I need some info. My '86 TA has an Lg4 from '83 in it. So according to the tech. data, it would've had 150hp and 240tq. The only mods I did to it was gutting the cat. and making a dual snorkel intake. Are those numbers close to what I had?

The reason I need to know is that I'm using my turbo buildup for my senior project. But, I didn't do a pre-turbo dyno run just b/c I didn't want to have the cost of doing it twice. However, I do need some numbers to compare then to now.

So if anyone has actual dyno graphs of a stock lg4 or a website that does (maybe GM?), I'd appreciate it.

Thanks

 

This is not exactly what you are looking for, but Hot Rod dyno'd their completely stock 82 LG4 and ended up with 145 HP @ 4000 RPMs and 165 ft/lbs @ 2400 RPMs. This is at the flywheel, not rear wheel horsepower. The LG4 is a pathetic engine in stock form.

 

BTW, I feel that the 165 FT/LBS was a typo. They made more like 265 ft/lbs when totally stock.

Not completely relivant, but my LE9 was very similar off the line and it made 160 RWHP @ 4,200 and 258 ft/lbs @ 2,800 with nothing more than some carb tweaks, a high flow cat, and a recurved distributer.

 

Isnt it 165 at the fly wheel? So thats only like 120-130 at the wheels

 

The factory did a pretty fair job of rating the original engines accurately. Age, time, modifications, and a lot of other factors can alter those figures (remember- they are carbureted engines with a zillion miles of vacuum hoses and tons of failure-prone emissions devices). 240 ft./lbs seems reasonable, but definitely on the high side for a stock motor. 150 HP is definitely reasonable- they were SLUGS.

It's was relatively easy to get some noticable increases in torque from these motors (bump up the ignition timing, richer secondary rods in the carb like those used in the L-69 305 HO motor) but meaningful peak HP increases were not as easily achieved. The pathetic cam, compression and exhaust system really put a cork in maximum HP production of these motors in stock form.

Reasonably fun up to 3000-3500 in sharp tune. Then the party went south pretty quick without uncorking some of the bottlenecks.

 

Yup...My old lg4 had full bolt ons and could only run low 15's.

 

Are the power ratings from the tech. data at the rear wheels or crank?

 

crank for the mag rating.

 

Also, is torque affected by the drivetrain loss?

 

Yup...20% for an auto, 15 for a manual.

 

Losses are not fixed, the higher the RPM the greater the loss. The 700r4+10bolt+thirgen driveline loses about 18% at peak HP and around 12% at peak torque.

160/.82= about 195 FWHP
258/.88= about 293 ft/lbs

298/.82= about 363 FWHP
305/.88= about 346 ft/lbs

 

With the turbo, peak hp and torque both occur around 5,000rpm, so would that make the losses 18% for both?

298/.82= about 363 FWHP
305/.82= about 372 ft/lbs

Also, if the tech. data is giving the hp and torque at the crank, shouldn't the rear wheel data be lower?

160*.82= about 132 FWHP
258*.88= about 227 ft/lbs


Dyno graph:

 

At my local dyno they say its the same amount lost for both horsepower and torque.

 

Torque is measured, HP is calculated. HP=(torque x RPM)/5252.

In order for there to be a drop in HP, there has to be a drop in torque.

Make sense?

 

2 different RPMs....

They lose the same percentage AT THE SAME RPM however. That's at the SAME RPM.



Ever wonder why it bothers those of us with some professional experience when people start throwing around HP numbers?



Also note, this DOES NOT mean the same thing as "the difference between Desktop Dyno and DynoJet". Desktop Dyno, or for that matter even actual dyno readings from an engine stand, are VERY VERY DIFFERENT from factory ratings. I would expect a RW reading NO LESS THAN 25% LOWER THAN a Desktop Dyno prediction, and probably closer to 30%, because there's more things in between those 2 numbers than just "drive train loss". I.e. if Desktop Dyno says your motor will do 300 HP, then expect 280 out of it on the engine stand and 220 or so at the wheels; and it probably would be "rated" at around 260 by factory methods.