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Building street 383, Howard's roller cam suggestions

16K views 22 replies 11 participants last post by  SilverChicken 
#1 ·
I'm assembling a good-parts-on-a-somewhat-of-a-budget 383 with a factory roller 4-bolt block. What I've chosen so far is:
SCAT cast lightweight 3.75" crankshaft 1pc rms
SCAT 6" procomp rods
Wiseco forged 4.030" pistons
Profiler 195 heads
QFS 750 Slayer Series VS
Edelbrock RPM AG

The compression ratio currently can be varied from 10.1:1 to 10.4:1 since I don't yet have the heads. The block is a Vortec truck block and will be zero-decked, it has the fuel pump boss and pushrod passage machined. The exhaust side past the heads is 1 3/4" short tube headers, 2.5" y-pipe and 3" mid pipe out the back with 3" cutout after the y. The engine is going into a fairly lightweight 3rd gen Firebird, hence the shorties for ground clearance with a th350 and 3.42 gears in back. I'm currently running a 2k rpm converter but that can be changed.

The entire valvetrain is Howard's, including their retrofit roller tappets they say are good to 6500rpm and work with late model blocks.
The cam is where I start second guessing every decision. I want to keep my peak rpm at 6-6200 so peak power needs to occur between 5500 and 5800. Ive been looking at cams that have a shorter duration to keep some vacuum but with enough lift to use the head's capabilities. Here's what I've whittled my choices to:
180255-10 .510/.530 (.544/.565 w/1.6:1) 231/235 @.050
180325-10 .525/.530 (.560/.565) 225/230
180525-10 .560/.560 227/233
180265-10 .530/.545 233/241
I've leaned mostly toward option #3 but again I don't want to limit power by shifting before I need to in order to stay at a safe rpm for the cast crank.

Thanks for any help any of you can provide.
 
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#2 · (Edited)
I like your choice of #3 as well. Lots of potential in this engine combo. Well thought out. I wouldn't worry about a converter unless you run slicks - it's going to fry street tires at will at any legal speed as long as you get rid of the shorty headers and anemic exhaust plans. Get a set of 1 3/4" long tubes on that car! Let her breathe! Otherwise you'll be defeating a lot of the good stuff you have chosen. I speak from experience and the shorty headers I used to have on my 383 S10. At least you don't need to have fenderwells in order to have decent headers!
 
#3 ·
Unfortunately on third gen f-bodies the underbody of the vehicle makes short or mid length headers almost mandatory for anything street driven. There's very little room and even long tube header's efficiency is greatly compromised by design requirements to fit and users typically lose a lot of ground clearance so I went with the best compromise I could, Dyno Don's 1 3/4" short headers. The weak exhaust is why I have installed the cutout. If the picture uploaded properly you can see how the y pipe shoots all the way off to the passenger side rocker panel before angling back to the driveshaft tunnel and going over the axle.
 

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#6 ·
I'm hoping the automatic and street tire's buy the rear end time until I can afford Hawk's 8.8" converted rear axle.

https://www.summitracing.com/parts/hrs-111815-10/overview/make/chevrolet

I ran this Howard's in both a 355 and a 383. Compression ratio was 10.6:1 using Edelbrocks RPM performer heads 64cc chambers. The cam I still have actually. Saving it back for a rainy day.
What was the power band like in the 383 with that cam? There's a roller block version of it, 181815-10. The duration just seems a bit long to keep peak power down where I need it is my only concern. Otherwise it's just the big brother to the one I'm liking.
 
#8 ·
The 6500 limit listed by Howards is the valve spring limit, not the cam limit. Hopefully someone else will chime in, but I believe the hydraulic roller lifter limit is good to right around 6500. They are too darned heavy to go much past 6500. After that you need a solid lifter with much stiffer spring. And then you get into needing stud girdles, etc. The springs act like a rev limiter.

Regarding the rear, without sticky tires that 7.5 will live a long time - don't get wamboozled into thinking that it will disintegrate the 1st time you get on it hard. Quick story, a local guy is running a 500 whp LS2 in a 4th gen Camaro with drag radials. This is the third season on the rear and it finally gave up. He's made at least 100 1/8 mile passes with it and he's burnt off 3 sets of drag radials with it. if he would've let me rebuild it last year when the pinion began to get sloppy, then it would still be working. Just keep an eye on it for leaks andkeep agood synthetic lube in it - you'll be fine until you can afford the 8.8.

