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  1. #1

    Default Repowering 454 to 8.1 - How much height and shaft length

    Swapping out a pair of 454's with some newer 8.1s. I know that the 8.1's are about 1 1/2 inches taller but I'm also going from Borg Warner 72 transmissions to Hurth 63A downangle transmissions so the engines will need to be lifted up a bit on the transmission side to match up. Does anyone know about how much it needs to raised. I currently have 4 1/2 to 5 inches of clearance between my existing flame arrestor and the hatch. Will I have enough room? I also know I'll need to get longer shafts. Can I just take the difference between the lenth of the two transmissions and add that to my new shaft length, or is there more to it than that?

    Maybe Linesix would know.

    Thanks for your help.

  2. #2
    Join Date
    Sep 2008
    Location
    Maryland - USA
    Posts
    7,883

    Default Re: Repowering 454 to 8.1 - How much height and shaft length

    This may help some:
    http://www.perfprotech.com/store/art...6-repower.aspx

    I also have some older Crusader installation drawings of the older Big Blocks. I can extract the ones with the 630 and the 72 gears or send you the whole manual ~ 9MB before encoding. Just send a PM with an email address that will handle large attachments. The newer stuff should be available on their current www site if you look deep enough.

    I think you'll have enough vertical room. I'd make the final shaft measurement after the new engines are in...nothing worse than having new shafts that are just "a bit short".

  3. #3

    Default Re: Repowering 454 to 8.1 - How much height and shaft length

    Replaced my 454's and velvet drive trannys with 8.1's and Hurth 63A trannys. The 63As are about 7 inches shorter than the inline Velvet drive trannys. I relocated the engines aft (the 7 inches) to mate up with the shafts. Had to relocate the engine mounts on the stringers. The down angle tranny allows you to lower the front of the engine, the engine sits more level in the boat and have addequate clearances to the hatches. The 8.1s are configured different than the 454s so that I can now reach my arm completely under the oil pan. Very happy with the installation and performance.

  4. #4

    Default Re: Repowering 454 to 8.1 - How much height and shaft length

    Viking76 - I assume the boat you repowered was a Viking? What Model? Also by moving the engines aft, did changing the engine weight distribution make any real difference in ride performance. One other thing - Did you need to re-prop? If so what was the old prop and what is the new? Do you see any real benefits in performance.

    Thanks

  5. #5

    Default Re: Repowering 454 to 8.1 - How much height and shaft length

    My boat is a 35 ft viking. The 63A trans are lighter than the inline Velvet drives trans (don't remember the exact weight difference, maybe 75 lbs each), engine wiehts are appoximately the same. Moving the engines aft has had no apparent adverse impacts. It is estimated that the center of gravity of the boat moved aft by 1/4 inch. Performance has improved substantially: Fuel burn rate went down approx 30%, cruising speed went from 19 MPH to 22 MPH , top end went up by about 5 mph (34 mph, all speeds by GPS). Had 4 blade 18X19 props and changed to 19X19 (med cup) Nybral Dynaquad. Very satisfied with the results, it's like a new boat.

  6. #6
    Join Date
    Oct 2007
    Location
    Germantown, TN, USA
    Posts
    227

    Default Re: Repowering 454 to 8.1 - How much height and shaft length

    I have a 50' Gibson Houseboat so my concerns for you may not be applicable to your boat. Be sure to think in terms of maintenance after the installation. Once you raise the engine closer to the hatch, will you have sufficient room to get to the spark plugs etc on the far bank? I have just enough clearance for a skinny mechanic to make the replacements. I am not that skinny man.

    Chuck Hanson

  7. #7
    Join Date
    Sep 2003
    Location
    New Tripoli, PA, USA!
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    16,278

    Default Re: Repowering 454 to 8.1 - How much height and shaft length

    Me neither!

    FatJeff

  8. #8

    Default Re: Repowering 454 to 8.1 - How much height and shaft length

    Correction - Regarding the new props for my repowering, the new props were Michigan DQX not Dynaquad. DQX props have a different blade shape and more surface area than Dynaquad props.

