Extension box

[Dave's ZT260]

I have been looking at extension boxes as a result of my quest for 100MPH. Has anyone put one on a mate? An IMCO 12" is a possibility with a shorty lower drive. IMCO claims I should gain a lot of bow lift, and hopefully more speed due to less drag. Opinions?

Scotty, I need more power!

[Dave's ZT260]

I have been looking at extension boxes as a result of my quest for 100MPH. Has anyone put one on a mate? An IMCO 12" is a possibility with a shorty lower drive. IMCO claims I should gain a lot of bow lift, and hopefully more speed due to less drag. Opinions?

Scotty, I need more power!

[F150GT]

I havent ever run one, but I here they do make a diffrence. It looks like all the fast offshore race boats run a good amount of drive set back. The fresh water and increased leverage will have a dramatic effect on trim and speed. The shorter mid section should help also, I had an old MAGNUM 27 Sport with the drives raised 3". It ran much better than a matching hull with standard height drives.
Set back and height make a huge diffrence in outboards, it makes just as much change on I/O's
Its just harder and more exspensive to adjust.
F150GT

[over board]

A buddy of mine put a imco drive extention on his 260 persuader (befor land and sea filed a law suit against imco for patent violations). Anyway it didn't help his boat at all

[Dave's ZT260]

over board-
Did your buddy raise the drive 3"? Also what kind of power did he have? This type of mod is really only for boats well over 80MPH.

Scotty, I need more power!

[over board]

ZT.
no he didn't raise the drive. hIS BOAT HAS A 645 HP TYLER CROCKET MOTOR, 250 blower dual 750 nickerson carbs, roller valve train, super chiller, etc. It runs 83 plus

[Dave's ZT260]

If he didn't raise the drive height via a shorty drive or motor mount height, I'm sure he wouldn't see any speed gains. The drive is far to deep in the water at that point. (to much drag)

Is the box still on the boat? If not, I might be interested.

Scotty, I need more power!

[Dave's ZT260]

I have gotten a lot of good feedback on these extention boxs. (with 3 inches of lift)

Scotty, I need more power!

[over board]

Sorry. it's still on his boat

[Dave's ZT260]

Then he needs to pony up the $$$ and buy a shorty drive. Otherwise it's a waste.

Scotty, I need more power!

[Kip Combs]

ZT.....i talked to a guy with a 253 Convincor last year that put the IMCO extention box and shorty drive on it.......he didn't have a bunch of HP in it though....and said he only picked up a MPH or 2 but the boat handled much better! The additional HP you got ...you would think would make a diffence in the MPH gain. Sorry i don't have any better info on this...we just haven't played with one here at the factory,Kip.

[Dave's ZT260]

Kip-

A few questions.

1) Does the Convincor 253 have a stepped hull?

2) How fast was his Convincor?

3) Can you describe the handling issues he was having prior to installing the extension box? For example- did he get more bow lift? Did it porpoise? Chine walk?

4) Do you know if Harold has ever tried an extension box?

Generally speaking I think it might be time for R&D to start testing more drive combinations, gear ratios, X dimensions, and extension boxes. Especially since you offer Mercury racing HP engines in the current lineup.

When your spending $100,000 on a mate, the few thousand extra it costs to get every last MPH out of it only makes sense.

You can sell a lot of mates if you can pass a $250,000 fountain at 3/4 throttle. It just makes my day. http://www.checkmate-boats.com/6/ws/,s,8626072361/Graemlins/xxrotflmao.gif

Scotty, I need more power!

[Kip Combs]

ZT.....the 253 just has a notch on the keel. It's a pretty fast boat Harold had one running 108 GPS this summer! Did talk to Harold about extention boxes yesterday he said he never had much luck with them ....you could give him a call and get it straight from the horses mouth @ 419-529-4446. Or just to compare notes on what your doing and what he did to get the 108 out of his boat!

