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#1
08-31-2010, 12:05 PM
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#77 heads on a 400?
I'm considering my options for a engine for my 65 GTO while still looking for a proper WS block. One possibility is to install my spare set of #77 heads on a 70 400 that I have. Here's the deal....
Years ago I started to build a nice 400 for my 68 Firebird. I had all the required machining done and bought all the parts that I'd need for it but never got around to putting it together and eventualy sold the car. Since my 65 will need an engine while I'm looking for a WS block I thought I'd just build up this old 400 and use it but I'd like to be able to use the earlier style valve covers, thus requiring the earlier #77 heads. Does anyone know if this can this be done? Thanks 
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#2
08-31-2010, 02:28 PM
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When I bought my '65, it had a '70 YD 400 in it with 77 heads and a Lunati bracketmaster 292H cam. It ran pretty well but the high compression was sometimes an issue with pump gas. Even though it had a Q-jet, I ran an original aircleaner and it looked very stock underhood.
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Matt 1962 Grand Prix - Cameo Ivory|389 4sp|One-Owner Survivor 1964 GTO HT - Silvermist Grey|389 3x2s 4spd|A/C|Hurst Wheels|Frame-off|SOLD 1965 GTO Post - Mayfair Maize|421 3x2s TKO600|Pro-Touring| 1966 GTO HT - Barrier Blue|389 3x2s 4spd|Red Fenderliners 2005 GTO Coupe - Yellow Jacket|Magnacharged LS2 6sp|543hp/561tq|SOLD 2006 GTO Coupe - Spice Red|LS2 6sp|20k orig miles |
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#3
08-31-2010, 06:35 PM
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Valve angle is different on these two heads . Piston valve releafs are in deferent place on pistons. But new junk replacment pistons have both (total of 8) valve pockets. If you have those in your 400 the #77 heads will work. But these pistons have a lower deck height and are LOW compression.
Next option is, custom pistons. not to bad $$$ |
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#4
09-14-2010, 10:13 PM
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Man I have so much on the go right now I almost forgot I asked this.
 So it will work IF I have later pistons...which I don't think I have... I'm pretty sure they are still the stock std bore ones. Is it possible to cut relief cut-outs or are these stock pistons too thin? A buddy of mine races a Mustang and he cuts his own valve reliefs with his cutter so maybe it would work on my build. Any thoughts? |
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#5
09-14-2010, 11:43 PM
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Yes, valve reliefs can be cut in almost any Pontiac Pistons. I did it on my '64 with a 428 engine with the "716" '64 GTO heads. While you're at it, you may want to cut a "dish" into the piston tops to lower compression. The size would have to be determined by measuring head cc and calculating "dish" size for the desired compression--about 9.5:1 max with these early heads.
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BONESTOCK GOATS '64 GTO Tripower Hardtop (Wife's Car) '64 GTO Tripower Post Coupe (My Car) '99 Bonneville SE Sedan |
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#6
09-15-2010, 08:17 AM
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I think my custom pistons were $600.00. Deck is .010 flat top. head is #77 and compression is 10.5 to 1 . With dist curve set and maybe a little cam 2. 3-1 mix.
Low compression is big h/p loss.and with any larger than stock cam it gets worse. These engines had big compression numbers for a reason.When you lower compression. You need to change cam ,jet carb. thermostat 195, timing. Lower compression makes the cam larger the jetting to rich. It lowers cyl. pressure witch lowers heat in cyl. witch means less power. |
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