tchever1

I am a newbee and went from Harley to Corvette this year. I need your input on what Camshaft kit to boost her to about 350 hp. I heard with that that kit and an Alum. manifold I can use the same carb (not that bad) and pull it off?! Is there still an original GM kit available? Any input is much appreciated. Thanx, Bill

billsfan

If you can double the HP with a cam and intake you'll make a zillion bucks selling the combination. You might do it if the intake has a blower on it, but the lower end will never handle it. Sorry, but it can't happen.

tchever1

You have been a great help, I hope you sent some of that Positive Energy to Jim Kelly in his hour of need I hope you are not indicative of the rest of the Forum members. I simply was seeking knowledge and you thought it necessary to be-little someone looking to learn. I'm sure the language I'd like to use is frowned upon by the Moderators so I Refrain.

billsfan

Sorry, I was not trying to be mean. It is totally unreasonable to get that much of an increase in HP from a '76 engine without spending a ton of money. If you want 350 HP, you will be much happier with an engine change. If you want to stick with your engine, a package including cam kit, heads, intake and exhaust could get you a decent HP increase. A cam and intake will only give you a small increase in power.

gerry72

Billsfan may not have a bright future in diplomacy, but he's correct on the engine. And his response was more tongue-in-cheek. You're confronting a challenge that can't be achieved with what the factory gave you. You need a good two points more compression and better flowing heads to get to your target horsepower. The compression is your primary limiting factor since it greatly limits the type of cam you can run. With your existing long block, you'd be looking at something like a Comp Cams 260 or 268 and at the most, that would get you around 25hp with a sharp tune up. The intake will get you about nothing.

cobrachuck

I agree with above & have a 75 L48 auto that runs very well but not a barn burner
I re curved the distributor $20 reset the timing with an advanced timing light. Tuned
With new plugs distributor cap wires, had the Q jet rebuilt then added 2 1/2" exhaust
& X pipe. This was all last year drove it 3,000 miles as a shake down.
Now adding a 700r 4 trans.
The car ran like a 327 300 hp engine from back in the 60s with all new suspension it is quite fun to drive .

gjohnson

Long tube headers/ duel exhaust/edlebrock performer manifold/comp cams xe268 cam/timing recurve will wake it up . Prob have 3;08 rear gears which suck for off the line.Chang out to 3;55 or 3;70 and you'd be amazed! Torque is better than big HP IMO.

Kubs

Like others have said, it will take a lot to make the factory engine make that much HP.

For a street engine, torque is what you feel at lower speeds and lower RPM. Torque will make the car very fun to drive on the street.

jb78L-82

What others have said is correct...You will need to completely strip down the engine but could retain the crank, rods, intake etc but will need a .030 bore, 9:1 pistons, good flowing heads (cast iron or aluminum), preferably a roller cam, LTH headers, etc...probs about $4K if you do most of the work, more if not.

Bloodzone

Warning Danger Danger...If you start, it never ends...Danger Danger Warning

jgcable

Hey, I did the same thing a year ago. From custom Wideglide to Corvette. Mine is an 77 with the L48. You can get about 25hp out of a cam which would put you around 225hp is you have a good free flowing exhaust. If you put around $5000 into the motor you could get 350hp out of it but it would be cheaper to just buy a new crate motor. Believe it or not... that little L48 in your Vette is pretty darn fun to drive. If you have a 4spd all the better. Put some headers and a nice exhaust on it and spend some money on getting the suspension and steering in order and you won't miss 350hp until you get blown away by a stock Honda Civic at a light to light drag race...lol..... which doesn't bother me. I let anybody pass me if they want. My car is cooler.

gunnersguru

my 76 L48 180hp is old and slow. if you put a high rise intake on and duals would you see 350hp ..no but im looking into higher gears .370-390 to compensate for lack of power. low power engine - high rear end gears to compinsate

hpxt

I used a Summit top-end kit; but on the second outing spun a bearing. I should have rebuilt the bottom end. That being said, decided to bite the bullet and replace the motor with a 383 4 bolt main (previous engine was a L-48 too).

