Small engine big head driveability

[ATw]

Hello everybody!
Im currently thinking about upgrading the heads on my low comp 383 in my 71 newport. It has a Stock short block including Stock cam. Ported Dp4b intake, 650 avs2, 1 7/8 tti Headers with 3" dual exhaust and Stock 346 heads. 3.55 gear and 2000 Stall speed. Weighs in at 4600.
My prefered choice would be the cncd stealth heads because if their oe looks and good Flow.
But i think the big Ports would give Up quite some low rpm torque. I know alot of the dyno Reports on the Internet (engine Masters, hotrod etc) but i was looking for some real World experience from the street, not from the dyno.
Did anybody ever try "big heads" with a small cam on a small Motor like eg cnc stealths, cncd rpms, trickflows etc.
How was the driveability, low rpm and Overall Performance? Would you Do it again? What Do you think about cncd stealths on a Stock 383?

(Im planing on stroking and installing a hydroller in the next few years, so the cncd stealths could be used perfectly later on)

Thanks
Andi

 

[MEV]

I believe all of the hi-po 383's and 440's came with the 906 heads, the stealths are a copy of them. If you didnt get the CNC'd versions you would likely be fine.

 

[ATw]

Hey mev!
The stealth heads are Not only a copy of the 906 heads concerning the Ports.
A stock 906 has roughly 170-180cc intake Port volume vs 210 of the stealth.
So you see, there is a big difference...

 

[FURYGT]

Going by memory, the 346 heads replaced the 906 heads in 1971 and they were very close to the 906 heads. Why not port your existing heads and put in hardened valve seats. You have to be very careful with what you do so that you don't loose torque. I believe that the '71 big blocks lost 5 HP vs. the '71's due to a half point drop in compression.

I don't think that you are going to get the benefits of the Stealth heads without a cam change and some ignition improvements.

Can you clarify the size of your exhaust system and tell us what your goals are so we can be of more help.

 

[65sporty]

The heads may be a little much with the stock cam, you may loose a little low end torque. They will be great for your future build though

 

[CBODY67]

The one thing which the Engine Masters' "big head, smaller head" dyno runs point out is that the heads need to be matched to the engine under them for best results.

The 383, due to its near-optimum rod ratio, will be more sensitive to head issues than a 400 cid small block Chevy (and it's much worse rod ratio).

You can look at dyno runs until you're blue in the face and not know really how the engine will drive in the car. Larger ports, by their nature, will have less flow velocity in the normal driving rpm ranges, even with your 3.55 gears, than the stock ports. This relates to "throttle response" . . . including both normal off-idle response and also just toe-ing into the throttle to pass a slower vehicle on the highway. To me, THAT's what makes for a good-driving vehicle. "Responsive power" in the normal driving ranges. All of those high flow rates might be fine at 6000rpm, and .500" lift, but you need to pay attention to the lower lift flow rates and how they relate to the engine's real needs.

You can build an engine that makes peak power at 6500rpm, with a great-feeling "top end rush" or you can build an engine with a camshaft which shifts the power peak down toward 5500rpm . . . which will push you farther back into your seat as you accelerate at lower rpms. And it'll usually beat the higher-rpm engine to the 1/4 mile finish line, too. If you use the higher rpm engine with 4.30 or 4.56 rear axle gears, to put that engine into its power production rpms, that might change . . . but you'll also compromise other parts of driveability in the process (including extended high-speed highway cruising AND fuel economy). But the main point is that while you're waiting for that top end rush to happen, you've compromised the lower rpm power to a point that the lower-rpm engine will beat you to the finish line.

Also pay attention to the resultant surface finish of any machined port! Too slick and it'll cause flow disruptions as the boundary layer of air (between the metal in the runner and the center of the main flow area in the port) can slough-off into the main flow and cause flow disruptions in the process. A rougher surfacr is much better than a mirror-glass smooth surface for this reason.

AS an alternative, seek out the Mopar Performance Porting Template Kit for the B/RB heads. Using them will increase the flow in the manner which Chrysler engineers approve of. Kind of an obscure relic of the old Direct Connection parts days, but a good one. BUT if you'd rather talk-up the brand/type of heads you bought, and their virtues, it's your money.

To increase your knowledge base, you can also get one of David Vizzard's books on cylinder heads. Most of them talk about Chevy small block heads, but the principles are the same on any engine. Lots of good information! Also, the Mopar Perfformance Race Manual particular to the B/RB engines. These original "race bulletins" were done by Chrysler engineers who raced what they sold, usually drag racing and NASCAR racing. Some of the information might be a little dated, but it still works. Vizzard's books are more 1990s era. Put those information sources together and you can have a better understanding of how things work and many of the dynamics involved

Enjoy!
CBODY67

 

[twostick]

As big heads go, those aren't that big. I think they would be OK on a mostly stock 383.

