Agree with much of what you said except the numbers don't lie. A typical 383 versus a built 355 in my examples above are making pretty much the same gross HP at a slightly lower RPM and similar torque, again at at even smaller deviation RPM (about 300 RPM). Remember this is not theory, but actual reality for a street engine. Again, in a perfect world, a maxed 383 build WILL make more than a Maxed 355 build...there is no argument but the reality is that most crate 383's and what I see folks build do not maximize the 383 advantage of 28 additional cubes. Lastly, the point that a 383 makes more average torque across all RPM's versus the 355 is somewhat true but again, AFR's on a 355 are making an easy 400+ ftlbs from 2,000-4,500 RPM which is almost identical to the typical street 383.

In terms of pistons, I used Forged JE Racing Pistons and rings for my 355 which are pretty much some of the best....

All I am saying is just because it is a 383 does not make it more powerful than a 355. It needs to be built properly to maximize the cube advantage. A 383 with 9/9.5:1 compression, no name aluminum/iron heads, a low lift/moderate lift flat tappet/roller cam will not make more power than a smaller higher quality components V8....it is simply not true. If you need a new rotating assembly for a 350 (crank, Pistons, rods, etc) then I agree go 383, otherwise I think folks need to carefully consider a 355 for the street. I would definitely put the added money for a 383 instead into a roller cam and top notch cylinder heads along with 10-10.5 compression. Pretty simply formula!

I often wonder why GM engineers who are very smart people did not produce a 383 instead of a 350 V8? Makes you wonder. GM did produce a 400 SBC but no 383. Why?
Chrysler built a 383 but not Ford. Why? Hmmmmm

 

I think we're in stark agreement on the basic facts and numbers, just maybe not the data sample selected.
Agreed that starting with a good 350 with good heads and a roughly right cam and changing only the bottom-end's cubic inches will result in roughly the same HP at a lower RPM, and an increase in torque at about the same ft lb / cubic inch ratio at all RPMs. -Let's say +33 ft lbs across most of the curve. 33 ft lbs IS something you'll notice, but like you said, as a percentage it goes down as your starting with a more and more powerful 350.

The numbers don't like, but the sample and sample size selected when making a generality is important. Vortec headed motors and other small intake port size heads aren't going to be able to take advantage of more cubes; having said that most good modern aluminum heads are significantly bigger than a 350 needs for anywhere near 6,000 RPM and WILL see additional improvements in torque from the increase in airspeed. Most 180cc and 185cc heads and certainly anything bigger is ready to take advantage of the extra cubes and average piston speed increases in moving to 383 cubic inches, assuming it doesn't have a baby cam in it.

MIN CSA = (bore x bore x stroke x RPM x .00353) / 613.8 (.55 MACH x 1116 fps)

This means an SBC 350 with a 6,000 RPM HP Peak should have a 1.92" Min CSA; a 383 with a 6,000 RPM peak should have a 2.1" Min CSA;
-If you run that calculation again with a 5,000-5,500 RPM HP peak that you see with a high teens or low 220s duration cam, you'll see that a smaller still Min CSA is desirable -if your Min CSA is bigger than the calculation, then you will benefit from the increased average port speeds. (The AFR Heads' min CSA is actually smaller than any other head I've seen for the same intake volume size- they're truly amazing on that front; they might run into sonic choke and not see the gains most of the other similarly rated-size heads would see from additional port speed.)

My take is that most modern 180cc and bigger street heads, and a cam of mid220s and up IS going to see a good bump in perf moving to a 383.



I think your build, RIGHTFULLY, highlights whether the added cost of a 383 stroker crank is worth the 33-40 ft lbs average increase if you're starting with a nice forged L82 crank. You're adding $500 worth of cost to replace a FORGED L82 crank with a Cast Scat Crank for 33-40 ft lbs avg more and probably near zero more HP... Having said that those cast Scat cranks are far stronger than the old L48 cast cranks, so not a perfect comparison. -All the benefits I previously highlighted in new piston tech you also get with the move to a 355 and new pistons vs a 388 so the real question is just whether 33-40 ft lbs is worth about $500 to downgrade your crank from a Forging to a high quality Cast crank...

