Are internal modifications to stock engines detrimental to value and or integrity?

[John M.]

Curious if internal engine modifications to a numbers matchine engine is a deterimental excersise in terms of value and or integrity per NCRS general consensus.

Taking a numbers matching 69 L46, and installing a 383 stroker Kit, port work, Roller Cam, Aluminum Flywheel, etc.

Engine builder's estimating 400-425HP on the dyno which should prove a fun little small block.

A 69 L46 isn't historically significant by any means and the modifications don't destroy the specimen.

But I imagine the lope will be a little heartier and it should be quite obvious to the average enthusiast's ear it's not stock.

Any thought's on significant internal modifications while maintaining correct external components?

[John L.]

Re: Are internal modifications to stock engines detrimental to value and or integrity

John,
Why don't you just install a crate engine? Keep yours original? Probably be about the same amont of money, wouldn't it?

[Duke W.]

Re: Are internal modifications to stock engines detrimental to value and or integrity

The biggest problem is altering effective valve overlap that changes the idle characteristic.

That power rating being quoted is "SAE gross", which is pretty meaningless, especially since your '69 only has a 2" exhaust system.

Also, the "similar engine" theory, which is unequivocally proven with decades of test data says that, all other things equal, a long and short stroke will produce about the same peak power at the same mean piston speed, but the longer stroke engine does have the advantage of producing more average power through the useable rev range.

Roller cams are way overrated. My suggestion is massage the heads, go with the longer stroke, but use the OE cam and OE valvetrain components. Put the money you save into the head and valve seat work.

The key to power is maximum head flow, not some "magic" camshaft. That's a myth!

Duke

[Warren F.]

Re: Are internal modifications to stock engines detrimental to value and or integrity

[quote=John McNeely (49684);384042]Curious if internal engine modifications to a numbers matchine engine is a deterimental excersise in terms of value and or integrity per NCRS general consenus [quote]


John,

In the rarer drivetrain optioned 'vettes, I would say this is very important. Once internal modifications are done, you no longer have an engine that was factory configured.

I have two 1971 LS6 optioned Corvettes. Both have original engine componentry, the engines were partially disassembled to inspect for original pistons, camshaft, crankshaft, rods. Both are at standard specifications with no milling, boring, porting, decking, etc. I have installed replacement correct GM gaskets, so these are no longer thee originals.

[Joe C.]

Re: Are internal modifications to stock engines detrimental to value and or integrity

Curious if internal engine modifications to a numbers matchine engine is a deterimental excersise in terms of value and or integrity per NCRS general consensus.

Taking a numbers matching 69 L46, and installing a 383 stroker Kit, port work, Roller Cam, Aluminum Flywheel, etc.

Engine builder's estimating 400-425HP on the dyno which should prove a fun little small block.

A 69 L46 isn't historically significant by any means and the modifications don't destroy the specimen.

But I imagine the lope will be a little heartier and it should be quite obvious to the average enthusiast's ear it's not stock.

Any thought's on significant internal modifications while maintaining correct external components?

400 SAE net horsepower with a 383 should be very easy to accomplish.
Post the specs for the camshaft the engine guru picked. Almost guaranteed that it will provide LESS, not more average horsepower and torque.
Your original L46/L82 cam is a very good one, and a roller will not improve on it. Besides, converting to a roller means paying close to 400 bucks for the billet cam alone. You'll then also need lifters, stiffer valve springs, guide plates, screw in rocker studs, and possibly, hardened pushrods. You'll need machine work on your heads, roller trunnion rocker arms (which might not fit under stock valve covers). All in all, you'll be spending an additional 600-700 dollars, with no improvement at all.
If you MUST keep your external appearance all-stock, then in addition to the head porting and multi-angle valve job, and other internal mods designed to minimize friction, windage losses, and pumping losses, then I would consider having your intake manifold ported, changing over to the 2 1/2" outlet exhaust manifolds used on '64-'65 SHP Corvettes. Your 750 cfm Q-jet is more than adequate for the larger engine.
If you want more average horsepower, why not dress your 383 like an LT1 and retain your camshaft. If you don't mind sacrificing some low/midrange torque for more top end horsepower, then swap in an LT1 camshaft. If you make this camshaft change, you will have to increase your static compression ratio, most likely by installing pistons with small domes, in the vicinity of 6 cc.

