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Old 05-13-2017, 01:13 PM
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Dyno #'s for alum head 383?

So this is my first real engine build-Not just fixing or modifying. I needed a new block, and I really wanted the torque of a 383. This is the build-- 0010 sbc, 0 deck , scat 9000 3.75 crank, arp rod bolts, lunati 268-276 dual pattern voodoo +-.5 lift, 1.5 stainless roller rockers, 1 5/8 mid length headers, Air gap summit dual plane(rpm air gap copy) 750 summit mechanical,64cc NKB 200 heads (basically came unshrouded for my 4.030 bore) 250 cfm @ .5 lift, Mallory unilite dist. Speed pro flat tops-5cc .042 Head gasket. Calculated compression of 11.07x1, dynamic of 9.4 ish depending on the calculator. 5000ft elevation. What I want to know is what kind of power I might expect from this setup and if anyone has a similar engine build to chime in about?--- Going in a 2100 lb vette kart

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Old 05-13-2017, 04:12 PM
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I may be off, but I guess 480-500 at the flywheel
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Old 05-13-2017, 04:19 PM
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Originally Posted by fat tire View Post
I may be off, but I guess 480-500 at the flywheel
Wooah, I was hoping to make 450. Might be I wasn't descriptive enough about the cam. It has a duration of 227 233 @ .050 and a lobe separation of 110*
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Old 05-13-2017, 07:42 PM
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Quote:
Originally Posted by fat tire View Post
I may be off, but I guess 480-500 at the flywheel
Perhaps a little optimistic in my opinion. NKB's are OK, but they don't flow like the Profilers and Airflow Research heads that WILL produce 500 hp on a 383. I would guess maybe 425 at sea level, less 100 hp or so off that figure at your altitude. That cam should work pretty well with your combination.

Last edited by techinspector1; 05-13-2017 at 07:48 PM.
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Old 05-15-2017, 08:39 AM
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I like the Unilite distributor; but they are susceptible to electrical spikes. There is a "filter" you can wire in line to protect it. You absolutely should. The coil has to be correct for the Unilite to last as well.

Why Mallory sold these WITHOUT the "power-filter" never made sense to me. They were like $30 retail. Which means, it cost them $10 or less. Include it in the kit and bump the price $15. The Unilite would have a much better reputation than it does today. The guy I knew who used these a lot, always had a modern alternator (solid state regulator) as it was supposed to offer a cleaner power supply.

If your cars wiring is a mess, square that away before you get too far.

You'll be in this an honest 400-430HP with a fairly flat torque curve. I don't think you'll hit the magic 450, without some dyno trickery. Remember on an engine dyno, and in your car....2 vastly different scenarios.
An honest 430hp 383 built at home is an awesome achievement!
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Old 05-15-2017, 09:25 AM
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Quote:
Originally Posted by B Curtis View Post
So this is my first real engine build-Not just fixing or modifying. I needed a new block, and I really wanted the torque of a 383. This is the build-- 0010 sbc, 0 deck , scat 9000 3.75 crank, arp rod bolts, lunati 268-276 dual pattern voodoo +-.5 lift, 1.5 stainless roller rockers, 1 5/8 mid length headers, Air gap summit dual plane(rpm air gap copy) 750 summit mechanical,64cc NKB 200 heads (basically came unshrouded for my 4.030 bore) 250 cfm @ .5 lift, Mallory unilite dist. Speed pro flat tops-5cc .042 Head gasket. Calculated compression of 11.07x1, dynamic of 9.4 ish depending on the calculator. 5000ft elevation. What I want to know is what kind of power I might expect from this setup and if anyone has a similar engine build to chime in about?--- Going in a 2100 lb vette kart

The NKB head flows extremely well at lifts above .5 but is a little weak in the off seat to .4 range. Especially for the intake it runs much better with a 1.6 rocker to get the valve off the seat faster and get the total lift up above .5 inch. This is a head that works well with .6 to .7 inch lifts on the intake side in particular. Back cut valves again especially the intake helps this heads from off seat to .4 inch flows a lot; another thing is to use one piece forged valves and those with a necked stem compared to cheap two piece valves with the fat weld glob at the joint with the head. This head also works very well with the characteristics of 6 or 6.125 inch rod which gives a little more time over TDC which allows the valve to get further open before the intake stroke actually begins. In this vein a large amount of overlap is useful.


