L48 being rebuilt

[Imran]

Well, here's the story...

I've got the original L-48 sitting on a stand needing to be rebuilt and put into the car. However, as everyone says, the L48 really sucks in putting out power.

So what should be done to it to make it into a streetable, low octane gas driver that puts out some more HP than it did when it came from the factory?

I've already got an Edelbrock intake, MSD 6a, already upgraded to HEI, new Holley carb...

I've heard heads from the L82, etc... so lets hear the suggestions...

Also a cost-analysis would be helpful too if you know off the top of your head!

Imran - 74 Convt

 

[Nomad78SA]

How much do you want to spend?
The L48 heads do not flow well and lack the punch of higher compression as its bigger brother the L82 with larger valves could move air and came with a steel crank for more bottom end strength.
A good set of heads is always good for the cause. Match a good cam for the powerband you are looking for and some good flowing exhaust and you are well on your way.

Shoot for good torque numbers in your modifications and so much horsepower. Depending if you have a manual or automatic transmission figures into all too.

You may want to stroke the motor, I did for the torque or go with a crate motor. Lots of good ones out there.

Throw out some figures and let us see what happens.
Neil in Tenn

 

[Imran]

Okay, here's what I got:

4-spd
about a $1500-2000 budget
Decent mechanical ability (7-8 on a 1-10 scale) but never done an engine rebuild. Don't mind rebuilding it myself, but would like a warranty so that money doesn't go down the drain. I found a place that's giving a 3 yr / 36,000 warranty with their rebuild for $1,300. Now that's bringing it back to specs, not including any modifications. I'll need to talk to them to see how much they'll charge or if they'll even honor that warranty with different heads/cam/etc...

The exhaust is already done up pretty well, it's true-dual straight through with no cats, (it's a 74) and going out to some Thrush Turbo mufflers with dual chrome tips

Another question, does the octane necessary depend solely on compression ratio? If so, obviously I'd like to stay with the cheaper gas, especially with the way things are going on in our World today

Lastly, what are some good books to read up on for this project?


Thanks everyone

Imran

 

[MaineShark]

I asked the same question a while back. The general consensus was that it would be cheaper to buy a brand new engine from GM, than to rebuild one. If you search for "crate engine" you should get a number of good responses.

Joe

 

[Jack]

Okay, here's what I got:

4-spd
about a $1500-2000 budget
Decent mechanical ability (7-8 on a 1-10 scale) but never done an engine rebuild. Don't mind rebuilding it myself, but would like a warranty so that money doesn't go down the drain. I found a place that's giving a 3 yr / 36,000 warranty with their rebuild for $1,300. Now that's bringing it back to specs, not including any modifications. I'll need to talk to them to see how much they'll charge or if they'll even honor that warranty with different heads/cam/etc...

The exhaust is already done up pretty well, it's true-dual straight through with no cats, (it's a 74) and going out to some Thrush Turbo mufflers with dual chrome tips

Another question, does the octane necessary depend solely on compression ratio? If so, obviously I'd like to stay with the cheaper gas, especially with the way things are going on in our World today

Lastly, what are some good books to read up on for this project?


Thanks everyone

Imran

Imran:
For budget & expectation you indicate... at under $1600 the Goodwrench pn 10067353 is the way to go. That motor specs out virtually same as an L48 ... an apples-to-apples comparison/replacement ... although Goodwrench pn 10067353 makes about 250hp right out of the crate. It is brand new ... not rebuilt. Comes complete ... EXCEPT water pump, fuel pump, damper, flywheel, distributor, intake manifold. Also, consider GM warranty. GM Goodwrench motors have GM-backed 3yr/50,000 mi warranty. For all intents & purposes, the GM Performance Parts crate motors (ZZ4, 350HO, HT383 etc) DO NOT have such a warranty. Sallee offers the Goodwrench w/ 280-285hp cam-intake upgrade while retaining the nice Goodwrench warranty ... however, I believe that particular turnkey combo (sallee pn SC285GW) is specific to Sallee. Dunno if your local dealer offers similar combo with 3/50 Goodwrench warranty?

http://sallee-chevrolet.com/ChevySmallBlockV8s/gen350.html

BTW, ANY GM dealer can provide Goodwrench pn 10067353 ... price it out.
JACK:gap

 

[mmvette80]

I installed the GM Goodwrench $1600 engine in my car. I installed the sumitt k1103 cam in it. Now I need a new head/cam combo. Its too friggin slow. Like you said, its the same engine.
I have a question regarding my L48 that was in the car. I want to rebuild it, how hard is it to do the bottom end? I know there are plastigauges and tight tolerances, what if one of the main bearings doesnt have the correct tolerance? Is it usually the machine shops fault? Or can the machine work on the bearings be at fault? Where are usual problems?

