Next month I will begin to tear down my completely stock 77 L48 in preparation for numerous top end upgrades. What I would like to know is if there is anything that I can do to the original short block without pulling it completely and sending it to the machine shop. I have a quote for reconditioning the bottom end but I did not want to pull the short block. Is there anything that should be done to the bottom end before the engine is reassembled? I know the best thing is to have it reconditioned and flatops installed. I just did not want to spend another 700-800 dollars. Any suggestions would be appreciated.

 

It depends. What top end upgrades are you talking about? How many miles are on the engine?

 

Reconditioned 186 heads ( 64cc combustion chambers, 2.02/1.6 valves, 170 intake runner) Lunati 60102 cam, Airgap intake, new timing set, 1.52 roller tip rockers, K&N Open element air cleaner. Currently has 3.08 gears, may install a 2400 stall converter if required after upgrades are complete.

 

Forgot to mention that the engine has 75k 1 owner (me) miles. No known engine problems. Only needs tuneup and routine maintenance before being road worthy.

 

You're asking for heartbreak if you add a bunch of compression, cam & flow to a 75K lower you know little about. Don't cheap out on lower ... Pull it ... disassemble ... inspect ... and freshen. Not what you wanted to hear, but hopefully you'll appreciate the gravity & sincerity.

 

That's 20 years of condensation,carbon,and all the other assorted guck laying around in that short block,that car has only been driven 3500 or so miles per year,I'm guessing a lot of short trips and a lot of storage,which can be extremely harsh on an engine.Adding cam, compression and more RPM can be a recipe for disaster.

 

Thanks for the good advice. I knew what the best option was but now it has beeen confirmed by individuals who have no vested interest in getting me to spend more money. Now I need to start agressively saving for the bottom end purchase or rebuild. Most prices I have seen online are in the $1000 range but shipping is at least $200.

Should I just have a local machine shop build the shortblock for me? I got an estimate of $700 for a rebuild of my original shortblock and then an additional $200-$300 for balancing. This price is just about the same a buying another shortblock but it would require me to tear down my current engine.

Any suggestions on where I can purchase a reconditioned, balanced, shortblock with flat tops? This may be preferable to a tear down and reassembly of the original motor. I can then assemble in the garage on a stand and then just pull the original without the teardown.

 

If you are not going to reuse your old crankshaft or pistons, you might as well build a 383 (It's the same price). There are some 383 shortblocks on ebay for around $1,200.00, or you could just buy the components or a kit and build it yourself.

 

I would prefer to replace with a 383 shortblock but every place I have investigated wanted at least 400-500 more than the price for a 350 shortblock.

If I go the ebay route I would not be comfortable unless I had recommendations from some forum members. Are there any members who build shortblocks for competitive prices. Iwould be willing to travel 4-5 hours to save on shipping. I live in upstate NY.

 

The stock Chevy SB bottom end is actually pretty stout. We've been running a 414-horse 350 in one of the racecars using a completely stock, untouched shortblock, and it's been running now for 5 race seasons at 6500 rpm every weekend. We've done nothing but heads, cam and top end work to it, and we run the heck out of it (it's in the Nova racecar pictured here on the Forum about a year ago).

If you want to go cheap and reliable, just pop the oil pan off it and install a fresh set of rod and main bearings. Torque the rods carefully to spec, and then run the poop out of it! It will hold up just fine.

 

Would you recommend pulling the engine to do this? Does this adress the concerns others have expressed about the impact of more compression and cam on the current bottom end? Should I assume that I would still have the original dished pistons and rings.

If I have to pull the original shortblock shouldn't I just bite the bullet and have it reconditioned or buy a shortblock? Am I back to square one? I have found rebuilt 350 shortblocks on ebay for around 700. Based on what Lars has said I do not believe I need a 383.

What I am worried about is how my current 75k L48 bottom will react if I make the topend changes listed below.

Recondition and reuse the original Qjet and HEI.
Install
3927186 heads 2.02/1.60valves,64cc combustion 170cc intake runner.
Lunati 60102 cam
Edlelbrock airgap intake
2400 stall torque converter
1.52 roller tip rockers

Goal
Weekend driver – responsive, fun to drive
Lots of low-end torque
Fast off the line, snap the head back, spin the wheels
Clean engine compartment – pre-emissions muscle car look and sound

Not necessisarilly looking for the easy answer. Just want the benefit of others who have faced this dilema.

 

That's a 383. You can get at 383 and a 350 to make about the same horsepower at the upper RPM range, but the 383 makes the torque at the lower RPM's that puts you in the seat.

Do you think that you can assemble all of the short block yourself, including some block machining? If so, 383 will be about the same price as a 350. If not, you will pay more for the 383 shortblock that someone else assembles just because it is a 383.

 

Thanks for explaining that to me. Now I understand why they are popular.

I do not feel comfortable assembling the shortblock. It is my understanding that changes must be made to the block and there are many parts decisions to make. If I was to go 383 I would need to buy an assembled shortblock.

Sounds like if I want torque I need to spend lots of money. I will keep saving.

