16’ Mantra Tunnel Black Thunder

[Fonz69]

Well this next chapter begins with me testing out a handmade shoe for my Stealth after another successful racing season with UMPBA. I made a plan to drive the boat back to our dock and offered up rides to my family since we had some X85 fuel left in the drum.

Well I figured why not let both my sons take the wheel for some nice photos and give them a taste of the driving fun that I’ve known behind this alcohol guzzling boat.

Turns out the apple doesn’t fall far from the tree and both boys now want to go racing. When your kids take interest in your hobbies you really no choice but to fuel the fire before it goes out…right?

And so the search for the right boat begins, I found several OB powered ready to race boats that would be great for the JR racer or 65mph class but after showing them to my oldest it was a solid “no I want a jet boat that’s loud like yours“

We had a small budget to work with so our options were limited and everything we both would find meant driving out to the west coast, way over our budget or are too far gone to afford to save.

With some sponsorship help from his Grandparents we finally found a boat that looked promising. A 1986 16’ Mantra Tunnel down in Illinois.

Texts went back and forth and a plan was made to drive down and check out this prospect.

Some things were worse then I had thought however it was a diamond in the rough that just needs some freshening up to make it a reliable race boat. We negotiated a price and started the long drive home. He couldn’t wait to get behind the wheel so at our lunch stop this was his first shot.

And after we made it home his younger brother wanted to share in the excitement as he will someday take the wheel when he gets old enough.

Like I have done in my last 2 builds recorded on this forum I’ll do my best to update our progress. This will definitely be a work in progress so some things will just need to wait until we can afford to do them (sponsors are always welcome ) however it will always be our intention to make this build safe and reliable with what we have to work with. Hope everyone enjoys the build and he has already named it “Black Thunder”

 

[Fonz69]

Both boys were excited to start the tear down of the new race boat. My shop started to look like a bomb went off

 

[n2otoofast4u]

Seems to have some solid parts! Congrats on the new project!

 

[Fonz69]

The pump was supposed to be good to go however I discovered the impeller is shot when we looked at the pump in Illinois. The previous owner adjusted the price and threw in a better carburetor to help offset the known damage.

Did a quick compression test and it seemed to be decent.

Off with the headers.

Out with the seats.

Long day of hard work, they look tired

Time to pull the motor!

 

[Fonz69]

A little digging into the motor shows things aren’t always what they appear…. The previous owner was told it was a fresh build with forged internals. Hmmm not so much. Found a 2 bolt main cast gm crank with speed pro pistons and some Chinese red rockers. Well it did run so we’ll have to make this work.

Heads are gm large oval 241s

Unfortunately an old edelbrock rectangular port intake does not help air flow, otherway around would be fine but this will be replaced now by a rpm air gap manifold.

 

[Fonz69]

Was able to dig around online and found a post of a past owner in the 90’s when this old girl was in her prime.

The original trailer is still here and we still have the original back seat.

 

[Romans9]

Very cool!

You cannot go back and make memories, you have to make them now, good job dad!

 

[n2otoofast4u]

Post up what parts you need! I’m not sure about a sponsorship, but there’s a LOT of us with a LOT of shit laying around that would be happy to donate to put a new hot boater on the water!

 

[JUSTWANNARACE]

So Rad!!

Fallowing for sure!!

 

[Fonz69]

Post up what parts you need! I’m not sure about a sponsorship, but there’s a LOT of us with a LOT of shit laying around that would be happy to donate to put a new hot boater on the water!

I’m going to reach out to David and Duane at HiTech Performance also but big ticket pump item would be finding a nice used AA impeller. I have a new standard wear ring but the impeller the boat came with is toast!

Really need a flywheel cover and a safety loop or shield for the driveline too!

Anyone has anything decent please let us know. Thanks!

 

[Fonz69]

Put a few more hours in the shop today.
Boys went to town removing parts while I started the clean up and tear down of the motor.

Definitely had the wrong intake you can see the rectangle port gaskets stuck on the oval port heads

Goal to pull the pump was tougher than expected. Had to drill out the back two loader bolts and there was probably about 3 tubes of silicon around the race plates

Motor rails coming out. Plan on making new ones since the motor will move forward some with the Jetaway.

New intake came in yesterday so doing a dry run to see how things line up.

Pumps out, shoe will have to wait until it’s flipped over only 1 out 4 bolts came out and I bet the others will be real fun to remove.

Getting closer each day.

 

[Fonz69]

Motor is about 90% complete now.

Cleaned off the cheap paint that just melted off with carb cleaner
Fresh coat of etching primer and engine black.

New timing cover since the old one had one of the pan nuts missing so someone smashed a nyloc nut and silicone

Had to machine down the cam button to accommodate the new cover.
The oil pump drive shaft sleeve had sheered off and was rattling around at the bottom of the pump. When I pulled the oil pan and seen the stellar weld job on the pickup I knew looking closer would be important.

