'89 292 SR1 60mph max!?
 

Ok so I have just purchased '89 SR1 292 with 454 mags. Engines are fresh with comp cams. compression tested almost dead even 170psi on every cylinder, a couple were 165 and a couple were 175. Anyways I checked base timing is set at 8degrees at 800rpm. and I'm getting wot on the carbs. I first tried 24pitch 4 blade bravo 1's and 60-62mph at 4500 rpms. Today I tried 22pitch 4 blade bravo 1's and 60mph at 4900rpms. What gives? Brochure says 66mph with stock 23p 3 blade mirages. Also this is at LOTO. Also new cap, rotor, plugs, wires, and fluids.

Just wondering if the 4 blade prop isn't fighting me with too much lift. I have the trim all the way up and it feels that it could benefit from more. Just thinking that maybe formula had it right with the 23p 3blade mirage. unfortunately I bought the boat with one 25p mirage and one 25p quicksliver. ..... please help !!

The four blades will typically be slower on the older Formula hull. State of the art technology back then was a clever prop :lolhit:You may actually see a higher top speed with the three blades on it, but cruise and mileage will suffer. Also in 89 they didn't have GPS speedos so that number is probably from a dreamometer which tended to run 3-5 moh faster than true radar or GPS.

jg1000 - have similar setup and hoping getting my bravo's 1 labbed with BBlades witch bring the max out of the boat. I plan to advance timing while using 93 pump gas too, though dont have the Mags. mike

All of this data is with gps.... what is everyone else getting with their 292 non stepped hulls?

did you purchase that boat from glencove marina?

I've got a 1990 292 Sr1 mags stock 23 mirage she does 65 seen 67 a few times

A good friend of mine has a 1990 292 with fresh 454 mags, his does 60 most of the time, I think he has seen 62 a couple of times. It has Mirage 3 blades.

I didnt buy this from glencove. now for the last two comments how does the same boat differ 5mph ?!? thats a big power difference. maybe the difference between salt water and fresh water? does anyone ever trim the 3 blade props to get more rpms?

My '89 311 with mags will do 67 mph (GPS) with Bravo 1 26 pitch props, and 68 with 25 pitch Mirages (not Plus). Motors are stock except for Gil Offshore exhaust. If your not making the speed you are not making the horsepower.

I know the dreammeter MPH pitot displays 66, handheld gps on mine displays 61 at most. Tides movement in my waters make a huge difference too, even though you can run "faster" in salt. Bottom line, the boat compared to others 60 mph boats in rough waters make it a nice ride. Grateful to own a Formula.

mine loves trim...ya, more rpms and bite still...though the bow with a wind feels loose at times, need hydraulics.

Yeah I agree that it doesn't seem that I am making the power that everyone else is. What rpms are you turning with the 25p mirages? Are you on saltwater?

I am not unhappy with 60mph but if the boat is down on power I want to know why. it has aftermarket cams, so it should be making alittle bit more. I am wondering if maybe the cams didn't add enough low end to push a higher pitch prop but instead just added power above 5k rpms? So maybe I need to try a 21p mirage, I dunno just throwing ideas out...

Your not trimming up at all at 60?
31sr1 comparison 400 more pounds than yours to start...
http://www.offshoreonly.com/forums/a...-1990-311a.jpg

I think you're starting to get on the right track...what do you know about this cam? This is really important as this changes everything! Changing a cam without adjusting for intake, exhaust, and carb settings can actually make less power.

With regard to your prop issue. The 23p 3blade mirage is the right prop (if you were running stock 454 mags). All things being equal, you may see some improvement running the mirage plus. If you've got your heart set on running 4 blade props, I've heard the SR1 hulled boats tend to prefer the Hydromotive Quad IV over the Bravo1.

Yes I bought the boat with the cams already installed. one of the motors ate a cam lobe so I tore it apart and figured out what was in there. anyways the cams are definitely designed to pull higher rpms. I am looking for the specs but can't find the right cam right now.

However I do know that the cams were spec to make power to 6k. And since it has stock mag everything else, they probably didn't add any lowend and just 20-30 on the top end. Which being that they are spec'd to 6k the extra power is probably above 5k. So this makes me wonder... do I try a 21p mirage and spin it into the 5.5k range?

the 24p bravo 1 was at 4.3-4.4k , the 22p bravo1 was at 4.8-4.9k , so I am guessing a 20p bravo 1 one would be 5.3-5.4k... however bravo stops at 22p. So I am guessing a 3 blade mirage is definiitely going to be my prop. And since a 23p mirage is going to pull same rpms as a 22p bravo 1 ... I am also guessing I need something lower than a 23p mirage to get me over 5k.

So ending my long winded rant ... should I try to spin this to 5.3-5.5k? it has racing oil and high volume oil pump and dual valve springs.

My 23 Mirage's rpms at 4900 WOT, my 22p bravo 1's at 4500...
Should let Brett from BBlades chine in here. He Knows this boat even if the build is producing strange results. my Heads dont even match motors but rpms do at WOT...:thankyouthankyou:

I can spin the old 25 Mirage 4900 rpm, shows 68 on gps. The cams in the motor might not be the best for your application.

Nope, I wouldn't bother trying to spin your engine any faster than 5000 rpm unless you're prepared to add components designed to operate in a higher rpm range. Keep in mind the blue HP425 engines operate no higher than 5200 rpm and were basically 454 mags with Gil exhaust, Wieland X-cellerator single plane intakes, and Holley 9022 800 CFM carburetors. I really can't comment on how long the bottom-end of your stock 454 mag will hold up at 5500 rpm.

