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head gasket/problem
https://www.slantsix.org/forum/viewtopic.php?t=24846		 Page 1 of 5
Author:  terrylittlejohn [ Sun Sep 09, 2007 5:05 pm ]
Post subject:  head gasket/problem
can anybody tell me the signs of a head lifting under boost. just back from the track and #1&#6have burnt the gasket into lifter gallery in both cylinders(again). all the plugs are fine(not melted) i hooked an o2 censor to a voltmeter and read 860mv at full throttle,it only was reading #4,5,6 ,so i don`t think it`s a lean condition, it seems to only happen under full load in 3rd gear.i have 2/600holley vac jetted 74prime/84sec and boost ref power valves,timing is set 25degs total and i have a big block vacum plate hooked to port vac that pulls time back 10degs at 30lbs vac so under load it should only see 15degs advance.the car 60ft well(1.57to 1.64) and 1/8mile ets are (7.42to7.65) but if i stay in it at 109mph and 12.00ets it will hurt the head gasket, any ideas or suggestion would be appresiated :?:
Author:  Joshie225 [ Sun Sep 09, 2007 6:14 pm ]
Post subject: 
A head lifting under boost will darken the head and block mating surfaces.

If it's only #1 and #6 with the problem I'd say you need to work on fuel distribution.

At the end of the 1/4 you've built up enough heat that weaknesses are being revealed. You aren't getting detonation until you get the engine hot.

Are you sure the timing is doing what you want? The description is leaving me scratching my head. Are you meaning that you have a big block vacuum canister connected to give 10° advance at 30" of vacuum so that when the vacuum falls you revert to 15° of mechanical advance? How much vacuum do you have at idle? Is the timing locked out other than the vacuum advance?

Why so much carb? Were you pulling too much vacuum under smaller/fewer carbs? Too much venturi area will kill the booster signal and play havoc with the jetting even with the blower. I'd think a single 750 vacuum secondary carb with a light secondary spring would be plenty.

How much boost are you running? What fuel are you running? Are you 100% certain the float bowls are staying full?
Author:  terrylittlejohn [ Sun Sep 09, 2007 7:23 pm ]
Post subject:  head gasket
yes i have a vac adv plate from big block in the dist, when it see 30bls of port vac the canisters pull the plate clock wise retarding timing,mechanical adv i set 25 deg total with normal weights in dist. i am running 5lbs boost with av gas and supreme mix, the same that i ran with no problems in my highcomp engine with no blower on it (11.4/1).the carb cfm could be one of my problems? the gasket has a section about 1in wide and the fire ring looks melted and as it get close to lift galley it fans out to about 2in. the engine is 0.080 over, head is 1.78in intake/1.47in ex valves,cam is .556lift/255@0.50/108s, i have 2 carter 72gal pumps run in parallel,if the head is lifting because clamping force in not great enough would the to end cylinder be more likely to hurt the gasket or not?if the cfms are to much the vac 600s should control how much the secondary open?i also don`t know what my finial compression ratio is at 5lbs of boost and if my fuel mix is suitable(8.9/1 static comp).any other ideas would help thanks
Author:  AnotherSix [ Sun Sep 09, 2007 7:44 pm ]
Post subject: 
I would try more octane, as well as be sure the timing is what it is supposed to be, as already pointed out.

Detonation at the top end in high gear is a normal thing to have to deal with on a boosted engine. Even good bolts can stretch at that point.

You might try some ARP head studs, since they are available. One remedy on the turbo regals was / is to use two stamped steel head gaskets very carefully coated with a silicone sealer. I never needed it, but it worked for quite a few people. They were having trouble with the factory gasket, which was very good, a graphite and steel laminate with wire o rings inside the stamped fire ring. It might be worth a try and the thickness should be close to a composition gasket.
Author:  terrylittlejohn [ Sun Sep 09, 2007 7:59 pm ]
Post subject:  head gasket
the timing i am running i have check in my garage, at 2500rpms it`s 25degs as i increase rpms and port vac increase to a max of 30lbs i see a reduction of 10degs at 4000rpms that puts the timing at 15degs total, i just hoping thats whats happens going down the track.is that much reduction in timing needed with my boost levels? the head studs are something i have not tried thanks
Author:  Joshie225 [ Sun Sep 09, 2007 9:38 pm ]
Post subject: 
Ok, we need to get past referring to vacuum in lbs. Vacuum is generally measured in inches of Mercury (Hg). Atmospheric pressure is typically only 30" Hg give or take and a stock cammed engine is doing good if it pulls 20" of vacuum. A cam with 255° duration at .050" tappet rise will probably make less than 6" Hg vacuum at idle.

Did you change the orientation of the vacuum advance can to pull the advance plate the opposite way? That would give vacuum retard. You need boost retard. What you're doing in the garage isn't loading the engine and making boost is it? If you're not making boost while checking the timing this way I'll bet you have 25° timing down track.

With that much cam I would set up a distributor with a locked advance mechanism and set the timing to 15° BTDC. No vacuum can at all! A lean burn (Electronic Spark Control) distributor would be easy as they have no advance mechanism.

The end cylinders have 4 bolt just like the others. I still think the end cylinders are lean and am baffled by what you're trying to do with vacuum retard.

I figured you'd be running head studs. Silly me. Use studs. You may also need to o-ring the block, but fix the fuel distribution first.

