Author Topic: High compression ratio  (Read 2790 times)

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frnkeore

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Re: High compression ratio
« Reply #15 on: July 24, 2022, 11:39:33 AM »
Ross, your quite a bit off of my CR calculations. Can you give tell us the specs that you use so, I can see how you came up with yours?

The .050/.051 gasket is the one to use, it will give a bit more detonation resistance over a .060 gasket.
Frank

My427stang

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Re: High compression ratio
« Reply #16 on: July 24, 2022, 12:20:13 PM »
Frank, I might have typo'd something, our numbers look close, all my numbers were in my post, I will go back and check.  Regardless, his 12+ numbers aren't correct

However, I would NOT say .044 quench will be more resistant than .054 quench, it isn't linear by any means.  We all like to hit the .046 range, but in practice, .054 is good quench, and in his case, might buy him a little less compression.

I will say I generally build them .006-,008 proud, and like to use the blue Felpro in street applications, so not arguing with a target of .046 when the engine is built for it, but the definitive statement that one gasket IS the one to use just isn't a true statement with quench, it's a range.   Additionally, this engine happens to have some quirks that  it takes a little flexibility to help him get there since compression and deck height were discovered after the part purchase...a little backwards, but we've all been there

Frank - On edit....I was just looking at the D cam he is running and trying to figure out where Greg really is.  I feel like we are running on assumption after assumption, chamber, gasket bore, valve relief clearance, ICL, effective duration, deck clearance procedures.... If he is on 107, assuming his deck clearance is correct and we get a resolution of chamber size.  I'd actually agree that .050 is better, both for compression numbers and a more common quench distance.

However, I am going to quiet down until we get some real numbers and/or procedure verification

« Last Edit: July 24, 2022, 12:43:54 PM by My427stang »
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Ross
Bullock's Power Service, LLC
- 70 Fastback Mustang, 489 cid FE, Victor, SEFI, Erson SFT cam, TKO-600 5 speed, 4.11 9 inch.
- 71 F100 shortbed 4x4, 461 cid FE, headers, Victor Pro-flo EFI, Comp Custom HFT cam, 3.50 9 inch

gregaba

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Re: High compression ratio
« Reply #17 on: July 24, 2022, 04:33:31 PM »
I guess it will ba a while before I can get final number's on what is really needed for my engine.
I am going to take the head's to Texas when Charles can get to them. He is a one man shop and is all way's behind so it take's a while before he can finish a job but his work is excellent.
I sure do hate the 6 to 8 hour drive there and back.
i degreed my cam last week and the number's were right on intake centerline was 102.
Lobe seperation is 107.
Lobe lift was measured at .3550.
Measured gasket bore on the cometic's is 4.143 [I ordered gasket's with 4.165 from Summit but that's not what I got] which I just measured today and am thinking this is wrong for my 4.164 bore so I will be buying new gasket's, after all it's only money.
I should have the head's back in a couple month's and will be able to get accurate measurement's when I get them back.
Thanks for all the help.
Greg

rockhouse66

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Re: High compression ratio
« Reply #18 on: July 24, 2022, 05:13:00 PM »
I think you could ship them to your cylinder head guy cheaper than you could drive them there at $4.50 a gallon.
Jim

gregaba

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Re: High compression ratio
« Reply #19 on: July 24, 2022, 06:19:54 PM »
I have lost to many item's shipping them.
last time was a $2000.00 stereo processor that it looked like someone drove a forklift though.
My gas is $2.09 a gallon as I run on CNG in my F-250.
Still would rather ship but can't depend on the shipper's not to losr my stuff and with the wait time for new head's I just don't want to chance it.
Greg









6667fan

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Re: High compression ratio
« Reply #20 on: July 24, 2022, 09:20:47 PM »
Greg, that is another product in their line. The Ultra will ramp up the octane even more. You may be fine with the 105.
I don’t run the Ultra at the full dosage. I can tell when I need to add some to the 93 that is available here.

Good luck
JB


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e philpott

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Re: High compression ratio
« Reply #21 on: July 25, 2022, 08:11:21 AM »
Out of curiosity, are there any octane boosters that actually work?  Something you could carry with you to throw in the tank if you were running on the edge with 94 octane and you were out of town and couldn't get "good gas?"

I have had very good performance with VP's Octanium octane booster
I see many good reviews about the Race Gas product.
Lots of folks swear by the Torco octane booster and have for years.
Might want to look into a water/meth system if you're running 12:1 on the street. I had a Snow system on my blown car and liked it very much.

Same as Tommy , VP Racing Madditive Octanium works and it works good , highly recommend , you can get leaded and unleaded

427LX

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Re: High compression ratio
« Reply #22 on: July 25, 2022, 09:19:56 AM »
Can you degree the cam so the intake valve closes a bit later which would reduce cylinder pressure and octane requirement?

