300plus ft/lb torque from '79 L48

[vetteboy]

My goal is 300plus ft./lbs. of torque from a '79 L48, THM350, 3.55:1. I've been following "Kenny's" thread on "Performance Combo for 1980 L82" and discovered that I had been doing similar studying of similar parts combinations. My question is whether the Edelbrock Performer Plus package is great as is or would it be a little better by substituting a CompCams Extreme Energy Cam in place of the Performer Plus?

Performer Plus: 204/214 Dur, .420/.442 Lift
CompCams XE256H:212/218 Dur, .447/.457 Lift
CompCams XE262H:218/224 Dur, .462/.469 Lift

I have already installed Hedman ceramic/metallic headers (true duals 2.5"), K&N air cleaner and re-curved the distributor. Next I would like to install the Performer intake,Performer 600 cfm carb and replace the camshaft(I'm leaning heavily towards the XE262H). Future plans include changing the gear ratio to 4.10:1. Will any or all of this get me over 300 ft./lbs. of torque or will I have to replace the heads?

Thanks;
Jeff (vetteboy)

 

[vetteboy]

Thanks, I'll check 'em out.

 

[80convertible]

I'll give you a little perspective based on my engine and dyno. I have an old Camaro 350 originally rated at 250hp. I have a Saginaw 4 speed and 3.55 rear. I installed rebuilt Vortec heads and run a Carter 625cfm carb and Performer intake. I have yet to change the cam or rebuild the bottom half of the engine. On the dyno I pulled a best 251hp and 310ft-lbs of torque at the rear tires. When I get the right cam installed and tune the carb and distributor, I should see a huge increase in power. Not to mention getting the engine rebuilt. Hopefully this gives you an idea of what you can do without spending huge sums of $$$$$.

Regards,

Jim

 

[vetteboy]

Jim;
Your info is encouraging. I was hoping that I was heading in the right direction.

Keith;
Your photo of your car is impressive. Unfortunately mine is going to look very similar(mine has the rally wheels).

 

[Nut]

Torque (lb/ft)

Jeff,

As JIm has noted you may be surprised what kind of torque you can get out of a L48 without a lot of expensive mods. My '81 has a L81 (damn near the same as a L48 with the Computer controlled engine), TH350 and 2.87 gears. I only have Blackjack Headers, 2 stage Cat and no smog crap and I pulled 219hp with 329 lb/ft of torque. I can't wait to juice mine up some more. Btw.... being in Mechanical Engineering, the correct reading of torque is (lb/ft or... newton/meters for our metric friends)

Let us know how the mods come along.

Regards.......... Nut

 

[Hib Halverson]

Should be fairly easy to get 300 lbs/ft torque from the L48.

I'd go with the Performer intake, the Performer Plus camshaft. I'd not use the Performer carb as they don't work very well on Vettes due to problems with fuel slosh under braking and cornering. Keep your stock Quadrajet but have it jetted and tuned for performance use. You've already got headers and dual exhaust, so you're set, there.

As for the gears, with the 3spd auto, you'll find a 4.11 axle will run the engine at pretty high rpms on the stret. I'd keep the 3.55s but watch that TH350. That's a weak transmission for high-performance use.

 

[Ken]

Re: Torque (lb/ft)

...being in Mechanical Engineering

:L You should include a little more data if you're going to correct someone Bob.

This from Mechanical Engineering Magazine Online:

"As my instructors in England 57 years ago never tired of telling us, "Don't confuse work and torque." 33,000 ft.-lbs. of work/minute is 1 horsepower, whereas 33,000 lbs.-ft. of torque x 1 rpm is 6.28 horsepower. Torque can exist without doing work, and the time-honored method of differentiating the two is to use distance-force for work, and force-distance for torque. Newton-meters follows this rule correctly, but the English units shown do not."

_ken

 

[Nut]

Ken.... My Machinist Handbook may differ. However in fairness to all, I will check it in the morning. I did not have it handy last night. But, this was a topic of considerable discussion with my Navy custom this year and (lb/ft) was the accepted usage to be specified on all military documents wherever "torque" is specified. If I'm wrong I will certainly post a correction and apology. There are a number of Mechanical Engineers in this site. Let's see if anyone else has an opinion on this? Just one last thing.... the print outs of the Dyno runs I did in September list the engine torque both SAE and STPT numbers in (LB/FT).

