I'm already running a 2600 stall 9.5" converter, so it should tolerate things pretty well, now I just have to keep within the range of my valve springs, because I don't want to have to rebuild my heads... I do wonder if I'm not planning to exceed 6k rpm though if I could possibly get away with the 450hp: .510”/.521” Lift, 231°/236° Duration @ .050”, 111 LSA, standard offering cam from Smeding even though my valve springs claim 235 max duration. My normal personality would be to maintain a buffer there and not push the limits though... I'm really not craving every last hp, but I just feel like the next step down cam, 420hp: .495”/.502” Lift, 220°/224° Duration @ .050”, 112 LSA, is a little less than I was planning for...

 

Keep in mind that to achieve 450 HP you'll probably see peak HP RPM at or at least approaching 6k.

Can you make an inquiry at Smeding to see if they would reveal the advertised duration of the cams in question? Without that, it's all conjecture.
And FWIW, don't get hung up on the HP number. It's been said a million times, that if you're not building to a specific RPM range as I am (4k-6k), then a broad torque curve as would be the result of a wider LSA (typically) would be what you're after. Case in point would the two specs from Jones that were "street performance" vs "drag racing". As my converter is (arguably) 4k, I don't have much interest in what happens below that. Any street driving would see little impact on drivability. I've lived it and can comment from experience.

 

Makes sense.

I'm expecting this full crate engine they refer to as a 450 hp extreme, same as the cam offering on the short block I'm getting, uses the same cam. I find it interesting though, that they use 180cc heads... of course the intake makes an effect too, but it could be vaguely similar.

Max hp on that chart is at 5500, with larger 195 cc cnc heads I would think that may shift the peak up a little right? Also just noticed they use 1.5 ratio rockers, so I'll be getting some more lift with my 1.6 ratio rockers!

450hp option but with 180 heads and 1.5 ratio rockers

https://smedingperformance.com/colle...11963651555364



And here is the 420hp option, but again with 180 heads and 1.5 ratio rockers.

https://smedingperformance.com/collections/383-small-block-chevys/products/383-hot-rod-420hp?variant=11963674099748

 

With that Jones cam spec (for the 383 that I didn't build) used a ~180cc port. It too through various sims showed peak at 5500. Port volume notwithstanding, there are other critical dimensions that will affect how the cylinder is filled. Minimum cross sectional area being a key player here. Your heads are larger in that regard and you could easily support power past 6000. Just not with either of those cams spec'd (Jones or Smeding). Mine on the other hand was head limited. That said, they fit very well with 357 cubic inches.
I've no doubt that either cam for your 383 will pull well past the peak HP RPM. But peak will be where it is at below 6k.

 

I just really want a pretty broad torque curve, not a high revving hp monster. I was leaning towards the 180 cnc afr heads untill I was convinced the difference would be negligible. Given this goal though, I think the slightly lower duration and slightly higher lsa 111 or 112, should help with broadening that torque curve, and the only cost is loss in power over 6k rpm where I don't currently plan to go...

Correct me if any of that understanding is wrong.

 

I've been watching a LOT of Engine Masters lately, so I had to see how the two options overlayed. Sorry for my low-fi word overlay, but it gets the idea across. Again though, both with 180cc heads and 1.5 ratio rockers. Mine are 195 and 1.6.

The crossover is at 2800, and with my stall at 2600 there is basically no benefit from the tilting of the curve for the smaller cam. So, I basically just need to see if he can bring down the duration a tiny bit to play nice with the valve springs in my heads, then go with it...

 

That's about it. Naturally, less duration will reduce output some. The wider LSA will reduce overlap (and any potential tuning issues real or otherwise).
I think though that it be a difficult call to tell the difference in power from a seat of the pants point of view. The drag strip might tell a different story.

That AFR note regarding duration is an odd one. It's not the duration that floats valves, it's RPM, all else being equal. So if you're done making power at 5500 or so due to the cam spec, there's no need to reach the limit of the springs. If I understand Smeding's graph, power is done by 6k. 6300-6500 RPM isn't needed. So there's that to consider.

 

Rereading some of the posts.
The general thought is that larger heads require less cam for a given output.
Here's a quote from Mike Jones:

"Normally when I have to design a cam for an engine that has too big a port, to band-aid it, I take about 4 degrees out of the duration, and add lift. I'll also pull the LSA 2 degrees tighter to help make up some of the torque the larger port will lose.I run into this a lot on Sprint Car engines, and this usually works very well."