Falcon67

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Re: High compression ratio
« Reply #23 on: July 25, 2022, 11:59:44 AM »
On that CR, I personally wouldn't run anything less than straight VP110.  I'm mixing 40/60 already pump 91/110 to keep the plugs clean on current US pump fuel.  I buy VP by the drum.

frnkeore

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Re: High compression ratio
« Reply #24 on: July 25, 2022, 12:14:49 PM »
I just ran the DCR numbers for the "D" cam, set at 102° ICL (3° advanced over factory setting) the intake closes at 87° ABDC, giving a DCR of 6.78, with a 76cc head and 6.9 with a 74cc head.

87 octane gas can run on 7.5 DCR but, when this engine get in it's tq range, it will need more. It could possibly get by with 93 octane but, you'll need to be careful approaching full throttle.
Frank

gregaba

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Re: High compression ratio
« Reply #25 on: July 25, 2022, 12:59:52 PM »
Thanks for the reply's.
I will try to answer in order. Will try not to miss anyone.
6667fan
I will give the ultra a look, didn't know about it.
ephilpott
Thanks, will check it out.
427LX
I have jay's adjustable timing set and can adjust timing fairly easy.
Falcone67
How much did the last drum cost and how many gallons is in a drum 55?. What compression ratio are you running?
frnkeore
Thanks for figureing that out. I wish I was better at math but it has been a problem my whole life.
I don't think I would trust 87 anyway and not sure I would trust 93 if I could get it.
Thank's everyone every answer is a help.
Greg

frnkeore

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Re: High compression ratio
« Reply #26 on: July 25, 2022, 01:48:02 PM »
To help explain DCR, you are working off of what I will call "net" CID, while your B&S are "gross" CID. Mechanically, you rarely produce your power from the "gross" CID, it's always "net" that produces the power.

The net CID occurs after the intake valve closes and compression starts building (just like you can't have compression while the spark plug is out of the head). DCR works with the position that the crank is in, when that valve closes. In this case, 87°. So, there is no compression until after 87° ABDC. With a 3.984 stroke, that only leaves a actual stroke of 2.408 or, 262.4 CID (4.164x2.408). That's why the DCR is so low, with the "D" cam. The engine doesn't get any bigger but, at higher rpm, the VE can increase, "ramming" more A/F into the cyl but, it can't regain it's 434 CID, unless it can exceed 1.654 VE. What ever it's VE is, it will occur near it's max engine torque and only a dyno will be able to give those numbers.

You could recompute the VE CR at that point but, you have to have that from the dyno. VE CR, is my term.
Frank

gregaba

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Re: High compression ratio
« Reply #27 on: July 25, 2022, 02:48:05 PM »
Thanks for the explianation. I really don't understand how to get a dcr as when I was learning mechanic's in the 60's it was never taught.
The guy on street outlaw's who drive's the red 55 chevy has his shop a 1/4 mile from me and I have talked to him about using his dyno to break in and tune my engine when it is ready.
We didn't discuse cost and I am a little concerned about that. I would like to keep it under a $1000.00 if possible but I havn't had a engine on the dyno other then a wheel dyno since I quit racing in the 90's.
Greg

blykins

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Re: High compression ratio
« Reply #28 on: July 25, 2022, 06:21:54 PM »
Greg, it takes a special calculator to figure it out.   The Cliff's notes version of it is that you can't make compression until all the valves are shut.  The cam dictates when the valves shut and we specifically look at when the intake valve shuts. 

DCR is a fun tool, but it's not the end-all-be-all.  You also have to have dyno experience to know what number correlates to "safe" and "not safe" with a specific octane rating.  I do say "dyno" because a dyno is harder on an engine than a vehicle can ever be.   You also have to take into account how efficient the engine is.  Some engines are over-achievers, in that they have over 100% volumetric efficiency.  That's when DCR kinda goes out the window.  You just can't keep increasing the compression ratio and putting a bigger cam in (or retarding cam timing) to make it work. 

Of course, you're playing it the correct way and waiting until you get all actual numbers.  We can all sit here and bench race compression ratios until the cows come home, but it doesn't mean squat if you don't have actual numbers.
Brent Lykins
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cjshaker

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Re: High compression ratio
« Reply #29 on: July 25, 2022, 07:56:05 PM »
And in the end, no matter how much info you have, you better be able to read plugs. Still lots of variables that just can't be accounted for, like elevation, air density, temp etc. All which can change from day to day, whether it's from travel or just weather changes. Better to be safe than sorry.
Doug Smith


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