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Lumpy L-48

R

rpounds

Guest
Okie doke, question for all you gear heads out there. I was considering a complete rebuild on my '75. However, after yanking the valve covers, I am convinced that this engine is pretty fresh. It just doesn't make sense to tear the whole thing down. Compression check confirms that the big vacuum pump is in good shape.

My original thought was to pull it and build some horsepower. You know how those mid 70's Vettes are - they'll hardly get out of their own way. But with the shape this engine is in, I can put it off for a while.

I have been considering an aftermarket intake. I'll figure that out later . . . especially since I have to be a little careful here in California what I install.

Question . . . I would like to yank the stock cam out of this thing and install something that makes sense. A little lumpy idle would be nice . . . but we also need something that makes a little more HP. Any suggestions as to what may work well with a basically stock L-48?
 

Tom Bryant

Well-known member
Administrator
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Nov 9, 2000
Messages
7,195
Location
Edgerton, Ohio, United States
Corvette
1959 black 270hp (9/2/69) 1981 Beige L81(10/20/80)
Hi Ron,

Gm Performance Parts has some cams that will make good power in low compression engines. You can access and even order parts through the online catalog. Go to www.gm.com and then parts, perf parts ect. til you get to the catalog. Here are 2 I find suitable. I'm leaning towards the 918 for my truck project with a low compression 350 but I have 3.70 rear gears. The 917 would be a good match with no other mods or intake and ignition upgrades. The 918 if you go to a performance rear gear also.

12353917 Camshaft Kit
8.0 - 9.5 to 1 compression ratio, 2200 - 2600 cruise rpm. Basic rpm range 1500 - 4000, 6500 rpm attainable with proper valve springs and lifters. All model small-block Chevrolet V8 1955-66 California, 1955-68 with federal emissions. All non-emission trucks, and 1966-92 for off-highway applications.
Technical Notes: These are hydraulic flat tappet camshaft kits. The duration at .050 lift (intake/exhaust) is 204/214 degrees, and the valve lift is .420"/.442". Lobe centerline is 112. This camshaft kit is designed and manufactured by Crane Cam Co.®. It contains one camshaft and 16 tappets.

--------------------------------------------------------------------------------


12353918 Camshaft Kit
All "Marine" and off-road small-block Chevrolet V8. Compression ratio 8.75 - 10.5 to 1, 2600 - 3000 cruise rpm, basic rpm range 2000 - 4500 rpm, 6500 rpm attainable with proper valve springs and lifters.
Technical Notes: These are hydraulic flat tappet camshaft kits. The duration at .050 lift (intake/exhaust) is 214/224 degrees, and the valve lift is .442"/.465". Lobe centerline is 112. This camshaft kit is designed and manufactured by Crane Cam Co.®. It contains one camshaft and 16 tappets.

If you need help figuring your cruising rpm use the Tool Box Calculator in the "Tech Center" section accessed from the top tool bar on this page. These cams should have a noticable lumpity,lumpity sound while performing well in your type of engine.

Tom
 
R

rpounds

Guest
Tom,

This is very very good information. I appreciate the feedback. Mrs. R Pounds will be in Seattle visiting her oldest daughter over the Christmas vacation . . . if I order now, I can work on it uninterrupted during that time . . .

Ron
 

Tom Bryant

Well-known member
Administrator
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Messages
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Edgerton, Ohio, United States
Corvette
1959 black 270hp (9/2/69) 1981 Beige L81(10/20/80)
Brilliant! :grinsanta
 
H

Hijinx

Guest
You might also try www.gmpartsdirect.com , they normally have good prices on go-fast stuff.

I have everything stripped off my '73 right now, about to install the Edelbrock performer intake, Ignitor ignition, MSD coil, SX fuel filter, Carter alumumium water pump, Flex Fan and a few other goodies. Also, powdercoating all the brackets and pulleys at the same time.

I have been toying with installing a new bump stick as well, since I have it all torn down to this level. I just don't know if I want to tear into her any further. Mine runs well, but I think has the original 82,000 miles on it. I will probably wait and drop in a built 383 next year some time.

Good luck with your project. Let us know how it goes.
 

Nut

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Bowie, MD
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Vette-less for now
Ron,

Don't ya love it when a plan comes together like that? :D I can't describe how much stuff I get done/thrown out/rebuilt when Mrs. Nut goes on a road trip.

............. Nut
 
R

rpounds

Guest
Does anyone have any experiance with the stock cam out of the 300 HP 327? That engine had a higher compression ratio. It would be interesting to see the results of adding that stick to an L-48.

Hmmmm . . .

Nut, you're soooo right. I work a 9/80 schedule, so I am off every other Friday. You would not believe how much I get done on that Friday off. And that with sleeping in!!! Problem is, Mrs. Rpounds likes to take that day off with me once in a while. I don't have the heart to tell her that I'd rather have the day to myself . . . . t-tops off, cruising the Southern California coast . . .
 

Nut

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Bowie, MD
Corvette
Vette-less for now
Ron,
Our (division) of the company shot down the 9/80. Said it was bad for morale. (Yeah right) Anyway, we're on a Flex-40 deal. Gotta work a minimum 4 hours in any day, throw in some 9-10 hr days during the week and I get 1/2 day off every Friday. Play it right, come in at midnight, work until 4:00am. Go home, take a nice combat nap and effectively I'm off EVERY Friday. Sweet! Cam work is low on my priority list. I suspect my L81 (1981) is a weak as your L48 in bone stock form. I added some headers, ripped off the AIR pump and smog crap, 3" pipes and picked up 28-30 Dyno verified HP. I'd love a nice "loping" cam. Good luck and let us know what you decide on.