[Dave's ZT260]

I spoke to Harold Kunkel today, and he has had no luck with extension boxes on checkmates. So there goes that idea.

We did get talking about his Convincor 253 that ran 108mph on GPS. It has 900HP with and XR 1.5 ratio outdrive with a nosecone. He has a Bravo 36 pitch prop on it and it runs 6000RPM to get 108mph. That works out to about 25% prop slip. He can’t explain why he has so much slip, but who cares when your running 108mph!!!

I’m going to rebuild my motor for 950+HP change to 1.5 gears and see what I get.

Here is a picture of Harold’s Boat from the shootout thread.
http://www.moorhuscomputers.com/harold.jpg

Scotty, I need more power!

[jrumon]

ZT...I put one on a buddy's 25' outlaw powered by a 525SC (yes, it's a Blaa-Blaa)...but we did it in two stages...
#1. Imco extension only, moving back the stock bravo XR...saw about a 2-3mph gain in the top end with the exact same prop (this boat has a higher X than most stock installs....GPS 83MPH at 5200RPM.
#2. The second was adding the new imco shorter lower unit...interesting that the same prop was under-pitched for this set-up...he jumped up two inches pitch (same prop series), and we picked up another 5mph at the same 5200RPM with very little positive trim....the combo change added 8MPH on this application.

We are now getting 88MPH (GPS) with a boat that would only get 79-80 (GPS) before. The bad part is that the swap was about $10G's when all said and done, and the parts combo may not give the same results on different hulls, power plants, x-dim, and props.

I believe you'll gain speed numbers, but it's a costly trial & error thing...Don't you wish they had a "try it and buy it program" to see how good their products are? Good luck, Jim.

[Dave's ZT260]

I'm going with 1.5 gears in a stock XR lower with a nosecone and more HP first. If that isn't enough the extension box and shorty drive will be next.

Kip-
Can I get the taller windshield for my boat? The wind hits you right in the face at speed. I'm getting tired of wearing a helmet all the time.

Scotty, I need more power!

[Kip Combs]

ZT....yea we have a 5" taller shield for the ZT 260. Have 2 in stock right now...Christmas present for yourself maybe? If you want one call my brother (Mike) @ 419-562-3881 he can get you a price....tell him i sent ya and what your running ....we'll hook you up! As for the picture above...that's not Kunkel...that's a guy from Michigan.. it's a Convincor 300 w/ 1,400 HP in it that Harold was beating all day..he said it runs over 120 but Harold was going by him all day!

[Dave's ZT260]

Kip-

Maybe you have adustable wind defectors that attach to the winshield? I can't be the first person to ask about this.

Scotty, I need more power!

[Dave's ZT260]

I was just going by what the thread at offshoreonly said was Harold's boat. Sorry...
Do you have a picture of his boat?

Scotty, I need more power!

[Kip Combs]

No problem.....don't have a picture of Harolds boat it had( Kunkel's Marine )in big letters down the side of it! I'll check and see if we still have some deflectors....a after market company (Windaway) in most magazines... makes some and we had some around here for awhile ..i'll check! (DON'T KNOW IF THEY"LL STAY ON AT 100 though! ) I think Harold is going to build a Convincor 300 next year to run at shootouts , etc ....hoping to run 110 or so w/a 3' bigger boat!

[Dave's ZT260]

I have the windaway deflectors, but at high speed they are scary. I wouldn't recommend running over 70 with them.

Scotty, I need more power!

[Kip Combs]

OK....didn't know you had a set.....sounds like you and Mike have the windshield deal worked out!

[Dave's ZT260]

I have not herd back from Mike yet, but it sounds like a plan. I just realized my cockpit cover will not fit after this. Can you provide a new one? (without having my boat)

Thanks for the help.

Scotty, I need more power!

[Kip Combs]

I'm pretty sure we have it patterned ....you'll just have to put the snap's on the cover in your self to make sure everything lines up correctly.