These are refinements that let this head produce its best power without going crazy carving out the ports. Assuming you've at least got modern forged one piece valves, the set up you have should deliver a solid 450-460 horses, with refinements you could look at 480 corrected for sea level with dyno headers and 3 inch duals.


Bogie
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Old 05-15-2017, 09:38 AM
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Bogie;
Are you including the 1.6 roller rocker in your 450+hp?
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Old 05-15-2017, 01:14 PM
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Quote:
Originally Posted by AutoGear View Post
Bogie;
Are you including the 1.6 roller rocker in your 450+hp?

Yes. These are almost a absolute on these heads because you just got to get the valve really open fast and high if you need the best these heads can deliver. It's not that they are terrible breathers under .4 but for the port size there are better breathing heads in this zone but they certainly more expensive. The 200+ port even more-so than the 190 needs this. These two breathe almost identically to about .4. While both get better and better in the .5 to .7 range this is really where the 200+ size port comes on. Put these heads on an engine with older design long duration/low lift cams they will be a moderate disappointment. Strap them to a Comp XE or Voodoo with short ramps and fairly quick lobes with 1.6 rockers they do a lot better. Put them against fast high lift roller cam with suitable aftermarket valve train parts that they come alive.


I don't think the way Sizemore ported those things on Headbytes is the way to go unless your racing as it doesn't change that zero to .4 flow much but it sure improves the flow above .5 inch. So if you're running a really big lift cam there's something up there to get but for a street engine that just isn't a really workable combination.


Bogie
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Old 05-15-2017, 02:25 PM
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On your blue print you list the summit dual plane intake , which functions best at mid range and lowr RPMs, a cam designed for more top end performance , a 383 short block for more torque at lower RPM, and your at 5000 ft.above sea level and then you have high flowing heads with very little velosity at lower RPMs and Higher compresson!!

All in my opinion not a well thought out blue print! No reflection on you because you are asking for advice and probably got your choices of parts from other advisers! Going from a sea level build to thin air (less oxygen ) elevation is tricky.

Unless you are running an engine in the upper regions of it's rpm range it will actually lose power in the lower 2/3 of its power curve (and potentially even the upper) by going with bigger ports at higher altitude.

The higher the air velocity the more air gets into the chamber during an intake cycle. As air is distributed to the individual intake runners from the plenum it's forced into a smaller area making it go faster. When you make any of the runners or ports larger you slow the air velocity down. In most cases the head port diameter is not the limiting factor in air flow and this is why when you see flow bench numbers for big port heads it's important to find out whether the intake manifold to be used was installed when flow benching was done because usually the big port heads can flow much more than the intake can !! With your dual plane intake you can only supply half as much CFM as you can with an open plenum type intake because you are actually dividing the carb in half ,with 2 venturys feeding 4 cylinders and the other 2 venturys feeding the other 4 cylinders, rather an open plenum intake with all 4 veturys feeding each of the 8 cylinder it every intake stroke !!!

In my opinion my HP estimation is very low ! around 350 HP even at sea level my estimate isn't much better!

But then again its only my opinion!! Figuring HP from flow numbers and cam specs isn't very precise because you need to know flow numbers with readings with the particular intake your going to be running and as altitude increases so do the particulars of flow and velocity !

It is the same for scavanging, Big exhaust big flow for peak RPM and smaller for higher velosity and better scavenging during the entire power curve!

Jester

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Old 05-15-2017, 10:53 PM
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change cam, install a turbo with controllable waste gate and make 500 plus hp from sea level to 12,000',convert carb to blow though,,,
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Old 05-16-2017, 08:49 PM
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Quote:
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change cam, install a turbo with controllable waste gate and make 500 plus hp from sea level to 12,000',convert carb to blow though,,,
I hate to say it, Vinnie read my mind. The solution to thin air is making the air more dense. PV=nRT all day long!! Meaning the solution to altitude is boost.

I'll bet boost isn't in your plan, but it's the altitude solution IMO.

I have no real world guess at the power you're going to make, but I think Bogie, Tech and Jester have identified the issues you ought to work on. Good luck - Jim.
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