Yes, thats a downside. An aggressive lobe can wear things more and any geometry issues will become quickly evident. Wrecked guides sucks. Happened to me but when i went shaft rockers and midlift geometry, issues went away.

I’ll never want to do another stud rocker again despite the cost of shafts

 

I've gotten pretty good at correcting valve train geometry but there are several thousand miles on these rebuilt heads already. For a couple of years, I held no quarter and beat on that engine until I wrecked it (I think). Examining these heads is part of the decision process regarding the build direction. If the guides are smoked (again), that's it for them. Then I'll be shopping for either A) new cylinder heads or B) an LS3. !

 

Since you already have some real-world experience and data with the 355, the heads, and a HR288 cam, I think you’re better off backing into things.

Based on the Wallace Choke Point calculator, for a given set of heads on a 355 an increase to 383cid will drop the peak RPM approximately 500rpm. Based on my own experience the RPM spread is more like 300rpm if the cam is on the big side for a 355 and around 500rpm if the cam is on the small side for a 383 - when nothing else changes except the cubes.

Earlier in the thread you said something to the effect your 355 with these heads and XR288 pulled like a freight train to 7,000 RPM. If you can make a realistic determination of where it actually peaked, or if you know what your optimal shift-point was (best ET for shift-point based on track data) you can subtract approximately 500 rpm off the shift point (based on my experiences with 355s in this power range) to have a pretty good idea of where the 355 engine was making peak power.

Once you have a pretty good idea of where the 355 and HR288 peaked, you can use the engine simulation software (if it has enough entry parameters) to get a good idea of what figure to use in the simulation for the head’s area based on the 355. Then when you change cubes and cam parameters it should closely represent the actual change in the power curves.

You also said that the vacuum pulled with the HR288 in the 355 was about as low as you would like to go. If your simulation estimates vacuum, then once you have a good estimate of the parameters based on the simulation for the 355, make sure the cam you pick for the 383 generates at least the vacuum made by the 355.

 

BadSS

 

I'll have to go back over my build notes and time slips to see which iteration of the 355 I was running. I raced in two different parts of the country with a DA difference of about 4500'. I tend to convert all to sea level for comparison sake but that engine ran with a couple of cams and two versions of these heads.
What I've learned outside of the track was what I found acceptable for overlap, IVC and the resulting idle vacuum and fuel economy (yeah, I care about the MPG, or did anyway). Much like your suggestion I'm basing some of this build on what worked in that regard. If I was able to tune the 355 with 71 degrees of overlap, I would expect to be able to work with a 383 that had somewhat more. One cam spec that was churned out had 74 degrees. I'm leaning that way. Predicted idle vacuum is said to better than the 355/288 so there's something to that. Having flow numbers helps in simulation side of things. Knowing the pinch, rather than calculating would be helpful too.
That said, one issue with any comparison is that the 355 shortblock was more or less worn out. Cranking compression was lower than before and that's accounting for the change in altitude. Leak down results weren't favourable either. Surprisingly it still ran well, cold start (like 20F) and idled with no choke in less than a minute. It did have a high RPM misfire that hasn't yet been diagnosed. I had a couple of high RPM lean outs that may have inflicted some damage. The occasional 7000 RPM adventure may have wounded the valve train as well.
So, I can agree that "backing into it" is part of the approach. The big deal for me is that the larger CID approach will allow for less maximum RPM without a loss in power. And I've decided that's a good thing. Just like the discussion about which lobe profile to go with, I think endurance rather than maximum effort might be better.

 

My 383 was 78 deg adv overlap. Idle was fine at 950-1000
82.5 i think on my 400 turbo car. Idle was good, 11-12” vacuum at 1000

 

That's encouraging. The added cubes can obviously eat up some of that.
286/286, 106/102. 74 degrees.

 

Granted it was 11:1 and efi but the brakes still worked even tho i think i had a bad booster.

 

The 11:1 goes a long way. At slightly more than 10:1 with a 102 ICL, I managed just over 10". But as mentioned, the engine was largely worn out then. Should have closer to 12" with nearly 30 degrees of idle advance.

 

Did a little digging. Same author as the TM program but additional details.

284/288 of seat duration and 240/244 @ 0.050 on a 106 degree LCA. Lift on this cam was .541 on the intake and .503 for the exhaust.

Now that's for a flat tappet grind. Quick to 50 thou but a little low on the lift. That's the dual pattern suggestion churned out by the program and an actual tested engine build. I'll have to dig up the results.

EDIT: Peaks were 484 lb-ft and 459 hp. 5600 peak.
TM predicts 501 TQ and 488 HP at 5600 with my heads and compression. (That seems optimistic...)

