Guest Night_rider_383 Posted October 26, 2002 Share Posted October 26, 2002 Might be a dumb question but i always heard folks talk about some heads as being open chamber and some being closed chamber. What is the diff. in the two? Thanks Quote Link to comment Share on other sites More sharing options...
grumpyvette Posted October 26, 2002 Share Posted October 26, 2002 (1)open chamber heads have the spark plug side of the cumbustion chamber layed back to speed flame travel and unshroud the valves, closed chamber heads are a much more oval and compact shape closed chamber open chamber Quote Link to comment Share on other sites More sharing options...
Guest Night_rider_383 Posted October 26, 2002 Share Posted October 26, 2002 grumpy... Thanks bud. Your the man with all the know how. I got 1 more question for you if you can help me out. I'm gonna buy a set of AFR 190 heads for my high rpm use 327. I was wanting to use dome pistons to get the compression up around 11-11.2:1. I talked to a guy at AFR and he said the 68 cc heads would'nt work with the domes cause they are closed chamber heads, but the 74 cc heads would cause they are open chamber heads. I know The tighter smaller better shaped chamber is better at keep knock out with higher c/r. The quench is better with them. Is the open chamber AFR heads gonna cost me hp/tq along with not being able to run pump fuel, higher compression, etc cause the chamber aint as tight? Any info you can give me would be great, and thanks again grump Quote Link to comment Share on other sites More sharing options...
grumpyvette Posted October 26, 2002 Share Posted October 26, 2002 go with the open chamber ,larger cc combustion chamber heads, they in most cases flow slightly more air and matched to the correct piston make more hp, while its true that its easier to gain compression with the smaller chamber heads the valve shrouding slightly limits the airflow on the small chamber heads. . in an ideal world the valves(two intake, to keep port velocities very high while haveing a combined flow greater than a single valve can supply and one exhaust to make the port cooling easier while not have any shrouding, the sparkplug would be centered and the quench areas would be about equal on both sides of the combustion chamber squishing the air into two walls of air/fuel mix slaming into each other as a piston with a slight reverse dome matching the combustion chambers shape swung past TDC so that the spark plug would almost instantly ignite all the mixture in the cylinder.like these Quote Link to comment Share on other sites More sharing options...
Mike C Posted October 26, 2002 Share Posted October 26, 2002 According to David Vizaed's "How to build and modify small block chevy cylinder heads" all thing being equal the closed chamber head is worth 20 hp on a SBC, even if you equalize compression. BBC the opposite is true. The 11:1 327 in the 1960's had either a .125 or .225" dome and they used closed chamber heads. It wasn't until 1971 that open chamber heads existed, so all of the 60's high compression motors (283,302,327 and 350) used domed pistons and closed chamber heads. Unless there is something incompatible with AFR's combustion chamber design then you should be able to use dome pistons and closed chamber heads. In a closed chamber head the spark has a shorter distance to travel and reasonable compression numbers can be had with flat top pistons. The flat top design doesn't impede the flame front as much as the dome piston and IMO is the way to go. I usually consider AFR to be knowledgeable, but after that info I would consider somebody else... Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted October 26, 2002 Share Posted October 26, 2002 Those are big-block Chevy heads, Grump. Quote Link to comment Share on other sites More sharing options...
Kevin Shasteen Posted October 26, 2002 Share Posted October 26, 2002 What about considering the latest trend? As a qualifier, all that follows is in regards to a typical wedge head & doesn not refer to a Hemi or Semi-Hemi head. I say trend, I'm talking about the the last 5 to 10 years or so, whereby one will use the Piston that has a Dish in a Dome. The Dome is not the typical dome but actually resembles an extended Flat Top Piston. The Flat Top extends beyond the factory Piston Comp.Height and will have a Dish in it to bring the Comb.Chamber cc's closer back to ground "0". This Dish in the Extended Flat Top Dome will also match the pirameter of the Closed Chamber Cyl.Head's Comb.Chamber. This relationship will exist in a near '0' Deck Clearance. I believe this is often referred to as "Squench" which is a combination of Squish & Quench. As said earlier the Dome with a Dish in it is not an excessive dome therefore it doesnt inhibit flame travel; because it has a dish in it some of the combusted gasses tend to stay with the piston longer: AKA-a little more power. I too have the understanding (book smart-not actual hands on testing) that the typical Dome, of the 60's/70's style, will inhibit flame travel. I guess we should clearify what we are talking about when we use the term Dome; as in mild or excessive. It would be nice to have a comparison of two engines that utilize the same compressions; yet one would have a typical dome while the other engine would have a Squench type piston matched to the Combustion Chamber of the Cylinder Head. What'dya think; comments-suggestions? Kevin, (Yea,Still an Inliner) Quote Link to comment Share on other sites More sharing options...
