Don Terrill’s Speed-Talk

Not having built a lot of BBC's I only have a rough idea what this thing will make.
Should have it on the dyno in January.

Stock 2 bolt block with 4 bolt steel centre caps & short grout fill.
Scat 4.25" steel crank
Scat H beam 6.385" rods
Racetech 21cc dome tops with metric ring pack

DRP (China, but decent china) 335cc rectangle port heads with 2.3/1.88" valves & a bit of a rub up.

268/274 on 110 solid roller, .730/.680" lift with 1.8/1.7 rockers.

Eddy victor ram with 1050 dominators

11:1 comp to run on pump fuel.

2" primary 4 into 1 over transom headers with 3.5" collectors, no mufflers or exhaust system (its a boat).

Msd crank trigger
Wet sump

I'm thinking around 800hp @ 6400rpm or thereabouts.

That sounds about right, I believe around 800 too.

Erland

Most people with that combo will make 740ish but I bet with your "rub" work on the heads and intake you should be in the 800 ballpark, might take 6800rpm though. Is this a jet or an I/O?

Something like this is always good in endurance marine to help with valve spring life..
https://www.hardin-marine.com/p-16736-b ... ilers.aspx

I usually put a 40lb check valve on to help low rpm oil pressure.

In-Tech wrote: ↑Wed Nov 23, 2022 9:40 pm Most people with that combo will make 740ish but I bet with your "rub" work on the heads and intake you should be in the 800 ballpark, might take 6800rpm though. Is this a jet or an I/O?

17.5' flat bottom shallow V ex circuit race boat.

The old 489 it's based on made 680hp @ 6300 with edelbrock E-street heads, 2.19 intake valves, pocket port only, untouched Vic jnr intake, 1050 4150 carb, 10.3:1 comp & the same cam.
It topped out at 100mph @ 6600rpm with 1.28 step up gears.
It'll get 1.42 gears this time.

I should have the heads mon/tues next week.

I would have guessed 700 - 725. I hope you are right with the 800. Lots of 540's don't make 800.

100mph in that boat is way respectable. The bigger heads and intake will definitely help with more mph. Keep the old gears around, you might find it will respond better to a half inch or so bigger OD and a pitch change, think of it as a bigger tire with same gearing.
As you know, marine is a whole different world than cars. The torque absorption curve of the hull is extremely high. HP has to be climbing straight up past what you want, or you will never get there. If it rolls over you can't get to the next rpm because of the absorption rate. The cat type tunnel hulls free up with mph so it doesn't show up as much with those. That flatty you're talking about must be hangin in out

In-Tech wrote: ↑Wed Nov 23, 2022 11:21 pm 100mph in that boat is way respectable. The bigger heads and intake will definitely help with more mph. Keep the old gears around, you might find it will respond better to a half inch or so bigger OD and a pitch change, think of it as a bigger tire with same gearing.
As you know, marine is a whole different world than cars. The torque absorption curve of the hull is extremely high. HP has to be climbing straight up past what you want, or you will never get there. If it rolls over you can't get to the next rpm because of the absorption rate. The cat type tunnel hulls free up with mph so it doesn't show up as much with those. That flatty you're talking about must be hangin in out

Props are hard to come by around here!
He has a couple of others to try & can borrow a couple more & potentially get the best copied by CNC.
As it was it was running past peak hp & with the little edelbrock heads it fell off fast after peak, so even with the old motor the 1.42 gears would likely have gone 103-105mph.
I *think* it'll work best with the 1.42 gears, but as you say if a different prop proves better you never know.

Yeah, props are a whole expensive world by themselves especially these days. I do understand why Merc charges $10-12k per prop.

In the early 90's I was lucky enough to have a prop made by Harold Kinsvater(ME airplane prop dude). I don't know crapola about this boat stuff. One of the coolest things he taught me was the slip factor. I showed him my homeade datalog crap and we were slipping the prop to 9800 engine rpm and it would settle to 8800 then climb to 11,200 shift with the lenco. In my mind I thought if I could eliminate the "cavitation" we would be faster. He explained it is not cavitating, it is boiling the water. That is your multiplication of torque turning small molecules into larger space and further explained it is not like an automatic transmission convertor. Heat, expansion, no control of the viscosity, etc but still still similar.

My sig line...gotta control the heat

I've had such good Mentor's. Bob Wyman Jr/Mallory Erson, Joe Boghosian, Bob McInityre, Gregg Koechline, Hans Hermann, etc etc etc, some really incredible people

My guess 750-770hp at 7,000 rpm......

Truly, for any of us that develop anything after 5252rpm...it;s about chasing torque where it changes the aftermath

bob460 wrote: ↑Thu Nov 24, 2022 12:36 am My guess 750-770hp at 7,000 rpm......

Shit I hope we don't have to turn it that hard!

I'll set my sights on 750hp, anything extra is a bonus!

I hate to say it, but I think IN-Tech might be right about gears in the boat. We run 1.40 gears with a twin turbo BBC making right around 1000 hp at 6300 rpm. That is in a ski race v-drive. When we put in a NA motor we had to drop the gears to 1.22 as there was no way it would pul the bigger gear. On our flats, we run gears between 1.12-1.22 with our NA engines. The key to that is having a good prop. A good prop and gear combo will run circles around someone with another 50 hp that is just trying to muscle the boat around the course. We did gear one of our boats with a 1.32, but it was a bigger CI junk engine that was severely under headed and power fell off a cliff, so we had to use its lower RPM range. I hate to say it, but just like in drag racing, it has to run past it’s peak to really make the boat perform its best. How far past is dependent on how quickly the power falls off. I can’t stress enough the importance of the boats setup and bottom work.

I was thinking 760-780 for power. Then again, your stuff never ceases to impress me, so more than that would not surprise me. The circuit boats you guys run down their are awesome. Great hull design and can run pretty dang dry when setup right. Our dinosaurs for circuit hulls are 50+ years old. There is no reason that boat should not be outstanding.

I have probably 8 props for my current boat. Each has its own character and some even want different gears than another. Testing is where he will find an extra 4-5 MPH. I wish I was next door, I would love to help with the boat setup.

Paul

Got the heads for this, they're the proheader/DRP/AFR eliminator casting.
I cut the intake seats for 2.3" valves with a 6 angle valve job, recut the exhausts at 1.88" to a nicer profile & rattled a grinder around a bit - nothing serious, just low hanging fruit type porting.
Bloody things went 400cfm intake & 300cfm exhaust.
I reckon we got enough head!

Assuming your cam is something like a Lunati 50204. (And that I'm any good at engine sims, which is up for debate...)

Depending on cam angle (8 adv vs 3 retard)