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Discussion Starter · #1 ·
Hey guys after reading a lot on here I've heard a few people talk about dyno simulators and not knowing much about them was wondering how accurate they can be and if possible, if anyone has one can you run some numbers for me on my 383 to give me an idea of what I got. This was my first build that was not stock so I kinda just did some research and got what I thought was a good all around package that would run good on the street. Let me know what y'all think. If I leave some important info out let me know. Here is what I got. So far it runs good. Also need some advice on what i should set timing at.



Vortec heads with upgrades Alex's parts springs and stainless steel valves, 1.94/1.60

Stroke:*3.750
Disp. @ .030:*383
Rod Length:*5.700 Forged 5140 I beam
Speed pro -12cc hyperuectic flat top
Eagle cast steel crank
Deck: .025 with .015 steel gasket

Xtreme Energy XE274H Hydraulic Flat Tappet Camshaft Only
Lift:*.490''/.490''
Duration:*274°/286°
Duration @ 50: 230/236
LSA:110
RPM Range:*1800-6000

Summit dual plane intake https://www.summitracing.com/parts/sum-226018

Stock 750cfm quadrajet.

1 5/8 long tube headers
 

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I can run a simulation later tonight, but just a educated guess says that's a 410-420 Hp combination, peak around 5800 rpm.

While the Vortec heads are good, their small intake port volume will ultimately be the limiting factor on a 383.
 

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For a beginner motor, I'd be happy with that. It'll be easy to tune, make plenty of street power and other than the flat tappet cam; be rock solid dependable.

Negatives?
*Without decking the block, if you upgrade to a modern aftermarket head later on; assuming aluminum, you'll suffer a bit on your quench height (at a minimum you'd be best to use the composition gaskets around .026" thick), but if you aren't building a bareknuckled street brawler, its fine.
* Hyd. flat tappet cams make me nervous. It just is what it is. And if/when they fail? It means a complete teardown and having everything cleaned by your machine shop. That would be a good time to address decking the block/quench.

Only thing I'd change would be a retrofit roller cam as soon as you can afford it.
 

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I have to agree with AutoGear on the cam
mine went out with 5000 miles .
it was broken in on the dyno using driven 30-w breakin oil and continued use of driven 15-50 driven/ joe gibbs oil
 

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I can run a simulation later tonight, but just a educated guess says that's a 410-420 Hp combination, peak around 5800 rpm.

While the Vortec heads are good, their small intake port volume will ultimately be the limiting factor on a 383.
What software do you use for your simulations?
 

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I doubt that a 383 is going to make max power at 5800 with L31 heads. Those little 170cc intake runners would just about be done at 4800 on a 350, much less a 383. I'd guess they'd be done at 4500 with more cubic inches. The motor might rpm higher, but it will be on the downside of the horsepower curve.
 

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What software do you use for your simulations?
Nothing real fancy...I've got DeskTop Dyno 2000, and Performance Trends Engine Analyzer ver. 3.2 (IIRC)

Also have Comp Cams CamQuest, but that's just a toy.

Desktop dyno says 412HP at 5400, 410 HP at 5300 and 5500 rpm,...Torque is 438-440 ft.lbs between 4000 and 4500 rpm, and is making 400 lt.lbs by 2800 rpm.

This is small tube(1-5/8") headers, open header, no exhaust.

Program figured compression ratio at 10.29:1

Techinspector, the heads are better than an old set of 461X Fuelie/"camel hump" heads, and most folks would say those won't die by such a low RPM on a 383 or 350 like you posted....so why would you think that in this case??
Power does fall off quickly after 5700 rpm, so you are correct, they won't still be making power at 5800 rpm like a took a guess at in an earlier post, but they pull right up to 5500 rpm smartly.
On a 350, you'd manage to make power to 6000 rpm....if fact, the same parts spec as above but on a 350 short block does a bit higher 420 HP peak @ 6000 rpm, but takes a big 30 ft.lbs torque loss at the peak torque point(4500 rpm) and an even bigger 35 ft.lb loss at 2800 rpm.
 

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Discussion Starter · #9 ·
For a beginner motor, I'd be happy with that. It'll be easy to tune, make plenty of street power and other than the flat tappet cam; be rock solid dependable.

Negatives?
*Without decking the block, if you upgrade to a modern aftermarket head later on; assuming aluminum, you'll suffer a bit on your quench height (at a minimum you'd be best to use the composition gaskets around .026" thick), but if you aren't building a bareknuckled street brawler, its fine.
* Hyd. flat tappet cams make me nervous. It just is what it is. And if/when they fail? It means a complete teardown and having everything cleaned by your machine shop. That would be a good time to address decking the block/quench.

Only thing I'd change would be a retrofit roller cam as soon as you can afford it.
To be honest what made me think to post this and ask your alls opinion was my cam choice. I originally planned this build to be a roller but just got in a hurry. The block is out of a 94 truck and has the holes for the spider tray. I read that the vortecs dont run as good with a cam over .500 lift so I tried to stick around that. Is that true. With winter coming I'm not going to be installing the motor till spring so I have plenty of time to make changes. What cam would you suggest. I'd like to have a rough lopey idle but not to where it hurts the motors performance. With what I have right now, can I make more hp/tq with a bigger roller.
 