Mike C Posted October 27, 2002 Share Posted October 27, 2002 I do agree with them being miles ahead of STOCK 60's heads, I don't agree after reading (and re-reading) Vizards book for years that they are much better than fully modified GM heads. No doubt the newer chambers are miles ahead of the 60's chambers, but airflow from the GM heads can come close to the AFRs. The trend in OEM chambers is to closed and I also believe that is still the way to go using two valve relief flat top pistons. If you have to pay somebody to port your heads you are WAY ahead buying something like the AFRs or the Victor Jr heads, but if you have a set of GM heads, can do reasonable port work yourself, and then get them rebuilt that is still a viable option to reasonable power output. I have had thought about upgrading the ported 492s on my 355. It puts (a guesstimate) about 370 hp to the wheels. Reasonable since the 3300# car plus my 180# butt runs 12.7's at 110mph. It is a TINY comp street roller (236 @ .050 .560 gross lift I run the lash a little tight .020/.020 so .540 net) and 9.8:1 trough type flat tops. If I thought I could swap heads and get 70-100 horsepower I would do it tomorrow, but I highly doubt it is the conclusion I have come to. Too many cars I see running with a similar combo to mine can't put that kind of power out. FWIW, the motor went in my car in 1988. It was a seriously fast street car at the time. It isn't any slower time wise, but mid 12's on street tires don't mean dick anymore. PS if anybody wants to loan me a set of AFR 195's to experiment with, just let me know! Maybe I should just drop it in the Z since the speed/hp calculator shows a #1000 weight reduction would be a 10.90 at 125... Quote Link to comment Share on other sites More sharing options...
Guest Night_rider_383 Posted October 27, 2002 Share Posted October 27, 2002 Thanks guys, yall really brought me up to speed on this whole deal. I have a set of 65 327 462's here with manley 1.94''/1.50'' valves. I done ported them a few years ago. Not bragging but im real good with a die grinder working heads. I always heard these was good heads but no match to the newer style chamber heads. Thats why i was looking at AFR's. I trying to get around 500 hp@7000-7500 rpm out of the 331 i'm building, plus run a nos cheater n20 system so total around 650-700 hp on bottle. The pistons i was thinking about aint what i would call a full dome. They look like a flat top piston with a smaller flat top on top of that one, then 2 valve pockets. Piston part number is TRW-L2166NF30 .125'' dome forged Here's the email i got back from AFR along with the questions i asked Hi John, The 68 cc chamber heads will not work with a dome piston, but the 74cc chamber will. The difference is that the 68 cc chamber is a closed chamber design that will not accept a domed piston at all, while the 74 cc chamber is an openchamber that will accept a dome, even when milled. I will warn you that a 60 cc chamber will need to have all the clearances carefully checked, but should accept the piston dome without an issue. The heads cost $1250.00, the valve and spring upgrade for a solid flat tappet cam will add $175.00, and the cost to mill to a 60 cc chamber is $250.00. If you have further questions, please e-mail or call me direct at (818) 890-0616 ext. 111. Thanks, Dave jja1614@juno.com wrote: > I'm looking to buy a set of AFR 190 cc heads for my street/strip 327 > small block chevy. I see in your catalog it says these heads will need > some machine work to work with dome pistons. I have a set of 4.030'' > forged pistons with .125'' domes and 2 valve pockets, what machine work > will be needed to make these pistons work with the AFR 190 heads? I have > a few more questions too. Do yall do the machine work on the heads for > use with domes and if so how much will that run? What spring size will i > need for a solid flat tappet cam with .580''/.591'' valve lift that will > see around 7,000-7,500 rpm? I would also like to have the heads milled > down to 60 cc (.048'') for the compression specs i need. Can this be done > useing dome pistons or will i run into probs because of them? If it can > be done on my setup do yall do that kind of work and what would the price > run to have them milled? > > Thank's for any help you can give me > John Quote Link to comment Share on other sites More sharing options...
pparaska Posted October 27, 2002 Share Posted October 27, 2002 Mike, I've thought about the same issue. Then I plugged the numbers for ported 461s and new AFR 195s into DD2000 and with even mild cams, etc., you see the 40-60hp on even a 327. Personally, I love the flow numbers you see for the AFRs. If you can believe them and the tests that Chevy High Performance mag had done, they are quite impressive. But $1250+ is alot of cash. I'm now also considering Canfield 200s (the 220s take offset rockers and I don't want to go there) and also Pro Top Line 200s. Quote Link to comment Share on other sites More sharing options...
grumpyvette Posted October 27, 2002 Share Posted October 27, 2002 "According to David Vizaed's "How to build and modify small block chevy cylinder heads" all thing being equal the closed chamber head is worth 20 hp on a SBC" true but thats highly miss leading because what hes refering too is the later open chamber SMOG STYLE HEADS compared to the earlier closed chamber CHEVY HEADS the AFR heads have a totally differant semi-heart shape combustion chamber designed to increase swirl they are not anything like the smog heads chevy produced. and not once have I even suggested the use of a high dome piston like they used in the 60s, a very smooth and contoured piston with a minimal dome or in many cases a reverse dome giveing you a dynamic compression ration in the 8.3-8.5:1 area is what your looking for in a high performance street strip engine BTW that 20hp falls in the who cares file when you realise a good cam and a set of AFR useing the modern swirl technology heads can quite easily make 70hp-100hp over the best stock 60s era chevy heads read this http://www.airflowresearch.com/ go to articles (top of the page) 401-Inch Chevy Stroker notice the semi-heart shape open 74cc combustion chambers just try getting numbers like that useing stock 60s heads Quote Link to comment Share on other sites More sharing options...