I honestly think you're probably right, that it's not a great $$ vs perf trade-off, but when I look at the total machine and parts cost of a rebuild the $500 tends to get lost and I like the idea of more cubes... Probably not a rational decision at that point...

Adam

 

Correct me if I am wrong but moving to a 383 is not just about the crank change but also all the rods are different and the block needs to be machined as well. I believe that a decent conversion with good , not great parts, to a 383 is about $1,800-$2,000 with labor, minimum?Lunati Voodoo 383 Stroker Crankshaft and Connecting Rod Kit Small Block Chevy

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Unless you need the crank, rods, pistons, etc, for your 350, these dollars ^^^^^^^^^^are better spent on the best heads you can find for your application and a roller cam for a 355.

 

If you're moving from a 350 to a 355 OR a 383 you need new pistons, rings, rod bolts, and a bunch of little stuff reconditioned, in addition to all the machine work that's required either way. You've found some pretty expensive stroker kit options there. Pretty much all the Skip White kits are @ $1,099 all in including a new harmonic balancer and flywheel, which you'll need if you're making any power. -The only significant difference I can think of is the crank and rods between a 355 and a 383. Everyone repeats the mantra that going with a new 350 rotating assembly vs. a new 383 rotating assembly costs the same, and this is true but it discounts that if you have a good forged Crank and Rods you can just reuse them and save $400-$500.


-Again, I'm agreeing with you that I think the best bang for your buck, if you're starting from an L82, is to reuse the forged crank and rods; $500 for a +33-40 ft lbs isn't a great deal.
But if you're at $1,300-$1,500 all-in for a 355 rebuild vs. $1,800-$2,000 for a 383, I DO find the extra 33-40 ft lbs and saying I have a 383 tempting, still, even if it doesn't make good financial sense for the increase in perf, if I'm honest. (I'm probably going to be $13k all in for my resto-mod project end-to-end so what's another $500?)

If you think the move from a 350 to a 355 can be done more cheaply than $500 less than a 383, I am curious how and where the savings come from.
If you think we're still disagreeing on something, I'm not sure what it is. -I process information externally and it takes me a while to get there, but I can't think of anywhere we're still in disagreement at this point.


Adam

 

Just for the record, a 383 can be built with 5.7 inch rods, like a 350. My 383 has reconditioned original L48 rods, with ARP bolts. I'm also using a cast steel Eagle crank, JE forged pistons and worked Vortec heads. I don't know the HP and torque numbers but this setup has survived 230 1/4 mile runs with a best of 12.15 at 110.

 

All good...........

 

It that's what you want it is.... I don't know that I'd ever want a 383. Its not always about HP/$.

 

I never had a thought of building my OEM L-82 into a 383 since I wanted to keep mine as much L-82 as possible and just seems weird to me to put/say a 383 is in a C3.....since it never came from GM with a 383(reminds me of Chrysler 383's). It is like saying I took an LT-1 and turned it into a 450 Gross HP 383..........Lots of folks would say, you did what?

 

It really boils down to cost and what condition your motor is in. On a budget and have a good compression 350? I would definitely stick with heads/cam/intake/exhaust.

Have a bit more cash on hand, or your 350 needs a rebuild anyway? DEFINITELY make it a 383. It costs about the same and has a chunk more power potential.

As far as caring what CI motor is in, if you have a chrome bumper numbers matching car, I definitely understand keeping it the stock displacement or as stock as possible. If you have a rubber bumper car, why worry about it? Whether you have a 350, 383, 406, etc... who cares, put whatever makes you feel happy. If you care about originality or what other people think, then by all means keep it original. Personally, if someone tells me they have a 383 or bigger motor in a rubber bumper C3 I think it's pretty cool, definitely wouldn't look down on it and I don't know anyone who would besides maybe a purist who wants an all original car right down to the original wing nut on the air cleaner lid.

I would have a 383 in my car right now if I had the budget for it. Almost pulled the trigger on a kit, and then decided to hold off. Chances are I will go with a bit more cubic inch (406/421) when I do build the next motor.

 

I agree...just my thing, no more than that.

I appreciate all motors, trust me. I'm impressed when folks tell me that they have a 500+ Gross HP 383, that's cool, to me over a 502 BB with 500 gross HP.I like your thought about the 406/421 for your car. I think Paul Dana has a SBC 427 in his 79 C3...now you are talking.......

