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#1
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How much compression is too much?
I have a 360 that I'm gonna warm up a bit, and I would like to throw in the Kieth Black 9.8:1 hypereutectic pistons. My truck will be basically all street, and I am sticking with the stock iron heads. There is 94 octane here, will that be high enough for 9.8:1?
Thanks |
#2
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That'll work fine with 9.8. Just be carefull not to over cam it for the street.
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#3
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Are the KB's #107? If so yes you will be ok with 94 octane and should be able to run 34-36 deg total timing! You may wanna run a step colder plug and a jet size larger in the carb. Hope you have aftermarket ignition like MSD.
__________________
68 Coronet 69 Super Bee......new 500 cid comin soon! 73 Duster witha missing 440/727 |
#4
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why do you hope I have aftermarket ignition? cause I dont
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#5
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Not at all a have to have item, sorry for that impression. It is a good investment, and simple to hook up.
__________________
68 Coronet 69 Super Bee......new 500 cid comin soon! 73 Duster witha missing 440/727 |
#6
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After market ignition or Mopar ignition would be a stronger spark and/or more precise. As they would be electronic, which is much better than points ignition. For example.
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#7
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Aaaaahhh yes, yes, these are the KB107's. I hope this sucker smokes em.
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#8
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Dont follow there ring gap procedures on those KB's. .018 is just right on the top ring and go a little closer on the second ring. They will bust the tops off if the rings hit and KB's specs are too wide. We use 'em in our race engines.
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#9
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IMO, your pushing the limit. If you have a problem with pinging, back the timing down until it stops.
When the pocket allows, Fel-Pro makes a head gasket thats .054 thick to help solve the problem. |
#10
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Yeah, I know I'm pushing the limit, but, it seems for a good quality, yet cheap piston, they're always around 8.6:1 with a 72cc chamber. I think, to avoid problems, I might go with a thicker head gasket to get it to 9.6:1 or so.
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#11
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Depending on the year of the motor and the cc's of the head ,unless you have decked the block milled the heads,You should end up with 8.9:1 if your lucky.Becareful It would probally do you good to have the heads cc'd. That way you'll have a truer compression ratio.I am putting together a 408 stroker motor.I've been doing a little home work.With edlebrock aluminum heads at approx.63 cc's the 10.5:1 compression piston I picked out turn into 10.0:1 .So you can buy 9:5.1 pistons but they are based on the size of the "squeeze "area in the head.
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#12
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Sorry valiant, but with 72cc heads, which I cc'd myself, keith black rates the pistons at 9.8:1. This isn't one of those bs 9.5:1 speed pro pistons, where the head size they use is 66cc.
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#13
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You can run 9.8:1 compression on 91 octane if the distributor is curved to the octane level, weight of the vehicle and it's properly carb'd.
If your running a stock distributor I can pretty much guaranttee that it's going to ping...as you bring the timing down to get rid of the ping you'll probably not have enough timing to make it idle clean...your whipping a dead horse. Email me direct and I'll send you the spec sheet and we can look it over and come up with a distributor curve that will give you initial and max timing events at the right time to make that thing ....... "I hope this sucker smokes em." "I think, to avoid problems, I might go with a thicker head gasket to get it to 9.6:1 or so." Do all the math and calculate the exact compression ratio with a .040 gasket, we can then adjust it up or down by using the Cometic MLS head gaskets from .025 to .125 thickness. Also allow for the bore size in the gasket...Felpro 4.180, 360 Mopar 4.00 bore so you have a big gap in the combustion chamber which robs big compression. The Cometics are custom cut to your bore size which will give you correct C/R calculations. Ignition system? What are you planning on running? What Carb are you trying to use? |
#14
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Well Cuda, you're probably gonna burn me for this, but I'm gonna go with a stock, re-curved electronic ignition.
Along the lines of a carb, probably a TQ 800. It's a heavier than average vehicle, being a truck and all, so I think I'm gonna tune down the comp. so I can safely run 91. |
#15
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I say BAH to settling. Just have a nice pow-wow with good old Don and you wont have to limit your compression ratio to a low number.
-Fox Deacon |
#16
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Damn your pretty lucky to get 94... here in Cali its 91 at best. But I bet you will be fine with that compression. My friends got a cougar with a 302 rated at 10.5 : 1 compression and that thing manages to run on 91... doesnt really ping but im sure hes loosing some power with our crap california gas.
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#17
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Fargo318
Do you have a deck height of 9.588" to give you zero top of piston to deck height and then gives you 9.8CR with 72cc heads. If you have a 9.6 stock deck height you will have 9.5CR to start with with a .040 th x 4.100 gasket. Send Don the distributor to recurve for you and you should be right on with 89 pump gas or worst case premium. M2cw
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#18
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Really 345 Dart, I was unaware of that. I just got off school, and will hopefully see my machinist before I have to go to work later, so I'll look into that, although I'm happy with 9.5 or 9.8:1 compression.
Thanks |
#19
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Fargo318
FMI, what brand of station sells 94 octane?
Best we can get here in Alberta (where the crude comes from) is 92 - just curious. 9.5 calculated with new parts will give you 9.8-10.0 after some miles depending on carbon buildup. 9.8 calculated with new parts will give you 10.0-10.2 after a few miles, thus it can make a big difference in the "Final" result. I think what Don meant by stock distributor is just that - no change in distributor curve will probably get you pinging @ 9.5. There is nothing wrong with the Mopar distributor. It just needs to be curved for your engine application. Good luck with your project. |
#20
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ultra 94
Sunoco is the only station that is selling 94 octane in New England.Although if your lucky enough to live near a race track there are stations that sell 101 or better............ but it costs !!!
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#21
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Here, Petro Canada sells 94 for sure, and I believe Chevron has 94 octane as well.
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#22
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I have a quick question. I was running a stock 68 340 with a cam that had too much overlap thus sacrificing some compression. The engine is supposded to have 10.5 to 1 compression. I am changing cams to bring the compression back to stock. Will I have a problem using pump gas?
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#23
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You'd have to use the highest grade. And be prepared to use an additive. You may want to get your distributor recurved, or at least checked.
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#24
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Canadian Guy's!
We're putting together a group shipment at Dave's Mopars in Calgary.
Because of the frieght costs in shipping one distributor at a time Dave and I decided to try and get a group shipment going. We can ship about 12 distributors for not much more than 1 and it cuts down on the massive paper work....6 copy's of invoice, cutomes declaration forms etc. Email me or Dave and we'll send you the form to fill out and include with your core, If you don't have a core to send just email the form back and we'll build you one from our core bin. bigdaddy@4secondsflat.com dave@davesmopar.com |
#25
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My distributor is the aftermarket mopar electronic one and I'm using a Msd6AL ignition.
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#26
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" My distributor is the aftermarket mopar electronic one and I'm using a Msd6AL ignition."
Good starting point so all you'll need is a curve and phase, everything else should meet spec. http://www.4secondsflat.com/Ignition.html |
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