You might see here how Jones cam spec is what it is.
Shorter duration . Tighter LSA.
So there's something else to think about.

 

I just got off the phone with Jacob at Smeding. He was very patient and was happy to answer all my questions. (Picked up on the first ring too!) He assured me they have built engines with the standard AFR head springs with the larger duration 480hp cam and have had no issues. That backs up what you guys have already said that that duration number slightly over 235 is really a non-issue. They also clarified that they do not really offer custom or alternative camshafts. "They have found that between the 4 offerings they have been able to cover the overwhelming majority of engine applications" they also said, "Even if they were to create an intermediate cam between the 450 and 420, you really would not feel much of any difference. Even on the dyno, there would only be a shift of may be 5 hp..."

They were able to confirm there will not be any promotion for black Friday this year, so there is really nothing holding me back from ordering. If I order today, they are estimating completion in about 6 weeks. Nice thing too, is that they only charge 50% to start the build, then you don't have to pay the second 50% till it is ready to ship in 6 weeks. Makes it a little easier to split it over two months.

Even if the cam is not precisely what would be perfect for my application, I think it should be plenty close enough for my needs. And, the convenience of a complete assembled short block that I only then have to put heads, an intake, and accessories onto, is worth the tradeoff to me...

Anyone have any final words, or should I just pull the trigger??? I think I'm going to shortly!!!

 

I think what you've just explained follows very closely with the conversations had here.
Now that said, there are few details you'll need to address once your shortblock arrives. Namely head gasket and pushrod length (amongst others).
The former for a final compression ratio as well as valve to piston clearance.
The latter to ensure proper communication between the cam lobe and the valve tip. Not to mention valve guide life which is a big player here (ask me how I know!).
Question though: Does their shortblock come complete with an oil pan and timing cover?

​​​​

 

So, AFR suggests a specific head gasket, the Felpro 1003, which I already purchased. That gasket has a 0.041" compressed thickness. (See my compression calculation below...)
I actually bought hardened pushrods back when I got my full roller rockers years ago, I expect to be in re-usable condition, if the length permits. I believe they are 7.200". I have a pushrod length checker on hand to verify.
I though I've seen that even with the factory flat topped pistons, there are no issues with valve to piston contact until you get to .600 lift. Since I am going to max out at .544/555 and the short block comes with 13.5cc Dish pistons. I thought I should have no problems. You can see the piston profile in the pic below.

Yea, since I'm getting the cam kit and the seal up kit with it, the short block will include: the cam, lifters, roller timing set, thrust plate, lifter dog bones & spring tray, oil pump, welded pump pickup, hardened drive shaft, black timing cover and oil pan. (All installed by Smeding)




This is the info I could find in Summit's calculator. Smeding confirms a 9.025" deck height, but I could not figure out the deck clearance based on the info I have. They clearly say though that with 64cc heads, I should end up with a 10.0:1 Compression ratio, so hopefully I end up with that and not something significantly lower...

 

Hmm. If Smeding states an .025" piston below deck, then with that.041" gasket and a 65 cc chamber you won't see 10:1. More like 9.5:1 to 1.
While some may argue that it's not a game changer, I wouldn't hesitate for a second to shoot for 10.5:1. Especially with the larger cam. We've regularly run 11.5:1 with those heads on a 355 with a similarly sized cam. And all good on pump gas premium.



​​​​​​But even an .026" gasket (like a Mahle 5746) you'll be hard pressed to see 9.75:1.
Further to that, your piston to head clearance will be at an exaggerated.066". Again, also arguably, it's not the best engine building practice. .040" tends to offer benefits that are lost with the larger quench.
Might be worth taking into consideration.

 

Yea, my goal was 10-10.5 cr. If they say 9.025 for the deck height, what is telling us the TDC for the piston is 9.000. I don't see that stated. Or is that the norm, and not normally deviated from? At this point I don't have a lot of options... I heard they make extra long spark plugs designed to take up more volume in the combustion chamber, don't they? Or like you said a thinner head gasket?

 

If Smeding says that it's a 9.025" deck height, what that means is that at TDC, the position is .025" down the bore. That's a typical SBC value. To get a zero deck requires having the block decked. I suspect they'll be unwilling to do this. (and probably say unnecessary).

