Help-- Stock Heads ?

Doing a an overhaul on a SBC motor, and pouring through cam choices, etc.

I'm using Desktop Dyno to get an idea about hardware....I'm trying to figure out exactly how lame the stock "882" (1.94/1.5) heads actually are (more specifically, exactly when they run out of breath)
Same story- not interested in leaving any low end torque on the table- that just won't show up in the higher RPM's..

>>Does anyone know the intake runner volume-- even on a typical set of SBC 400 truck heads? I'm guessing somewhere around 175-180cc- maybe smaller.....

>> Also, what's the largest runner volume, that a 1.94" valve can actually utilize? A 2.02"?

I understand that some of these questions are a mute point, because guys usually end up just buying some aftrmkt heads at this point, but it all helps. Thanks

 

I'm certainly no SBC guru but I'd guess the "lame" stock heads will give you more low end torque than aftermarket heads.

Re-do the motor, buy a cam that makes lots of low end grunt (the stock one is probably better than most aftermarket ones in that respect) and bolt it back together.

Screw the big dollar stuff. After you close the hood no one will know, or care, but you.

 

I hear ya...
But that's kinda the point. I can't afford to buy a set of heads.
The worn out smog era camshaft is already in the trash can. The motor will also be getting new pistons. So there are some variables to play with here..

Two things will determine the cam choice- not just "bigger is better":
1) breathing ability- that is, my motor's ability to actually use more cam duration and lift,
2) ...And the static compression ratio I end up with- since duration effects the amount of cylinder bleed-off, and can lower the DCR// hurt low end torque.
(again- that I can't gain back above 4000-4500 rpm because my heads run out of air)

 

For a stock 882 heads a 4 barrel, and an auto. go with a 260H, 268h for more rumble, or a XE256. All work well for fairly stock low compression motor. Or, call Comp.

 

I'm looking at the XE262, and the XE268. I'm considering a mild port job (at home), and pistons that give a 9.6:1 static CR.

I'm sure that any of the smaller cams will be fine, but looking at it theoretically reveals alot about limitations of stock components, and also-- how dramatically LSA can affect where the power is distibuted. It's pretty damn interesting to a novice like me...

 

XE series is better for lower compression. XE256 or XE262 will work well. XE 268 has a bit too much lift for cheap rebuild springs. You will have to do too much head work on them. .

 

probably anything over 450 lift is a waste of time. 270-280 dur 110 lobe c. flat top pistons are cheap. 202's a waste. save your money for performer manifold, 600 cfm, magnum type roller tip rockers, 1 5/8 primary headers with a crossover and a good ignition. 2500 converter and 3.30-3.50 gear and a shift kit and youl be happy. i think.

 

Some more specifics about the car, including it's weight/intended usage, and engine size would be useful.

 

Thanks for all the help guys.

I have a software program, called "Desktop" Dyno" and looking at everything theoretically right now. I have narrowed things down to a specific question about intake runner volume on a stock head. Why?

It's a limiting factor in how my motor can take advantage of a cam with additional lift/duration. If the heads are cashed out at 4500 RPM- that will essentially answer my question about camshaft choice- piston choice (and resulting static CR) will follow that.

I just want the hard #'s so I can see for myself.

 

I would guess 180-185 cc after you smooth them out, but once you start gasket matching and smoothing, it *could* be more.

 

The displacement is another factor to consider, as a larger motor will run out of breath sooner.

No solid #'s here, but; I ran some stock 461's on a dished piston 350 with a solid lift Crane SS350, 1 3/4" headers, 780 dual line on a C3BX, light flywheel, and several different gears in a '55. This combo revved well to 7500 pulling all the way, didn't feel flat down low even with the tallest gear(3.36), and punked a buddy's big block Camaro more than once.
A little pocket porting might of helped also.

The same heads on a 301 revved to 8500, although with different springs, but it needed 3500 rpm's to get up on the cam.

 

Really?? I'm surprised by that. I was guessing more like 170 or less.

here's what I've found:
............ You cannot go much bigger because of Valve seat restrictions. If You go past 2.00" and 1.55", You have to install larger seats. "The intake runner volume is about like the old iron double hump heads, in the 160-165cc range." I've flowed these heads stock and They flow about 195 cfm at 28". We've ported them and got as much as 255 cfm out of stock size valves......

