. I know it depends on preference, but for me, the recipe you described just wouldn't be as fun.

Sorry for reviving this post but i feel strongly on that issue.

 

is it me or is anyone thinking for $3895.00 for that 383 motor and another 200 or so in swap parts woudnt it be cheaper to find a good used 350 roller block adn get a 383 storker kit and do it yourself?? then you could build it right the first time instead of getting it and then swapping out parts. I you definitly make more HP doing it that was and it woudl prob cost less then what your talking about doing. i mean heck figure 150 for good motor and around 1100 for really good stoker kit. that still leaves a bunch of money for everytihng else and your woudl be happer with it.

just my thoughts

 

Since HP IS a function of TORQUE you can't have HIGH HP without high torque or high rpms.

Since I don't have a pit crew to push start my "street car" I would rather have torque.

My Torque to HP curve is nearly equal in terms of maximum output. The only difference is my peak torque occurs about 1500 RPM lower than HP. hower I am making high torque the whole time, the graph is almost linear. Neither curve ever falls flat. That is what I wanted a good balance.

To each his own.

 

good point, but, horsepower can be high while torque being low, I didn't really mean that to be taken so literally.

If you made 1 ft/lb of torque you could make 10000 hp if you revved high enough.


Regardless of that, I run a 305 with the aforementioned combination, and I had buddies telling me I was gonna have to push start the thing.

big cam, single plane, hogged out heads...

guess what, it hauls ***. 13.6@103.67 and ive trapped 104.97 before which incidentally is pretty close to what you trap Formula88 . Im still waiting to hear about anyone with a 305 that runs similar times (and it still be a street car) I launch and that s the only time under 4000 rpm i see in the quarter mile. I dont seem to have a problem wasting people on the street either so that whole "streetable torque" thing is way overblown.

I should mention that with the TBI the torque difference down low between it and the carb is tremendous. Even with the spongy low end on the carb because of lack of fuel the car still flew like a bat outta hell.

 

that's only true when your only consideration is quarter mile time and you are running enough tire (slicks) to make traction at the line a non-issue.

if the l03 makes max power at around 4400 rpm, it would take a 4.10 or even a 4:30 to put it there at the finish line in high gear. try launchin that gear on your street tires.

additionally, engines built for drag race-only cars are generally biased towards horsepower. when you're dealing with a combination that biased towards torque (as l03s are), they'll always be faster with less gear than a hp biased car, even if they both make max power at the same rpm.

i've driven a car with a non-overdrive automatic and 4:56 gears as a daily driver before ... it sucks. more importantly, with street tires on, the car was faster with 3.31s than it was with 4.56s or 3.73s.

 

is that high? i shift my 164,xxx motor at 5200 in first to second, and from second to third i shift at 5500. im pretty sure my tach is accurate. wot from a stop in d it shifts right under 5k. i think thats where it should be shifted. my cars a 92..

i now have a 3.73 posi, open exhaust manifolds (lol),open filter. my car ran like crap for about 15 minutes after the y pipe was takin off. i put the y back on to quiet it down some, and it ran sooo bad. it would cut out or bog down around 4200 rpm.took it back off, and pulls strong to 5300 (well, according to me and my friend it does)

ive takin my high mileage L03 to 6300 rpm before. and realized, after the sounds it was making, that i was never goin to do that again. lol

 

Most tachs I've seen are higher than actual RPM readings (from the computer and dyno)