my bravo outdrive gear experiment
#91
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Thanks for the info Smitty. I need a 2 inch spacer and am looking around for one. I am just not ready to buy it new....yet.
Are you staying at Brower?
We are heading there on Friday. Hope to see ya there Dwight
Are you staying at Brower?
We are heading there on Friday. Hope to see ya there Dwight
#92
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Originally Posted by Whitey
Thanks for the info Smitty. I need a 2 inch spacer and am looking around for one. I am just not ready to buy it new....yet.
Are you staying at Brower?
We are heading there on Friday. Hope to see ya there Dwight
Are you staying at Brower?
We are heading there on Friday. Hope to see ya there Dwight
#93
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Originally Posted by articfriends
Kurt,looking at marrens injector calculator your 55lb injectors will support 586hp at 80% duty cycle,.6 bsfc (common number on supercharged motors) and 43.5psi. Now increase your fuel supply pressure with a boost referencing regulator and sufficent fuel pump to 70 psi under boost your injectors new flow rating is 69.7 lbs per hour which will support 750hp at a safe bsfc like .6. If you can get 75 psi under boost they will flow 72.2lbs per hour which will support 770hp. If you run your motor at a slightly lower bsfc or open duty cyle up a little bit further past 80% you could support even more hp so you will probably be ok for what you are building. Make sure your new injectors are high impedance so they will work with your mefi computer. Here is a link on the subject if you want to play with different pressures,bsfc and sizes,Smitty
http://www.injector.com/injectorselection.php
http://www.csgnetwork.com/fiflowcalc.html
http://www.injector.com/injectorselection.php
http://www.csgnetwork.com/fiflowcalc.html
Don't forget to subtract boost psi (intake psi) from fuel psi to figure out actual psi at injector .
Example: 75psi fuel measured at rail minus 10psi boost = 65psi actual at injector.
#95
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Originally Posted by SB
I'm not sure if you accounted for the following:
Don't forget to subtract boost psi (intake psi) from fuel psi to figure out actual psi at injector .
Example: 75psi fuel measured at rail minus 10psi boost = 65psi actual at injector.
Don't forget to subtract boost psi (intake psi) from fuel psi to figure out actual psi at injector .
Example: 75psi fuel measured at rail minus 10psi boost = 65psi actual at injector.
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I ran my numbers thru the calculator,unfortunately I don't have bsfc from the dyno because Crockett doesn't measure it when doing EFI motors.
I'm using 63lb injectors at 75 psi under boost,they become 82.7lb injectors from 75psi and 77lb injectors if pressure is changed signifigantly from the 10 psi of boost I'm running to 65psi.
82.7lb inj will support1058hp at.5bsfc,882hp at .6bsfc 77lb inj will support 985hp at .5bsfc,821hp at .6bsfc
My motor made 944hp/962ft lbs tq with a correction factor under 2% so either my bsfc is between .5-.55 or dyno was incorrect. I do know that Crockett checked the calibration after we made 900 plus ft lbs in the first pull to 4800 rpm's because he was in disbelief,Smitty
I'm using 63lb injectors at 75 psi under boost,they become 82.7lb injectors from 75psi and 77lb injectors if pressure is changed signifigantly from the 10 psi of boost I'm running to 65psi.
82.7lb inj will support1058hp at.5bsfc,882hp at .6bsfc 77lb inj will support 985hp at .5bsfc,821hp at .6bsfc
My motor made 944hp/962ft lbs tq with a correction factor under 2% so either my bsfc is between .5-.55 or dyno was incorrect. I do know that Crockett checked the calibration after we made 900 plus ft lbs in the first pull to 4800 rpm's because he was in disbelief,Smitty
#97
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I believe the .6 BSFC's used really aren't accurate anymore. Remember how people thought near .5 was normal for NA BBC ? Well, today we are in the lower .400's due to better components and better understanding of stuff. Oh, and this is with carb's too .
Now, add into the equation much more effecient centrifugal SC's with big intercoolers and the .6 BSFC's (typical roots , carb's, older engine parts) for the most part dissappear.
Also, old thinking said 'add way more fuel then you need' to keep detonation at a minimum.
Anyway - as you can see with your math, a difference in injector needed at .5BSFC is much different tha at .6BSFC.
Those equations are to give you a baseline to go from when deciding what injector size you'll need when planning an engine build.
Last important notes:
1) You need to know what psi the manufacturer uses when rating each certain injector
2) You need to know how accurate / close to those ratings your injectors actually are. Some manufacturers/models of injectors are a lot 'looser tolerance' than others.
3) The dyno or vehicle w/measuring equipment will ultimately tell you what's happening.
![Big Grin](/forums/images/smilies/biggrin.gif)
Now, add into the equation much more effecient centrifugal SC's with big intercoolers and the .6 BSFC's (typical roots , carb's, older engine parts) for the most part dissappear.
Also, old thinking said 'add way more fuel then you need' to keep detonation at a minimum.
Anyway - as you can see with your math, a difference in injector needed at .5BSFC is much different tha at .6BSFC.
Those equations are to give you a baseline to go from when deciding what injector size you'll need when planning an engine build.
Last important notes:
1) You need to know what psi the manufacturer uses when rating each certain injector
2) You need to know how accurate / close to those ratings your injectors actually are. Some manufacturers/models of injectors are a lot 'looser tolerance' than others.
3) The dyno or vehicle w/measuring equipment will ultimately tell you what's happening.
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Smitty - did he atleast use the fuel flow meter ? If not, I guess this explains why no BSFC's.
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Originally Posted by articfriends
Sent a set of gears out to be cryo treated and iso-rem finished,We'll see what that does. Ran boat with the 1" drive spacer yesterday,airs bow out nice again,cavitation is gone,porpoising is gone. Hard to believe 1" could make such a difference on a boat that has such a deep propcenterline to hull dimension to start with. Will see how boat handles in rough water and if top end is back soon and post,Smitty
You may want to check these guys out:
www.metalax.com
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Great info guys. I fear i may be a little small on the injector sizing, I'd rather go larger with less fuel pressure.
60 Lb/Hr injectors should be correct.
60 Lb/Hr injectors should be correct.