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12-01-2010, 11:22 PM
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CC Member
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Join Date: Nov 2010
Cobra Make, Engine:
Posts: 11
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Not Ranked
High compression motor build questions
Hey guys, n00b here and I'm building a 351W, stroking it to a 427 and was wondering what the highest compression ration you can have and still run on 93 octane. I'm trying to get all the horsepower I can out of the motor, but don't want to set the compression too high and mess with the timing so much that i defeats the purpose of it being a high comp. motor. Any input would be appreciated, about the fuel and what parts have worked best for hp gains.
I want something that's still streetable but also a good weekend racer. So far these are the mods I've been planning on doing; this stroker kit from Coast High Performance http://www.coasthigh.com/Ford-427W-F...7-ps-f427w.htm, with these AFR aluminum heads, a custom ground cam from comp cam, wasn't too sure about the intake manifold but was thinking maybe an Edelbrock Performer RPM, or a dual quad, with maybe an 800 cfm Edelbrock carb. If I'm missing anything let me know, or if i left out some info please ask, I'm half asleep while writing this.
Foti
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427 build in progress
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12-02-2010, 02:51 AM
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CC Member
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Join Date: Dec 2001
Location: Louisville,
KY
Cobra Make, Engine: I'm Cobra-less!
Posts: 9,417
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Aim for 10-10.5 and you'll be pretty safe.
Where are you from?
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12-02-2010, 03:18 AM
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CC Member
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Join Date: Dec 2001
Location: Castalia,
Oh
Cobra Make, Engine: EM cobra, 450 inch sbc running a best ET of 9.14..so far..ALL MOTOR...approx 800 horse.............ERA with 482 FE..All Aluminum Engine
Posts: 1,395
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highest C/R for 93
Same guy, same question asked here...
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Jack
XSSIVE .....
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12-02-2010, 04:02 AM
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CC Member
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Join Date: Dec 2001
Location: Louisville,
KY
Cobra Make, Engine: I'm Cobra-less!
Posts: 9,417
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I knew something sounded familiar.
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12-02-2010, 08:11 AM
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CC Member
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Join Date: Oct 2003
Posts: 4,078
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Quote:
Originally Posted by blykins
I knew something sounded familiar.
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Yes he's the same guy. He finally answered my posts in his first thread over in FE's. He realizes he made a mistake. I told him in future to post here in Small Block Talk as many small block guys don't look at FE. I told him he could get more help from the SB guys here. I also got him started on some advice.
See here from post 18 on:
highest C/R for 93
So how about helping out a newb-Brent this is you kind of stuff...
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Chas.
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12-02-2010, 08:35 AM
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CC Member
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Join Date: Aug 2006
Location: Broken Arrow,
OK
Cobra Make, Engine: FFR MK III,462 FE/TKO 600, IRS w/3.27
Posts: 129
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Not Ranked
427Bullitt......Only one comment, and that is for your carb choice. Just my opinion, not being critical of you!
I've had several engines w/Edel carbs, and they're OK (for me) if the cams are mild, for stock/medium performance engines. I don't know how much cam you are planning on, but I've never had any satisfaction w/Edel carbs if my cam had much duration, or if I was looking for high performance. I always wound up going back to a Holley/clone.
Good luck!
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Wideglidejoe
FFR#6143 Mk III: FE 462" w/four 48 IDA Weber's w/TKO 600 .82, IRS w/3.27, 17" Team III's w/245/45's & 315/35's. Gas N's.
Picked it up end of Aug '08
First start May 12, '10
First go kart May 26, '10
Tag & title 5-26-11, driving in gel coat
Painted Nov 2015
'05 Harley Wide Glide (60 hp stock, now 107 hp & 107 ft/lbs at wheel. Mid 11's in the 1/4 mi.)
'55 Bel Air hot rod project (WIP)
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12-02-2010, 09:12 AM
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CC Member
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Join Date: Dec 2001
Location: Louisville,
KY
Cobra Make, Engine: I'm Cobra-less!