I don't know if he's taking about a 327 head-- the heads I have (882's)were commonly used on 400's.......

 

Wow!
Ok. I was thinking of shifting @ about 5500 max. Lame, I know- but realistic for my combination I think.

OH- and it's a 400. Sorry about that.
I realize that this motor can swallow additional lift/duration alot better than 350- which is what most people think about when making recommendations.

hence, my dilemma- my thinking is that a "2000-5800" cam (spec'ed for a typical 350) would probably be a good cam for my target shift point of 5500(assuming that a 400SB will shift the powerband down about 300-500 RPM from the typ 350ci)....BUT- I don't think that my heads are worth crap after about 4500, especially if the intake port volumes are @ 165cc...

 

Man... you're taking this much too seriously for a driver.

 

HI,
According to Stan Weiss' website the 882 head is only 151cc's and peaks out at 204-205cfm. If your stuck with these heads, read up on "pocket porting" to get a little more flow. The 400 is a great torque motor and you don't need to spin it hard to make some good numbers. With those heads I'd max out at something like 220-224 degrees duration @.050 and a little more on the exhaust side. If you don't mind giving up some idle quality get a cam ground on a 108 degree lobe center to pick up the midrange torque. Use a good dual plane manifold, and some cheap 1 5/8" headers and you'll be surprised by how hard it pulls.
Rick

 

dont go to crazy with the desktop dyno on that motor it just isnt rocket science with the small combo you're looking at. in other words you dont need trick heads. with motor size, cam and hp figures you will end up with an 882 will flow enough....just a thought. save the desk top for more exotic stuff. i have one also and its alot of fun but on low hp/tq stuff it will drive you nuts....the cam for the street motor @ .510 lift is too big. start backing carb size and cam specs down and you will see that with the comp, carb size manifold etc for a streetable engine the cam is just too big. i've had the dyno programs back to the first ones and have found that motors in the 350 cid, 600 cfm, 450 lift, 270 dur.small heads with dual plane manifold the motor is pretty genaric. just like if you built without the dyno. once you get into 10-11 to 1 pocket ported big valve heads, big ports 190-215 etc and rpms up in the 4000-8000 range that program is really helpful. also try swapping rockers (ratios) and advancing retarding cams and carb spacers etc. within your parameters that is when fun begins. which dyno program do you have and do you have cam iterator? good luck

 

Listen to parksquid-- sound good solid advice.

 

Maybe- I just want the most bang for my buck, ....and I'm learning a WHOLE lot so I won't have to bug you guys next time.

 

Yikes-- 151's- That's kinda small.

Well- here's something interesting: my original target cam was the Comp Cams XE262 (218° /224° - .462"/.469"), and then the XE268 on the big end of my choices. I also played around with the Lunati 60101, 60102, and 601013.

Anyhow- Interesting that you should mention the 108 LSA. I'm considering a small cam (206° /212° - .425"/.440"), BUT with a 108° LSA.
Why??
It makes more HP than even the XE268- about 30 more HP, and has a broader HP curve. ALL of the other cams I "tested" fell flat on their faces about 4700-4800. Kaput. I assumed that this was because of intake runner volume.
When I tried the small 108 LSA cam, the motor made an almost identical amount of torque, but woke up about 4000 RPM, and pulled peak HP numbers (again, 25+ HP) all the way to 5000 RPM, dropping off in a gentle curve. If I could show you the curve, you'd see a dramatic difference.

To your comments, I don't plan on ever shifting this thing over 52-5300, so it sounds really close.
With a little research i found several sources that say a narrower LSA is good for "weak heads"-- and that this is due to scavenging on the exhaust side. It seems to work wonders for this motor somehow.

Make sense??


__

 

Yeah- I realize that this is a "small" combo, but alot of people have this combo, and doing this still isn't cheap. Anyone who is spending $1500 or so, and busting their own knuckles owes it to themselves to do a little research IMO.

Anyway, as above- my target cam is right about what you mentioned. I was just experiencing a strange problem on the "Dyno". No matter how much lift/duration I threw at it, dual pattern/split pattern, it would fall on it's face about 4750 RPM- pretty drastically.

