Priya

I'm planning on modifying my stock 79 L82 with the aim of getting the most fuel efficient 325-350 horsepower motor I can. The motor has 60,000 miles on it and was rebuilt several years ago at an unknown mileage. I don't want to increase horsepower down the road beyond the initial goal so there is no need to plan for future horsepower increases which might sacrifice gas mileage. People always ask about budget, I hope to do this for $3000 but if it can be done for less that'd be desirable and if its going to be up to about $4000 I can do that but wouldn't like it too much.

To start with I'm planning on using one of the following set of Vortech heads:

http://www.racingheadservice.com/Inf...rtec-Heads.asp

Both heads have 170cc intake runners and 64cc combustion chambers which if I remember correctly will bring my stock L82 compression ratio up to about 10 to 1. They are also dual pattern intake so if I understand that correctly can use either Vortech or non-Vortech intakes. RHS says the heads with the 1.94 intake and 1.50 exhaust can make up to 325 horsepower which sounds ideal if I actually can get that much out of them. Does it sound right that my stock 2.02 intake and 1.60 exhaust L82 heads can be far lower performance than the small valve RHS vortech? The small valve vortech is only available as a bare head while the larger valve RHS vortech (2.02I & 1.60E) is available complete with valves springs, etc. and is at a much better price than what I could complete a bare head here in Canada. My husband says for this reason I should order the 2.02/1.60 RHS vortech head and that it won't be any less fuel efficient than the small valve vortech. I thought the small valve vortech should maintain a higher flow velocity and thus be more fuel efficient - is that the case?

To increase driveability, fuel efficiency and power I was planning on using a 90-92 TPI system. I understand that this speed density system is preferable to the mass air flow TPI due to space concerns under the hood of the Corvette, but it is also less tolerant of changes to the TPI system. Should I look at integrating a Megasquirt system with the TPI for this reason?

I understand that the factory TPI motors run out of steam at about 4500 rpm. My L82 revs to 6000 nicely and with the gearing I'm going to have in the car (3.70 rear end, keisler five speed with 3.37 first) I want my modified motor to produce peak power around 5400 rpm and to rev to 6000. I know the long narrow intake runners in the stock TPI system are the reason stock TPI motors are low reving, high low speed torque motors. I don't need low speed torque with my gears, is there an aftermarket TPI runner system that has shorter wider runners that will be fuel efficient and suitable for my horsepower and rpm goals? Alternatively would it be possible and preferable to get a dual plane intake well matched to my performance goals and drill holes in the intake runners for the injectors and mount the throttle body where the carb would normally go? Maintaining the stock hood is a must so anything that would rule that out is a deal breaker.

I've been studying cam shaft selection in motors people have producing 325-350 horsepower. Some say that kind of horsepower can be achieved with my stock L82 cam and its aprox .450-.460 lift, that doesn't make sense to me given its 225 hp rating. I spoke with another forum member who has a 335 horsepower 350 and he is using the Lunati 60102 cam with 262 (i) and 268 (e) duration and valve lift of .468 (i) and .489 (e) and LSA/ICL of 112/108:

http://www.lunatipower.com/Product.aspx?id=1983&gid=287

Am I correct in assuming that the most fuel efficient cam for a 325-350 horse motor is one that will produce at most that much horsepower in a 350? Is the aforementioned cam such a cam?

I also plan on a set of long tube headers and full dual exhaust.

7t9l82

the L-82 actually makes about 312 horsepower according to super Chevy magazine. the t.p.i system would be a bad match for what you have. tpis makes a mini ram tpi that would be better but is not great for your application either.there must be a hundred different companies making fuel injection systems for a small block. i don't know how much more mileage you want but I'd optimize what you have and save the money. I'd say headers and exhaust, advance the cam 4 degrees, it was made to run there mill the head and a thinner head gasket and have someone pocket port your heads you can really do that yourself. set up the distributor like the Lars paper and change to a performer r.p.m intake and a spreadbore Carb and IF you can keep your foot out of it you should be pleased with what you have. and over your power target by a good bit . then you will have a couple thousand dollars for fuel.

