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Cam for towing truck, 383 SBC with a turbo

22K views 43 replies 7 participants last post by  96lt4c4 
#1 ·
Hey guys have not been on this forum for a while but it seems like when I do a google search it always brings me back here so I figured I would see what you guys think about my new build. Long story short I put a turbo on my old tired 383 in my Blazer and it lasted a couple months before I melted a piston down. Now I am building a whole new motor.

https://www.youtube.com/watch?v=1ZLIowlMBEw





The old setup (2 bolt non roller block) was not optimal for towing, the heads were 170 cc World Product SR Torquers, I could feel the truck hit a wall at 4000 RPM before the Turbo. Even with a single plane intake. Heads were just too small for a 383. The cam was a Lunati Voodo 60101 213/219 112/108, 450 ish lift. Flat tappet.

I am pretty sure I had too much timing and not enough fuel, I was running around 12-12.5 AFR should have been around 11-11.5 AFR, I have backed the timing down in the tune to. I am also adding a MAT sensor so that should help as well.

I am going back 383, forged Scat 4340 crank, 4 bolt roller block with main studs and line bore, forged Scat I beams with ARP bolts, SRP forged pistons 18cc dish, Small port Bowtie Vortecs 185 cc intake runners. As far as cam I am having a hard time making up my mind. I am looking at the GM HT 383 cam and the ZZ4 cam. The HT 383 builds torque almost immediately according to Desktop Dyno, if I run this cam it will be with 1.6 rockers, which would make it about 199/209 449/481 LSA 109. I have read a few posts about guys being disappointed with the ZZ4 cam in their 350 trucks. Which I could easily see why. None of GM's cams have any advance ground into them. The HT 383 cam does not need any advance but the ZZ4 in a 350 or 383 truck advanced 4 degrees helps build low end torque. I think if I had a 350 with a ZZ4 cam or a crate ZZ4 I would advance the cam 4 degrees.

I like the GM cams because they are easy on the valve train. Here are a couple screen shots from Desktop Dyno, with each cam. The ZZ4 is advanced 4 degrees. This is also with 10 pounds of boost, over the entire graph so the low speed 2000-2500 RPM number are high. The truck does see 10 pounds till around 3000 RPM.

I have found Desktop Dyno to be fairly accurate, I used the flow numbers for the Vortec head and entered the HT383 cam specs, I was able to duplicate GM's torque and HP ratings on the HT383 crate engine +/- 1 or 2 HP/TQ.

HT 383 1.6 Rockers



ZZ4 Advanced 4 degrees

 
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#2 ·
The HT383 & ZZ4 cam are both ground 3 to 4* advanced.I'm not up to snuff on boost,so'I can say how either cam will perform in that situation.The HT383 cam in a 383,IMO'would make the better towing cam.It's torque comes on below 2000 rpm & is flat out to about 4800 or so @ over 400 ft/lb.Advancing it any farther will likely cause excessive cylinder psi.The ZZ4 cam does perform better advanced.It can be a little soft on the bottom if not.You may lose some topend power,but,for towing,I wouldn't think,that would be that big of a deal.I would want the most torque from the lowest rpm for towing.
 
#4 ·
Using 1.6's with the HT383 cam does help with quicker valve action,higher lift for better breathing'but'it does not increase duration of the cam.IDK what kind of gearing you may be running,but,for towing,I would want smooth flat powerband.Not a peaky or narrow higher RPM band that the bigger cams would offer.Towing is not a high RPM situation for me.Either of those cams will make good torque/power out to any rpm I would deem safe for towing & still set you back in the seat when not.
 
#5 ·
Before I went out and spent $1200 on a set of cast iron vortec heads I'd be looking into a set of air flow research aluminum heads. You'll have a lot nicer cylinder head for just a few hundred more. Then you could choose a larger combustion chamber like a 75cc and get into a flat top piston.

I don't see a need for all forged internals on this build. The scat 9000 crank should be sufficient. I'd still run a 4340 connecting rod. The power output will be the same either way you'll just be able to put the saved money from the rotating assembly into the top end of the engine where the power is made.
 
#6 · (Edited)
If the GM cams have advance ground into them, then they do not list it anywhere that I can find. In the Chevrolet Performance catalog they only list the LSA. If thats the case advancing the HT383 cam 4 degrees kills HP and torque in Desktop Dyno. What ever cam I use I will degree it and find out. I am pretty sure GM just grinds what ever LSA for what they want the cam to do, no advance. I know for sure that my stock LT4 camshaft did not have any advance ground into it, I checked it.

