I have a 76 455, and am going to look at a set of 71 heads on the weekend! The engine has about 80000 miles on it. I haven't run this engine yet, (friend has owned it for about 10 years in garage) If everything looks OK, and all thats really needed is a light cylinder hone, gaskets and bearings, what kind of performance increase can be expected from the 71 heads? Thanks guys:TU:
The heads will help.... Thought about a new set of stock 70 pistons? Or something other than the 76 stockers?
Essentially, you've created a 1971 motor. The pistons were the same. The loss in compression between the 75/6's was from open chamber heads. You'll see the difference once you remove them. In my 71 GS455, with headers, TA exhaust, 3.42 posi, and a Performer, I went 13.43 with it and a best of 101 mph. You may as well step up the cam a bit while you've got it apart. Put it mild cam and a set of Stage 1 replacement springs (require no machining) and there you go.
Wow the replies come pretty quick here!!! I was kind of thinking about a cam, I plan on using a 200R4 with 3.42 gears, and tires about 26.5 inch in height. I may be able to step up the gears to 3.73's, since the 200R4 will offset and high rev concerns! I didn't realize that 455 had the same compression in 71 as they did in 76! What would the compression be on a stock 71 engine? Headers are on the list, also an HEI ignition, and aluminum intake.
They didn't have the same compression, since the 76 heads are really huge, but they did have the same piston design. Compression should be around 8.5:1. With a set of 1970 pistons (like I posted for sale about a week ago ) you would get about another point or so.
8.5 for 71 compression... I believe it went way down again in or before 76 to around 7.9 to 1?o No: As Steve mentioned, the 76 heads are open chambered, and will decrease compression some compared to 71 heads.
Using the steel shim head gaskets would help even more, to get the compression up slightly more.:TU: Have you done any work to the heads? Perfect time to get a valve job and have the heads slightly shaved (just enough to make flat again).
Well I haven't gotten the heads yet, going to look at them this weekend! If they check out ok, no cracks, I plan on getting them cleaned up, maybe milled a little to flatten them out! For the kind of general street cruising I'll likely be doing I'm not sure if going to the stage one valves would be worth while!
It wouldn't be very cost effective to go to Stage 1 valves from the sounds of it. You would have to have the seats cut for the larger valves, and you would also want to unshroud the valves. The cost to do this would be better spent elsewhere. You could put it into some mild work on the heads. Or just have them cleaned up with a good valve job and resurfaced, then use the money towards the rest of the package.
Here's a set of 71 heads for you in Ontario. http://cgi.ebay.ca/ws/eBayISAPI.dll?ViewItem&item=2452015308&category=40931&rd=1 Harvey
Well Harvey, thanks for the lead, but those are the heads I'm going to look at, thanks anyhow!:TU: Also I'm just curious why the steel shim gaskets can't be used on a 76 block? Just wondering what is dirrerent from the other years!
Later blocks has different shaped water passages. Here is a link to a page containing a Buick service bulletin that explains it better. http://www.buickperformance.com/idblock.htm Hope this helps. Larry
overheating I too was having a overheat problem. I've got a 1975 455 with 1970 heads with felpro gaskets in a 1964 Riviera. The heads are stock except for a three angle valve grind, the motor was bored .030 over with a Comp Cam (mild grind), sterling pistons and rings, Edelbrock aluminum performer manifold and 750 cfm performer carb, new water and oil pumps and stock exhaust. I built a new shroud, running a 7 blade fan, a pusher electric on a thermostat to help the motor from overheating when shut off. It runs about 180 degrees to 190 degrees (160 degree thermostat) in about 70-75 degree outside temps. at an idle it slowly creeps up to 210 degrees. i've also got a 2"x19"x28" aluminum Howe racing radiator. i'm afraid if it get to over 80 degrees that it's going to boil over again, so i'm thinking about rebuilding the 1975 heads with a three angle valve grind, putting in a stock cam and seeing if this will help the heat problem. I've checked with Summit when i ordered the parts for the motor and was told that the compression ratio was about 9.4-1 with this set up. Before i rebuild it again has anyone have an opinion on wheather this will help? thanks, Duane Walters
Re: overheating Your 75 motor with 70 heads will not be 9.4 to 1 compression unless you changed to the high compression pistons when yo did your rebuild. Jim Burek
