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#1
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Can you run 11.5 on the street without octane boost in a 360? What cam and also what sort of stall would be required? The car has 3.73 in it now and weighs 4000 approx. Anyone have any ideas?
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#2
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I personally don't think it can be done efficiently. Yes, you probably could get away with it, but it wouldn't be a good combination for the street or strip for that matter. The cam would have to be very large and probably wouldn't idle much under 1800 rpm.
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#3
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Does your engine have a true 11.5:1 compression, or is that what pistons you installed? It is possible to run 11.5:1 pistons in an engine and only achieve 10.5:1 true compression. Also, Are you using Aluminum heads? They will allow you to run more Compression without pre-detonation, due to their more efficient dissapation of heat.
------------------ Mike (440trk) |
#4
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Aluminum heads, good quench chamber and a huge cam, and it can be possible. I'm running 11.3 in my big block and about 93 octane pump gas, but with 0-deck pistons, closed chamber aluminum heads and a cam with more than 275 degrees at .050" lift.
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#5
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440trk; The pistons are rated at 11.5. How can I achieve 10.5 actual? The cam is a 288/292 with 458 lift, if that helps at all. Thanks......
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#6
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Well, The pistons will only give you 11.5:1 under a given set of circumstances, of which you may or may not have met. A simple change to a different brand, or type of headgaskets can alter actual compression to some degree (due to differences in material thickness when compressed). I can not really say what combo will give you 10.5:1 with the pistons you have..I would need MUCH more information. (such as...How far down in the cylinder are the pistons at TDC? What is the CC of your Cylinder head chambers, what is the compressed thickness of your head gasket, etc...). Is this engine assembled? Have you run a Compression test on the cylinders? (This will give you cylinder pressure, not Compression ratio) If so, what reading did you get? If you can give me the above info, I should be able to tell you what your Compression Ratio is (relatively accurately). Also, Are you running aluminum heads? They will make a difference. So will your cam choice. Chances are, you are not really running a true 11.5:1 (it is possible though...)
------------------ Mike (440trk) |
#7
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440trk; The 360 engine is not assembled yet, just gathering the pieces together. The pistons are TRW forged, stock '78 heads with a mild porting and polishing, Felpro head gaskets,stainless small valves.All I want is an engine that does'nt self destruct due to pinging or adding gallons of octane boost! lol
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#8
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Are the pistons hollow domed or are they solid. I presume they are solid. If so, you could opt to mill all or part of the dome off to get to a more streetable compression ratio.
The cam you have selected isn't really a big cam, considering the compression ratio you want to run. It should have something like 240° duration @ .050" lift. I was thinking along the lines of 265° plus @ .050" lift to get away with your desired compression ratio. You could also purchase a thicker head gasket designed to lower compression ratio. I think you can get them up to .080" thick. You may also be able to find a shim for the head gasket. Either of these will lower your compressio |
#9
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sanders.... it shouldn't be that much of a problem with a set of alloy heads and some duration on the cam
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#10
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If you've got 11.5:1 true mechanical compression and unmilled open chamber heads youll need a .040 head gasket and a cam w/duration @ .050 of 260-265*,this is huge for anything streetable and 4000lbs.I know you can mill the TRWs subtansially,I had 10;1s milled and they became 9:1s safely.So if you end up with 10.5 youll need a cam w/duration of 240-245* this is much more reasonable.If your heads are milled .060 add 8* more of dur. and 16* if milled .060. All these #s are taken from data I've acquired from actual engines I've built and swapped cams on so they should be very close.Your looking for 135-145 cranking compression.You have to take into consideration 3 things to decide stall,cam,comp,gear,weight ,w/o more info I cant guess....PRO...
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#11
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Pro, Rowdy, and 340King all have workable solutions. It would be cheaper to buy new pistons, than to purchase the aluminum heads, however, you can probably have your pistons milled down to a more reasonable Comp. Ratio. That is going to have to be your call. If you know someone who is willing to purchase your 11.5:1 pistons, sell them and purchase a set of 10:1's with the $$$$ from the 11.5's. The 10:1's will be much happier on the street, running pump gas. Again, depending on what parts you use, you could end up with a compression ratio that is not a true 10:1. You are really going to need to talk to TRW and get some info on how much you can mill your pistons, how far down in the cylinder they sit at TDC on a stock engine (then figure out where your block is in relation to a "stock" measurement). Did you have your heads CC'd when they were ported? If so, what is the CC for the cylinder head chamber? Also find out what the compressed thickness of your headgasket is. From there, we can start to get an idea of what your TRUE Compression ratio is gonna be. THEN, figure out the best way to address your situation.
------------------ Mike (440trk) |
#12
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440trk, Pro,Rowdy and 340King,thanks for all your help so far! My heads got messed up during the machining process.Just my luck. They are going to be replaced with fresh '79 heads. Now I'm leary about getting any work done to them. I checked a few web sites,Crane and Hughes etc.,and my cam comes fairly close to what they say can be run with 11.1's.I just do'nt have the same lift. Will this be a factor? I'm hoping that with a thick gasket and stock heads I'll drop close to a point. If I just go with a thick head gasket, stock heads and 104 octane boost at fill up, will that cut it?. I'm so frustrated with my machinist that I'm not wanting any more work to be done, if possible! Thanks again for any input .
