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#1
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I currently have the 915 Closed Chamber heads on my 440 Challenger? The car runs 10.5 to 1 compression with a six pack....
Would the 906 heads offer any advantages over the 915's? |
#2
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all you would do is lose compression,the 915 and 906 ports are pretty much the same.
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#3
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I think you would lose about .3 tenths of a point of compression going to the 906 heads.Some of my friends that race big blocks run 906 heads ,i've heard they do flow better that the closed chamber head.Also i don't know if you can run domed pistons with 915's unless there custom made.
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#4
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You would lose about a hole point in comp by going to 906 heads. The 915 should work good enough.
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#5
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The "advantage" was better(more efficient)combustion and therefor less pollution. Mopar Muscle did a build-up a while back and found it took alot more time and work(porting and flow-benching) the 915s to flow only slightly better than a full ported 452 or so-called "smog head". But the 'closed chamber' is reported to flow better at lifts of .500+ up to .650. Chamber size is 83cc and 74cc for the open and closed, respectively. Unless your objective IS to lower compression and be able to find gas any where, most would stick with the 915.Otherwise find some no-lead freindly ported 452s to lower your compression some.
------------------ [This message has been edited by montrose ram (edited July 15, 2000).] |
#6
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Wait...
Don't the 915 heads have the smaller valves? If so, the 906 or 452's would be a better choice because of the bigger valves. I like the 452 heads since they are close to the 906 for flow and have hardened valve seats for pump gas. You can get them milled to retain the higher compression number and port match them for decent performance numbers. The big question is what are you cam specs? This is very important, since most of the MOPAR heads don't flow very well over .500 lift without some work. Also what is your exhaust system? Another question, is this car being run on the street? If you are running 10.5 to 1 on the street you must be mixing fuel (avation +pump) since pump gas would never get it done in a 10.5 to 1 motor. If you were to switch the heads to a 452 then your compression would drop around 1 point, making it 9.5 to 1 which is very streetable with pump gas. What pistons are you running? [This message has been edited by Dart (edited July 15, 2000).] |
#7
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I haven't pulled the motor apart, so I am just going on what the previous owner has told me.... The pistons are TRW but I'm not sure which ones...The cam is the .509 Purple shaft. I am running the MP headers with flowmasters. The motor is relatively stock, (Heads have hardened seats). I am just thinking of tearing the motor apart this winter and was just wondering whether or not to do any head work with the 915's?
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#8
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I haven't pulled the motor apart, so I am just going on what the previous owner has told me.... The pistons are TRW but I'm not sure which ones...The cam is the .509 Purple shaft. I am running the MP headers with flowmasters. The motor is relatively stock, (Heads have hardened seats). I am just thinking of tearing the motor apart this winter and was just wondering whether or not to do any head work with the 915's?
PS: I live a few minutes from the 'Strip' so I get 110 fuel there... |
#9
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I run them on the street.If they havent been milled then they could be very easily 80 cc , mine are 78 cc and I have cut .030 off them.They work great,I had a set that came with 2.08 & 1.74 valves , I also have a set that had 1.60 exh . I put in hard seats and 2.14 & 1.81 . Use the .038 gasket and set the piston down the hole .010 to .020 and you will be fine.If your around .040 over bore you will be around 10 to 1 comp.Do the math. If you need more chamber cc ,unshroud the valves and polish the chamber.Or buy a dished piston that still has a quench area. Hopefully they havent been milled excessively.
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#10
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Whoa, I just went back and read some other postings on heads.... The concensus seems to be 'Invest in the Indy SR Heads' for a good staring point (Assuming you have the $$$). Just don't call their customer service dept. They seem to flow better from the get go than the Stage VI heads. Don't throw money at the cast iron heads even though they can be adequate for a medium modified BB. Does that sound about right?
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#11
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well you can lose a full point of compression by taking the 915's off but thats only if the motor now has a steel shim head gasket and when you put on the 906 you use a composit gasket but if you use the same style gasket as it has now when doing that type of swap you will lose 1/2 point in compression.
Some of the 915's have the smaller 1.60 exhaust valve but not many,I have had people out right tell me that I am full of it when I tell that but I have a set here right now that have never been touched and still have the 1.60's,it was a surprise to me.otherwise most of the 915's have the same valves as the 906/452/346/902 did I miss any? |
#12
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Brian-wo,
Your not full of it, I had a set of 915's that had the 1.60 exhaust valve also. I not absolutely positive but I think the early 915's where on the '66 440 engines that where in the Sport Furys, they were rated at 365HP and where real torque monsters. They increased the exhaust valve size in '67 on the GTX and RT engines. I don't know if it was because it was an earlier casting but there seemed to be more meat around the intake port on the 915's than on the later 906's. We were able to port this particular set out to 238 cc's of intake volume and tried to duplicate it on a set of 906's keeping the walls the same thickness as best we could (using a sonic tester)and could only get 219 cc's with one of the two sets we had. Don't know if I could ever find another set of 915's that would port out that much and sometimes wish I still had them. The only reason I sold them was because I changed over to alcohol and I got tired of cleaning the rust out of the ports. |
#13
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I just read an article in this months 'Car Craft' talking about low budget big block build ups from the 'Big 3'. The article on the 440 Cube build up talks about the heads available and does say that the early 915 heads have the 1.60 " valves, but then switched to the 1.74"... They also said that most of the heads are pretty much indentical for the BB after the early 915 heads...Ufortunately I don't know the exhaust valve size in my 915's....
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#14
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At anyrate, I think you have the heads most everybody wants. They most likely have the larger valve. I guess there's only one way to find out...if you decide to work them some, why not enlarge the seats for the 2.14 in. and 1.81 ex. valves for even more flow. MoparMuscle went as far as to use a 2.25 in. but I think thats really pushin' it!! Good Luck! ---montrose ram(72 Challenger440)
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