......... Bob

 

[Ken]

There was an easier explanation that I can't quite recall, but it went something like; ft-lbs is work, the amount of effort it takes to lift so much weight so high, and lbs-ft is for torque, the amount of effort required to move an object... Nah, that ain't right. I forget how to explain the difference between the two forms of torque. But there IS a difference. :L

Tightening fasteners is measured in ft-lbs, your engine puts out "lbs-ft" of torque to the rear wheels.

_ken

 

[JHL]

Jeff,

My last vette was an 80 L48 4spd and it had a comp cam in it with the original quadrajet carb and it ran great. These new XE cams are supposed to be excellent and I see a lot of people posting on some of the other sites I visit that have been using them with great results. Someone once told me it is "Comp" that make Edelbrock cams but I have never been able to verify the comment.

Check out the performance section of www.chevytalk.com and you will find lots of guys running XE cams who might be able to give you some comments as to how they run. One guy runs your combo on a desk top dyno and will make some comparisons for you.

Hib,

I would be interested to know what information you base your comments on regarding the Edelbrock carbs. I have one on my car and it ran great straight out of the box. When I rebuilt the engine I bought a calibration kit and it was far easier to set up than a Quadrajet and still runs great. It runs 13 second quarters, brakes and corners as fast as the suspension set-up will allow without any problems.

J.

 

[vetteboy]

Thanks for all the info, guys! Hib & JHL may have saved me $400 to $500 (CDN) by not replacing the Q-Jet. I'll order a calibration kit from Edelbrock and have the carb "performance" tuned when I do the other modifications (cam & intake) and see what kind of results I get. I'll leave the 3.55:1 axle ratio issue for now as it was a couple of years off anyway but, I would like to ask Hib (or anyone else) his opinion on splitting the difference and going with a 3.70:1. Would there be enough difference to warrant spending the money?

Thanks Again Guys!
Jeff

 

[79er]

re:

I had the preformer cam and switched to Comp Cams XE262 and am very gald I did.

 

[Stingray74CC]

What my government education tells me...

From a fellow Mechanical Engineer (I guess I should say prospective Mech E since I still have 3 semesters.)

Work done by all the forces acting on the object as it moves from its initial to its final position: joules (J) or ft-lb (energy)

Torque sometimes called moment is the force to cause a body to rotate about a point or axis: (N-m or lb-ft)

This confirmed by text. I can't believe I just looked that up....Nut knows I have nothing better to do than dream about my car waiting for me on the outside.

 

[Hib Halverson]

(snip)
I would like to ask Hib (or anyone else) his opinion on splitting the difference and going with a 3.70:1. Would there be enough difference to warrant spending the money?

Well...three-sevens are a great gear for a motor with weak bottom end and a close-ratio four speed. I think, with the engine your building, which will be strong on low-end and mid-range, coupled with a wide ratio four-speed, I'd stick with the 3.55s and take the better mileage and less noise at highway speeds. I think you'll find with the mods you're considering and the 3.55 gear, you'll be able to spin the tires pretty easily. If that's the case, the 3.70s won't do you much more good unless you go to a more aggressive rear tire.

 

[rpounds]

Okay, here comes another mechanical engineer to muddy up the lb/ft - ft/lb issue. My understanding of the two terms is as follows:


ft/lb is the actual work that is being accomplished

lb/ft is the ability or potential for work which exists

Say an engine/transmission is capable of 300 lb/ft of torque. If you are cruising at 45 mph, you are not using 300 ft/lb, however the capability of the combination is 300 lb/ft.

Betty bought some butter, but the butter Betty bought was bitter, so Betty bought some better butter . . .

 

[Stryker_78]

It is nice to see a fellow Canuck on the forum. I too have an L-48 engine( in my '78). I am running 3:55.1 gears and a TH350 3-speed. I still have the original Rochester 4bbl carb. I am planning on making pretty much the same changes you are but not until next year. This year it is suspension, brakes and a bit of cosmetic surgery
Let me know what you come up with.

Sorry I couldn't be aby help.

Later.