mbeeman350

Started looking at aftermarket heads for BB's. The intake runners range from 270 cc to 350cc. So a 396 could have a 270 cc intake runner up to a 350 cc.
So why would someone use a 180, or a 190cc or a 200cc or even a 215 cc intake runner. Seems way too small. I just build a 383 with what I think are 190's. Seems to be some uncertainty on the Pro Comp heads if they are a 160 or 190 cc on the intake runners. Thougt I bought the 190's.
If I fouind out for sure they are 160's they are history. Considering something like the 200cc or 215 cc intake runners. Car is a 383, TH400, 309 rear, roller cam, with 224/230 duration @ .050 and 503/510 lift.
Mark

MotorHead

You might be on to something there, hey wait a minute, haven't I been trying to say that since....the beggining of time it seems

Gordonm

Don't go by runner size alone. My old AFR 190s will outflow a lot of 210 heads. Look at the flow numbers of all the heads before plunking down your cash. The new Eliminater 195s from AFR outflow a lot of 220 size heads from just a few years ago. I made a measly 500 HP with my small 190 heads on my 385 with a solid flat tappet cam.

Guru_4_hire

I expect that at some point valve and port size dont play as big a role as they used too. So the relationship between port size and flow is probably a curve and not a direct relationship.

L88Plus

Looks like you're trying to compare SB and BB heads and it doesn't work. BB head runners are much longer, they'll always show as bigger than a comparable small block head. And a 396 with 350cc runners will most definitely be a dog, probably won't get out of it's own way.
It's kinda hard to say about your combo. The Chinese knock-offs you're running have tolerances all over the place, you won't know until you measure 'em. Intended use and the rest of the combo dictate head runner size. Vortecs are only 170 but they outflow some at 190. If yours is a hydraulic roller engine, that cam should support runners up to about 215cc's but it'll be lazier on the bottom end. It's all about compromise and building a combination - no single part of an engine does it by itself, they all have to work together toward a common objective.
By the way, the junk Pro Comp heads are available for big blocks in 310 runner size, might work for a street head but I sure wouldn't want to run any serious spring pressure on 'em.

Little Mouse

they are longer and much bigger cross section, I think original oval
runners were around 254cc and the rectangle 305cc. 396/375 hp
engines had 305cc runner rectangle heads and ran great, they would
out run a 325/350 hp hydrulic cam oval port 396.

Ganey

As L88Plus says, it's not a direct comparison.
The BB was designed to be 427+, not 396! It was debored in 65 to meet an old GM policy of no more than 400 C.I. in the smaller cars, which is why Delorean used the 389 instead of the 421 in the GTO. Olds BB heads are said to be 170!

63mako

Well said!!! Been trying to get this point accross in numerous posts lately but always get grief about it. That said with a 3.08 gear and a turbo 400, anticipating street use, a low duration hydraulic roller with under 10 to 1 comp. and a 6000 RPM max you you DON"T want to be lazy on the bottom end. Looks like YOUR intended use is better geared toward low and midrange torque where a 190 or 195 runner head that flows well will shine!

tt 383

i bet if you cammed an oval port 396 the same way you do a rectangle port they would be pretty close especially if valve size were kept the same. that solid cam is made to make high rpm power. that comparison is in no way close to comparing aftermarket sbc heads that have a common valve size or have a comon chamber shape. i dont believe( dont know for certain) the chamber shape is the same between high performance rectangle heads and passenger car ovals. this can affect flow and timing and can relate to significant power gains. race rite ovals from brodix will destroy gm castings with 30-35cc less volume, they will make more torque down low and horsepower on top.

rklessdriver

I would like to point out that you are comparing 2 completely different engine desgins also. First off this is not every reason why a BBC can use a port tha big and a SBC cannot but its the main reasons. There area lot of little things (piston speed and cam timing differences between the 2 engines) that add up but...

Reason 1. Cyl head valve angle and port lay out.

The BBC has canted valve heads, as the valve opens it moves tward the center of the cyl/piston away from the cyl wall. Due to the less shrouding of the valve when it opens a BBC can keep port velocity up with a big port and aviods turbulance which causes port stall.

The SBC's inline valve arrangement couldn't possibally utlize a port in the 270-350cc range due to the shrouding of the valve by the cyl wall when it is open. No matter how big cubic inch wise the SBC is. Even the biggest inline 15&18 degree rolled deck heads have port sizes in the 260cc range and only because the valves have been moved around a bit in those heads in respect to the bore centerline... The Dart little Chief and Chevy/Brodix canted valve SBC head start in the 260cc range and only get bigger with porting. But due (in part) to the port lay out they can utlize all that port volume.