Priya

I had a 70 Torino with a 351 Cleveland 4 barrel rated at 300 hp gross, 285 net. I made some slight modications to it (hotter cam, holley 4 barrel, headers and electronic ignition) I estimate it produced 325-350 hp and the stock L82 is nowhere near that so I don't believe Super Chevy magazine, I'm sure the advertised 225 hp is right about where its at.

I also posted this on the C4 forum and a member posted the following lower intake baseplate:

https://sdparts.com/details/scoggin-...-center/sd3816

According to Scroggins/Dickey testing, this lower intake and Vortech heads alone boost a stock L98 from 250 to 300 hp which is very close to my goal. Perhaps a little more cam than the stock L98 has and I'd reach my 325-350 hp goal with a highly driveable and fuel efficient 350. I have no desire to go over my performance goal by a good bit, or even a little bit. I want maximum fuel efficiency at the same performance level my Torino had which was a real blast to drive and perfectly adequate for my desires.

7t9l82

they aren't the only ones who put it in that range. i think its accurate. there is a big loss just with the catalytic converter that was used on the order of 40 horsepower.

Priya

Well, all I can tell you is that the 79 Corvette with L82 is a big disappointment compared to 70 Torino with the 300 hp 351 Cleveland. I know all Ford, Chrysler, and GM boys like to claim their favourite motors put out sooo much more than the factory rating but I don't believe a word of it. The chrysler hemi and the chevy 427-435 didn't put out 600 horse and the Ford 428 CJ didn't put 165 more horse than the factory 335 rating. Look at the quarter mile times published in the magazines of the day and its pretty clear the factory ratings were about right.

7t9l82

beleive what you want.

l88rocket

a well tuned carb will be efficent, and 325 hp is easy to build,

rcread

Get a Prius and call it a day.

wcsinx

It's a well known fact that the L82 is severely choked off by it's stock y-pipe going down into a single, bead cat. Once the exhaust is uncorked and the carb retuned, the difference is huge.

What kills your fuel economy more than anything is gearing though.

Mexican Bob

...very well put. A 700R4 and a mild 350 with a 2V carburetor will be less expensive and have all-around better performance and economy.


MxB

billla

At the flywheel with no accessories, electric water pump, large-tube dyno headers and open exhaust...need to be real careful comparing highly optimized engine dyno numbers with what something will actually make between the framerails.

"What did we learn from this test? The results indicate that the L79, L46 and L82 were all accurately rated by GM in terms of power output, despite the difference in the gross and net power ratings."

http://www.superchevy.com/technical/...ng/holley.html

billla

I think if I were approaching this build with a GEN I I'd start with a late model roller-cam engine and Vortec heads. A very careful rebuild paying a lot of attention to detail - exactly correct quench, 10:1 CR, etc. Long-tube headers, etc...

Top it off with the FAST EZ EFI and spend some serious time optimizing tuning, and put a 4-speed auto or 6-speed manual behind it.

http://www.fuelairspark.com/ezefi/default.asp

I think with careful design you could get right in there and still have a decent engine. Probably around 6K for the engine if you're careful.

Or, swap in an L31 and assocated trans and get that milage pretty much for sure...and still make serious power

billla

scottyp99

The L82 is basically an L46 with a little less compression, 9:1 as opposed to 11:1, and the L46 was rated at 350 horsepower in '69 and '70. You really have to take factory horsepower ratings from that era with a few grains of salt.

I like the Cleveland motor, too, I had a '71 Mustang flatback with a Cleveland in it, and it was pretty quick! My 'vette is the first Chevy I've ever owned, I always tell my Ford and Mopar buddies "I'm not a Chevy guy, I'm a Corvette guy!"


Scott

Vette5.5

Friend of mine has a 79' L82, and a true dual exhuast, Q-Jet recal, and Keisler 5 speed really made things livable. He has an original GM dyno sheet showing a higher hp number than rated, but dont know the test conditions. As for 60's muscle car ratings, read a couple articles mentioning 325 rwhp was a rarity for any of them. For the direction you're headed with fuel milage consideration, maybe an LS swap, or World Product crossbreed block, that's original SB on bottom and LS on top. Drops right in.