As far as the heads, I think the large port vortec may be too big for what I am wanting to do with the engine. The large ports would work better on a 383 that was being revved up to 6000-6500 RPM and had over .500 lift. For a truck that revs to 4500-5000 RPM it does not make sense to have a 225 cc intake runner. The larger runner may actually hurt low speed torque. Also the heads can be bought for $1000.00 through SDPC.

I already have the Scat 4340 crank, my old crank was 2 piece rear main, I am going to 1 piece. I already have the pistons as well which work just fine with the 66 cc Vortec chambers.

And yes 1.6 rockers do add about 2-3 degrees of duration to any given camshaft that you put them on. The 1.6 rocker will bring the valve off the seat earlier and close it later than a 1.5 rocker, more duration. This has been tested and proven.
 
#7 ·
It has the "effect" of raising duration,but,it does not actually increase the duration of the camshaft.That HT383 cam if installed straightup will put you on an approx 106 centerline,if memory serves me correctly.GM doesn't provide a lot of info on their cams.Crussell,IIRC,degreed his HT383 cam in & I think he came up with a similar #.He'll correct me if I'm wrong.
 
#10 ·
Thats not really the case anymore with more efficient turbos. If you have a lot of exhaust back-pressure then yes that type of cam is great. The 2 cams that I have mentioned do not have enough overlap to worry about.

The youtube link up top shows the setup. I will post it again.

https://www.youtube.com/watch?v=1ZLIowlMBEw

I am thinking about just going with the HT383. With better flowing heads I think it will make more power everywhere than what I had before, and it ran great before it blew up..:D

If the HT 383 cam is advanced I may have to retard it back and run it straight up.
 
#19 ·
So I changed my mind on the Promaax heads, got to thinking about my compression with a turbo and the 64cc heads, 9.5:1, plus they were iron, so I sent them back. They would have went back anyway because they were packaged poorly and the decks had dings all in them. Not to mention the rocker studs were sticking out the side of the box. Summit covered the shipping back, so I went with the Dart 180 cc SHP heads and got them bare, 72 cc combustion chambers. Now my compression will be around 8.9:1, more boost friendly, plus the aluminum heads help dissipate heat better.

I am using the 2.02/1.6 Manley SS valves and studs that came out of my other heads. So far I really like what I see with these heads, they are a major upgrade over what I had.

I also sent back with the HT 383 cam and now I am going the this cam, with the 1.6 rockers.

08-408-8 - Xtreme Energyâ„¢







Springs are LT4 Corvette, I do not need guide plates because i am using roller tip self align rockers.
 
#22 · (Edited)
From the looks of your original picture I cannot tell if the piston is melted (heat) or has detonation damage. Do you know? How were the exhaust valve guides, seat and faces? Melted? I ask because knowing which happenned would affect my build plans. IMHO, building a 383 with a turbo for a towing application is atypical. Seems like you would want a quick spooling (smallish) turbo to compliment a low rpm/high torque engine that is going to spend most of it's life below 4500 rpm's. Back to how the previous build failed, if it is heat, then perhaps you were running out of turbo capacity at a low rpm and on extended hard pulls you were developing ALOT/TOO MUCH heat in the turbo, which then was transferred to the manifolds, then the exaust valves&seats and then the piston. Again, IMO, pulling 8-15000 lbs up a two mile hill at too high of an rpm is like running a dyno pull 60 consecutive times without giving the system a chance to cool down. A pyrometer would answer that question or determine if what I'm describing was the issue and when the issue is develping in the future.

If detonation did in the last motor, then disregard most of the gibberish above. Highly recommend a knock sensor such as :

Engine knock detection and indication for all vehicles

This won't retard the timing, but can depending what you're using to maintain your timing. If using an MSD with timing control, then it can knock the timing back with an input from the knock sensor. Or running an aftermarket ECM such as a Mega or Microsquirt. But at the very least you can have a light in the cab that will let you know when detonation is occurring prior to trashing another build.

Sounds like you already have an AFR gauge, which for your application is a must.

Keep in mind that with a turbo build, the amount of forgiveness in regards to a tuning error will show up just a tad bit quicker :)

Afterthought, I wouldn't consider your build without a set of aluminum heads and forged pistons - much more forgiving to heat and tuning issues such as too much timing or not enough fuel.
 
#23 ·
the valves and seats in the heads look fine, not melted at all. I am actually cleaning the valves up to use in the new heads. I will post pictures of them.

