# Pesky leak



## 66GTO7.5L (Jan 8, 2009)

Couple of questions. Just replaced valley pan gasket and intake gasket. I still get a small amount of oil on front of pan. I believe it is coming up from the front pan bolt. If this is the case, any tips on stopping it? 

Next question. My 455 is .030 over. I calculate 462CID. After discovering it has 400 heads, I am wondering if that is correct. Any corrections to my calculations?

Also, son drove it to work today and he said he really didn't feel any 1st to 2nd shift and he didn't feel any downshift. He said the vacuum line to the tranny (TH400) was good. I am questioning the need for an adjustable vacuum modulator since I am running an Edlebrock 048 cam with very low idle.

Still trying to figure wires from in-dash tach to distributor.

Thanks


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## geeteeohguy (Feb 2, 2008)

Valley pan bolts: GM RTV under a dry and flat washer. Let set up for about 5 minutes before you install. Do NOT overtighten. Heads: not a problem. '67 thru '79 heads all will fit yur 455 and will ont change displacement. Head chamber size WILL change your compression ratio. '70 455's came with 87cc heads, '71 up came with 111--114cc heads. Your 400 heads, if '70 or earlier, will be about 72cc. Does it ping? You're probably at about 11:1 compression or more. Kickdown: Is the electric switch at the accellerator pedal hooked up and adjusted? That's what controls kickdown, for the most part. The modulator on the trans controls the shift point on upshifts. What is the casting number on the heads? (number over the center exhaust ports)


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## 66GTO7.5L (Jan 8, 2009)

Cast number is Gm 62 f...with date stamp of B289. So 72cc heads from 1969. Then 11.25 compression, I believe is correct. I have left son a message to check what you have told me. Thanks for the reply and I'll post again with results, geeteeohguy.

Oh yeah, haven't really noticed any ping.


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## geeteeohguy (Feb 2, 2008)

YIKES! You need to go with some dished pistons or some bigger chambered heads. In my experience, just because you don't hear it ping does not mean you're safe. At the very least, please run Octane Booster!!! Check out Rock 'N Roll Engineering's website about compression. IT's interesting.


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## 66GTO7.5L (Jan 8, 2009)

*geeteeohguy - Thanks for the Rock 'N Roll reference. Excellent information on inaudible detonation and octane requirements. I definitely will get son to do the dyno test to determine octane, even though I am sure it will be good 'ol race fuel. I certainly don't want to damage this engine. I sent him the links. He is going to check them out after his work shift. Thanks again.

I am thinking next winter, at son's suggestion, to drop in a '06 GTO engine drivetrain with dedicated pcm or get a period correct GTO engine to rebuild to spec. I am going to keep the built 455 unless a trade would be across-the-board trade. But I have a long time to consider the options.*


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## 68greengoat (Sep 15, 2005)

66GTO7.5L said:


> Cast number is Gm 62 f...with date stamp of B289. So 72cc heads from 1969. Then 11.25 compression, I believe is correct. I have left son a message to check what you have told me. Thanks for the reply and I'll post again with results, geeteeohguy.
> 
> Oh yeah, haven't really noticed any ping.


Sorry to hijack, but I too have a 455 bored .030. What size chambered heads should I get to bring the compression to around 10.0? 72cc at 11.25 is a little too much for me..... I plan on using aluminum heads.


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## geeteeohguy (Feb 2, 2008)

Green Goat: with your .030 over 455 (462cid) engine, you need one of the 87cc 1970 455 heads for about 10.25 compression (good luck finding the heads, and that's a little too high for pump gas in these engines). The BETTER solution is to get a set of 98c heads, which are waaaay more common, and will net you 9.4 compression. I put the 87cc heads on my 400, and It gave my smaller motor 9.2 compression and I love it. Good power, economy, and it does not detonate. Check out some Pontiac Head charts to determine the casting numbers you can use on your 455. Some heads that measure 98cc are: 4c, 4x, (1973), and 46. 6X are ok too, and have 101cc chambers. You could also install the Edelbrock 87cc heads, and have 10.25 compression WITHOUT pinging due to the aluminum head's ablility to dissipate heat. That's more $$$$, tho'.
Good luck!


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## 68greengoat (Sep 15, 2005)

Thanks for the info GTOguy. I saved the info as a word doc for future reference. My 455 is a '73 with 4x heads. But, mine must be the 114cc version. The '73 400 came with the 98cc. Not sure how a guy would tell the difference between a 400 and a 455 head with both being 4x and both having screw in studs. They did make one '73 400 w/out screw in's at a whopping 200hp. I really would like to get Edelbrock RPM Performers w/87cc, but I see thru Summit they're $2000 for the pair. You do get a "retro mechanics jacket" with a pair of heads!(yee haa)....... Do you have a feel for how much a set of used 98cc heads would approx. cost and how much to rebuild them? I know prices differ. Just looking for an idea on the cost... Thanx....


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## geeteeohguy (Feb 2, 2008)

Figure on 200-600 for usable cores, and another 400 to 1000 to get them done. the '70 455 heads I'm running are the samller valve #15 heads with the 87cc chamber, and they needed ALL seats replaced, ALL valves replaced, the press-in studs wee changed to big screw in studs, bronze guides, etc. etc. It ended up costing me about 1200 bucks. If I were to do it over, I'd probably bite the bullet and get the Edelbrocks for an additional 7 or 8 hundred bucks. BTW: I did the math on 66GTO7.5L's engine/head combo: He's running 11.8 to 1 compression!!! 11o octane only, that's for sure. I'll bet it screams, though!


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## 68greengoat (Sep 15, 2005)

Well, if I didn't have to spend $12k on a new lawn mower in the next couple of weeks I'd be calling Summit today! Unfortunately, I need to. Maybe next year, unless a good pair of heads cross my path at a reasonable price.............. Thanks again....:seeya:


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## geeteeohguy (Feb 2, 2008)

12k? For a LAWNMOWER? You must own a golf course!!!!


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## 66GTO7.5L (Jan 8, 2009)

geeteeohguy - What did you use to come up with the 11.8:1 compression? My 11.25:1 is close using some comp-figuring websites; just wondering what other variables you might have used?


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## 68greengoat (Sep 15, 2005)

geeteeohguy said:


> 12k? For a LAWNMOWER? You must own a golf course!!!!


No, I'm in the lawn mowing/snow plowing business......


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## geeteeohguy (Feb 2, 2008)

66GTO67: I went on Wallace Racing's website and used their calculator. With a .030 over 455, with 72cc heads, you're looking at 11.8 to 1 compression. Check it out...it's a great website with a lot of useful calculators, etc.


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## 66GTO7.5L (Jan 8, 2009)

I was using projectpontiac.com calc. Will have to check out Wallace Racing's. Been to their site before but didn't use their stuff. ProjectPontiac will also take a lot of variables if u have them available or you can just click your engine for stock spec auto-entries.


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