Never dynod the L48, but think it made about 250hp (net) before the bearing spun. See the dyno sheet from Summit on the top end kit.



Good luck on your build,
Mike

jb78L-82

I was thinking of doing a head and cam change only on my stock L-82 but was advised against that route for the same reason you had an issue: Increasing power substantially on a stock bottom end with miles on it (although the L-82 is MUCH stronger than the L-48 passenger car engine) often leads to other engine problems like you experienced.

The summit top end kit certainly is a cheap route to go if someone wants to take the chance and is a deal. The 367 Gross HP shown on the chart offers no engine details and I am sure is with a 383/400 SB since the kit is for 350-400 engines and probably an engine with at least 9:1 compression or higher. The issue using the top end kit on a worn L-48 is that the compression is probably at best 8:1 and bolting on those heads may get it to 9:1 which is as low as you would want to go but probs ok with a 214 duration cam. The cam in the kit looks similar to the L-82 stock cam so 250 Net HP is probably a reasonable guess with better heads than the L-48 cast iron GM heads. If you are looking though for 400-425 Gross HP from the L-48 block, a complete rebuild will be required with more money...I built my L-82 into a 355 for about 6K but used the best components to do it and it was more expensive than a crate engine but much higher quality parts..you can do it for a lot less than me.

Little Mouse

Pull your engine apart go at least 10.0 compression and use Ohio made aluminum profiler heads good cost for there heads. Plenty of head for more then a 350 hp goal known to be very good quality. Get rid of as in your plans the dismal L/48 cam with 195/205 .050 duration .390/.410 lift. You don't need any high dollar forged pistons or forged cranks and your two bolt block is capable of far more then 350 hp. You won't need to spend a lot of money if you shop smart for your goal. Keep your goal in mind and don't build something strong enough for a 500 hp goal that you don't intend to do. Try to come up with a high lift 212 . .050 cam with your tall 3.08 gears so it will pull early enough in the rpm band. The L/82 cam around 222 .050 worked just barely any good with rear gearing in the 3.70 range stay away from a cam that big if your using a flat tappet for sure. You could simply use a scat rotating kit there pretty reasonable at www.flatlanderracing.com and build a 383. The balance on there kits are better then what the factory ever did so don't waist money on a re balance to get it real perfect. Your not building something that is turning high rpms where a spot on more perfect balance becomes more desire for a high end cost build.

StraubTech

We have a crate engine program for circle track around here called the Charger series. These are 1997-1999 GM 350 engines that have to have:

OEM heads with valve job
1.260" OD Single spring
Stock valve size, 1.94 and 1.5
Hyd Roller lifter
Spec'd Cam 460/470 210/215 110 LSA
Flat tops
Max milling of heads .020"
stock Rods
Stock Crank
Edelbrock RPM dual plane for Vortec Heads
650 Holley HP Carb

These engines make between 360-370HP and 380 to 390#/ft.

StraubTech

Flatlander Racing shut the doors.

jgcable

I am no expert but..... the L48 that the poster is starting with is 180hp. The 350 that you are starting with I believe is 255hp. That's a huge help in getting to a 350hp motor. It would take a few thousand in upgrades and a perfectly tuned L48 with a free flow exhaust to even get to 255hp which is what you are starting out with. Of course.. correct me if I am completely off base.

StraubTech

Since HP is a calculation you have to look at rpm. The old flat tappet stuff is rated at 4200 rpm. The newer roller stuff if rated at 5000 rpm.

The roller cam will make more power than the flat tappet and carry it higher in the rpm. All will agree the modern Vortec head flows better and has better velocity but only by around 20 cfm.

A flat top piston is a flat top piston in either engine. A 5.7 rod is 5.7 rod. Stroke is 3.48. Using a carb and intake of the same on both makes it equal.

The vortec's having around 20 cfm calculates out to a HP advantage of 41HP. So based on the crate engine build one would be able to modernize a L48 to the tune of around 325HP. Not double but a very nice increase.

hpxt

Hope the OP comes back, lots of good discussion here.
Mike