 

[RLP]

I would have the engine rebuilt at a discount engine rebuilder. About $650.00 for a longblock and then use your aftermarket intake and carb. This would give you good performance like an L-82. It would idle and have good vaccum to run the headlights and climate control. The block and heads on the L-82 and L-48 are the same.

 

[Vette/Berlina-coupe]

500hp for $1,500....

-Ha!! -caught you dream'in... -but I would check with a machine-shope that specializes in cyl.heads and: a.) see if they happen to have a pair of good used breathing/aluminum-heads you could swap-in; b.) see what they think of shaving porting/relieving your L48/cyl.heads to get 10:1-comp.ratio (10.5:1 with aluminum which runs cooler); c.) leave the crank be, unless you are going to really modify the engine extensively, the castiron-crankshaft is fine (is always good to go-over the crank with a grinder to smooth-off any rough-casting areas); d.) install $300-(Summit-800/230-3030)/Fluidamper viscous-hub for greater power/smoothness; e.) don't stroke the engine to 383cid, it results in a less-efficient engine because of excessive-angle at which conrods are placed at when crank-throw is half-way up (and thus trying to shove the piston scuffing into the cyl.wall), --thus more heat, less fuel-mileage; f.) have a skilled/machine-shop do a 7to9-angle valve-grinding job, -resulting in more aerodynamic air-flow between valve-head and valve-seat, --hence, greater volumetric-efficiency (more air gets sucked-in); g.) high-volume oil-pump; h.) $19-Cloyes/double-roller type timing-chain set; i.) $99-Summit's mild/hyd.-cam; j.)$99, 6:1 Summit's/roller-rockers (less-friction/less-heat); k.) slap-on a used '80-'82/alum.Intake-manifold($25+ship. Ebay); l.) so-called zero-clearance/self-sealing/no-leak Piston-rings; m.) after 350-miles, Mobil-1 oil ! Woops, --we're probably exceeding your tight budget here, but sure enjoyed spending your money... -Bob vH

[JohnZ: -well such differences of opinion are what makes a good racers-edge... while it is obvious that the larger you make an engine the greater its torque, --however, I chose to go the other direction and prefer destroking a 400ci-sbV8 down to 350ci via a chevy-327ci/forged-crankshaft (w/FluidDamper, -yes for extra-power owing to precise balancing at all rpm's), 6.25"-longrods(H-beam, vs. stock 5.7"/I-beam), Crowler/Roller-hyd.cam & lifters w/Crowler/roller-rockers(steel); -the result of which is "bullet-proof at 425hp/8,000-rpm" naturally aspirated, --which would disintegrate your 383ci(stroked via 400ci-cast-crank); --plus this combination also nets much superior fuel-mileage owing to the significantly reduced reciprocating-friction as result of greatly reduced conrod-angle, and still further reduced via the self-sealing Piston-rings(which use chamber-pressure to energize them against the cyl.wall)! However, I realize this is relatively sophisticated stuff beyond the pervue of what above MaineShark is entertaining, but tis indeed beautiful to hear that baby wind, and wind, and wind (better than my Lotus Esprit actually)... ~Bob VonHeck]
:TALK

 

[mmvette80]

What cam/head combo is the best to get 400hp? What cam specs are best for 0-100 times.

 

[JohnZ]

Re: 500hp for $1,500....

[Bd.) install $300-(Summit-800/230-3030)/Fluidamper viscous-hub for greater power/smoothness; e.) don't stroke the engine to 383cid, it results in a less-efficient engine because of excessive-angle at which conrods are placed at when crank-throw is half-way up (and thus trying to shove the piston scuffing into the cyl.wall), --thus more heat, less fuel-mileage; f.) have a skilled/machine-shop do a 7to9-angle valve-grinding job, -resulting in more aerodynamic air-flow between valve-head and valve-seat, --hence, greater volumetric-efficiency (more air gets sucked-in); g.) high-volume oil-pump; j.)$99, 6:1 Summit's/roller-rockers (less-friction/less-heat); l.) so-called zero-clearance/self-sealing/no-leak Piston-rings[/B]

After 40 years of building small-block Chevys, I'll offer the following:

1. A Fluidamper doesn't gain any power, waste of $300 for a street engine; SFI-rated balancers are only required in certain modified race classes due to suspect durability of the OEM balancer at sustained extreme rpm.

2. 383's are built for torque (where the fun is on the street), not efficiency; you'd need NASA-level instrumentation to find any additional heat. There are tens of thousands of 383's out there, and they run just fine.