If 10:1 is a minimum target then an .015" shim style gasket will get you there.
Two things happen here. One is that your CR gets to a reasonable level. Still low but reasonable. The other is you tighten that piston to head clearance which will provide those other benefits mentioned. Better combustion efficiency more or less (although the dished piston will reduce that effect).
With a fresh block and fresh heads, the shim gasket has proven reliable. The FelPro 1094 appears popular although I've no direct experience with them. It comes in at .015" compressed thickness.
There's also the option of milling the heads. I've done it time and again. Usually as part of a head refresh but also to reduce the chamber volume in order to raise the CR. It's more involved but sometimes the only option.
Combining those two steps will get you even closer to a more suitable compression ratio. 10.5:1 sounds ideal. But now we're splitting hairs!

 

I called Smeding back, and let me first say, I have a complete short block on order!!! (4-6 weeks)

I got some answers too. Because Smeding uses custom (standard for their engines) pistons, the deck clearance is actually 0.010". We also discussed options to increase compression. (He agreed 10-10.5 is ideal for my application) He informed me that the standard head gasket they use, and that was used for their calculation was a Felpro 1003 (0.041") what I have on hand already. He suggested I could use a Cometic C5245-030 which is 0.030" to up compression. He also informed me that for an up charge of $750 they can offer a forged piston with a dish of 9cc instead of the standard 13.5cc to up the cr to about 10.5, or even a 5cc flat top that will get to about a cr of 11.

So, Options:
Felpro .041 Gasket, Standard 13.5cc dished piston - CR 9.79
Cometic .030 Gasket, Standard 13.5cc dished piston-CR 10.02
Felpro .041 Gasket, Upgraded 9cc dished piston - CR 10.25
Cometic .030 Gasket, Upgraded 9cc dished piston - CR 10.51
Felpro .041 Gasket, Upgraded 5cc flat top piston - CR 10.70
Cometic .030 Gasket, Upgraded 5cc flat top piston - CR 10.98

My name is in the que, so I have at least a week or two to make up my mind if I want to switch to the upgraded pistons for higher compression... Thoughts? I can't tell if this is one of those things where the difference is so incremental I shouldn't be worrying about it, or if I'll be kicking myself in the future for cheeping out and using the parts I have on hand... I'm liking the sound of a $90 gasket over $750 worth of pistons at the moment though...

 

Well done on pushing the discussion. Now you're getting somewhere.
Does the upgraded 9cc piston have a thinner ring pack than their standard which has a 5/64ths old school 1st and 2nd ring? If it's 1.5mm/1.5mm then there's something to be gained there with reduced friction and potentially better ring seal. That was one of decisions I made when I went with a Wiseco Pro Tru Street piston. Also forged.
I like the sounds of the smaller dish, not to mention a forged piston. It would also be interesting to know what the piston dish profile is. If it's a D-shaped dish, as opposed to a full circle, then that's another benefit with a quench pad in the right place giving that better piston to head clearance a chance to do its job.
That would mean another call but you've placed an order and the least they could do is to answer another question.
There's also a less expensive head gasket option through Mahle. They offer a .032" composite gasket for something like 30 bucks a piece.



​​​​The 10.5:1 route , from a personal perspective, I think is ideal. The HP gain is one thing and arguably difficult to quantify. 10-20 probably. But the lower RPM torque bump seen with the increased cylinder pressure is where it'll shine. Another upside too is better MPG if that means anything.

 

How do you decide which gasket bore to get. Is it normally to account for bored over blocks? Since my block will be new it is 4.000, that's on the listing. The afr suggested gasket is 4.166" and the one you suggested from Mahle is 4.100". Since im looking to maximize compression do I go with the smallest one over 4.00 that matches the rest of my requirements?

 

The lower rpm torque is one of the biggest things I'm looking for, so achieving at least 10.5 cr seems like a must... I need to be able to accelerate out of slow corners without bogging down or having to wait to get back in the power band...

I looked through their site and couldn't find anything about the piston ring or dish arrangement. I'll have to call next week. In the end I think I'll kick myself if I feel like I'm lacking low to mid torque, and I didn't shell out the cash to get up to a cr of 10.5...