 

Since the 350 shortblock is much less expensive what mods can be made to maximize torque without going to a 383? Maybe a gear change? I currently have a 3:08 diff.

Possibly switch to a 3:73. Would the cost of that change be equal to the additional cost of a 383 shortblock vs a 350 shortblock? The diff change would also cause higher revs @ highway speeds. Since this car is almost never used as a highway cruser this may not be an issue.

If the net cost is the same then it would probaly be better to do the stroker. I would then have no issues if the car is used for a lengthy cruise. Just thinking out loud.

 

With having equivalent parts, you won't make a 350 have the same torque as the 383. The extra torque comes from the extended stroke of the crankshaft.

The engine that I am in the process of building has the following numbers, based on Desktop Dyno:

383
471hp @ 6000 RPM
459tq @ 4500 RPM
402tq @ 2000 RPM

If I had a regular 350 with same components, it would be:
456hp @ 6000 RPM
434tq @ 4500 RPM
373tq @ 2000 RPM

For both engines, you can get more torque with a smaller cam, but then you sacrifice horsepower.

A gear change would give you the feeling of having more torque but, as you sugggested, would also rev higher at higher speeds. I have never changed the gears, so I don't how much it costs to do. However, I don't think it would be any less than the cost difference between a 350 and a 383.

 

Since you are well on your way to building a 383 I imagine that you have already resolved many of the issue I am concerned about. I would appreciate any information you would like to share about the parts you have selected.

I would be rebuilding a bone stock 77 L48 with a THD 350 and 3:08 diff. I have already purchased the top end components that I included in a previous post. My real concern is my lack of understanding about what is different about bulding a 383 shortblock.

 

You don't have to build a 383 to make power and torque. 350s have been used in street and race engines for over 30 years. And building a 383 or 406 is no assurance of going fast and making power. A 383 is fun to build, and it's easy to produce good numbers with that engine, but you can make incredible power with what you have.

You can keep your stock 350 bottom end, slap on a set of good Dart heads (clean up the ports a little) to produce 10.5:1 compression, use an XR294 hydraulic roller, a good set of headers, a good flowing single plane intake and a 750-carb. This combo, properly set up, will make over 500 horsepower and almost 470 ft-lbs of torque. Of course, it will idle rough, and you need some good rear end gears and a 3500 stall converter or a 4-speed.

I wouldn't recommend building something this radical for a daily driven car. Point is - you can make power out of anything. If you don't want to go to the trouble and expense of doing a 383 stroker, build what you have and have some fun with it. Slap a good set of heads on your 350, put a nice cam in it, a set of headers and a good intake. The car will rip your head off and you'll never miss having that stroker engine. (And get some gears in that rear end...).

 

From my experience, it will cost you more to rebuild the rear and install new gears than it would to convert your 350 to a 383. But still,for what you are trying to accomplish, you should get rid of those 3.08s and go to 3.55 or 3.73. With a converter and some engine mods you'll be burning rubber with no problem.

 

I agree with Lars that you can get a 350 to make excellent power. I just chose the 383 because it is easier to get even more. I did just go through the same process that you are going through. I posed the same types of questions to fellow forum members. I have a stock 1976 L48 that developed a knock a long time ago that I am just now getting around to doing something about. It has been awhile since my car has been on the road, so I figured that a little more time off the road would be worth it to build it how I want it built.

The main difference between the 350 and the 383 is the length of the piston stroke. On a 350, it is 3.48 inches. On a 383, it is 3.75 inches. the extra length of the stroke usually creates a clearance issue with the block. This is resolved by grinding down small portions of the block at the bottom of some of the cylinders and sometimes on the panrail. (I had a thread a few weeks ago where many forum members posted pics of their clearanced blocks). I have not clearanced mine yet, but will be using an inexpensive die grinder and an air compressor (again, upon the recommendation of fellow forum members).

The pistons are also different. The pistons cannot be as "tall" on a 383, otherwise they would extend out the end of the block. A 383 kits comes with the correct pistons, or you can buy 383 pistons separately.

From what I have found, a local machine shop usually charges a couple hundred bucks to clearance the block for you. Like I said before, if you feel comfortable doing it yourself, you will save some money.

If you buy all of the parts, you can ask a local shop to assemble it for you.

As far as the parts I will be using, they are:
383 forged rotating assembly from M and R Engines (haven't bought yet)
World Products Sportsman II heads with mild porting and oversize valves
Crane 272 Powermax cam (216*/228*; .454/.480)
Probably will use a Weiand Stealth intake
Holley Street Avenger 770 carb

 

Thanks for the advice. Does this mean that I can use my L48 bottom end? Since I will have the engine torn down down to the L48 short block should I just replace it with a new 350 shortblock with flat tops? I am worried about having to replace the bottom end soon after the top end rebuild is completed. Based on the parts I am planning on using what gears would you recommend? Since this vehicle will not see much highway mileage I was leaning toward 3:73. Others have told me not to go above 3:55. BTW Lars would you consider rebuilding my Qjet and HEI? They are untouched since 1977.