I really think you NEED to find out exactly what cam you have in your engines. If your cam is too big, there's a good chance you have a more narrow and higher rpm power band that actually has you loosing power on both the bottom and top end of the rpm range for different reasons. If you have a more reasonable cam (closer to stock) than you might have a problem elsewhere.

Here is the cam that is in the motors

View Specs 11-240-4 XM278H Hydraulic Lifter Hydraulic-Jet w/ A impeller, needs improved intake, likes headers. Chevrolet 396-454 c.i. 8 CYL. 1965-1996 Xtreme Marine™ Hydraulic Flat Tappet Camshafts

how do the plugs look? is it running lean; did you add fuel? change intake and add headers?

These heavy hulls love trim, cant get enough. try more trim

My 272 w/ 330hp's pulls 65 at 4900 with 23p 3 blades any load any water- and I love how easily it comes out of the water and midrange. With 25p I can hit 68 at 42-4300rpm but its a pig coming out of the water.

thats with 330hp's - you should be getting more than that...

I have some 25p props for sale btw...

That cam is HUGE! Way too much for your application and stock mercruiser components. As installed, I would expect your engine to make less power than a stock 454 mag across almost the entire rpm range.

Yeah , so what is the best upgrade ? I'm thinking ported 496 exhaust and maybe port the heads and intake ? New cams isn't an option...

That is a great cam if you have the intake,heads and exhaust for it. FYI i have the XM 270 H with AirGap intakes, Dart heads and Imco exhaust. I would have prolly made more power with the cam you have. Do you have a true mag as in rectangle port heads?

Ya, but it sounds bad ass at idle...which is really all that matters at LOTO.

Once you leave the dock you're just another dumb ass out driving too fast, riders on the sunpad, throwing occupants around....EVERYONE knows this...now.

Your not thinking anywhere big enough, a ported 496 exhaust isn't going to get it done. Are you prepared to spend between $8000 and $10,000 dollars in bolt on upgrades?

If not, I strongly encourage you to rethink going back to the stock cams or something much closer to stock.

Yeah this is a true mag , forged short block , rectangle port heads, high rise aluminum manifold.

I said that changing cams out isn't an option because I don't have the facility to pull the motors. When the starboard motor ate a cam lobe my boat mechanic felt sorry for me and let me use his shop to fix it, which even then I had to over night the cam and get the whole project done in a very limited amount of time.

So I am just going to have to make the best of the situation. What limits rpms on these mag motors ? I have valve springs, I'm sure the rockers are good for 6k. Can the stock bottoms ends be spun to the 5.5k range?
Maybe I should just save my money on gaskets and exhaust and just shove more air down its throat with a Vortech ; ) I'm sure with 5 psi through a properly sized vortech I could max out my bravo 1's .

What power are you making with your setup?

I quickly have realized that when wanting to upgrade twins it is crazy expensive. So I think that aftermarket heads are out of the question, but porting the stock heads is viable and probably flow pretty well being that they are the rectangle port.

446@5400

497ftb@3600

and yes porting the heads will help!

i don't run mine past 5500 i'm sure the bottom end is good for it but no sense in building a motor to run that high if you don't have to!

Yeah I totally agree. I want to spin mine up to that range to see if it makes more power.

What dart heads do you have ? Are those numbers at the flywheel ?

Dart 308's out of the box no portwork

Yes that is on the dyno.

hmmm wonder what the flow test comparison is between those and magnum rectangle ports is? I can say that these cams adleast sound fkn kick ass at idle ; ) I think that I will port the heads, manifold, and a set of 496 manifolds and call it done. That is more work that I was thinking of doing but valve guides could use replacing and rest is just port work. I would think that would kick me into 70mph level but if not maybe just be happy and put the money into gas; )

keep in mind the Darts have the raised exhaust ports and are
2.25 intake valves compared to the 2.19

stock rectagle ports will make good power ported though!!!

Rec Heads
 

Al ittle off subject but...I found two mag motors with both motors having bad rods...
Its a gen IV with rectaglar heads. intake shot as with eshaust.
I have a pair of stock non mag motors which I would like to beef up upper end. The long block has 50 hours on it, but I beleive remains non forged internals. My mechanic thinks the cam is beefer but cant confirm. Its a 292 1988. I plan to purchase aftermarket Exhaust. My intakes are new and carbs just rebuilt. My heads are mismatched. One is small oval peanut, the other is lage oval. the boat still runs in its specs range. Will porting Rec heads make nay differnce? Will it need a new carb/intake to get the max out of the hp? Will the internals really brak down. I run it hard 20-30% of the day.

That bottom end is good under 5krpms but cast pistons can't take detonation. IMO the juice ain't worth the squeeze. adding the top end will put your rpm range higher and you will probably only gain couple mph. I think the exhaust is a good investment because they add power and save weight, plus cast are gonna rust out eventually and possibly damage your motor. Just my 2 cents. You would also need the intake and carb setup to match for that rpm range.


It seems to me that the dart heads aren't that much better than the stock rectangle ports. Looking at my cam specs vs. merc 420 specs it just seems to be a tad to big if I upgraded my motor to 420 specs , which I believe is gil exhaust and 1.7 roller rockers.... the gears are turning hard now; )

Thanks JG...what exhuat people recommenad keeping in mind the space is tight...and why 496 Mercs? They special/made well compared to GIl/Stainless Marine/ImCO, etc?

i disagree on the heads they lend themselves for more power to be made.

my motors make more power than a 420 and with WAY less cam and dual plane intakes!

the power is in the heads

no gil , or some stainless system would be better than 496 exhaust is just a cheap option to upgrade to. If i were to personally use it, I would port them as much as possible to flow as much as possible.

I don't doubt that they are better but I personally don't want to spend the extra money over just porting mine.

i agree