Ok I've been talking to Ignitionman Dave about the problems that I'm dealing with on my 350. Some of you have already tried to help and I appreciate it. This is the scoop. I have detonation problems at high RPM's. I'm talking 4K and above. Dave thinks the major problem is Quench area. To much that is. I have some where right around .080 in. clearance. The piston is .035 down the hole and the gasket I'm using is a felpro blue which should have a crush thickness of .045 in. This gives me around .080 in from the top of the piston to the head. I calculate that I have 10.1 to 1 compression now. If I have to mill the block any further to bring the pistons to a 0 deck clearence how much higher will my compression be? The heads have a 54 cc combustion chamber. Is milling the deck the only or best answer? Have any of you run into similar problems before? What does every one think?
Jason, the 350 Buick has a unique situation here. Unlike the 455, the 350 uses a full open chamber, so even if you deck the block to zero deck, you will still have no squish area in the chamber . The squish area would be the area where the flat part of the piston is against the flat part of the head, there is no flat part of the head on the 350 Buick. So in answer to your question, decking the block will raise the compression, probably about 1/2 to 3/4 of a point, but I don't think it will help your problem. One way to possibly help your problem would be to use an rpm activated timing retard that could activate at say 4000 rpm and you could pull out however much timing you need to in order stop the detonation. Feel free to contact me via phone again if you'd like to. Jim Burek P.A.E. ENTERPRISES
I'll ask a question, then give an answer. On the solder pattern, are both sides flat? As in piston top and head flat? If the head pattern isn't flat, tapers upwards twords the chamber center from the edge of the bore, then I'd go for no quench area at all. ANY flat on the head side of the solder pattern indicates a clear quench situation. What does the solder pattern show, and how thick is it? Your appx setup is, piston down appx. .035 in the hole, and the head gasket of appx. .045 thick, with an overall distance of appx. .080. I just ran this all through my head once again, and feel even if the chamber tapers upwards from the bore wall, you still want .039 to .045 in the tightest part of any area, even the edge. Instead of decking the block, and since the compression ratio will possibly go too high if the block is decked, I'd have a new set of pistons made, with zero deck, an inverted dome (dish, 3.200 diameter, .042 deep, and run the .045 gaskets. I know, expensive, but...... No matter what, I'd maintain the distance between any part of the head and the piston top at those distances normally considered "proper quench". From what we have spoken of and what happens, that'd be what I'd do.
All that sounds pretty expensive.....what would you guys think about goin to a thin steel head gasket like the ones TA offers. Theyre available in 0.020, maybe thinner sizes to, but the catalog says 0.020
They are only available in .020 thickness. That will raise the compression the same way as milling the block . The point I was trying to make was that the chamber design on the 350 does not allow for any squish area , it is the same diameter as the cylinder bore. Jim Burek P.A.E. ENTERPRISES
The chamber has to have a roof, even out at the bore wall. From what Custom says, is .080 from the pistion top. I'd make that distance .039 to .045 and dish the piston to get the right compression ratio I desired. My 215 derived engines use an aluminum head, with very, very little quench area, and all the 350 heads I have seen had chambers like them. I still set 'em to the dimensions I specified.
The 350 head is nothing like the 215, I have both here. The chamber is exactly the gasket size all the way around, and it is a bowl shaped chamber, it goes straight up from the edges. The 215 head has a flat area that mates up against the piston. Jim Burek
Would it work to have a small dome on the one side, such as a Mopar? They have a small .140" dome as an option.
k... I'm not too educated on "quench".... but... I had my heads milled .060. Now, it got real close, and on one or two cylinders, actually touched the combustion chamber with the mill. So would milling say .080 off of the head give a flat spot on the head? Sort of make them closed chamber heads... like I said I'm not edsucated on theese things, so... just a thought...
I know a guy that did something similar with a set of 360 Mopar heads - they have a circular combustion chamber too. Did exactly like you said...went right into the chamber and took out the 'dead space'. I was always curious if the 350 heads could be angle milled, or how much they could be flat milled - before striking water! Hopefully, if and when TA comes out with some much needed aluminum heads for the 350, they will incorporate a heart shaped chamber like the Stage 1 alum. heads!!
customsky, I'd still like to know what physical dimension you came up with on the solder test we discussed. I never mentioned I used 215 heads, just 300 aluminums (which are somewhat the same as 215 heads), on 215 DERIVED engines. I don't build an aluminum engine smaller than 309 cu/in and NEVER use 215 heads. I'd be surprized if KNOWLEDGEABLE head designers/builders these days DIDN'T build a heart shaped combustion chamber, or a real Hemi. I weld the 300 heads up and cut them into heart shaped chambers, and then have Ross build the pistons with a pantogram heart shaped matching dish in them. Doug Roe and I did the heart shape chamber mods to Vega heads almost 30 years ago now, when he and I worked it out at GM, and then at his place in Phoenix, Priminion Enterprizes.
what about the cheap obvious Why not back your timing off? You guys have more experiance than me, but not every 350 has problems over 4K, mine didn't. Isn't trying to achive zero quench a relatively new idea? Where the flat part of the piston pushes everything right to the valves, and in doing so gets a real good air fuel mix for combustion?
Hey Dave I tried the solder test you suggested and wasn't able to squish any part of the solder. I bent it and inserted it all the way up to the top of the chanber and nothing. I tried all angles and became confused as to why I couldn't get it to squish. I went out to check some of the clearances on my spare 350 and evan without a head gasket (just the heads on the block ) I turned the crank over and could not get a squish of any kind on the solder. It comes down to there just isn't any thing to squish it against. The piston would have to come way out of the hole to get any contact area with the head. As a side note I changed the jets in my carb and noticed a dif. I didn't eliminate the ping but it was almost gone. I talked to Demon and they say I have to big of a carb on this type of setup. they would only recomend a 650 or 675 cfm carb. They recomend that I jet up another 3 jets just for a new starting point. I plan on doing that this morning. The plugs are still pretty clean so I don't think that I will get too rich making this adjustment. Who knows maybe this is all the adjustment I need to get rid of the ping. My only concern now is how much extra gas do I have to poor down this engine?
Josh retarding the timing is not the answer here. I have already turned it back enough to get rid of the pinging problems but that means less than 27* of total timing. The engine runs like a two legged dog. Retarded.
Sounds like they're not familiar with Buick carb sizing! Pretty hard to 'over' carb one of our V8's. They just seem to like the big carbs.
Whew, wouldn't even make a dent in the solder, that's a lot of room for poor end area lean mixture induced detonation. No wonder it talks back. Sounds like you 350 guys despirately need a decent head with a much better heart shaped chamber. Might be the only way IS to drown the daylights out of it. Poor way to fix it, but if that's the only answer...... No pics of the head mods, but I'm doing another two sets fairly soon, and will take pics then. Latest revised chambers are much like a new LS1.
Well I just went up in jets again and it didn't solve the problem. As a matter of fact I'm now facing 2 new problems. First the engine wants to bog or stall when you floor it from a stand still. Second the trany won't stay locked in first no matter what I do. Talk about a total kill joy. I think I'm going to have to jet down again. although I have driven the car a few miles under different conditions and the spark plugs are just starting to take on a little color. As a side not the jets I put in are 78 primary and 86 secondary. Demon recomends keeping a 8 jet dif. between the pri. and sec. jets but I thought I would give it just a little more gas during wide open throtle. Back to the drawing board.
