I want to swap out a 305 L31 for a 350 L31. The only thing I can afford to start with is an aluminum intake and a 4 barrel carb.

Will that combination get me 300 HP ?
What intake and carb do you recommend (street car, so good low end) ?

 

L31 factory is about 255 hp with a full set of headers, exhaust and a properly tuned carb you could get more but I would suspect you would need a new cam to get 300

 

Was that with TBI or EFI ?

 

Richard Holdener has run one with a dual plane intake, carb and headers sans accessories. Made about 310 HP with the stock cam. Put a full exhaust system on it with accessories and it will be in the 270-280 hp range at the crank and about 220-230 at the tires through an automatic and maybe 240-250 with a manual trans.

You will need headers and exhaust to make good power.

 

250-255 on EFI with stock manifolds and intake. IIRC GM stopped TBI in 1995 and 1996 was the first year of the 5.7 Vortec. It used a single TB and a spider fuel injection scheme

 

With a stock L31 and stock exhaust you will probably top out around 200 to 230 at the rear wheels through the auto. I just dropped a 397 HP Blueprint crate engine in for a customer with stock TPI and stock exhaust and it made 202 at the rear wheels. Only thing we changed was to install an S10 converter. To me it was slow, but he seemed to like it.

You won't be anywhere near 300 HP even at the crank. Definitely nowhere close at the wheels. It would need cam, valve train, headers, full exhaust, intake, etc. My 97 Vortec put down 325 wheel with ALL the mods.

GD

 

The factory "rating" on those, FWIW, was something around 250 - 260 HP. That's at the crank of course, with all "accessories" (emissions devices... NOT power steering, A/C, etc.) installed and operating. Obviously there's considerable variation from one individual motor to another due to production tolerances. The intake arrangement isn't particularly conducive to high HP #s. The cam is even less so.

With something like a Performer RPM and a typical Holley carb such as a 650 or so Street Avenger, and of course headers, you should get maybe 280 - 300 out of it. Not too bad for yerbasic junkyard motor. With a better cam it's not hard to exceed 400.

With 280 - 300 at the crank and a 700 transmission you should see right around 220 - 240 at the wheels in one of these cars.

Keep in mind, the devil is in the details. Just like the people that buy the "435 HP" Performer RPM "kit" and get 225 at the wheels because they half-a$$ed everything about the rest of the motor. If your exhaust sucks, you haven't tuned the carb and distributor curve to the motor's liking, etc., your performance will suffer. As well as dyno #s.

For a good street cam, look at the Comp XR276HR, or the Lunati Voodoo that's just slightly smaller. Either of those with the intake & carb above, and good exhaust, will put you at 375ish at the crank and 320ish at the wheels.

 

True budget throw in a stock L98 or LT1 cam in it with the performer rpm and a good carb. Headers exhaust tuned well should easily be 300+

a bolt on L98 with 1.6 rockers can hit 250-260 whp in good condition. Thats 300 flywheel for sure

my buddies vortec 350 with performer rpm intake carb and lt1 cam from a 94-95 fbody ran mid low 13’s at over 100 mph in a 83 step side short bed chevy pickup truck. Not a light vehicle.

 

Vortec headed, 10:1 350, RPM Air Gap, 600 VS Holley and Comps good old 268H (flat tappet, 218@.050", 454") with short style headers (single 3" exhaust) put down 280 RWHP on a dynojet. 700R4 and 12" converter.

 

Just a 4 bbl and a cam ? No headers ?

 

Headers first and foremost.
Further to my post above, that same combination with the XR276HR netted 107+ MPH and put the car in the 12's. A heavy, not drag race orientated, street car.

 

We threw a used Vortec 350 in an S10. Used L98 cam, headers + dual exhaust, 650 Holley, Performer intake, 373 gears and S10 converter. It ran high 12s! Very budget setup. Same setup pretty much in my old car with just a bit more cam 218-218 465 lift, stock gearing and TC, 650 Holley and Performer intake along with headers and 3in exhaust ran well into the 13s. Outran the LT1 cars at the time no problem.

 

No of course not. Don't take quotes out of context. Otherwise you'll find yourself involved in presidential politics or something.

The rest of the quote included:

"Good exhaust" of course referring to headers and everything else behind them.

 

Also should be noted - that's max effort and still *at the crank*. That's not likely to hit 300 at the wheels without some valve train. Bigger cam, and control the valves at higher lift - beehives, etc.

GD

 

True enough. I've been through all of that. And more. Then something went sideways.

 

I see some varying guesstimates here on hp loss through the converter, 700R4 and 7.6 axle.

When I ran my 100% bone stock L03 (factory rated at 170hp) on a DynoJet, I came up with 144hp at the wheels. So a very respectable (I thought) 15% loss. I see some here suggesting it may be much higher than that.

Without too much science, and not to take the OPs thread too far off the rails, what things impact that?

Do you lose a higher percentage as you make more (more friction in the trans and rear gears)?
Does the TC stall speed have an effect on this? Or is it more a question of efficiency?
Does rear axle ratio have an effect?

 

The more power you make, the more will be lost, to a degree. It's generally going to be somewhere in the 15-20% range though. Double the power of your L03 and it would probably go up a few percent.

GD

 

theres fixed loss and dynamic losses. Dynamic losses are friction based as well as inertia based. Faster you accelerate the gears and shafts, more friction and heat is made, more losses associated with that.

gearing can change numbers on some dynos because it can change rate of acceleration. I have seen cars dynod in different trans gears and seen slight changes in hp and trq on back to back runs