 

Try this calculator from Wallace Racing. It has an input for gasket bore diameter.

http://www.wallaceracing.com/cr_test2.php

Fiddling with that and you can see the kind of impact a .025" diameter difference (4.100" or 4.125") has on the results. With an .032" gasket it's 10:43 vs 10.42.
Some of the more intense calculators will have provisions for crevice volume as well. They'll take into account the clearance between the piston and bore and include how far down from the top of the piston the 1st ring is.

Yes, ideally the gasket diameter and the bore could be the same but I found the decision was often a price point thing. I'm not into paying 90 bucks a gasket when I can get the same level of performance for a third of the price. In my case, I also take into consideration the possibility that the heads are coming off more than once so replacements also factor into my decision. Probably not the case for you but there's still the up front cost. And they'll be enough of those long after you've got your assembled engine ready to drop in.

 

Sounds like you're talking yourself into a piston upgrade to a 9cc forging and head gasket to suit.
I doubt you'll be disappointed. If you had more of a drag racing bent and a higher stall converter, I'd say get to 11:1. But at that level, the low RPM stuff gets difficult to handle due to the propensity towards detonation. There are workarounds of course but there's no need to put yourself in that position really.

I've got a Edge 3800 stall converter so when I'm at the track, my effective rev range is 4000-6500. You can see there's not a lot of low RPM action. When street driving and cruising on the highway with the lockup converter in play, there's no heavy throttle so that risk of detonation is diminished. I do however, with 10.4:1 and iron heads, have to pay attention to timing and fueling. That said, I like to run as much cruise ignition advance and as lean an AFR as is practicable so as to maximize my MPG.

 

Just finished watching the Engine Masters Episode on Does Compression Make Power. (Season 6, Episode 11) they clearly show it does across the entier rpm range, plus it benefits low rpm torque and power even more than higher rpm, which is exactly what I'm after.

I think the right direction to go in for me is going to be something in the range of the Cometic .030 Gasket with the upgraded 9cc dished piston to get a CR of about 10.51:1. I could possibly be comfortable with a slightly thicker gasket as long as my compression stayed above 10.4 if there was any benefit...

 

I think you're on the right track. Not only are you getting a better CR but you're also tightening up the piston to head clearance. That will also aid in better combustion as does the increased compression ratio. A win/win in my books.
I'd like to see that 9 cc piston. I would hope it has a D-shaped dish as I mentioned. That's a bonus in terms of that piston to head clearance (commonly called quench) I've prattled on about. .040" is generally considered a go to number.
The Cometic is a pricey gasket for sure but it's well suited for what you're now trying to achieve.

 

FTR:
I reached out to Smeding for further cam specs.
Their 450 HP version is 281°/286° @ .006.

 

Good to know for calculating dynamic compression, thanks. That @ 0.006" lift is basically the same as advertised duration for hydraulic roller cams, right? That's what I'm finding on the web.

So, last night I went down the "Quench" rabbit hole. I think I understand what it is, the thickness of the total clearance between the flat parts of your piston at TDC and the flat part of the head. Basically your deck clearance which in my case is .010" plus your head gasket thickness. My take away is that the logical range for it should be between .035" and about .050". Sounds like the sweet spot between performance and safety is .040 - .045. Also since I'm switching to forged pistons, I guess they have a more aggressive thermal expansion rate, so they are made to fit a little looser in the bore, meaning I could have slightly more piston rock. Given this I think I want to go with either a .030" or .032" head gasket. I'm probably splitting hairs at this point, but I'm leaning towards the .032" for that tiny bit of extra safety factor, both in quench space and CR.

Cometic .030 Gasket, Upgraded 9cc dished piston - Quench .040" CR 10.51
Cometic .032 Gasket, Upgraded 9cc dished piston - Quench .042" CR 10.46

Regarding styles of head gaskets and manufacturers. I am seeing very good reviews for the Cometic gaskets (C5245-032 or C5245-030) and they seem to be intended for high performance use like my engine. I'm a little concerned Mahl (5776) gaskets specifically say, "These gasket sets are not intended for race applications." Should this keep me from using them despite the cost savings? I really feel like a set of head gaskets should be a buy once cry once kind of selection... I'm also seeing people say the Chevy branded gaskets (14096405) are pretty good, but they are .028 thick so that brings up CR and down quench slightly more than I would prefer.