New HV Melling pump with matching pickup for the new 10q Champ Oil pan. Figured some of these upgraded parts just made sense to try and keep this questionable motor alive.

Champ pans are made in WI and I’ve used them before with good success and they are not terribly overpriced like some pans can be. They come with trap doors and a crank scraper built in.

Picture above is during cleaning with the scraper off.

Pan with Moroso 1 piece gasket and stainless ARP hardware.

Dusting off my original set of HTP valve covers. Have to make some custom tower breathers because of the blower setup they were on last time I used them.

Went with the Edelbrock RPM Air Gap manifold and went through the Holley 850 carb.
At least this intake will actually match the heads….picture is mocking up.

So the headers that came with the boat will need to be re chromed so I brought down off the wall my set I used on the 582 motor in my boat. Sanded up his scoop, set the intake, distributor and wires. I’ll have some brackets to make for the coil and 6AL box but that can wait for now.

 

[Fonz69]

Mission to complete the hull stripping is almost complete!

Fuel tanks out!

Pulling all the wiring out, past projects have taught me even if you think it’s ok you better check it. I found my harness in my stealth rubbed across a bolt and chewed off the coating on all the wires in the same spot! It’s just not worth it so this boat will get new wires installed in a poly conduit.

Max hard at work removing pounds of silicon.

New wheel came in so had to quick mock it up before we removed the steering.

All out!

Checked out the boat cover, it’s original and was nice but unfortunately has shrunk and only snaps the first half before it won’t stretch anymore.

 

[Fonz69]

Time to figure out this loose bow eye problem.

Marked out the light then drilled holes under the light area to expose the loose eye nuts. It doesn’t seem to be damaged on the inside but will definitely need attention on the outside.

Up she goes!

So this would make it 450lbs with the intake, carpet, tank straps, horn rub rail and rigging so probably around a 420 lbs shell.

Now we’re rolling.

Note to self, wait for help, this was not my best of ideas to attempt myself. When it goes back over again there will be more people involved as the cherry picker had a mind of its own and caused me some more gray hairs lol.

Well somebody loves to beach this ol girl

Will address the through bolt tank straps to make sure they don’t leak but thinking I’ll leave them thru hull still.

Have to address the water absorption issue, the bunks are rotted a
so that explains some of this.

We’ll time to fight with the shoe bolts and hope they will come out….I want to be able to adjust the hardware so now is the time to fight with it while she’s upside down.

 

[Fonz69]

Well after some drilling and broken tools the shoe is out. Looks like it was set when the intake was installed and never removed. Opening is 14 3/8” way larger then my stealth. At least now we can make adjustments as needed.

Old rusty tank straps need to go. Found some nice stainless ones online.

 

[n2otoofast4u]

Heck yeah! This thing is going to come out great.

 

[Fonz69]

Quick refresh of the trailer started today. It’s in pretty good shape but needs wiring, lights, axle seals, bunks, fender panels and tires.

Using some composite material left over for the fender skirts. It’s aluminum skin with a plastic core.

Stainless hardware and spray glue with some new rug.
Trailer selfetch primer and gloss black for now.

New treated bunks and rug with stainless hardware through bolted so hopefully they stay in and not fall out like the old ones.

Panels worked out great long as my boy doesn’t crash into them loading the boat. Part of the reason I’m not going with a high dollar powder coat finish lol.

Well no more room in the shop so you stay outside. At least I can use this canopy I bought for the races and somehow never end up using anymore.

Now it’s back to boat bottom and a goal to get her back on the trailer before the big snow hits!

 

[Kachina26]

One word, WOW!

 

[Fonz69]

Sanding fiberglass my favorite past time… not really but it’s got to be done. Not going to go crazy with it but address some of the sponson gel cracking which is in line with the main bulkhead so I’m guessing some wave pounding and past owners popping wheelies led to what I’m seeing.

Ground out and added some glass back to the damage I found at the bow eye.

Max was back at silicon removal duty, his favorite

Owen was helping save my lungs while we drilled out and countersunk better fasteners for the new stainless tank straps.

80 grit fun

Some filler for the intake holes to smooth things out.

Much larger opening than my Stealth. Might make a shoe to close that up some since we don’t need any overcharge issues. And might try an open loader I had instead of the old rusted V blocker.

 

[17 10 Flat]

What a great project to do with your son's!!! No doubt boat will turn out amazing.

 

[Fonz69]

Worked a 70hr week this week so not allot of progress made though was able to finish the keel mods, speed coat the keel and finish the crack repairs. Hope to shoot the black gel coat next Saturday.

Modified the keel to less of a V hull design. Only testing will prove if it works

These cracks are right in front of the main bulkhead so I’m sure everyone’s popping wheelies in this didn’t help matters. Had to grind them down and build it back up.

Touched up the scratches and more bow eye detailing.

Gel coat seal the keel work.

Final filling on the crack areas in the front.

Scuff up for speed coating.

Hope the keel works.