The 108 LSA seems to be the hook for my combination- on paper anyway.
I'm just going to have to watch cylinder pressure. My static compression ratio is right about 9.9:1 ( +5cc dish)-
With the larger cams on a 110° LSA, the dynamic compression ratio was below 8.5:1. With the smaller cam and narrower LSA it's creeping towards 8.75:1, depending on the head gasket I end up using. I'd say that's cutting it pretty close for 91 octane in the low desert. What do you think??

 

So about the 400 small block; They come with a short rod, which increases side loads on the cylinder walls, accelerates wear, and also makes me leary of them, so limiting your red line is wise. Many folks use a 350 rod(5.7"), but that requires custom pistons, the crank pin is the same size. Many others use an aftermarket rod, usually 6". On the other hand, I have a very low mile 400, and because of that I'll probably just use it with mild mods like you are proposing. Your cam play is interesting, thanks.

You can get away with a c.r. around 10:1 if you not only keep it cool, but spend the time to tune the ignition curve, usually right on the ragged edge of detonation. Also, a vapor injector helps more than most people realize.

 

By the way fellas-- Thanks for your help!!

 

Well.....I talked to Ron Iskendarian, at Isky cams today.
He was extremely cool. He thinks that my magical 108 degree LSA is, well..........mostly a glitch in the software. %$@*!

We did talk about the real difference between all of the 110/112 LSA cams out there, and he thought my 108 degree 264 Mega cam choice was very right-on. Very straight up guy.

 

ow much needs to be done on your heads? if you have to put alot of money in the i would think about the world products sportsman 2 heads.
you can get them from speedway motors loaded with springs good to .550 lift for 799 a pair. i am planing o buying a pair for my 327.

 

Really need to know what you're putting it in. In general I don't like a 400 for a street engine, too detonation prone.

I have a snowplow truck w/a tired 400 in it. Thinking about putting newer fast-burn Vortec heads on it. Haven't researched it yet, just thinking. Wonder if their chambers would help suppress detonation?

Otherwise, junk heads, I'd build a 383.

 

Using stock type iron heads you will be limited to about 400 -450 hp if everything is done right and you match ALL the components.

It sounds like you are somewhat budget limited. The 400 will make the same power as a 350 but will do it at approx 1000 rpm's less. Ihave built a couple of 350's and they pulled hard to 5500 rpm's with only mild port job. The trick is to pick the right intake manifold and cam. I know that most recommend the performer manifold but I would recommend a Wiend 8118(?) and 327/375hp cam profile. You will want only about 650 cfm of carb and a good electronic ignition. An older HEI will work just fine. You can build a very strong small block very easy and cheap. Remember that a rule of thumb is that you get about 2 hp for every cfm that your head flows. Unless you are willing to buy aftermarket heads and turn the motor 6500+ rpms you will only make about 400 - 450 hp and 350 - 375hp is easy and the motor will give you lots of life. Set/limit your compression to 9.0 to 1. If you want cheap hp you should deck the block, surface the heads, balance the recp assemblies, match port the heads, match bore the clys and assemble the thing keeping all deminsions at optimum (use the right thickness of head gasket)(clearences/fit). Small blocks really respond to proper cams/heads/intake/exhaust,,, No rocket science.

 

Hi,
Your cam choice seems like a good one to me. Rule of thumb is pick the smaller of two cam choices and you will usually end up happier. The 108 degree lobe center does help underported heads and will improve midrange torque. The 400's especially seem to like it. The camshaft is the key to any engines performance characteristics, so picking the right one is one of the most important decisions to be made. Computer programs are good for looking at trends more so than actual numbers. You can manipulate the parameters to keep making more and more horsepower but it probably won't materialize on your accessorized and muffled steet vehicle, but the planning and collecting parts is half the fun.
Rick

 

i didnt mean small in a money sense. i just meant that obviously you are like the rest of us and if you are thinking of using 882's you right off the bat are looking at more of an rv type cam, dual plane of your choice , small pri headers etc. otherwise do as these people were saying and buy a aftermarket iron head but i would go to flat top pistons first. maybe a hypereutechtic. for 1500 you can build a pretty stout motor with one of these kits from northern auto parts or the source of your choice. still would do the magnum rockers and the dual plane with 600 cfm and dont overdo the cam. stick to one that starts to come on around 2000 or so and good vacuum for your power junk. you never did say what this goes in so dont expect to much advice. what did you tell iskendarien? 108 lsa may put you in the higher stall low vac area. gears make a big difference.