Re: How much compression is really enough?
[Re: johnzgarage]
#818084
09/29/10 11:02 PM
09/29/10 11:02 PM
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Joined: Oct 2004
Posts: 8,165 Left Coast
BobR
master
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master
Joined: Oct 2004
Posts: 8,165
Left Coast
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Quote:
just depends on the spec of the cam ,It will affect your compression. Also buy using an aluminum heads, you can knock 1-1.5 compression off the top , due to dissapation of heat from the heads. I would go with 11 to 1 and pick the right cam .
I agree. Altitude also lessens octane requirements.
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Re: How much compression is really enough?
[Re: dOc !]
#818085
09/29/10 11:04 PM
09/29/10 11:04 PM
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Joined: Nov 2003
Posts: 6,293 Rock Springs
Bob_Coomer
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master
Joined: Nov 2003
Posts: 6,293
Rock Springs
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I have personally built this very same engine, about 6 years ago. It ran strong, was able to push my 3800 lbs full interior 69 Coronet to 7.20's in the 8th mile, thats a easy high 11 second 1/4 mile pass. I also ran pump 92-93 fuel also. Compression was right at 11:1 With a zero deck engine, your stroke and 84 cc heads your will also be 11:1+ my pistons were in the hole by .005-.008 with 4cc valve reliefs. I set my timing at 32 deg total. This was plenty of timing for the engine, and help keep spark knock out of it also. IMO having the compression up so high that it needs to be backed off a fair amount is a waste, and the little gain you tried to shoot for in the increased compression is now lost with the NONE optimal timing. You might even loose 2-3x as much pulling out timing. You would be surprised to know how much HP one can loose by pulling 8-10 deg out away from its optimal timing point. Maybe as much as 50HP in some combo's. Consider the gain you only get from 1 point in compression on a typical engine, what maybe 3%-5% overall. So what on a 500hp engine you talking maybe 15HP??
Last edited by Bob_Coomer; 09/29/10 11:07 PM.
[color:"red"]65 Hemi Belvedere coming soon [/color] [color:"#00FF00"]557" Indy engine 1.07 60ft 144mph in the 8th 2100 lbs package [/color]
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Re: How much compression is really enough?
[Re: Bob_Coomer]
#818087
09/29/10 11:23 PM
09/29/10 11:23 PM
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Joined: Dec 2004
Posts: 10,558 Rittman Ohio
fourgearsavoy
I Live Here
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I Live Here
Joined: Dec 2004
Posts: 10,558
Rittman Ohio
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I have just a tic under 11-1 compression in my 493 with flat Wiseco pistons and Indy EZ's.I run 93 pump gas with total timing set at 32 deg.and it puts my 3550# car at 11.13 @ 123 with a 1.8 60' time. I just run a small street flat solid Comp XTQ series cam. Gus
64 Plymouth Savoy 493 Indy EZ's by Nick at Compu-Flow 5-Speed Richmond faceplate Liberty box Dana 60
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Re: How much compression is really enough?
[Re: frank]
#818089
09/29/10 11:56 PM
09/29/10 11:56 PM
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Joined: Oct 2003
Posts: 7,506 Az
Crizila
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master
Joined: Oct 2003
Posts: 7,506
Az
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I'll just say this; Listen to your engine builder. If your motor gernades, no one on this thread will loose anything but you. As the CR numbers go up, the HP gains deminish - rapidly. Leave some room for error. You ain't always gonna be pumping 93 octane, even if that's what the pump sez. What happens when you are running on the ragged edge of detonation and you get stuck in staging with the motor running and gotta leave hot - or you launch the fan belt at half track? Trust me, it ain't worth the additional 15 or so HP.
Fastest 300
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Re: How much compression is really enough?