 

JB78L-82,

For what it's worth I played around with your motor in desktop dyno, specifically to test the higher rocker ratios.

Desktop Dyno estimated with your current setup:
359 ft lbs torque @ 2,000 RPM
Max Torque: 436 ft lbs @ 4,500
Max HP: 452 @6,000 and still 445 @ 6,500

Switching just the intake to 1.65 rockers would get the intake valve up to 0.578":
Using the previous estimates of 275 cfm @ 0.600" (which is a huge jump that I kinda doubt; or wouldn't AFR advertise that?)
And the rough math of the duration increase @ 0.050" increasing about 2 degrees with a 1.6 ratio rocker and 3 on a 1.65 ratio rocker, I get:
360 ft lbs @ 2,000 RPM (+1 ft lb)
Max Torque: 439 ft lbs @ 5,000 (+3 ft lbs) -Desktop dyno only shows the results in 500 rpm increments, but as far as I can tell the extra 3 degrees moved the torque curve and hp curve up by about 250 RPM
Max HP: 458 @ 6,000 (+6 HP) and still 451 @ 6,500

You'd definitely have to switch to Roller Rockers for a 1.65 ratio, too.

I initially didn't like the extra duration on that cam for the AFR heads as I always hear that AFR heads should have no split, but HP dropped by 14 @ 6,000 with the durations the same on the intake and exhaust. I think the extra duration on the exhaust helps your motor hang on into the higher RPMs, obviously as does the bigger header.

Retarding the cam by 2 degrees with the 1.65 rockers got you up to the magic 460hp@6,000 RPM mark...
Stepped tube race headers were the only thing that made a big jump in HP to 487 on your motor.

Your 355 is hard to improve upon in your desired RPM range, at least according to Desktop Dyno..

Adam

 

Could you run it again using 1* in duration?
When I was researching this subject before buying mine.
"Doing my homework!" lol

I noticed 1*-1.5* frequently used as the increase in duration.
I'm curious to see if that would change anything?

TIA

R

 

The above poster is making sense & you bet its worth it all day especially with a long tube runner setup.

 

Thank Adam...that's pretty cool stuff.

I have a sense that my builder who is an expert on GM V8's did not recommend the 1.6 rocker ratios since I pretty much am in the sweet spot for a sub 400 cube V8 with my 355 and the roller cam and AFR's. These numbers are pretty much in line with his educated estimate for the power of my 355:

Desktop Dyno estimated with your current setup:
359 ft lbs torque @ 2,000 RPM
Max Torque: 436 ft lbs @ 4,500
Max HP: 452 @6,000 and still 445 @ 6,500

The only difference is the documented articles provided earlier and my builders guess with the AFR 180's/roller cam 219/225 is for the 450 Gross HP number to be slightly less than 6,000 RPM peak (around 5,700-5,800 RPM) and the 440-450 Ftlbs torque to be at 4,500-4,600 RPM as you suggested but slightly higher closer to 440-450 torque. Either way your calculations are again spot on with the other multiple sources for the HP/TQ and RPM's of my 355. The only other notable item is that AFR's with 355's like my combo show more than 400+ ftlbs torque starting at 2,000 RPM -5,000 RPM which is VERY wide versus other heads. Add in my 1 7/8 long tube headers and you can begin to understand why I say what I do about 355's with the right combo of parts versus a 383 with less than optimal parts for that motor. Unless you are building a street 383 with more than 475+ Gross HP(ideally 500 Gross HP)/460+ torque (which the majority are not), the advantage over a 355 like mine probably does not justify the 383 except in certain circumstances. You see why I say what I do now?

Forum member, Karol, was in my L-82 355 just today and I demonstrated to him the 400+ torque at very low RPM that a 355 can generate by 3 and 4th gear acceleration with light throttle BELOW 1,000 RPM (600-700 RPM) with zero hesitation, no bucking, no pinging, nothing......................he could not believe it! The car can idle (700RPM) in 4th gear with no throttle and move forward with zero protest from the motor.

 

 

This is a crate 383 that I would want in place of my 355:

https://www.jegs.com/p/ATK-Engines/A...94747/10002/-1

10.2 compression almost .600 lift cam-Holy smokes-actually ,597 lift
195 CC heads

Almost all of the standard 383 crates have LESS power than my 355 across the RPM range...shame....no need for the cubes if you don't utilize them fully with the build.....