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#13
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Some of the new cars run compressions about that high and they don't need octane booster of course, so the answer is yes. (BMW M5 is a 300 cubic inch V8 with 11:1 CR that makes 400 hp on pump gas. Also costs a fortune)
Now the real question is: "can I run 11.5 CR on the street in a wedge head Mopar engine without spending a fortune". The answer to that question is no. Not at least if your defination of "running" means, starting easily, idling without fouling the plugs, actually capable of being driven in stop and go traffic, etc. If "running" means driving it over to Telegraph road after midnight for a date with a 427 Nova then damn right it will work! |
#14
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I would look for the thickest (comressed) head gasket you can find for the 360, and find out the Combustion chamber CC of those STOCK 79 heads. I am guessing that by doing that, you will possibly drop to the high 10's or low 11's on the Compressin Ratio. Using stock CC heads (combustion chaber CC) will definatly help you out. Let us know what you find, and we will help ya as much as possible.
Good Luck! ------------------ Mike (440trk) |
#15
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451 boy:
Yes some new cars run on high compression. The Chrysler 300M and Chevy Corvette both have a 10:1 ratio. BUT, that is totally different technology. Fuel injection and other advances will allow new cars to run high compression. |
#16
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Don't forget, the new high compression engines are also running aluminum blocks and heads.
------------------ '96 Dodge Ram 1500 SLT CC 360 4X4 '68 Charger 383-4 |
#17
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Thanks guys,if it was'nt for this forum I'd be in a real mess. Took a look at the '79 heads. They look good , BUT, the chambers do not match. One head has the chamber taper off near the spark plug hole, the other has an approx. 1/8" ridge in the same area. Both have the letter 'A' cast in near the casting number. One casting number is 4027596 (the one with the taper), and the other is 4343475A (the one with the ridge). Other than that, they are twins. They both have nailhead intakes but the top of all the valve stems have been ground down.This has left them all equal in height.Should I trust these heads any further before I get them checked for cracks etc.?
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#18
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Have the 79 heads checked. Have them CC'ed and match each chambers CC. Then if you need new valves go for it and have them also enlarged and unshroud the heads for the valves will be better to start out with the right heads than just something you slapped together. Also work on proting these heads too they will perform alot better.
Christian ------------------ 68 'Cuda 383 Working on adding EFI |
#19
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Why do you have 2 different casting numbers? I would try to find a matching set of 360 heads.
Just my .02 ------------------ Mike (440trk) |
#20
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If you're gonna build an 11 : 1 compression engine, then it's safe to say that whatever you do it not gonna be a ghetto job - well it shouldn't. If you don't have a matched set of heads then you're backin' up. If you don't want to fork over allot of money, look for a set of 587( easy to find) or another 596.
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#21
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This is what the machinist wanted to give me in exchange for my heads that he messed up. Needless to say , I passed on them.....and him too. Now I have to find a match for my other'78 head that he never touched. And the saga continues........
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#22
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Sanders440,
So which casting number are you looking for in the "'78" head??? Maybe we can point you in the right direction. |
#23
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MopART; the lone head is a 4071051 casting number. The 4343475-A casting that was offered to me seemed like a match, but the way things are going up here, I'm not sure that I can pair them up. Or can I? (Maybe I should change my name to"Lost in parts"! lol)
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#24
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My Duster has 11.5 pistons {360+.30}with an old Direct Connection cam {606 lift/312 duration}and a 10" TCI converter{3000 stall}. Sometimes I would run premium gas with octane booster or mix racing with regular gas{kinda expensive}.Heads are "x" casting. Run CHAMPION R-11 plugs on the street and R-7 for racing. Never had any problems,knock on wood. MOPAR or I walk!@#$%^
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#25
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Sanders440 wrote :
>>The 4343475-A casting that was offered .... Sanders440, I don't even see this head referenced. Do you have the head there to recheck the numbers? The 051 head you have is not the best thing in the world - used on '77 - '79 360's and the '81 -'83 hp 318's, but it's workable in a budget crunch. If you can stand it, I'd look for a matched pair of maybe 587, 596 or even just get another 051. It's not clear if the 360 051 and the 318 051 heads had different cc volumes. Just guessing, and I hate to guess, but the 318 may have a smaller chamber. If I'm not mistake, and someone correct me on this, but the inside top of the head, around or inbetween two of the spring perches should have a 318 or 360 cast into it. This would be your clue. |
#26
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MopART; The 475-A casting number is correct....the only other number is 15 cast into the side and between the perches. The 051 head has no reference to 318 or 360, but I do know that it came off a stock 360.Are these heads less desirable because of the larger chambers? Larger would be better for me since I need to calm the compression down.If I can get these 2 to work together...all the better. If not...want to buy some heads? LOL
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