3. Any decent shop with a Serdi machine can do a good 3-angle valve job; anything more than that is wasted on a street engine, and you'd never see the difference. You'll gain much more with minor cleanup of the bowl area behind the valves and port-matching the intake to the heads.

4. No need whatsoever for a high-volume oil pump - the SB Chevy has an outstanding oiling system with the stock pump; oil pressure is a function of downstream restriction (bearing clearances, lifters, etc.) to flow, not volume; the additional oil just unseats the bypass valve in the pump and dumps back into the sump.

5. Roller or roller-tip rockers reduce friction and valve guide wear, but going to 1.6:1 isn't worth the hassle of enlarging the pushrod holes in the heads, checking/replacing springs to avoid coil bind, etc. - any power increase from the change to 1.6:1 is insignificant in a street engine.

6. "Gapless" or "step-seal" rings are expensive, time-consuming to file-and-fit individually, and you'll never see the difference in a street engine. A good set of moly-faced conventional rings (Speed-Pro, etc.) will do the job just as well for far less cost and hassle.

 

[mmvette80]

johnz-
383. With a stock block I would have to have the notches done so the rod bolts wont hit, correct?
Is it true that a 383 needs the stronger crank?
What is the max rpms for a 383?
How much torque is the norm for a small block 383?
Sounds like you know your stuff!!

 

[JohnZ]

Yes, the bottom of the cylinders and a couple of spots on the pan rail need to be clearanced, and there can be rod-to-cam lobe clearance issues as well with really wild cams.

I've built three 383's, all with factory cast 400 cranks, and never had a problem; if you're building for big power and intend to race it, a forged 4340 crank is probably a good investment, but it's not necessary for a street engine.

383's are all about low- and mid-range torque, which is what makes a street engine "fun" - no need to wind them to the moon like a 302 or 327. I built all of mine fairly mild (RPM aluminum heads, 9.4:1, hydraulic 222/228 cam, RPM intake, 650 VS 4150 Holley, etc.), and they pulled 428hp @ 5600, 435 lb-ft. @ 4100 on the engine dyno.

Here's the one I put in my tube-frame Grand Sport:

 

[mmvette80]

The 383 you described is the power im looking for. What kind of 0-60 and 1/4 mile times will that produce?
The 383 can use a 400 crank with stock 350 rods or a 350 crank with 6.0 rods to get the displacement?
The 9.4:1 you described is pistons?
What is the specs on the heads?
I have seen that GS in a magazine somewhere. Its sweet.

 

[JohnZ]

Don't know how my times would translate to a stock Corvette, as the tube-frame Grand Sport only weighed 2340# wet, about 1000# lighter. It ran 12.40's @ 118 on street tires, with an M-21 and 3.08 cruise axle.

I used the stock 400 crank with 5.7" rods, KB Hyper pistons, and 70cc RPM heads; you have to use a 400 crank to get the added stroke, with the mains turned down to 350 size.

The car had color features in the 11/97 issue of "Vette" magazine, and an 8-page color feature and step-by-step buildup article in the May, 1998 issue of KIT CAR magazine; it was also judged as a 100-point car by the Classic Car Club of America. Two years of work, but well worth it!

 

[mmvette80]

Thanks. Im sure the car was worth the time. It must be a ****er to drive. Do you drive it regularly?

 

[JohnZ]

Re: 500hp for $1,500....

[B[JohnZ: -well such differences of opinion are what makes a good racers-edge... while it is obvious that the larger you make an engine the greater its torque, --however, I chose to go the other direction and prefer destroking a 400ci-sbV8 down to 350ci via a chevy-327ci/forged-crankshaft (w/FluidDamper, -yes for extra-power owing to precise balancing at all rpm's), 6.25"-longrods(H-beam, vs. stock 5.7"/I-beam), Crowler/Roller-hyd.cam & lifters w/Crowler/roller-rockers(steel); -the result of which is "bullet-proof at 425hp/8,000-rpm" ~Bob VonHeck]
:TALK [/B]

What kind of spacers did you use to get the 2.30" 327 crank main journals to run in the 400 block's 2.65" main bearings? Would also love to see the pistons that work with a 3.25" crank and 6.25" rods, since that only leaves 1.15" for compression height, which doesn't leave enough room for an oil ring. BTW, the Fluidamper (or any damper, stock or otherwise) has absolutely nothing whatsoever do do with engine balance (except on 400's and 454's) - only dampens torsional vibration in the crank. If your hydraulic roller runs to 8,000 rpm, you should run (not walk) directly to the patent office, 'cause that's a first.

 

[JohnZ]

Thanks. Im sure the car was worth the time. It must be a ****er to drive. Do you drive it regularly?

I used to, put about 4,000 miles on it in two years; sold it a couple of years ago to a collector on the east coast.