My 311 Formula.

You all pretty much know the specs… 509s, AFR 325s, 9.4 comp, Rookie’s 235/241 .650 lift roller cams (using Crane hydraulic rollers), Merlin intakes, custom Demon 1025 carbs, closed cooling, CMI etops, TRS. 27P solid hub Mirages (these came off the Cig Bullet and were on the boat when we got in 2007 - may be labbed but only way to tell would be to send them out).

The engines run super strong. A/F ratios are good especially at WOT. If I want it to, the boat comes out of the hole surprisingly hard and planes immediately (would rather not break a lower though so usually I’m easy on her). From a planing perspective I could probably run a 29P and not lose anything down low.

My problem is too end. We ran into the 70s but we’re hitting a wall at 5k. This was while running the oceanfront Saturday. I couldn’t run a lot of trim maybe only 4 on the card (back when I had the 502MPIs the best speed was with it trimmed off the scale…71-72 with the same props but turning 4700 maybe just under 4800).

The engines are not taxed. Oil temps (thermostatically controlled) however right around 200 degrees and coolant runs about 175-180 except above 60 where the temps drop to 150 (pegging water pressure). They sound great!

So is this just a trim situation? Too much wetted boat? I feel conditions were optimal.. not too hot and just enough swell to allow fast running and get some air under the boat but the ocean can be unpredictable and finding a hole at 70+ would not have been good. I have a pair of 26P Bravos that I won’t be using on the Bullet (too small for the new power). I would think these would be TRS breaking props but I’d be willing to give them a brief try.

Running at dusk after the temps dropped into the upper 60s seemed to make them even happier, but the Bay got rather snotty so we were limited to how fast we could run without getting the boat airborne.

Comments critiques and suggestions welcomed.

You have 3 factors:

Hull and wetted surface /weight

Engine HP

TRS Drive/Prop

For some reason the 80s and early 90s Formula boats have a hard time running fast and need a lot of HP to even get to 70mph. Is this from the weight? Or weight and hull design? One option is to put her on a diet. As an example, I yanked my fridge...don't need it...new coolers are great and contain spills. Have you still got the Formula alcohol dispensers in there??? Lol

How your hull is trimmed out is likely something you've already played with. Different props will have an affect on how the hull behaves.

TRS drives are typically really deep in the water. Have a check with the prop shaft aligned with the hull...how far down is the center of the prop shaft from the hull? Newer prop designs don't need to be as deep. Raising the TRS drives up would reduce a lot of parasitic drag in the water. Water resistance is cubed. Air resitance is squared.

I appreciate the effort of filling in the transom and recutting to raise your X-Dimension, but you are asking what can be done.

You probably already know, the TRS drives don't like 4 blade probs. The re-entry bite on them seems be the culprit. Ha e you got the Bravo 1 shims on your TRS drives? Or the crush to tolerance shim?

Not much you can do about the TRS bullet hydrodynamics. Mixed reviews on nose cones. You can just as easily make it worse.

You've got healthy engines. Why are you limiting them to 4800-5000 rpm? Let them breathe a bit. 1.65 ft lbs of torque is the max NA you can really ever achieve. To get more power, you need to move up the rpm scale.

Obviously, you would need to spring the engine to operate up there if you aren't already. With the 235/241 cam, you likely are not even in the peak HP rpm range at 4800. AFR 325s are healthy heads, no issues there.

The 72c velvet drives are rated for tq not HP. Like most transmissions. Turn them a bit faster, and they have an easier go of it. Obviously, there is a limit.

Didn't the 311s run 60mph with the 330 cast Mag engines?

With the 502 MPIs, you don't have much weight change to the 509s? You have better trim results, that you can't replicate now with the new engines? Any other weight changes?

You closed cooling engine coolant drops to 150°f at 60mph? Or is the the raw water exit temps?

Cylinder bore wear skyrockets at cyl temps 150°f and below. It's pretty low in the 160°f + area.

try REV 4s. They're a great upgrade for lower X boats.

Just kidding Tom!

Tom,
Just for reference. My 30' TRS Scarab Panther ran 82.
454's 9.0:1
Dart (Valako) custom 345 Pro1's
Your Cam Motion cams, 235/241 (1.8/1.75 rockers) Isky solids on HR cam
Crane HI-6M 35° timing
120°F thermostat, 180 max oil
Stainless marine
approximately 575HP
Stainless marine TRS dry to the tips
25 Mirage slid hub 5800 RPM
Ran 71-73 with originaorl 420's
My TRS boat hates Bravo 1's, too much stern lift.

I'm running Merlin intakes (and heads) on custom built 468's in my 27/29 Fountain.. My next perf upgrade will be to rpl the intakes with some alum ones. I've never had to open these engs but prev owner did and said the intakes felt like they weighed 100 lbs each. Pretty sure I could lose well over 100 lbs with the swaps.

I'd start with what's easy....borrow some props.

years ago I had a 382 with big power. I usually ran a set of weird custom props being 15.625 diameter 28 Maximus (I tested them on a whim and the cruise speed was awesome). These would cruise 60@3,500 but only hit about 83mph at 5,150rpms. I also had a set of labbed 30P Bravos that cruised 53-54@3,500 however they would spin 5,700 hitting 87-88 mph......and yes, the motors were built for the rpms.

ironically the motors were Procharged when I bought it and ran a best of 98. However the negatives were such that I repowered N/A.

I'm with Team Saris on this one. Sounds like your motors are really healthy you're just hitting a water wall at 70mph. A nice work around is a prop designed to free up some of the drag at WOT.

You were running Mirage plus 25s, or non-cupped?

Stern lift is going to put the bow down a bit? Triming up the drive would counter the stern lift to try and air out the hull? HP loss there?