[Re: frank]
#818093
09/30/10 01:42 AM
09/30/10 01:42 AM
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Joined: Aug 2003
Posts: 43,295 Bend,OR USA
Cab_Burge
I Win
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I Win
Joined: Aug 2003
Posts: 43,295
Bend,OR USA
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I've built and dyno tested a bunch of Mopar wedges motors over the years, stock stroke N/A pump gas street motors, NHRA legal "Stock" motors, high compression bracket motors and so on. 10.0 to 1 up to 10.5 to 1 comp. ratio is very safe with todays pump gas using the heads you have as long as you use a big enough cam to feed the motor not a RV cam The 4 speed and tires will determine how good the car ET, the motor will determine the MPH I built a iron headed (ported 906 heads) low deck pump gas 512 C.I.(4.25 stroke, 4.375 bore) stroker motor that had a true 9.25 to 1 comp. ratio. It had (I have since hopped that rascal up some more ) the ported big valve iron heads(same size valves as the stock Eddy RPM do), stock type six pak intake and carbs. comp Cams custom solid roller cam and kit. I had the motor dyno tested on a DTS engine dyno in Ontario, CA on CA pump gas, it made 644 ft. lbs at 4500 RPM and 612 HP at 5600 RPM I put the motor in my 1971 Duster, 3450 LBs with me in it with full 3 inch exhaust system and a full tank(stock 14 gal.tank) of pump gas, 727 and 315x60x15 ET Street radials, 727 trans, ten inch Continental converter, 4.10 gears in a 8 3/4 with ladder bars. the car ran 10:69 at 124.5 mph the first time at a 1/4 mile track. My car does not spin the tires at the track, it flat hooks and moves. I lived in Hesperai, CA 3300 ft. altitude, when I built that motor and car so the compression ratio was determined by the CA pump Gas and where I lived at that time The clutch and 4 speed trans will be the real channel to hooking your car up, sorry The motor will make all the power you need, maybe to much power Good luck
Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
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Re: How much compression is really enough?
[Re: Cab_Burge]
#818094
09/30/10 07:54 PM
09/30/10 07:54 PM
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Joined: Jan 2003
Posts: 27,421 Balt. Md
383man
Too Many Posts
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Too Many Posts
Joined: Jan 2003
Posts: 27,421
Balt. Md
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I plan to start building my 500 inch stroker real soon and it will be close to yours. I plan to use CNC ported Eddy RPM heads and I will run 11.0 to 11.2 comp at least and I still plan to use 92 or 93 pump. I plan on a pretty stout solid roller as I want to make alot of power out of it. I also plan to have nice quench in it as it will be a zero deck closed chamber head eng using a .039 head gasket. I want to have aleast 600 to 650 hp as I want to put my 3700 lb 63 solidly in the 10's. Thats why I will run at least 11.0 comp and then use a stout cam to keep the cyl pressure where I want it. Ron
Last edited by 383man; 10/01/10 03:53 AM.
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Re: How much compression is really enough?
[Re: 383man]
#818095
09/30/10 08:12 PM
09/30/10 08:12 PM
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Joined: Sep 2003
Posts: 2,008 Sweet Home Alabama
MRMOPAR622
top fuel
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top fuel
Joined: Sep 2003
Posts: 2,008
Sweet Home Alabama
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If I was spending the $$$$ to go up to 500 cu. in. and aluminum heads. I think I would want all the CR I could get and be safe on pump gas. You can run 11-1 and be safe on pump gas. So why drop down to 9.5 CR and give up the extra HP you just spent all the extra $$$ to gain?
It is however wise to ask others who have run that just to be safe.
"To Be The Man'You Have Got To Beat The Man"
"T/D and Pro-Bracket Racer"
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Re: How much compression is really enough?
[Re: Crizila]
#818097
09/30/10 09:02 PM
09/30/10 09:02 PM
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Joined: Jan 2003
Posts: 15,439 Val-haul-ass... eventually
BradH
Taking time off to work on my car
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Taking time off to work on my car
Joined: Jan 2003
Posts: 15,439
Val-haul-ass... eventually
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Quote:
I'll just say this; Listen to your engine builder. If your motor gernades, no one on this thread will loose anything but you.
, but true...
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Re: How much compression is really enough?
[Re: 440Jim]
#818099
09/30/10 09:18 PM
09/30/10 09:18 PM
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Joined: Jan 2003
Posts: 4,247 Newfoundland
codfish
master
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master
Joined: Jan 2003
Posts: 4,247
Newfoundland
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Quote:
It depends on several things, including how much cam duration you will be running. I would build it with 10.5 to 11.0 CR and 260ish duration at 0.050". And that will be mild.
Yep.
I have 11.2-1 comp with an engine identical to the build you are describing. My cam has 263 duration at .050". Runs fine on 91 octane. 36* total timing.
codfish
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