 

500 lb ft is alot for a sbc. I know chads 379 deal i think made 500 but had very good induction

 

I agree. The dyno results I think are probably not something I could achieve either.
But the cam spec is coming into focus. Not too far off the earliest suggestions either but the tight LSA is certainly appealing.

 

Going through this thread and I found that the cam listed above was #4 on the list in post #1.
Full circle....It's the one that stands out I guess.

 

flat tappet is one thing. Hyd roller i dont see any lobes being that fast esp on a standard .700-.750 roller wheel .842 lifter

comp has 288/236 stuff and 289/237 stuff. .390”+ lobes so thats very aggressive imo.

 

.390! Yikes! That's .625" lift with the1.6 rockers.
The XR288HR in the 355 (288/294, 236/242) has a .346" lobe. Definitely friendlier. Probably the lobe profile I'll go with. Wouldn't mind stretching that out to .575 though. These heads are essentially flat (+/- 5 CFM) from .400 - .600.
I need to keep the rockers I have. They're 1.6 but more importantly have a .050" backset on the trunnion to work with the 1/10" taller valves. Not cheap either.

 

Skinny, did you ever get anywhere with this?

 

No sir. Other than nosing around and asking questions there hasn't been the budget to move forward. It's been 15 months since wages were dialed back and other things have taken priority over my hot rodding hobby.
I'm hopeful that there may be some action this fall and over the winter.
​​​​​​Thanks COVID. Not to mention the crazy industry I'm part of that took a real hit.
Thanks for asking though. Stay tuned for a build thread coming this way...

 

I feel your pain... spun a rod bearing in my ZZ4 back in January. Hoping to have the budget to do a 383 this winter. But for now, car is down and low priority on the family budget....

 

Lack of physical progress notwithstanding, I've still been working through the cam spec.
I've kind of zeroed in on using Vizard's Torque Master program to dial it in. While everybody has an opinion and results to back them up (or so it seems), Vizard's approach has always peaked my interest and I figure I'll give it a go.
I've run the spec using a couple of different criteria.

Port CFM. While heads have been flowed at ~255 CFM @ .550" lift, I've dialed that back to 250. I can't say exactly how that will play out once there's an intake and carb in place.

Compression ratio, ranging from 9.5:1 to 10.5:1. From that I can see what kind of port CFM I would need and the resulting maximum HP RPM.

Max HP RPM. I put a limit of 5500 just to see where that goes.

I've also built profiles for single and dual patterns although I'm trending towards a single pattern cam. My plan is to run open headers for racing and maximizing the overlap and scavenging and whatever happens once a full exhaust is on for the street will be what it is.

The following three shots are based on a 250 CFM port with varying compression ratios. All single pattern.

Any of the fields in white are my data entry points. Anything in yellow is calculated.
The induction length is a different calculation altogether.




9.5:1 with a 250 CFM port.





9.8:1 with a 250 CFM port.





10.5:1 with a 250 CFM port.

 

Interesting. You bump up the compression a little bit and the program spits out a smaller cam.
All three have Target Intake Port cc's at 178, which should be almost be spot on with your heads.
It looks like Induction isn't even part of the camshaft calculation. But it does show that it is not a restriction.
Am I reading that correctly?

 

I spoken with Vizard about the lower compression and increased duration deal. His comment was that if you can't squeeze it enough, you better be sure the cylinder is full. More duration. More overlap.
That said, that TM program is built around a 10.5:1 engine spec with a 2.02" intake valve. I find that an engine spec outside of those values tends to produce results that seem counterintuitive. But who am I to argue? I can build close to the program ideal so the outliers don't enter into it.
As for the induction length, that part of the program tells where peak TQ and HP happen with the default 11.5". If I adjust that length (it's a data entry point) I can bring it inline to where the cam makes it's peaks. If I extend the length I can pull the effect the intake has down to more compliment the cam.
At one time I knew where 11.5" fell into the intake choices. Certainly a single plain. I've an RPM Air Gap to go with now but little data to zero in on it's length.

 

Okay, now this is making sense. But lower compression and increased duration (lower DCR) makes a lazy engine with a soggy bottom end.
So then, going in the opposite direction, more compression with a smaller cam (higher DCR) and you can run into detonation problems and having to use high octane fuel.
Did you ever see this article? http://purplesagetradingpost.com/sum...%20engine.html
I am just going to put up some links to NOT take your thread off track:
https://www.thirdgen.org/forums/tech...ould-have.html
https://www.thirdgen.org/forums/tech...ked-350cc.html

 

Look at the peak HP RPM for the low compression spec. It looks to me that it's a forgone conclusion that the bottom end is compromised. Peak HP RPM is 500 revs higher.
So, build accordingly with the rest of your spec I guess. More gear. More converter. Or whatever to suit that rev range.

