Installing a bubbleback on a crossflow

[tvpear12]

I have a 1989 90 horse that i would like to put a bubbleback exhaust on. would it be worth it for a power gain? will i see a noticable diff in power? and can this be done? what do you guys think?

 

[rodbolt]

Re: Installing a bubbleback on a crossflow

while its technically possible to modify the flat back block, the cost is not worth it. it will also require filler blocks and exhaust pipe/power head adapter changes. the bubble back was a tuned exhaust system. save your money for a larger motor

 

[tvpear12]

Re: Installing a bubbleback on a crossflow

Thanks rodbolt, your the man.

 

[fast_c_class]

Re: Installing a bubbleback on a crossflow

i do agree that its not worth changing to the bubble unless you have the bigger carbs and heads too, and a lightweight boat that responds good to changes in hp, such as an allison, hydrostream, laser, or other padded v hulls<br /><br />However, you do not need to change the powerhead adapter on the v4 models,and you could leave the filler blocks out, sacraficing alittle bottom end power.

 

[Dhadley]

Re: Installing a bubbleback on a crossflow

Adding the bubble back exhaust plates is very easy and you may not lose any rpm but you may not gain much either. You'll still have the 90 hp port timing. <br /><br />If you were to modify the ports you may see some improvement. It depends, as stated, on how your hull reacts to small increases in torque. And what your set up is like now.

 

[tvpear12]

Re: Installing a bubbleback on a crossflow

ok check this out would this give me more top end power? would this engine be worth the swap? please look at the link. http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&rd=1&item=4504034548&ssPageName=STRK:MEBI:IT

 

[tvpear12]

Re: Installing a bubbleback on a crossflow

hull is a 1989 tracker 1600TF tournament fiberglass hull. tach says 5200 rpm but not sure if it is accurate. speedo says 45 mph not sure if it is accurate either as it is a water pick up type of speedo. P.S 1989 90 horse crossflow rude.

 

[Dhadley]

Re: Installing a bubbleback on a crossflow

5200 -- good guess, huh?<br /><br />Is the boat a pad bottom style? Does it have a step (notch)? What pitch prop?<br /><br />5200 is lugging the motor. It may not live long set up like that. Lets work on getting the rpm's up. Jackplate?

 

[tvpear12]

Re: Installing a bubbleback on a crossflow

I have installed a jack plate, but to lower the engine not raise the engine. it was blowing out of the water before i installed it and it was setting on the transom. 13x19 prop. not sure if it is a pad or not. not sure how to tell. now at wot the cavitation plate is out of the water on the top and water is touching the bottom at wot trimmed out fully. now what?

 

[Dhadley]

Re: Installing a bubbleback on a crossflow

All V4 crossflows 90 hp and above have the same bore, stroke and gear ratio. To know if any change will give you more top end we'd have to know what your set up is now and what hull design you have.<br /><br />We're back to the ol' road map deal. To figure out how to get to where you want to be, we have to know where youre at now. <br /><br />If you have a hull that responds to small torque increases and your 90 is set up at - say 5200 - and you install a 140 CF set up at 6000, yes you probably will see a top end increase. However, if you set up your 90 to 6000 rpm, it may be only slightly slower than the 140. It really has a lot to do with the hull design.