Mike C Posted October 27, 2002 Share Posted October 27, 2002 Pete, David Vizards Ported 186 castings (identical to my 492s for all intents and purposes) flow 280+ cfm on the intake and have 81% of that on the exhaust almost exactly the same as the AFRs. My heads were ported by a local machinist and are really pretty. They also have 1.437 springs with Manley undercut stainless 2.02/1.6 valves, titanium retainers and 10 degree cc superlocks. With such small cam timing I don't see any way that the AFR could make 60 hp more. Actually it could conceivably happen,I guess, but I am NOT going to spend $1500 to find out(I would have to upgrade springs) on this motor. My flat top 355 is going into my 'vette and will be replaced by a more radical 355 for my Camaro. It WILL get aftermarket heads. The Pro Toplines have excellent numbers and with the new setup I won't be concerned about driveability as I was when my old motor was built.I will probably pony up for the fully ported Dart Pro1 (320cfm intake 240cfm exhaust) $2400 with roller springs fully assembled. Although the Edelbrock Victor Jr has gotten my attention lately. A box stock set on my friends 427 SBC made 540hp and 580 lb ft. This motor is going into his hybrid, a 93 S10 extended cab. Quote Link to comment Share on other sites More sharing options...
grumpyvette Posted October 27, 2002 Share Posted October 27, 2002 one factor you are forgeting is that the modified shape of the combustion chamber and that semi-heart shape promotes swirl and tumble of the fuel air mix in the cylinder greatly speeding the burn time and building cylinder pressure through at least in theory a more complete burn. that little raised area above the spark plug boss if properly shaped can cause the intake ports charge to much more effectively clean the cylinder of the previously fired cylinders exhaust gasses, something the old closed chamber heads were poor at BTW, as they relie almost totally on the pistions upward movement and the headers exhaust scavageing to clean the cylinder. now don,t forget the piston is only 3/4" to 1.25" down the bore by the time the exhaust valve has opened and the headers have started scavageing the cylinder, so the chamber shape has a major effect on how well the exhaust gasses exit the exhaust port Quote Link to comment Share on other sites More sharing options...
Mike C Posted October 27, 2002 Share Posted October 27, 2002 I agree with all of the science presented, but also recognize that it doesn't always translate into more power since the entire package has to be analyzed. ie if max flow and efficiency of ones cylinder heads is in the .700 lift range and you have a camshaft of .480 lift, this is definitely not the best use of said product. This is especially true on a street driven vehicle tht has to contend with a less than ideal exhaust system which can negate many of the advantages of said cylinder head. Another factor I forgot to mention earlier is that smaller combustion chambers have less surface area exposed to the initial heat of combustion. This keeps more heat in the chamber to do work meaning more power and less loss to the cooling system. The 292 turbo head is an antique these days, but was GMs early attempt at a more modern chamber and plug location, but in reality, even after modification, they aren't much, if any, better than the 041,186/492 series heads. I guess the whole point of posting earlier was to try and suggest that horsepower isn't always made by spending more money, but by better decisions and craftsmanship, I think too much time is spent on $ upmanship and not enough time on engineering the combination of parts. Quote Link to comment Share on other sites More sharing options...
grumpyvette Posted October 28, 2002 Share Posted October 28, 2002 Mike C on that point youll get no argument from me! "but also recognize that it doesn't always translate into more power since the entire package has to be analyzed. ie if max flow and efficiency of ones cylinder heads is in the .700 lift range and you have a camshaft of .480 lift, this is definitely not the best use of said product. This is especially true on a street driven vehicle tht has to contend with a less than ideal exhaust system which can negate many of the advantages of said cylinder head.....horsepower isn't always made by spending more money, but by better decisions and craftsmanship, I think too much time is spent on $ upmanship and not enough time on engineering the combination of parts." in fact I think most money spent on parts is wasted by most people who would rather buy parts than THINK EVERYTHING THRU AS TO THE FINAL RESULT AND MAKE SURE EVERY PART MATCHED THE GOAL AND RPM RANGE BEFORE BUYING PARTS THAT AT THE TIME SEEM A GOOD DEALI constantly try to tell everyone that you need a well thought out plan, then only buy the parts on the list that advances the well thought out plan!!! Quote Link to comment Share on other sites More sharing options...
pparaska Posted October 28, 2002 Share Posted October 28, 2002 grumpyvette - good point on the parts selection issue. I continue to TRY to do this right, but I usually mess up something. One thing that the newer heads seem to do better at is low and mid lift flow. That is even more important for lower lift cams. More area under the flow curve is more power. Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.