I'm assuming I should be sticking to the Stainless Steel and Graphite Multi-Layer style for my build over the composite type, is this correct?

 

My attempt at calculating dynamic compression. Do my inputs look right, is this the range I want to be in?

 

For the purposes of this discussion, yes, .006" is the advertised duration lift point.

"Rabbit hole" indeed.
Short story, .035" is pushing it. There are variables in play here (such as the piston rock you mentioned) that could mess up the measurements and/or operating conditions that might not favour too tight a clearance.
.040" is generally accepted as a go to value where the benefits of a tight quench (which you've probably read about at this point) are realised without the risk of piston to head contact. Especially at high RPMs. Beyond 40 thou those benefits tend to be diluted so the stack up parts to get you there is what you're after.
This is also where the piston crown profile has an impact. If the dish is D-shaped, then there's a quench surface that meets the same on the cylinder head. If it's a full dish, like the 13.5cc version, then the quench area is considerably less.

As for gaskets, not sure what's meant by "racing applications" but I can assure you the Mahle graphite composite gasket has served in all manner of small block Chevys we've put together. 7000+ RPM 11.5:1 aluminium headed drag racing engines to 9.5:1 iron headed street engines and everything in between.
Not one issue to report with over a dozen different installations.
Presently I'm using the Mahle 5776.

https://www.summitracing.com/parts/mah-5776

This is in my recently assembled 357 SBC. 10.5:1 with iron heads. 6500 RPM all day, every day deal.

Far be it from me to say buy this or buy that. I'm just relating relative experiences.
It seems to me you're doing your due diligence and with good effect too.

 

UPDATE! The 9CC forged pistons are added to my short block order!

They confirmed they are D shaped dishes on custom JE forged Pistons. Which should be perfect to maximize quench! He confirmed they do still use the standard 5/64" rings, but I don't think I needed anything special.

I asked his opinion of the Mahle head gaskets, and he said as long as they are the multi-layer stainless steel with graphite type, they should be totally fine, so I will look strongly into getting a set of the 5776's.

I also asked him about the difference between the CR and Quench of the .030 vs .032 gaskets, and he said I'm splitting the hair of hairs, or something silly like that, but I get what he was saying. If the Mahle gasket is a .032, and the price is right, and it is available to ship, those may be reasons enough to go with those.

So, who needs a set of Felpro 1003's???
Clearly, I'm not using them anymore because they are too thick for my setup. They would be perfect for a zero decked block since they're 0.41 thick.

 

I meant to reply to this earlier but I never got around to it.
Those calculations are incorrect. Mainly due to an inaccurate input of the IVC. You've stated the advertised duration of the intake lobe. It's not that but rather the actual number of degrees after bottom dead centre (ABDC) the intake valve closes. That's something that will be revealed with the cam card and the actual installed position when the cam was degreed. You can check that for yourself or ask Smeding what the IVC really is. I'll guess that it's in the range of 64°-68° ABDC.
With 10.5:1 and cam of 281/284 @ .006" your DCR should be in or around 8:1. Again, that's dependent on how the cam was installed and where the intake centre line actually ended up.
FTR, some builders completely dismiss the DCR number. While there are arguments that can be made on both sides, with respect to an SBC of these build characteristics, that number will give some insight into how well the engine might handle various grades of fuel.

I've got a DCR tech paper to share but for some unexplained reason, i can't upload it. You may find it interesting. Stay tuned...

 

Excellent. I'm liking the build and the attention to those details.
I can't say I've heard anything bad about Smeding. They've popped up in a couple of older car mags I've been going through so they've certainly been and around and have managed to survive. Many didn't get through the covid BS and the fallout from that.
Solid heads with an equally solid reputation.
That is step one mind you. Lots more to go with the top end assembly and all the bits that go along with it. I've brought the subject of valvetrain geometry up before as it's a particular area of interest to me. You've got that checking tool but with that said, it's not part of my methodology for establishing the proper relationships. I'll bet though that you'll work your way through much like the process of getting the shortblock dialed in.
Looking good and also looking forward to updates.

 

I realized this thread is no longer really discussing the order of engine upgrades, since I'm basically going all in now. So, I have created a new thread where I plan to continue this discussion as I build my new engine, and probably continue through as I try to swap it with my old L98.

Fuel Injected 383 SBC Build for Street and Autocross - Third Generation F-Body Message Boards