Posts: 9,417
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Be glad to...
Hey 427, give me a call when you get some time to chat.
502.759.1431
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12-02-2010, 05:14 PM
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Join Date: Nov 2010
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Quote:
Originally Posted by blykins
Aim for 10-10.5 and you'll be pretty safe.
Where are you from?
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Orlando, Fl... turns out there's more than one Orlando in the U.S.
Quote:
Originally Posted by Hotfingrs
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Yea that's me, during my brain fart.
Quote:
Originally Posted by wideglidejoe
427Bullitt......Only one comment, and that is for your carb choice. Just my opinion, not being critical of you!
I've had several engines w/Edel carbs, and they're OK (for me) if the cams are mild, for stock/medium performance engines. I don't know how much cam you are planning on, but I've never had any satisfaction w/Edel carbs if my cam had much duration, or if I was looking for high performance. I always wound up going back to a Holley/clone.
Good luck!
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Plan on having a really big cam
Quote:
Originally Posted by blykins
Be glad to...
Hey 427, give me a call when you get some time to chat.
502.759.1431
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will do
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427 build in progress
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12-03-2010, 09:54 AM
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CC Member
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Join Date: Jan 2008
Location: Nashville,
TN
Cobra Make, Engine: Backdraft, SBF 351w (463 CI)
Posts: 272
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Not Ranked
Hey Brent isn't that a little to simple of answer? (10.0 to 10.5) Correct me if i am wrong, but what he really needs to know is how much DCR he can get away with on 93 octane. SCR is really ambiguous without more info on the engine build. So what is the safe limit on 93? 8.5 can he do 9.0 (Aluminum heads)?
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12-03-2010, 10:37 AM
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CC Member
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Join Date: Dec 2001
Location: Louisville,
KY
Cobra Make, Engine: I'm Cobra-less!
Posts: 9,417
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No....DCR is a good tool to use IMO when you really want to fine tune a build, but you're pretty much safe with 10 to 10.5 with most street cams and aluminum heads. I use Pat Kelleys calculator and I wouldn't go over 8.5 on 93 and aluminum heads.
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12-03-2010, 11:01 AM
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CC Member
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Join Date: Dec 2001
Location: Castalia,
Oh
Cobra Make, Engine: EM cobra, 450 inch sbc running a best ET of 9.14..so far..ALL MOTOR...approx 800 horse.............ERA with 482 FE..All Aluminum Engine
Posts: 1,395
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Not Ranked
Just ran my figures and have a static of 11-1 and dynamic of 8.59
__________________
Jack
XSSIVE .....
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12-03-2010, 07:07 PM
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CC Member
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Join Date: Dec 2001
Location: Louisville,
KY
Cobra Make, Engine: I'm Cobra-less!
Posts: 9,417
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Quote:
Originally Posted by Hotfingrs
Just ran my figures and have a static of 11-1 and dynamic of 8.59
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I'd do it on an engine that I'd build for myself...or a race engine, but I wouldn't build one that tight for a customer. It can work and often does, but it would be more of a worry than a benefit for an engine builder. The amount of horsepower that you gain by an extra 1/2 point of static compression really doesn't outweigh the risks. The customer could always install the engine in a 5000 lb car that runs uphill at 1500 rpm all the time in 100° weather. 
For a regular street engine, I usually aim for 10-10.5 and don't have any problems with that and the camshafts that I run.
Block prep/piston prep/good machining also eliminates a lot of issues with the higher compression ratios. Eliminating all sharp edges on the pistons, running a tight quench, and running efficient chambers helps a ton. I always try to run about .040" quench on the engines that I build. That means that the block gets machined so that the pistons are sitting at zero deck.
Last edited by blykins; 12-03-2010 at 07:10 PM..
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12-05-2010, 10:06 PM
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Join Date: Nov 2010
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sorry i haven't called yet, been super busy with some legal issues and keep forgetting.
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427 build in progress
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