Yes, too big a carb can cause problems. That's why I brought it up. Not enough signal will lean out the mixture. Running vacuum secondary carbs has likely saved you a lot of grief there. Still, you're probably pulling 75% of your air and fuel through the primaries. If you haven't opened up the power valve channel restriction you probably should.

Sounds like you have enough fuel pump, but what size lines and what kind of regulators are you using. Can I assume these are single feed Holley 1850 type carbs? I wouldn't run anything less than AN-8 feed line (AN-10 would be safer) with a Holley regulator for each carb or a single better regulator. If it were me I'd be running one carb with an AN-10 feed line and a good bypass regulator.

Good luck and don't give up!
Author:  terrylittlejohn [ Mon Sep 10, 2007 4:43 am ]
Post subject:  head gasket
sorry for the lbs/in mixup wasn`t thinking :oops: . i was running a stock dist with no vac adv, slot closed to give me 15degs in the dist and total was set at 25degs,with this dist i still hurt the head gasket,so i tried to make a dist that would retard timing as it went down the track,i was told that a slant with turbos like timing in the teens when under boost so i thought it was worth a try. as for head studs when i ran the smaller blower it worked great with stock head bolts and 5lbs of boost so i didn`t think it would be with this bigger blower.with all that behind me i still have a lot to learn on setting this think up to stay together.i will put head studs in as for o-ring that will have to wait, there is only one weekend of racing lift. i can go to the 750cfm that i ran on the smaller blower it worked great on that,with the dist i can go back to what i had, for fuel thats a problem race fuel has to be order by the drum early in the year and at $840can/45 gals,av gas i get at local airport $1.18/litre, i could run it with no mix, i have alot to do to make the next weekend so thanks again :?:
Author:  terrylittlejohn [ Mon Sep 10, 2007 4:57 am ]
Post subject:  head gasket
forgot, fuel line are 3/8in steel all the way from front to rear,the regulator is from summit, no by pass, with the dist the port it is hooked to see zero vac untill 1500rpms and at 4000rpms it see 30ins vac checking with timing light it does pull timing out, whether this is good or bad, i didn`t see it, there was only one full pass.thank again
Author:  Charrlie_S [ Mon Sep 10, 2007 4:57 am ]
Post subject:  Re: head gasket
Quote:
the timing i am running i have check in my garage, at 2500rpms it`s 25degs as i increase rpms and port vac increase to a max of 30lbs i see a reduction of 10degs at 4000rpms that puts the timing at 15degs total, i just hoping thats whats happens going down the track.is that much reduction in timing needed with my boost levels? the head studs are something i have not tried thanks
If I understand this, correctly (the way it is hooked up), it is wrong. You have no vac to the pot at closed throttle, so max advance. At part throttle, you have some amount of vac at the pot, which gives you some retard. If this is what you have, then, at WOT, your port vac will drop to near zero, and you will advance your timing.
Author:  fredmueller1 [ Mon Sep 10, 2007 5:06 am ]
Post subject: 
I've found you need NO vac. adv.

head studs at least 7/17 (I use 1/2" )

all the octane that you can get at anything over 10# boost

Fred Mueller
Author:  terrylittlejohn [ Mon Sep 10, 2007 5:55 am ]
Post subject:  head gasket
charlie i didnt have a chance to check the reading at full throttle, i do have a vac gauge tee in to that line so i can see,but does the port signal normally go to zero at the port on the primary metering block at full throttle? if so what i have done, it will go back to full advance.looks like that was a bad idea.thanks
Author:  terrylittlejohn [ Mon Sep 10, 2007 6:09 am ]
Post subject:  head gasket
fred what are you running and what are your timing and jetting set at ? just for a reference for me, i found a formula on line that with my engine @5lbs of boost i have total compression ratio of 11.79/1and need 599cfms, with the octane ,av gas here is 103 it is the only affortable option i have right now.with the head studs do you run stock head gaskets and do you have a prefference.thanks
Author:  Charrlie_S [ Mon Sep 10, 2007 6:59 am ]
Post subject:  Re: head gasket
Quote:
,but does the port signal normally go to zero at the port on the primary metering block at full throttle? if so what i have done, it will go back to full advance.looks like that was a bad idea.thanks
Normally the port vac will go to the same vac/pres you have at the base of the carb, once the throttle blades open past the port. I don't recall what blower setup you have, (blower, turbo, blow thru or draw thru).
Author:  terrylittlejohn [ Mon Sep 10, 2007 7:43 am ]
Post subject:  head gasket
charlie i have a 4-71 roots with2/600vac holleys,they might be the other source of my problem :?:
Author:  Charrlie_S [ Mon Sep 10, 2007 7:54 am ]
Post subject: 
Two solutions for your vac advance/retard come to mind.
1) boost timing master (electronic)
2) similar to what you are doing now (mechanical)

If I remember correctly, Ford used a Vac advance/retard pot, setup at one time. The diaphram was centered in the chamber, it had one source of vac connected to the front side of the chamber for advance, and another sourch of vac connected the the side of the diaphram near the distributer for vac retard. If you could find and adapt the unit to the slant distributer, and hook up the front vac connection to intake manifold vac, leaving the dist side of the diaphram open the air, you could have vac advance at idle and part throttle cruise, and pressure retard while under boost.
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