For me, I can target an ideal CR. There's more predicted HP and TQ (like 50 ft lbs) with less RPM (500) using the optimized spec compression ratio. That's with a given intake port and intake valve. For me, my latest upgrades weren't ideal for the 355 and 288/294/110 cam. Not enough gear or converter. The 383 will dial that in. Or that's my hope. I crossed the stripe at less than 5500 with that 355 spec. About 1000 less than ideal. A 383 and the same supporting parts will bring me closer to finishing at peak HP if the TM program predicted HP peak is accurate.
I'm in.

I haven't read the links but I'll be sure to.

 

I see that as saying don't use that CR with a CFM limited port. You need the breathing and the cam will be spec'd larger. Less DCR.

 

This is starting to feel like this:

 

Exactly lol

 

Maybe I'll keep the rest to myself and spare us all the entertainment! Might be ANOTHER year before it all shakes out. If ever....

 

It has been a minute since I have posted in this thread. Due to emissions reasons here in Texas i went back to a stock looking intake manifold on my 383 to help hide it. I went back to the smaller Comp Magnum high lift based cam. 383 still runs strong and idles very smoothly with good vacuum. The Rhoads lifters are not all that loud although the microphone on my phone loves to amplify the sound of the valvetrain.

This was running with a Quadrajet that had not been touched in 10+ years and old parts store plug wires, cap and rotor on an untouched distributor from about a 1979 G20 van.

This was the first start of the 383 with an 850cfm Q-Jet I had just built, with the high idle cam set it fired up as soon as the dry fuel bowl got fuel into it. Ended up opening the idle mixture screws from about 4 turns to 5.5 and it idled noticeably smoother. I had done a complete ignition tune up and modified the advance curve as well. Plugs gapped at 0.060" on this test.

This is one of several fuel consumption tests I ran. Freshly built and jetted up Edelbrock 1406. Quadrajet with the APT adjusted correctly blew the Edelbrock out of the water. Also discovered that the knock off Rumble 40 series flowmaster clones actually cost 1 in/hg vacuum at 2,000 rpm while increasing the engine run time 30 seconds on the same quart of fuel.

 

While I had the timing cover and thus oil pan off recently, I decided to take a look at the general condition of some of the engine since it has some run time on it now. I have redone the wiring harness in the van, plumbed the trans and power steering lines with AN. Added a massive power steering cooler. Detailed it inside and out. In the process of swapping out the head unit for an Android 9.0 based 10.1" touch screen with all the modern touches including OBD2 link gauges. Repaired the front door panels and swapped in Rockford Fostgate speakers all the way around. I have swapped the steering gear box and rebuilt the a/c system with a new modern parallel flow condenser and a Sanden SD7H15 meant for the van. I swapped on new larger 2015ish Express van dual glass power mirrors. I swapped it to a 2005 PCM as well running a Mexican L31 GMT800 based tune. I have swapped all the exterior lighting to LEDs and rewired the headlights with an added relay off the fuse box to give me all 4 headlights when you select the high beams. I also added an automatic day night mirror with compass and homelink. It is almost road trip ready.

 

One other thing I plan to source and install based off what an OBS owner did. Cadillac steering wheel and spiral cable. My new head unit supports steering wheel controls. The blower and a/c temp switches will probably be re-purposed for wireless phone and menu/audio source changes. Cadillac wheel fits right in with the interior color of the van and the wood as well as the wreaths embroidered into the conversion seats. I just wish someone made an Escalade looking grille for the 96-02 vans. I would do it because I always loved the OBS Escalade look. There are also so many people rebuilding these vans into mobile apartments that LMc has even come out with a van catalog. I will likely also swap to a turn signal stalk without cruise and wire up the cruise switches in the wheel to function. I have gotten so spoiled to the steering wheel controls on my Nissans and Infiniti cars and trucks that I just have to have them. Caddy wheel looks so much nicer than the bland factory truck wheel.

 

My eyes can't help but to notice things out of place.
Is the big end of this rod still on it's crank journal?
If so, then why is the pin end of this rod so far over to the right on this piston?

 

I think it was loose from the crank in that picture. They do have some side to side play even when it is fully buttoned up. Crank has a wide filet radius and required narrow rod bearings. Makes the full floating rods have a substantial amount of rod side clearence.

 

I just wanted to point it out in case you didn't see it.
It would be a shame to lose what looks to be such a nice engine.