Reason 2. 1960's engine desgin/theroy and intended engine purpose.
As some one already pointed out. The BBC was orginally desgined as 427inch motor. With a huge 4.250 bore and short 3.76 stroke. They based their engineering of the BBC on the old W head 409's and its limited breathing on the top end. It was intended to turn 7000rpm for NASCAR race cars, thats why it was orginally know as the Daytona mystery engine. It was common engine theroy back in those days that high RPM engines needed a large port volume. They figured a 310cc rectangular port would do what they nedded and it did. When the prouduction versions of the engines came out obviously GM saw the need for lower performance versions of the BBC so the oval port heads were born. Due to the sheer size and port arrangement of the BBC port size turned out to be about 260cc. But the ports are so low in releation to the valve that they don't flow worth a crap really limiting the BBC to a low RPM tq moster.

Now days we know that if you take a set of rectangluar port BBC heads epoxy up the floor and basically make a set of "raise runner" oval port heads you can end up with a port volume of around 280cc and a head that offers low RPM performance and high RPM performance (to 7000rpm). Same thing with the bigger SBC heads , raised runners and a more line of sight pathe in the port to the valve. They had little/no clue back in the early 60's about this.
Will

L88Plus

Oval and rectangle ports follow approximately the same path. Problem with a honker rectangle port head on a small engine is air speed. Air moves thru the intake tract with speed which causes inertia - the air wants to keep moving. The faster it's moving, the more inertia you get and the better the cylinders fill. When you have a small engine pulling on huge port heads, it doesn't generate much airspeed or inertia, but the air moves much faster thru the smaller port and the cylinders fill much better. As long as we're talking street stuff, a 396 can barely spin high enough to get good airspeed/inertia thru big rectangle ports. A 496 can use either, depending on use. Ovals work well with hydraulic/hydraulic roller cams because the cam's rpm limit is about the same as the capacity of the heads. Drop a solid or solid roller in and they can shine with some 325cc runners.
It's all about the intended use and entire combination.

mbeeman350

Thanks for everyone's response...and thanks for not flaming me!!
As soon as I posted this last night I turned in...then it hit me. The runners are longer on a BB, as mentioned above, due to valve placement. So the longer runners equates to more volume. I have had BB's...been a few years. Mark

MotorHead

I new we would get into cross sectional volume and runner length, point is a 396ci is a 396ci whether it's a small block or big block and needs bigger heads and more air flow than a 350ci, my 406ci is 10ci bigger and I run 220cc heads, does it look lazy at 2000RPM ?

This is last time I am posting this, if you guys want to run puny heads ( I am not taliking about one head here the new AFR 195's Comp heads would be suitable because they flow big numbers ) on your big inch small blocks go ahead and leave power on the table, I have built one with bigger heads and it works perfect I am not making this stuff up or reading about it



Here is a chassis dyno run, when was the last time you saw a dyno pull starting at 2000 RPM ? The throttle response is so good at 2000RPM that the operator was able to go WOT in 4th gear at this RPM with a 3.08 rear end. THe proof is in the pudding as they say

63mako

Ok Check this out: Tests NOT DONE BY AFR!! http://www.adperformance.com/index.p...duct s_id=208 Check out the flow numbers, Comp.,Torque curve and peak HP. These are AFR 195 Street heads for under $1500 that outflow the old 210's. This power comes from using well matched components!!!THAT IS MY POINT!!! He is building a street motor with dual plane, hydraulic roller under 600 lift.

MotorHead

Straight from AFR "The street 195cc head now outflows our previous competition version ( 195cc ) "

It doesn't outflow the original 210's, the new competetion version out flows the 210's but they are $2000.

It does look to me like the street 195's flow in the 280-285 cfm range and if they are under $1500 then they are a good buy but you still have to look at what you are putting them on. AFR recommends them for 350ci-400ci. So when you get into the 406ci and bigger it is better to go with a 210-220cc head

BTW I see no reason why you can't make 500+HP on a 383ci with these new heads, my problem was post #17 on Ryan's Car page, they were obviously using the old 190cc heads and to make over 500HP at 5500RPM with a puny cam is infact a big load of

73, Dark Blue 454

The take from this is, if you have a 383+ SB, you need heads that flow to BB levels. As I've stated before, routine-duty '049' oval port heads, used on 402's (396 bored .030") in the early 70's, outflow many of the aftermarket SB performamce heads. 049's were used on trucks, station-wagons, and big Chevy sedans, with 2.73 gears and A/C. I still contend, that for a performance 383+ SB, you need to go big. I have a 406 with AFR-195's, and they're too small for a 4-speed 69 Camaro with 3.73 gears. I'm peaking way too early in the RPM range.

Lastly, have you ever heard anybody with 383+ SB say "I wish I had smaller heads,..I have nothing down low"?