........ Nut
 

Hib Halverson

Technical Writer for Internet & Print Media
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13,453
Location
CenCoast CA
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71 04 12 19
Don't waste your time with 327 cams or anything else that old. Camshaft technology has come a long, long way in 30 years.

If you can afford it, the best bet for this L48 would be a mild hydraulic roller lifter cam (I prefer cams from Crane because of its quality control) the Edelbrock Performer intake and a set of headers. Keep your stock carb but have it overhauled and recalibrated for a high-performance application.

For more info on flat-tappet to hydraulic roller conversions, see http://www.idavette.net/hib/reman.html
 
R

rpounds

Guest
That's great info Hib. What would you suggest as to configuration? I would like to go fairly aggressive. However, too much cam would be a waste, given my stock heads, compression ratio, etc. An Edelbrock Performer is what I'm planning to install on the top end. And, the stock Q-jet will remain. What are your thoughts?
 
R

rpounds

Guest
Okay, one more question. Does anyone have the specifications for the stock 1975 L-48 cam?
 

Ganey

Well-known member
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Jan 7, 2001
Messages
94
Location
Texas
Corvette
385 CI 77 CORVETTE FE-7 Hi-Perf Sus.
rpounds

What is trans. & gears- needed for cam. That 917 is not enough cam even if you have a stock auto. !



59Tom

You may be able to run more cam than either of those w/ your gears, depends on wt., c.i., trans., etc..
 
R

rpounds

Guest
Ganey,

L-48, 350 CI, TH400, 3.08:1, 8.5:1 Compression, stock Q-jet, will add Performer intake at the same time.

Ron
 

Ganey

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Jan 7, 2001
Messages
94
Location
Texas
Corvette
385 CI 77 CORVETTE FE-7 Hi-Perf Sus.
Ron

Comp Cams XE256 will work great w/ 350, stock auto. & gears.
If you have stock ex., see my exhaust topic.
 

Jack

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Messages
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Florence, SC (Timmonsville SC)
Corvette
71 War Bonnet Yellow VERT 71 BH Blue CPE (SOLD)
L-48 cam specs & 383 ruminations

/ Hijinx ... Mine runs well, but I think has the original 82,000 miles on it. I will probably wait and drop in a built 383 next year some time.
Hijinx:
If one goes the crate motor route, most of this is irrelevant. If in future you're gonna keep your 350 and drop in a different built motor such as a 383, you also might consider larger options ... those combos using a 400 small block (406, 415, sb427, 434 etc). If you're gonna use a core motor (not your 350) for your 383, you'll still need a crank (aftermarket or heavily-machined core 400), rods (maybe), pistons, cam, machinework, balancing, flywheel/flexplate, damper etc. Note that similar things (& similar $$) used in larger combos. If you have the time, you might "gather" a tired 400 ... & begin there. Or even go BB.

I'm presently assembling a 383 ... but doing so from my existing 350. It started as a simple rebuild, but "former" machinist trashed my 350 crank. I had not planned to "build" my 350 ... only to rebuild it. If I'd planned for a "built" or bigger motor, I may've begun by collecting a 400 small block or a 454/502 big block ... most likely BB stuff.

If one plans to convert an existing 350 to 383, an "average" STARTING cost for ONLY basic conversion parts & balancing might be about $600-$700 ... additional machinework (headwork, clearancing etc) and upgrades/parts will drive it higher.

One thing I can attest to that seems to hold true: along with a project's natural progression, a tendancy to "grow" often creeps in also. In my case, both growth & procastination.

/rpounds ... Does anyone have the specifications for the stock 1975 L-48 cam?
rpounds:
About .390"/.410" lift, ADVERTIZED duration 280/288 degrees. I got this from Doc Cobine's vette cam specs page; some L-48 specs are listed there too ... here's the link http://www.geocities.com/MotorCity/Downs/3000/cmspec.html

JACK:gap
 

Jack

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Location
Florence, SC (Timmonsville SC)
Corvette
71 War Bonnet Yellow VERT 71 BH Blue CPE (SOLD)
? cam ? for GANEY?

What cam & specs are you running in your 385? What tranny/gears? How does your cam meet your expectations?
JACK:confused
 
R

rpounds

Guest
Does anyone have any opinions (I know, I know . . . that's a dumb questions to ask around here . . . we all have strong opinions about this stuff!!) about the Crane Energizer?

Here are the specs . . .

Crane part # 100182
Grind # 286 HO6
advertised duration: 286/286
Duration at .050" 230/230
Valve lift .465/.465.

Sorry, don't have to offset numbers . . .

It would be my understanding that, with stock heads, anything over about .460 lift is more than necessary, simply because that's already at the limit of the ability of the head to flow. Duration is another story . . . this cam appears to be a decent middle of the road compromise.

Comments?
 

Ganey

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Messages
94
Location
Texas
Corvette
385 CI 77 CORVETTE FE-7 Hi-Perf Sus.
Ron

Max. safe lift is .460 for the stock heads so new valve springs would be needed. That cam needs a manual trans. or a high stall converter. Lower rear gears rec. as well.
 
R

rpounds

Guest
Ganey,

Yeah, after I posted, I did a little more looking . . . way too much cam for this beast.

Ron
 
R

rpounds

Guest
How's this one sound?

435/455 In/Ex lift
283/286 dur
209/216 @.050
lobe center = 112

According to the seller, it has a little idle lope, runs well with stock compression and stock torque converter. Comments?
 

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