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Discussion Starter · #10 ·
Also before I started the build the plan was to start with AFR 195cc heads. I planned on still doing that but basically your saying I need to have the block 0 decked.
 

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To be honest what made me think to post this and ask your alls opinion was my cam choice. I originally planned this build to be a roller but just got in a hurry. The block is out of a 94 truck and has the holes for the spider tray. I read that the vortecs dont run as good with a cam over .500 lift so I tried to stick around that. Is that true. With winter coming I'm not going to be installing the motor till spring so I have plenty of time to make changes. What cam would you suggest. I'd like to have a rough lopey idle but not to where it hurts the motors performance. With what I have right now, can I make more hp/tq with a bigger roller.
In a flow sense .5 is about as good as these get and for that fact most heads get. So it's not that they do poorly at lifts over .5 but rather there isn't additional flow gain to be had the flow actually curves over a little but doesn't stop.

From a lift stand point the L31 needs modification to the upper guides to permit lifts above .45 to .47 inch.

The big issue is the aftermarket is just full of heads in aluminum or iron that equal but most often exceed the L31 in burn efficiency, port flow, and physical robustness which is sorely lacking in the L31 Vortec. It is a thin wall casting and is quite crack prone as they age, it's hard to find wrecking yard versions that are not cracked.

Another advantage of aftermarket heads is you have a choice in port size and chamber size. In the case of chamber size the large 70 cc something are still the Ricardo style chamber like the L31 popularized at Chevy not the blank open chamber of early emission days. This is useful when getting into stroker engines as it is another tool to use in compression ratio management, piston crown shape selection, whether to deck the block or not, and certainly head gasket selection.

Bogie
 

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Techinspector, the heads are better than an old set of 461X Fuelie/"camel hump" heads, and most folks would say those won't die by such a low RPM on a 383 or 350 like you posted....so why would you think that in this case??
Power does fall off quickly after 5700 rpm, so you are correct, they won't still be making power at 5800 rpm like a took a guess at in an earlier post, but they pull right up to 5500 rpm smartly.
On a 350, you'd manage to make power to 6000 rpm....if fact, the same parts spec as above but on a 350 short block does a bit higher 420 HP peak @ 6000 rpm, but takes a big 30 ft.lbs torque loss at the peak torque point(4500 rpm) and an even bigger 35 ft.lb loss at 2800 rpm.
Thanks Eric, no harm, no foul I hope. :thumbup: I just have the L31 heads nailed in my mind as a nice, limited rpm torquey head for a 350 motor or a nice, limited rpm ultra-torquey head for a 383. I have never looked at it as a real hot rod head any more than I would look at any other production head as a real hot rod head. Anything with a factory casting number was designed basically to serve the purpose of taking the family on an annual vacation or taking Aunt Sadie to the grocery once a week, but might be modified and put into service to add a little performance to an otherwise mundane ride. I have even offered recipes myself for improving the performance of an otherwise stock motor using the L31 heads, but again, with a fairly short cam, for instance 215 max intake duration and 9.5:1 max static compression ratio. If a fellow wants a STRONG HOT ROD MOTOR, then he should begin his build with some strong HOT ROD parts.
 

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Yeah, I'll agree with you on that. The Vortec may be the best Chevy ever put on a production engine, but once you reach their limit at that magic 400 Hp mark it is far smarter to use an aftermarket head if you wish to shoot for higher power numbers than that....they aren't worth the cost of wholesale modifications like bigger valves and heavy porting.
 

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Discussion Starter · #14 ·
You all think I can run 87 octane and be alright. That's what I used to break the cam in and it seemed fine to me. Is there any benefit to using higher octane.
 

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You won't ever notice detonation on a engine run-in, there is no load on the engine.....for detonation to occur requires a load trying to slow the engine's acceleration.

At 10.3:1 comp, you probably better have at least 91 in the tank if you are going to use WOT at all.

It'll probably run on 87 in cool weather, and will if you never put your foot down hard.....so you could get home from a long drive on it just as long as you keep you foot off the floor while you've got the 87 in it.
 

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Discussion Starter · #16 ·
You won't ever notice detonation on a engine run-in, there is no load on the engine.....for detonation to occur requires a load trying to slow the engine's acceleration.

At 10.3:1 comp, you probably better have at least 91 in the tank if you are going to use WOT at all.

It'll probably run on 87 in cool weather, and will if you never put your foot down hard.....so you could get home from a long drive on it just as long as you keep you foot off the floor while you've got the 87 in it.
I used 87 cause that's what I had at the house at the time. I will definatly run this motor at Wot after I break it in. This is strictly a play toy for me so if i need 93 I'll run it. This motor wont be ran everyday so it wont hurt the wallet.
 

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Discussion Starter · #17 ·
If I changed my .015 steel head gasket to the stock fel pro .039 compressed gasket it would change my CR from 10.3 to 9.77. Would I be able to feel the difference in that. How much hp/tq would I loose.
 

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Bad idea...even though you lower the compression ratio, you absolutely murder good quench, with the result being the thicker head gasket, 9.7:1 combination being even more octane sensitive and prone to detonation.

Sounds wrong to your brain cause you have lowered compression, but it has been proven many times that good quench outweighs the compression ratio change.

The only safe ways for you to lower compression are to grind the head chamber to a larger cc volume, or change to a dish piston.....never try to do it with a thick head gasket.
 
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