Priya

My 79 L82 has no y-pipe, no catalytic converter, its true dual exhaust and I sure don't notice a "huge" difference - performance is all-right for what it is, but its nothing to write home about.

As mentioned in my initial post, the I've got a Keisler 5-speed on order with .67 overdrive so that will make a big difference in fuel mileage off the bat. A 2V carb would be cheap, but I don't believe that changing to one of those is going to add 100 hp to the motor.

As previously mentioned, Keisler 5 speed with overdrive is on order. Cost is a concern in this so a 6K motor is out of the question. I'm aiming to do this for 3k, 4K if I absolutely have to. I've looked into the Fast EZ EFI and pretty much ruled it out. Its cheap at $900 but doesn't include sensors, intake, throttle body, fuel rails, etc. so it looks like a used 90-92 TPI system would be quite a bit cheaper. Plus the Fast EZ EFI doesn't include spark control which is a feature I want.

Now, if you could recommend a fuel efficient cam that would add 25-50 hp to the stock L98 TPI/vortech/Scroggins Dickey lower intake combo they say produces 300 hp I'd really appreciate that.

http://sdparts.com/category/sdpc-tpi-vortec-baseplate

Or do you think flow on this system is at peak and a hotter cam wouldn't increase horsepower? I'll be adding long-tube headers and the compression ratio will be 10 to 1, might that alone add 25-50 hp to the 300 hp stock L98 with Vortech heads and scroggins dickey intake?

Shark Racer

Not a lot of serious optimization you can do with EZ EFI - just pick a target AFR for WOT, cruise and idle. Obviously you can play with the idle/cruise learning to get it perfect. (best fuel econ, no surging)

The "cheap" EZ EFI solution is for an ECM that plugs in to an existing TPI setup. It's a lot smarter than the GM TPI setup (should be, after 20 years) but as you said it does not control timing.

They offer more comprehensive solutions that provide a throttle body with integrals sensors, injectors, etc, that are designed for dual plane intakes.

Speed density or MAP based tuning is less tolerant of changes to the *engine*, this is due to the fact that the fueling math is all based on estimates of volumetric efficiency. The numbers are based on the ideal gas law (PV=nRT) and you solve for the amount of gas to go in. Pressure is a reading from the map sensor, R is a constant, T is IAT (intake air temperature), V is the estimated volumetric efficiency from the MAP look up table. (Which is a simple table with RPM and manifold pressure as the lookup points)

All that being said, going to MegaSquirt will NOT help you, as MegaSquirt is MAP based as well. (Well, MS1. Apparently the MS2 supports MAP, MAF, alpha-N)

If you dial in your base MAP table (not difficult to due with a wideband and a couple hours of driving), you'll be set until you do a major change to your engine. Minor changes can still be compensated for with fuel trims.

It's also worth noting that due to EZ EFI having a wideband O2 sensor instead of a narrowband, it can also rebuild the MAP table on its own. (Hence the "EZ")

Good luck.

mrvette

What ever you do, stay away from TPIS and their cams, I had one that ran raggedy as hell with wiped lobes, and drove me nutz until I finally changed it out...finding the wiped ROLLER CAM lobes....go figger, any properly made roller cam should last 50 billion miles....not theirs.....

Priya

Thanks Sharkracer, that was over my head so I'll have to have my husband look at it to explain it to me.

Mrvette, I'll keep that in mind

billla

The EZ EFI is available in a number of levels, and does include the items you note. It doesn't have spark control...but you could easily add a simple version of this with with one of the electronic advance distributors from MSD.

I agree with others here that chasing TPI as a solution isn't going to bear fruit for a number of reasons.

This is one of those situations where the budget and goals aren't quite in synch, at least with some of the criteria identified. You may find that you can get 90% of your goals with 10% of the outlay by simply swapping the cam to a milder cam and spending some serious time with a wideband tuner like the Innovate LM2. I'm kinda scratching my head to come up with something that fits into exactly what you're looking for...