Diego9040

iTrader: (1)

Trying to bring this thread up from a couple of years back. Planning on doing some tests next week when i get back from vacations, i am running 25p props now, getting also a pair of Mirage 23's .

What speed is everyone getting, any mods, swim platform mods? I will install SM manifolds and risers from my other project in the Formula in about 2 weeks.

would love to hear everyone, I spoke to Todd in this website he is getting 70mph with stock 330's and Headers in his 89 272 sr1

TylerBurich

For what it's worth I never saw any real world gains from ditching platform, adding crossovers, imco exhaust. I did see a huge improvement with roller cams and aluminum heads (done at same time). However, I love the functionality of the aluminum platform over st box, have you ever pinched your fingers in the stock ladder? The exhaust was done for reliability, that's a no brainer.

Diego9040

iTrader: (1)

i agree that i will not see major gains with these and i am not thinking of getting rid of the platform,actually i like it a lot, my main interest is knowing what everyone is using as far as props go. Lil Red advise me to get 23's Mirage in order to get the max out of the 330's but i know Ian from this site that had the fastest 272 i have heard going over 100mph and he mentioned when he took off the swim platform he gained a lot of speed,he had over 600 a side plus shorties plus hyd.steering etc

so what props is everybody using on the 272s ?

gary20099formula

I have a 272 sr1 with 500hps and 27p mirage on it now and i will do 80 at 5500rpm so i think i need to go with 28p or try 30s what do u think? ..........Diego my boat came with some 25 mirage pluses and ran good 65 with 330hp Traded them this past summer to my buddy with the 34 scarab i may be able to get them for you to try

befu

iTrader: (2)

I am really interested in this one from two fold. One, I wonder what I will get out of my 272 with the vortec 350's I put in it. I imagine I should see low 60's up to 65 with the "supposed" 300 hp vortecs and alpha drives. SBC are lighter and the alphas more efficient from what I understand than the BBC/ bravo setups. Well, as long as the alphas are holding together! So definately interested in seeing what it will do compared to the 330HP BBC setups.

Second, most 272's seem to run 60mph for the stock 260's, 65 for the newer 300 HP SB or 330 HP BBC. That is generally what you read about. Gets thin as you go north of 65 it seems. But what is scary is how much HP it takes to climb that hill.

An 87 with 425HP sbc's in it topped almost at 70 mph. Wow, another 250 HP in the boat for 5 mph! 29% more HP over the BBC for 8% more speed.

One with 500 HPS does 80. A solid 51% more HP for a 23% increase, which sounds about right. Still, 400 more HP for another 15 mph! These things do not like to go fast, do they? I mean, I remember when the 31' Scarab Thunders came out with the SC 454's making 525HP running 80 mph. A 31 scarab is a lot more boat than a 272!

Definately lets me know that when I get this thing running and I get it reliably north of 60, to just shut up and be happy and run the gelcoat off it!

Still, curious about this thread and look forward to adding my numbers to it this summer.

Brian

Diego9040

iTrader: (1)

Gary,

I bought a set of mirage 23's non plus ang was doing over 4900 which is on the high side for the 330's bbc , I am going to install sm exhaust on it in about 3 weeks (this would give me an extra 200rpm ) so once I install these ,I would love to try those 25 mirage pluses to see if I keep rpm at around 4700 at wot , does this sound right?

Gary , have you seen the thread "fastest 272 sr1" this guy Ian (cayfomula) got over 100 mph with 650 hp a side , see his set up amazing speed.

http://www.offshoreonly.com/forums/f...st-272sr1.html

Diego9040

iTrader: (1)

Brian,

As you might know I built twin 383's 400 hp 460 lbs/ tq and I know I could only get to 70mph if I installed them on the 272 so , since the bbc I have are running great, I did not want to go that route and get into that mess just for a 5 mph difference, I want to enjoy my boat as it is for now.

FIXX

iTrader: (2)

we ditched the twin big blocks,,glassed up the transom,installed a ssm#5a. on a box-2up..in front of that we installed a 632..best speed with a 28p 4 blade was 96mph @ 5800..that was years ago and a few computor crash's ago..since them i pulled the engine,sold the drive and still have some parts like the crank from the 632..stringers were weak in the front part of the boat so we put it through a tree grinder and blew it into a friends field on his farm..

Diego9040

iTrader: (1)

This is one of the highest speeds I heard of on the 272 hull,nice.thanks for sharing it.

sprink58

Diego...as a matter of comparison, my '86 272 LS with twin 320 EFI SBC's thru Alpha SS drives would run 74~75 with 23" Cleaver props. The RPM was pushing 6000 depending on the drive trim. The swim platform on mine was teak on brackets with thru hull exhaust. The 320's were stock except for the addition of a larger Lingenfelder throttle body..they made solid power past 5500 RPM. There was another OSO member that had a boat like mine that was the '86 272 LS Miami Boat Show "Demo" boat. He changed the engines in the early '90's to LT-1 350 SBC's and reported 754 MPH top speeds. http://www.offshoreonly.com/forums/f...-vs-272ls.html If I recall the SS drives had a short lower unit which may have helped the top speed due to a shorter "X" dimension. Shorter lower units on Bravo I's may be a quicker ticket to more top end for you than more power. B-I's do run a deep "X" on our boats due to the hull configuration.

The EFI was revolutionary for the times...but "Cave Man" compared to today's MPI systems. The thing I truly enjoyed about the boat was being able to start the engines after sitting idle for a month with a simple twist of the keys. No throttle pumping was required...they started first time...every time.