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Possible engine swap :)
Been a while since I posted anything at the Formula Forum ,) Still have my Formula 271 SR1 496 HO, my old XR drive was broken and I changed to a Bravo1X drive 1.50 .. So this summer I saw 64 mph at my Garmin GPS under ideal conditions spinning my Mirage+ 23`, not so bad for an old 271 SR1... The owner before me, who did the total rebuild of the boat by the way, told me that he lifted the hight of the drive a bit. I do not know how much, if some one have an original 271 SR1 could be so kind to meassure from the bottom of the boat to the Bravo Transom it would be very helpful ::: https://www.offshoreonly.com/forums/...ilies/wink.gif Then I would know how much higer my drive is set … I have heard that Formula original is very conservative with drive hights.. I am consider to swap the 496 to a total rebuild 500 Efi dynoed @ 530 HP. ,) Anyone have any experiance with the 500 EFI in a 271 Fastech or SR1 ? What kind of top speed and crusing speed could be realistic I hope the +105 hp should give at least 70 mph ++ ? My only concern is that the 496 HO is a very good engine, and also the fact that it has closed cooling is big advantage … My boat are in the water the whole season… I have installed the posibility to flush the engine … I will appreciate any comments and tip Br Runehttps://cimg2.ibsrv.net/gimg/www.off...fa3a3ac5d7.jpg Having fun in the Oslo Fjord |
i would think a proper 500 EFI should get you to 70 easy. As far as X dim you should be around 17.5" for a good performance set up without being overly high. Raising the X will allow you to take advantage of props much better then the Mirage. What year is your boat?
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Originally Posted by glassdave
(Post 4716081)
i would think a proper 500 EFI should get you to 70 easy. As far as X dim you should be around 17.5" for a good performance set up without being overly high. Raising the X will allow you to take advantage of props much better then the Mirage. What year is your boat?
thank you for the reply This 500 EFI will be 530 HP ;) ;) i am running 2 different props now Mirage 23+ and a Bravo1 24 and as mentioned the Mirage are the fastest one :) The X dim are already raised, how much I do not know, so I hope someone can tell me what it’s supposed to be originally at the 271 SR ? :) I think the reason that my 271 SR1 deep V without step are a couple of mph faster then others with the same power could be because of the higher xdim :) :) Its 1 mph faster then most test result from the 271 Fastech with stepped hull ( Newer version of the boat) same power.. One more think with my boat “The Silent Thunder” is removed ;) ;) |
Keep in mind that your engine is rated at 425hp AT THE PROP. A stock 500efi is rated at 500hp at the crank and 470hp at the prop. The 530hp on the dyno may or may not have been in full marine dress. If it was dynoed with dry dyno headers and without all the accessories, it could be more like 500hp in full marine dress. So, realistically, you could only be picking up a true 55hp at the prop. It may be more. I would say you are more likely to gain 3-5 mph. In perfect conditions with the moons aligned and wind blowing perfect, you might touch 70mph.
Not sure what the original propshaft height below the bottom was on a 271 but I'd guess around 7" below the bottom. As Dave said, a 17.5 X works well for a performance straight bottom V Hull. That puts the propshaft about 4.5 inches below the bottom. |
Originally Posted by Griff
(Post 4716109)
Keep in mind that your engine is rated at 425hp AT THE PROP. A stock 500efi is rated at 500hp at the crank and 470hp at the prop. The 530hp on the dyno may or may not have been in full marine dress. If it was dynoed with dry dyno headers and without all the accessories, it could be more like 500hp in full marine dress. So, realistically, you could only be picking up a true 55hp at the prop. It may be more. I would say you are more likely to gain 3-5 mph. In perfect conditions with the moons aligned and wind blowing perfect, you might touch 70mph.
Not sure what the original propshaft height below the bottom was on a 271 but I'd guess around 7" below the bottom. As Dave said, a 17.5 X works well for a performance straight bottom V Hull. That puts the propshaft about 4.5 inches below the bottom. This engine will have 530 Hp @ the crank :) :) I also heard that tje 496 HO has 425 Hp at the prop shaft. But when I started to check it, all real documentation shows that the 425 Hp is measured at the crank thats also what Mercruiser says if you ask them ... I was very surprised of the result ... |
Originally Posted by Monaco20
(Post 4716122)
Thanks for the reply ;) This engine will have 530 Hp @ the crank :) :) I also heard that tje 496 HO has 425 Hp at the prop shaft. But when I started to check it, all real documentation shows that the 425 Hp is measured at the crank thats also what Mercruiser says if you ask them ... I was very surprised of the result ... 2005-2010 496 Mag and Mag HO Intercooled ProCharger Systems with M-1SC
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The engine before rebuilding ,)https://cimg8.ibsrv.net/gimg/www.off...4a070a7f82.jpg
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