[John M.]

Re: Are internal modifications to stock engines detrimental to value and or integrity

The builder did say he'd be porting the intake, he said only a slightly larger than stock camshaft, but not a Monster. He basically said the 383 kit, larger Cam, but streetable, ported intake and 10-1/5 compression to produce 400-425 HP with the exhaust manifolds on the dyno.

The rollers won't fit under the stock covers so he said he's going to install standard rockers.

I'm running the side exhaust so hopefully that helps slightly with the back pressure. Probably not enough.

I'll get more detail on the specs after he tears it down, gives me an estimate to compare notes.

This guys a good builder though winning national build-offs.

I want to keep it as economical as possible so I'll make sure we discuss that.

I did think about running an Aluminum intake and better carb but he thinks he can hit those numbers keeping the stock heads, intake and carb so that's my only real objective along with keeping it economical.

I'll make sure I talk to him about these things to ensure he agrees what he's doing will provide bang for the buck. More on the line of Head and intake work along with the stroker kit.

Thanks

www.besracing.com

[Joe C.]

Re: Are internal modifications to stock engines detrimental to value and or integrity

The builder did say he'd be porting the intake, he said only a slightly larger than stock camshaft, but not a Monster. He basically said the 383 kit, larger Cam, but streetable, ported intake and 10-1/5 compression to produce 400-425 HP with the exhaust manifolds on the dyno.

The rollers won't fit under the stock covers so he said he's going to install standard rockers.

I'm running the side exhaust so hopefully that helps slightly with the back pressure. Probably not enough.

I'll get more detail on the specs after he tears it down, gives me an estimate to compare notes.

This guys a good builder though winning national build-offs.

I want to keep it as economical as possible so I'll make sure we discuss that.

I did think about running an Aluminum intake and better carb but he thinks he can hit those numbers keeping the stock heads, intake and carb so that's my only real objective along with keeping it economical.

I'll make sure I talk to him about these things to ensure he agrees what he's doing will provide bang for the buck. More on the line of Head and intake work along with the stroker kit.

Thanks

www.besracing.com

The roller lifters won't give you as much friction reduction as when used with full roller rocker arms. You will be reducing friction losses probably in the vicinity of less than 5 HP @ 5500. Hardly worth an expenditure of 600.00, IMHO. If you post the specs on the cam card, we can better analyze its characteristics.
If your engine builder is looking to build in 10.5 SCR, then the camshaft that matches it has relatively long duration. Most of today's "mild" roller camshafts only require about 9-10:1 SCR. 10.5 makes it borderline "circle track" or "hot street/strip".
Stock GM side exhaust, or reproductions of the same, which employ similar design, are in fact MORE restrictive than most conventional reverse flow mufflers. If you intend on using side exhaust, especially with a large displacement smallblock like a 383, then it would behoove you to look into aftermarket reproductions designed with at least 2 1/4" inner diameter perforated tube. If you plan to rev your 383 beyond, say, 6200-6500 RPM, then you should be looking at sidepipe mufflers with at least a 2 1/2" inner perforated tube.
The carb is fine, but the intake needs improvement, especially with the longer crankshaft. I have heard that iron Chevy intakes can be made to flow very well..................it is expensive, though. Call Brzezinski in Wisconsin, give him the casting number of your intake, and he'll give you the straight scoop on what he can do with it. He will not try to sell you something you don't need. Keep in mind though, that it can be very expensive to do this. If you don't mind changing the look of your engine, you would be better off with an aftermarket intake, for less than 200.00.