The question is if I had AFR 195's with 10.5 compression and a .597 lift roller cam on my 355, what would the actual difference be between that 355 and this 383^^^^^^^.....50 gross HP and 50 Gross TQ?...I doubt it........20-25 HP/TQ at about 300-400 RPM less....at most...

 

" Forum member, Karol, was in my L-82 355 just today and I demonstrated to him the 400+ torque at very low RPM that a 355 can generate by 3 and 4th gear acceleration with light throttle BELOW 1,000 RPM (600-700 RPM) with zero hesitation, no bucking, no pinging, nothing......................he could not believe it! The car can idle (700RPM) in 4th gear with no throttle and move forward with zero protest from the motor. "

True, I was amazed we could drive around with that rpm and the motor could handle it !

 

This article pretty much says it all and covers most of what has been discussed here before:

Will a 383 Chevy stroker give me big block power in a small block package?



To put it simply, no. This is a misconception a lot of people have and because of so many bogus magazine ads for wanna-be engines out there, you see the statement, "big block power in a small block package", and the truth is, you certainly won't get THAT much more power out of 33 extra cubic inches. Actually, we need to compare apples to apples here. A 383 is a .030" over bore and when comparing this to a "350" cubic inch engine, we need to compare it with a .030" over bore 350 as well, to keep a level playing field, and a .030" over bored 350 is actually 355 cubic inches, so a 383 is actually only 28 cubic inches larger than a typical / comparable 355, and you think 28 cubic inches is going to give you "big block power"? Hardly.

Let's use the standard, 1 HP per cubic inch rule of thumb, just for the ease of math here. So a .030" over 350 is actually a 355 cubic incher, and at 1HP per cubic inch, we would get 355 HP, and the same for a typical 383 using the same rule of thumb, so we are comparing 383 HP to 355 HP, which is 28HP difference. Certainly not going to give you "big block power", and when you are talking big blocks, you are talking "torque" rather than HP, and it's "torque" that you feel in the seat of your pants when driving around. So, if a typical 454 big block, (also at .030" over) makes 461 cubic inches, and at 1HP per cubic inch, we are talking about 461HP, which is quite a jump from 355HP. A heck of a lot more than the 28 extra HP a 383 would typically make in the same comparison. But keep in mind, we are only using the old 1HP per cubic inch rule of thumb. Of course it would be more like 1.2HP or so per cubic inch in reality, and on more radical engines, upwards of 1.3 -1.4HP per cubic inch in really nasty street / strip engines liek what we typically build for most people.

So why choose a 383 in the first place? Because the extra cubes are all by stroke, not by bore. Although a 383 might be making the same 1HP per cubic inch rule as the 355, it will inherently make more torque per cubic inch simply because of the physics of increased cubic inches via stroke rather than via bore size. Stroke means "leverage" and leverage gets vehicles moving, especially at lower RPM's. So even though you might not get true "big block power" out of a 383, you will certainly feel the added cubes in the seat of your pants compared to an identically prepped 355 because the 383 will make much more torque.

Now, if you really want big block power in a small block package, we can certainly do that for you with one of our 434 small blocks, or one of our monster 454 small block strokers, but as with any serious stroker of this caliber, you are also talking a minimum of a $11,000+ price tag, so the much less expensive 383 is an all around way to go for the guy that wants a little more grunt than what a typical 350 (or 355) can give.



My Note: "The 383 will make MORE power compared to a 355 that is IDENTICALLY prepped as the 383!!!!!!!! THIS IS THE KEY POINT^^^^^^

 

 

Understand the shortcomings of that motor.

My point is and has been that if you go 383 and are not making over 475+Gross HP/475-480+ Gross TQ in a streetable RPM range, you are not really getting the benefit of a 383 over a strong 355. Again, just having a 383 does NOT mean that you will make more power over lesser cube motors. The 383 will only make more power than an identically prepped 355 if built to maximize the few additional 28 cubes..It's not an automatic given just because it is a 383. There are literally dozens of examples going back to the 50's and even today where lesser cube/liter motors handily will out power and perform bigger cube engines with more liters...has always been that way.