Modern Cylinder Head does the CNC on those heads for 440Source so another option would be to buy the regular Stealth heads and have Modern CNC them when you stroke it. The cost should be close to a wash.

OOTB flow #'s on the non CNC head are apparently less than advertised so I'd be going CNC myself. They are still a standard port window so they should be fine from a bottom end torque standpoint.

Kevin

 

[bajajoaquin]

A better setup for about the same money would be to get the regular stealth heads, a new cam with about 0.485” lift and 220* duration at 0.050”, and a piston kit that gives you 10:1 compression. You’ll have more power, similar torque, and better drivability.

 

[moper]

Just put a cam, timing set, and performance valve springs in it. When you're ready to rebuild the whole thing, then upgrade to the stealths. 346s are basically 906s with a little different approach to the bowl and flame hardened exhaust seats.

 

[70bigblockdodge]

Just put a cam, timing set, and performance valve springs in it. When you're ready to rebuild the whole thing, then upgrade to the stealths. 346s are basically 906s with a little different approach to the bowl and flame hardened exhaust seats.

But that's not the shiny new part way?

 

[ATw]

Thanks for your replies.
Of course, there are always different ways for more power.
Sure, I could port my 346s, put another cam in right now, or go one of the other ways you mentioned. But that is not my plan ;)
As I wrote in the first post, I plan to stroke the engine in the future (489 or 496), put CNCd stealths on and a Hydroller (e.g. CompCams XR280HR or lunati 20230712).
And thats why I was thinking about buying the heads now and do the rest later on.
I was just curious, if somebody ever tried such a combo.
I still hope, that there is someone out there who tried big heads on a tame engine and can tell us about the performance

I dont need shiny new parts, otherwise i wouldnt go with stealths and a DP4B and paint everything in bright blue ;) I want the stock look with a tad more performance.

Thanks for your replies
Andi

 

[bajajoaquin]

I think that the "small cam big heads" element on Engine Masters was a relative thing. If you listen to those guys, they always tend to go to big cams with lots of lift and duration, and they were surprised at how well a "small" cam worked. But that "small" cam is pretty big in a heavy car with a 383.

As it stands now you've got headers and a 3" exhaust which are way more than you need for a stock cam. The heads will also massively outflow the stock cam. You'll still have low compression. I think you'll spend $3000 all in on heads and have the cam be the limiting factor to the point you don't see much in the way of gains. Maybe that's worth it if you're going to stroke it later, but that seems to be an awful lot of time to have the money in the car but not "paying off" in the expected performance.

Can you tell me about your DP4B? I just got a CH4B for my 440, and I'm curious how your under-hood fitment went. I know they're totally different applications, but I am curious.

 

[twostick]

He'll actuall have higher compression. The Stealth has an advertised 80cc chamber. The 346 will be in the mid 90's.

If I was planning on CNC Stealths I'd buy them now. They run bigger heads on small block Chevs.

Kevin

 

[ATw]

The dp4b is the same height as a ede performer (without rpm) and I have no issues with clearence. I use a dual snorkel and a 1" spacer. Have about 1" clearence to the hood if i remember correct.

 

[Slantsix]

Imo, unless u go B1/Max Wedge on B/RB mopar, u cant go "too big". 383 likes to rev, so it likes "big port" heads, but dual plane will tame it down alot. With 1 7/8 and 3" exhaust, it will flow all u can feed it in.

 

[70bigblockdodge]

I ported the crap out of a set of 516 castings and put them on a low compression 400. With a 284/484 Mopar cam and a Wiend dual plan(about the same as a dp4b), engine is a measured 8.43:1 compression. Pulls like a locomotive above 3000 rpm, 2000-3000 is flat. I'm probably going to put a smaller cam in it as that's cheaper than a new converter for a combo I am not sticking with. If that helps.

 

[MEV]

Thanks for your replies.
Of course, there are always different ways for more power.
Sure, I could port my 346s, put another cam in right now, or go one of the other ways you mentioned. But that is not my plan ;)
As I wrote in the first post, I plan to stroke the engine in the future (489 or 496), put CNCd stealths on and a Hydroller (e.g. CompCams XR280HR or lunati 20230712).
And thats why I was thinking about buying the heads now and do the rest later on.
I was just curious, if somebody ever tried such a combo.
I still hope, that there is someone out there who tried big heads on a tame engine and can tell us about the performance

I dont need shiny new parts, otherwise i wouldnt go with stealths and a DP4B and paint everything in bright blue ;) I want the stock look with a tad more performance.

Thanks for your replies
Andi

I started with the stock stealths (later had them cnc'd by modern) on my 505/512 and it ran very good with the XR280HR,


However that cam and its matching lifters suffered catastrophic failure driving down the road at 55mph going to a car show. Comp left me out to dry. I am going in another direction cam wise.

Comp cams hydraulic roller lifter failure