[Duke W.]

Re: Are internal modifications to stock engines detrimental to value and or integrity

If you can achieve I/E port flow coefficients in the 50/60 percent range, which is doable with proven pocket porting and multiangle valve seats a 383 will make useable power up to 6000, and with the OE stroke to the lifter pump up speed somewhere between 6000 and 6500.

As stated with massaged heads the biggest restriction is the inlet manifold, not the heads, and not the cam. The L-46 has the same CI manifold as the base engine.

If you want to keep the project "economical" forget the stroker and reuse all the original cranktrain components. The rods can be reused without Magnaflux, new bolts, or resizing - just check that the bearing bores are still to OE spec. Since your crankshaft is Tufftrided, DO NOT GRIND IT, which will wipe out the Tufftride. Just check the journal diameters, straightness, and polish the journals.

Put all the "performance budget" into the head work and valve seating, and use Sealed Power OE replacement valves. You don't need stainless steel valves all around.

Lab dyno testing is of little value except to make sure the fresh engine has no problems prior to installation. Power data is also meaninless. What counts is SAE net output, so a chassis dyno test after the engine is broken in and tuned will tell you what it really makes.

A "performance build" can be done on a tight budget, but only if all unecessary machining operation and "parts upgrades" are eliminated, and you put what you save into the heads.

Duke

[Jim H.]

Re: Are internal modifications to stock engines detrimental to value and or integrity

Most of the posters on this thread have focused on the performance mods you can make to your original engine. An early poster commented that it would be better to yank the original motor and install a new motor. No response to that post makes me think you are committed to modding your original motor. But before you go that route, consider that GMPP makes ZZ383 and SP383 crate motors that pull 425hp and slightly more torque for about $5,500. They are warranted for 24 months and I forget the mileage limit, but I recall thinking I wouldn't do that many miles in a decade. I installed a ZZ383 in my 57 Belair and was extremely pleased with the results. Unlike other stroked motors that are long on torque but breathless at the top end, the ZZ383 was designed to rev as well as make tons of low end torque and it delivered. Every time I have modded an original motor I end up approaching the new motor cost w/a very short warranty and a non-standard bore original block. If it were me (and I recognize it's not), I'd retire your original to garage art for originality purposes (and to avoid a rebuilder mistake) and go with a proven GMPP or other aftermarket new motor. You can dress them up in almost all cases to look original. Whatever you choose to do, however, good luck with your project.

JCH

[Kevin G.]

Re: Are internal modifications to stock engines detrimental to value and or integrity

Most of the posters on this thread have focused on the performance mods you can make to your original engine. An early poster commented that it would be better to yank the original motor and install a new motor. No response to that post makes me think you are committed to modding your original motor. But before you go that route, consider that GMPP makes ZZ383 and SP383 crate motors that pull 425hp and slightly more torque for about $5,500. They are warranted for 24 months and I forget the mileage limit, but I recall thinking I wouldn't do that many miles in a decade. I installed a ZZ383 in my 57 Belair and was extremely pleased with the results. Unlike other stroked motors that are long on torque but breathless at the top end, the ZZ383 was designed to rev as well as make tons of low end torque and it delivered. Every time I have modded an original motor I end up approaching the new motor cost w/a very short warranty and a non-standard bore original block. If it were me (and I recognize it's not), I'd retire your original to garage art for originality purposes (and to avoid a rebuilder mistake) and go with a proven GMPP or other aftermarket new motor. You can dress them up in almost all cases to look original. Whatever you choose to do, however, good luck with your project.

JCH

Jim, Do you realize this thread is from 2008? I'd think that motor decision has long been made, but thanks for the info.

[Jim H.]

Re: Are internal modifications to stock engines detrimental to value and or integrity

Kevin, Lol - I got buried in the subthreads to a thread and didn't read the dates. At least I'm on the record. Happy New Year.

JCH