Good luck - Jim
 
#17 ·
Tuned headers are sized for individual cylinders because you can't tune for the firing order and it would be pointless to attempt. The sound waves generated from a single cylinder travels down the pipe at a given speed. Those impulses travel back and forth several times in the amount of time it takes for the exhaust gases to move down the length of the pipe. Tuning requires that the gases exit the primary tube at the same time that the sound wave pulse finds the end of the tube. This combined force multiplies the vacuum signal that is used to evacuate the last remaining exhaust gases and helps initiate the filling of the cylinder.
Getting the primary tubes the same length (within no more than 1/2 inch) is important to this kind of tuning. If you use just the exhaust exit from the primary tube to scavenge you are leaving a lot of power unused. Remember that each cylinder is operating for its own benefit and not to aid any other cylinder. You use the collector size to tune the secondary pulse of the individual cylinder and to help the other cylinders in the peak torque area. This is a simplified explanation of what I found when researching how the exhaust tuning is done. Any interference between cylinders can be modified with the collector design and should not be considered for primary pipe design. Tuned headers are a critical tune - that is the tuning effect is only correct within 1500 to 2000 rpm and most effective at wide open throttle. At part throttle tuning has little effect because all the pressures are lowered which also lowers the returned vacuum signals. Most "off the shelf" headers have primary pipe differences of a foot or more from the longest to the shortest. They are in no way tuned but they do flow freer than older stock exhausts.
The benefit of tuning headers is that you can take an engine with a "peaky" power band and extend it from lower rpm or widen it at the upper rpm band to better suit your needs. For street driving, where you rarely use wide open throttle and you are at various rpm constantly, tuning is pretty much a waste of time.
 
#18 ·
Just so you know; your theory is sound, however slightly dated. More recent theories and testing show that minimizing the number of bends in order to optimize the flow path and diameter of the pipes; is more critical than "all pipes must be within a half inch of each other LOA." DV says that lengths within approx 6" of each other show no statistical difference
See here:
Login • Speed Talk
 
#19 ·
I don't have an account at speed talk so I can't see what you link to. I will admit that some of my references were from the early 1960s but I also have some from the early 2000s. On the exhaust pulse side the number and severity of the bends can make a difference but the sound pulse travels mostly through the center of the tube and bends don't affect it much. Balancing the two fractions so they reach the "open" end of the primary tube at the same time is what is critical. If you disallow the sound waves then the length is less critical but you don't get the complete tuning effect. Also if the pipes are not the same length then you lose all sound pulse benefits from the collector. The collector is tuned to the length of the primary tubes for the sound wave amplification. If a primary tube is substantially shorter or longer then the reflected wave from the collector is going to disrupt the tune.

BTW, the software that I have was written in 2015.
 
#20 ·
On a carburetor engine all eight holes have slightly differing needs in A/F and timing. Treating each cylinder as a separate entity makes more sense to me however all holes are pulling from a common plenum so perhaps that needs accounted for as well. Equal lenght? Naw! just which give each one what it needs and don't worry about the rest.
 
#22 ·
Your cam option of number 3 would work excellent for your build. I got a custom made Mike Jones hydraulic roller cam made that was based on a howards hydraulic roller cam and my previous lunati cam and it specs at 276/280 228/232@50 547/547 lift 107/110 lsa 1.5 ratio and I get 14 inches of vacuum in park and it runs up to about 6000 rpm and does excellent in street driving on my 96 s10 with 3.42 rear gears and a turbo 350 with a 2800 plus rpm stall. I have a similar build but its a 377 dart shp build (4.155 bore x 3.48 stroke) and I have similar compression range as yours and it runs nice on 89 octane.
 
#23 ·
This is an older post from when I was laying out everything with none of it actually machined and assembled. Because of the lack of availability of the 72cc chambers in the Profiler heads at the time I went with AFR’s instead. I also chose a single pattern camshaft toward the tamer side of the cams I listed (278/278 [225/225] .560/.560 lift with 1.6 rockers on 110). The first time it ran it sounded great but the transition slot was WAY too exposed and it’s since tamed down, a lot to where it’s hardly noticeable really. Since my original post my first kid came along and the builder took much longer than anticipated to finish the short block so I’m just now getting all this finalized, engine has only just recently ran and now I’m figuring out how to tune this thing to run the way it should.
 
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