How much compression is too much?
#2464199
03/10/18 10:12 AM
03/10/18 10:12 AM
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Joined: Aug 2009
Posts: 2,074 Mooresburg, Tn
'72CudaRacer
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620ci RB, B1 MC heads, cam is .850" lift solid roller, duration 286/306 @ .050", carbureted on gas. Bore 4.600", stroke 4.665", piston 10.3cc dish volume, combustion chamber volume 52cc, head gasket compressed thickness .066", 4.600 bore size". How much compression ratio would be considered too much? This is a bracket engine, to be raced on a weekly basis. The engine was brought to me with 16.4:1. I can change head gaskets to get it to 15:1 with out doing anything else. The question is, how much is TOO much?
Thanks, Brian
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Re: How much compression is too much?
[Re: '72CudaRacer]
#2464239
03/10/18 12:22 PM
03/10/18 12:22 PM
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Joined: Oct 2007
Posts: 4,219 New York
polyspheric
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I can change head gaskets to get it to 15:1 with out doing anything else. Losing your quench isn't a good idea unless your VE is very low.
What does your chamber wall look like adjacent to the intake valve?
Boffin Emeritus
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Re: How much compression is too much?
[Re: '72CudaRacer]
#2464270
03/10/18 01:44 PM
03/10/18 01:44 PM
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fast68plymouth
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I'd run the thicker gaskets and not worry about the quench.
68 Satellite, 383 with stock 906’s, 3550lbs, 11.18@123 Dealer for Comp Cams/Indy Heads
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Re: How much compression is too much?
[Re: '72CudaRacer]
#2464306
03/10/18 03:23 PM
03/10/18 03:23 PM
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Joined: May 2006
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JD Dart
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Buddy of mine had the same problem with C/R. He called Koffels and they said the B1 heads don't tolerate much over 15.3. I'd go with the thicker head gasket too. And I must ask what block is that to get 4.600 bore?
best so far 8.53 @ 158.59 MPH 60'1.240
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Re: How much compression is too much?
[Re: '72CudaRacer]
#2464308
03/10/18 03:32 PM
03/10/18 03:32 PM
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Al_Alguire
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No reason for a basic bracket engine to be at that kind of compression ratio for sure. My little B1 was at 15.5 and worked pretty well for what it was. The one from the dragster is 15.3-1 and works pretty well too.
Id like to see the piston that gets you that kind of compression number for sure. I though I saw it was a world block somewhere but maybe not. 4.600 aint gonna leave much room between the cylinders on a 4.800" BS block for sure.
"I am not ashamed to confess I am ignorant of what I do not know."
"It's never wrong to do the right thing"
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Re: How much compression is too much?
[Re: gregsdart]
#2464319
03/10/18 03:42 PM
03/10/18 03:42 PM
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HotRodDave
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I'd run the thicker gaskets and not worry about the quench. I have heard that quench effectivness diminishes as rpm goes way up? One of the guys on here did an experiment with a 440 and went from bad quench to tight quench and saw the biggest gains as the RPM went up, big time, like 50 HP. I think it was jesse lackman but don't quote me on that.
I am not causing global warming, I am just trying to hold off a impending Ice Age!
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Re: How much compression is too much?
[Re: '72CudaRacer]
#2464342
03/10/18 04:38 PM
03/10/18 04:38 PM
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Joined: Feb 2008
Posts: 452 Monrovia, So-Cal, USA
racerhog
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If it's been working?? Just use it as is... Just dont lug it in some heavy azz turd car and changing the combo to much... Just my 2 cents... Or drag the junk over to Greeneville TN and have the Johnsons dyno it...
Last edited by racerhog; 03/10/18 04:38 PM.
Bob(Cowboy)Hogan Monrovia So-Cal
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Re: How much compression is too much?
[Re: '72CudaRacer]
#2464344
03/10/18 04:48 PM
03/10/18 04:48 PM
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Joined: Jan 2003
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gregsdart
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If you do consider running methanol, a very sharp engine builder told me 15/1 is about the max that works well. Over that, more fuel is needed to run well, eliminating the advantages, and it is hard on parts.
8.582, 160.18 mph best, 2905 lbs 549, indy 572-13, alky
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Re: How much compression is too much?
[Re: fbs63]
#2464377
03/10/18 05:52 PM
03/10/18 05:52 PM
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Joined: Aug 2009
Posts: 2,074 Mooresburg, Tn
'72CudaRacer
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What's the lobe separation on the cam? Crane cam, lobe separation 114.
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Re: How much compression is too much?
[Re: LSP]
#2464382
03/10/18 05:57 PM
03/10/18 05:57 PM
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Joined: Aug 2009
Posts: 2,074 Mooresburg, Tn
'72CudaRacer
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Show a picture of the piston, most aren't finished before installation IMO I can post a picture later tonight, but it is finished. Diamond custom piston, comp height 1.530", intake pocket depth .340" (2.600" titanium valve), exh .390". Piston weighs 654 grams. Not much left to take off of it.
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Re: How much compression is too much?
[Re: '72CudaRacer]
#2464402
03/10/18 06:45 PM
03/10/18 06:45 PM
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Joined: Jan 2003
Posts: 31,200 Oregon
AndyF
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620ci RB, B1 MC heads, cam is .850" lift solid roller, duration 286/306 @ .050", carbureted on gas. Bore 4.600", stroke 4.665", piston 10.3cc dish volume, combustion chamber volume 52cc, head gasket compressed thickness .066", 4.600 bore size". How much compression ratio would be considered too much? This is a bracket engine, to be raced on a weekly basis. The engine was brought to me with 16.4:1. I can change head gaskets to get it to 15:1 with out doing anything else. The question is, how much is TOO much?
Thanks, Brian The only way to know if you have too much compression is to test it. Flame travel inside the combustion chamber is very complex. There probably isn't anyone who can read a post on the internet and then tell you if you have too little or too much compression. Even if you had a bunch of pictures of the piston and the combustion chamber I doubt anyone could give you a positive answer. Personally I think that is way too much compression for a bracket engine. The tuning window will be narrow and you'll have to run expensive race fuel. If the car is being raced just for fun then what is the point of the sky high compression ratio?
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Re: How much compression is too much?
[Re: AndyF]
#2464453
03/10/18 08:35 PM
03/10/18 08:35 PM
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Joined: Aug 2009
Posts: 2,074 Mooresburg, Tn
'72CudaRacer
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Personally I think that is way too much compression for a bracket engine. The tuning window will be narrow and you'll have to run expensive race fuel. If the car is being raced just for fun then what is the point of the sky high compression ratio? [/quote]
This is my line of thinking also Andy. I'm thinking any advantage (IF there is any) to having this much compression is out wayed by the toll that it will take on the engine parts (rings, rods, bearings piston pins, head studs, ect.).
And just so everyone understands, this engine was running when it was brought to me. The last two passes in a 2200lb door car was 5.13 @ 139mph (1/8 mile), even with the problems that I have uncovered. In working through the issues on this engine, I'm hoping to head off as many future issues as I possibly can. I feel like this much compression is just not needed.
Thanks, Brian
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