  9. #9
    Join Date
    Oct 2009
    Location
    New Haven, CT, USA
    Posts
    633

    Default Re: Repowering 454 to 8.1 - How much height and shaft length

    [QUOTE=rrrwel;319576]Swapping out a pair of 454's with some newer 8.1s. I know that the 8.1's are about 1 1/2 inches taller but I'm also going from Borg Warner 72 transmissions to Hurth 63A downangle transmissions so the engines will need to be lifted up a bit on the transmission side to match up. Does anyone know about how much it needs to raised. I currently have 4 1/2 to 5 inches of clearance between my existing flame arrestor and the hatch. Will I have enough room? I also know I'll need to get longer shafts. Can I just take the difference between the lenth of the two transmissions and add that to my new shaft length, or is there more to it than that?

    Maybe Linesix would know.

    ----------------------------------------------------------------------------------------------------------------------------------

    Picking up on this old thread (and happened to speak with Rick @ Linesix today). I am looking at doing the exact same swap from 454's to 8.1's. A lot of people have mentioned the need for the "down angle" transmissions as part of this upgrade.

    If I have enough clearance to make up for the 1.5" add'l engine height, doesn't that mean I am ok re-using my straight drive Borg Warner transmissions (reversing rotation on one)?

    Is the only reason people have gone to the down angle transmissions is to make up for the add'l engine height?

    Thanks
    Bob
    Last edited by bobct; 08-20-2019 at 05:47 PM.

  10. #10
    Join Date
    Oct 2009
    Location
    New Haven, CT, USA
    Posts
    633

    Default Re: Repowering 454 to 8.1 - How much height and shaft length

    Just did some quick measurements, I have at least 3" add'l clearance from the high point of my 454's (flame arrestor and oil cooler are about the same distance to the bottom of my hatches. Worst case, I have another couple of inches of insulation depth to play if there was a high spot.

    Thanks
    Last edited by bobct; 08-20-2019 at 05:46 PM.

  11. #11
    Join Date
    Sep 2008
    Location
    Maryland - USA
    Posts
    7,883

    Default Re: Repowering 454 to 8.1 - How much height and shaft length

    big reason for the popularity of the 'down angle' gears is they are 'full power' rated forward and reverse....all on the 'newer' GM engines are LH rotation....so to get the counter-rotating props, they use the gears. A benefit of the down angle is the installed angle of the engine is less; ie the crank sits closer to horizontal.

    If you have the correct set of BW gears, you can use them. my guess is only one will work.

    as far as the what if game, I'd suggest making use of the installation drawings....if they all get printed so they are on the same scale, you can print one on a transparent sheet and just do the overlay game...it should address clearance as well as how short the current shaft is...

    Finally, Rick is a huge knowledge source.....and very deep in the experience department...

  12. #12
    Join Date
    Oct 2009
    Location
    New Haven, CT, USA
    Posts
    633

    Default Re: Repowering 454 to 8.1 - How much height and shaft length

    Mark,

    That's a really good idea , I have them printed out now and will play around with the scale so they match.

    The 7.4's I have now do sit at a noticeable downward angle and have been that way for 30 years. All things being equal, is that something worth "correcting" with the 8.1's? The only downside to the current setup that I can think of is the oil level and relationship to the crankshaft. I talked to someone who worked at Trojan when I got the boat and he suggested not going to the top of the oil fill line but closer to the lower part (for this reason).

    Is there any other advantage that would tip the scale if this becomes an either/or decision? How has the reliability been on the Hurth transmissions?


    Bob

  13. #13
    Join Date
    Sep 2008
    Location
    Maryland - USA
    Posts
    7,883

    Default Re: Repowering 454 to 8.1 - How much height and shaft length

    I think the down angle gear will take care of most of it....and running them at the bottom of the fill band is the first 'fix' if the engines aren't happy with their installed angle...

    on the pros and cons...the 8.1's are all electronic so, eventually, a scan tool will be on the horizon....you can also dump thousands on networked displays if you want and tie the engines in there....i think its overkill but everybody has their preferences....

    On the Hurths - ZF bought them a while ago....the only guy I know of that wasn't happy had them but behind a set of diesels (5.9BTA) that where 'modified'...I didn't know him well but the dock talk said he was 'rough' on the boat. As long as you keep the oil clean and change the filter, I'd doubt they will be a problem...and, I believe they will take trolling valves if you need them for striper fishing....

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