I am pretty sure it was lean, I was running in the 12-12.5 AFR range, most guys run 11-11.5 AFR. The truck was also running 10 pounds of boost. I am going to start off small and work my way up this time. I am going to put a 3 pound spring in the waste gate and more than likely install a boost controller. I am also going to monitor EGT to make sure its not getting too hot. I am running the stock PCM on the truck with the knock sensor disabled, was fine like this for years NA, but its going back on now that its turboed. Also installing a MAT sensor to help with timing when it gets hot out, the TBI trucks did not have a MAT, but the CPI 4.3's did in 94-95, same PCM. So I am turning on the MAT in the tune. I am also thinking about ditching the MPFI single plane and going back to the TBI. 2 reasons, single plane is not good for low end, and blowing through the TBI would actually help cool the charge down like blowing through a carb.


My turbo is small, and does spool quick, Borg Warner S366. It is starting to spool at 2000 RPM. But is may also be causing a lot of back pressure.

As far as the heads, the 180 cc SHP head flows better at low lift than the 200 cc. The 200 cc only beats the 180 at .500-.600 lift area. My cam will have right at .500 with 1.6 rockers. It does not make since to put the 200 cc heads on this motor. It will rev to 5000 RPM max.

As far as the cam, I am going for a flat torque curve, 220 ish duration on a 112 will be a dog down low. The cam I listed still has negative overlap and will have great low end.

My goal here is to not need the turbo all the time, to make the truck run as good as possible off boost, and only use it when I need it. The only thing I am afraid of is my turbo may be too small, I will deal with that after its back together.

This is a good read on a small cam with a tight LSA in a turbo Buick motor.

Turbo Camshaft Guide - How to Select the Right Cam for Your Turbocharged Engine - Car Craft Magazine
 
#24 ·
I run a very similar cam from Comp in my Mopar small block. It's definitely brutally strong on the low end.

As far as compression, with aluminum heads, I'd try to get it up a little higher (low to mid 9s). You'll still be plenty safe under boost and the higher compression will make it a bit stronger off-boost and might help cruising mpg a little too.
 
#30 ·
I am updating this thread and looking for some pointers. I got my motor up and running, and I was not happy at all. Felt like it was down on power and did not like boost at all. I have checked everything and can not find anything wrong.

Things I have checked.
  • Verified cam timing
  • Verified top dead center and TDC on balancer
  • Compresion test 175-180 pounds on all cylinders
  • valve ajustment

I did have a few head studs leaking water, so I went on and pulled the motor back out. I think the head studs were leaking because I installed the studs one day then put the heads on the next day. When I torqued the heads down I think some of the studs spun and broke the silicon loose.

I already had it so far down, instead of leaning over it, I went on and pulled it. The intake gaskets were sealed good. I pulled the heads and do not see anything out of the ordinary. I did decide to CC my heads while I had them off. Supposed to be 180 cc intake runner and 72 cc chambers. I came up with 195 cc intake runner and 65 cc combustion chambers. These are the DART SHP heads.

I am probably going to go ahead and change the cam to something more along the lines of what was in the old motor. I ordered a Lunati cam 215/224 112/108.

The only thing that scares me, is that somewhere online I read a bad review on these heads. A guy said his motor always felt low on power with the SHP heads. He changed them and was way happier. I figured maybe his valves weren't sealing. Mine have a fresh valve job, the chambers I filled with water did not leak.

As of right now the old motor was way stronger than this one, until it went boom...:D
 
#31 ·
Geesh, would've been nice to get it on a dyno before you disassembled and played with the tune some. Also being able to put a check on your AFR gauge/sensor as compared to the dyno's sensor would've been nice. you're describing a too rich condition. How'd the plugs look?
 
#35 ·
. About a week after reading up on those heads on YellowBullet, I tried to get back into the same pages, but for some reason, I just couldn't seem to find where I had been... I didn't bookmark it, because I thought a search would always just put me right back in there... weird how that happens, sometimes...
 
#36 ·
Apparently the first post I read dogged them out pretty hard. The latest post I found they tested them on a mild 383 and they made pretty good power right out of the box. Then they cleaned the chambers up and did some port work, which made them even better. I have already ground the grove out from around the seat, which should help a lot.
 
#38 ·
ATK HP ENGINES / Eric Weingartner Dart SHP 200CC Test - Page 4 - Yellow Bullet Forums
Here is the last thread I read on them, that showed them making good power. I blended that grove around the valves back into the chamber like the pictures in this thread. But, I did not do any other porting on them. They are still a way better head than the World SR Torquer heads on the other motor, those were more like an old 882 head.

I got the truck back up and running this weekend, so far so good. It runs way better. I am embarrassed to say that I did find some issues in my tune that may have been causing the problem all along..:D. My MAT sensor may have been pulling to much timing, I have not run it much, but it does seem to like boost now. I will report back after doing some more tuning.
 
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