Compression

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Also depends on how high above sea level you are. I will be running 8.8DCR Iron magnum heads and 91 octane 10.1 static compression. This is what Brian at IMM told me to run and said he has run it before and it will be fine. Should have mentioned my camshaft is 251 and 260 @50
 
Has the block been square decked to the blue print height of 9.6? If the deck height is not "set" (because they are all tall by a bit from the factory) then the quench and true compression will be off. At that point the best way to get the true compression is to measure and calculate using the 1" down method.
As far as acceptable pump gas compression ratios - for an aluminum head built with no regard for quench my max is 10.8:1 static, or 8.25 dynamic. For an engine built with a quench distance of no more than .040 my max is 11.8:1 static or 8.75:1 dynamic.
You can go lower with not big issues, and you may be able to go higher depending on the quench distance (tighter is better) and camshaft choice.

If race gas is not a problem I'd build for 12:1 by milling to reduce the chambers and the cam would be a flat tappet solid in the 260° @ .050 area with lift around .650 lift.
 
Moper what would be your dynamic with iron heads with ,04" quench and pump gas ? I was shooting 8.3:1 after reading what you said its looking high
 
OldmanRick said:
I see they were flowed to .600" but that doesn't always mean the clearance is there for the springs via cut down guides or longer valves. You can obviously use some substantial lift with those flow numbers, but the intake timing will be crucial at high 9ish to 1 to keep some cylinder pressure. The easiest way to get big lift and conservative cam timing is with a roller, or 1.6 rockers, but let me run some numbers and i'll get back and give my opinion......which may only be worth what you paid for it..lol :D.
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I looked at alot of grinds and this is what i came up with. Tried to compromise on raciness and decent manners if you chose some street cruising. I settled on a range of mid/high .500" lift and high 240* to mid 250* @ .050. Mainly looked at Comp & Lunati and these looked the best as far as off the shelf cams for what i was thinking........

Solid.....Lunati.. http://www.lunatipower.com/Product.aspx?id=1542&gid=317
http://www.lunatipower.com/CamSpecCard.aspx?partNumber=60442


Solid Roller....Comp.. http://www.compcams.com/Company/CC/cam-specs/Details.aspx?csid=689&sb=0


No matter what cam you end up with, make sure you discuss the proper springs for your installed height, which i believe is 1.80" on as delivered Eddy heads.
 
273 said:
Moper what would be your dynamic with iron heads with ,04" quench and pump gas ? I was shooting 8.3:1 after reading what you said its looking high
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If you do 10.7-10.9 compression with the XS282S which is 67IVC that will give you 8.5 or around that DCR and I ran that on 91, but I did have Magnum heads aka closed chambers for help.
 
Rick, the first Lunati cam is one I've actually been thinking about. I referenced it in an earlier post. Do you think Ill have issued if the pushrod tubes havent been clearanced?
 
75dartsport said:
Rick, the first Lunati cam is one I've actually been thinking about. I referenced it in an earlier post. Do you think Ill have issued if the pushrod tubes havent been clearanced?
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Wow, i never clicked on that link...lol.
I think with the solid lifters it will be ok. The extra height on a roller lifter may cause a issue though. I can't say for sure. Hope a member running a similar head/lift will chime in for confirmation.
 
273 said:
Moper what would be your dynamic with iron heads with ,04" quench and pump gas ? I was shooting 8.3:1 after reading what you said its looking high
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Closed chamber iron heads with tight quench my target is under 8.25:1. I've gone as high as 8.5 for our 10% ethanol pump 91. But that takes careful tuning and if you just gas up at the local Quickie Mart you might get more then 10% ethanol, or lower octane than 91 even tho the pump says that. Then you may have a problem. Remember that dynamic compression ratio is a constant, but the cylinder pressure is not. It will rise with rpm. So you might be fine at idle or 2K, but at 5K it's beyond the fuels detonation threshold and you may not hear it, but it's detonating enough to hurt stuff.
Also bear in mind these are my self-imposed limits. Others I'm sure have thier own thoughts.
 
75dartsport said:
Do you think Ill have issued if the pushrod tubes havent been clearanced?
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OldmanRick said:
I think with the solid lifters it will be ok. The extra height on a roller lifter may cause a issue though. I can't say for sure. Hope a member running a similar head/lift will chime in for confirmation.
Click to expand...

I assumed with 1.5 rockers, 5/16 pushrods and standard height lifters it wouldn't be much of a issue, but after checking other threads here, some did have to clearance the Edelbrock heads.

Bump for more input.
 
As a rule I always add some pushrod clearance with the RPMs. You may be ok, but I'd check carefully.
 
i am running a custom grind comp cams solid that i find to be pretty nice i coppied the build from mopar muscle where they dynoed 477hp on a fairly stock bottom end 340 and some mild porting.here are some of the specs .573/.586 gross lift with 1.6 rocker gear 265/269 advertised seat dur at .020 239/243 at .050 and 157/161at .200 the article was in nov 2002 issue mopar muscle.
 
What could I expect my HP/TQ to be with this combo and the Lunati solid cam listed above?
 
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