Looking at new hd gaskets. Need advice

kickascii · Mar 1, 2004

I have an 85 Capri that is running a Powercharger at 12psi. I changed the stock gaskets and now they are blown again after about 4 months. Last time it melted between 2 cylinders. I'm guessing they have a better head gasket that might hold on a little longer? Or should I pan on changing head gaskets alot running this much boost on a stock motor?

Shoud I go up a # on my jets in the carb? It's a 750 Holley that is setup for a blower and I'm using the stock jets that came in it.

Let me know if you need more info peeps...

billheis · Mar 1, 2004

Sounds like its running lean. How do the plugs look?, What is fuel pressure? You do have some kind of pressure increase system right? Probably would be good idea to have car dynod with A/F meter. If everthing is good in fuel system you may need to pull heads and have the m oringed and use Fel Pro lock wires gaskets

kickascii · Mar 1, 2004

billheis said:
Sounds like its running lean. How do the plugs look?, What is fuel pressure? You do have some kind of pressure increase system right? Probably would be good idea to have car dynod with A/F meter. If everthing is good in fuel system you may need to pull heads and have the m oringed and use Fel Pro lock wires gaskets

The plugs are do show light-grey to white in most cylinders. Keep in mind the fuel pressure is controlled by regulator and stays around 7-8psi going into the carb. No, I don't know how I would hook a pressure increase only under load.

I would love to get the car dynod but being a carb, where would they put the sensors? My guess is where I have spark plugs as fillers in the holes where the o2 sensors would be...

To have it o-ringed, I would need to have both block and heads machined right?

One more question: Should I replace the head bolts again? Can I get away with re-using them?

billheis · Mar 1, 2004

If I would have looked at sig I would have realized that your running roots type blower. the carb doesnt need ref. because it is before the blower it sees the actual presure drop. The way youre describing plugs it is definitely running lean. Id go up at least 2 jet sizes all the way around and maybe 4 or front. As far as o-ring you only have to do the heads and the gasket has wire that fits the groove. And the head bolts should at least be ARP bolts. and I would replace them there onlty about $37 cheap insurance

kickascii · Mar 1, 2004

billheis said:
If I would have looked at sig I would have realized that your running roots type blower. the carb doesnt need ref. because it is before the blower it sees the actual presure drop. The way youre describing plugs it is definitely running lean. Id go up at least 2 jet sizes all the way around and maybe 4 or front. As far as o-ring you only have to do the heads and the gasket has wire that fits the groove. And the head bolts should at least be ARP bolts. and I would replace them there onlty about $37 cheap insurance

How much do machine shops charge for that head work? Is it worth it on my 165,000 mile heads?

Summit or Jegs the best place to buy or someplace cheaper for this stuff?

kickascii · Mar 2, 2004

kickascii said:
How much do machine shops charge for that head work? Is it worth it on my 165,000 mile heads?

Summit or Jegs the best place to buy or someplace cheaper for this stuff?

Anyone?

Michael Yount · Mar 2, 2004

The dyno will still work for you -- they simply install a wide band a/f ratio sensor by shoving it up your tail pipe/muffler dump. Then you'll have mixture data which may give you a clue as to how much to enrichen things with jet changes. Watched my buddy tune his 69 383 GTX using the wide band data, and making jet changes on the Holley carb. In his case he was rich to start with and the a/f meter showed him exactly how his jet changes were bringing him back to where he wanted the a/f ratio. For a supercharged application, you probably want something not any higher than about 12. If it is leaning out as others suspect, your numbers may be higher than that - up around 13-14. And if that's happening under boost, you should consider yourself lucky that all it's doing is eating headgaskets and not eating pistons/valves.

If you're having gasket issues, I'd wouldn't reuse the bolts. You may want to consider studs/nuts - they seem to provide more even/predictable clamping force than bolts do. Talk to your local machine shop about o-ringing and what's involved. You may find that if you get your mixture right, you won't need to have it o-ringed - just a quality set of gaskets, and the bolts/studs to keep things from moving around.

kickascii · Mar 2, 2004

Here's what I'm going to do:

-Replace both gaskets
-ARP Head Bolts
-Dyno Tune

Question: Do I need to have the heads resurfaced? It never overheated...

Also, what brand of head gaskets should I buy? I know there are metal gaksets, but aren't they for reusability?

Thanks people!

Michael Yount · Mar 2, 2004

A clean up cut wouldn't hurt as it will provide the right surface for the gasket to "bite". Don't run it hard until you have it dyno'd. Also, have someone watching the a/f ratio on the first run very carefully and give you the sign -- if by 4500 rpm it's much above 12-12.5, I'd shut the run down and rejet richer before I let it rev on up. You'd hate to have it blow the new gasket before you get a chance to check the mixture.

kickascii · Mar 2, 2004

Michael Yount said:
A clean up cut wouldn't hurt as it will provide the right surface for the gasket to "bite". Don't run it hard until you have it dyno'd. Also, have someone watching the a/f ratio on the first run very carefully and give you the sign -- if by 4500 rpm it's much above 12-12.5, I'd shut the run down and rejet richer before I let it rev on up. You'd hate to have it blow the new gasket before you get a chance to check the mixture.

How much do machine shops charge for something like that?

Michael Yount · Mar 2, 2004

You really need to check in your area - prices vary with geography, time of year, current backlog of business, etc. It's been a long time since I had a head surfaced with clean up cut. I did have an exhaust header flange trued recently - cost $18. The head's gonna be a bit more and there are 2 of them.

billheis · Mar 2, 2004

Resurface just cost me $50. Thats an ave. price As Michael Y said its different place to place and so forth. Ive always used felpro race gaskets and never had a problem. Back in 87 & 88 when the FI 5.0 came out I put a bunch of NOS kits on and the factory gaskets let loose on everyone. Cleaned up the gasket surface with about a .010 cut and Fel Pro race gaskets and not one problem after that. Oh yeah, I replaced bolts w/Milodon bolts and some with studs too (Milodon & Mr. G only co. that had bolts atthat time) ARP stud kit is the way to go on yours

Looking at new hd gaskets. Need advice

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