1990 larson senza 210lx

[bspeednut]

I just bought a 1990 larson senza 210lx i would like to know if anyone can tell me what the speed range of these boats are . Mine has a 260hp volvo engine (5.7 chevy) and a duoprop outdrive. I cant find anything in the order of mph ratings or anything on the net. I am puting a late model engine back in for the one in it has a busted block. I am raplacing it with a 1998 vortec 350 longblock- The hp rating on this block,head and cam combination is about 350 hp. Basicly a RAMJET 350.
My question is if the original engine was 260 hp and im adding 90 hp then what would the mph i should be able to reach.
Oh and i have never driven nor owned a boat with the duoprop system
anyone have the pros and cons for this setup.

 

[mkast]

Re: 1990 larson senza 210lx

My question is if the original engine was 260 hp and im adding 90 hp then what would the mph i should be able to reach.

About 9 mph faster than the old engine.

 

[John_S]

Re: 1990 larson senza 210lx

Make sure to check the ramjet cam if it is compatable with marine wet exhaust.

The 350hp rating is probably at the crank using headers. Assuming that and a boat rpm limit of 5Krpms, loss of hp through drive, would put you around 300 at the prop. Your 260hp current spec, should be an at prop rating. So your improvement is in the 40 to 50hp range, vs 90. This would be approx 1-3mph at wot improvement, in most boats.

I don't know your boat or hull or load, but would expect most runabout 21fters with that powerplant to be mid 50's or so.

 

[Bondo]

Re: 1990 larson senza 210lx

About 9 mph faster than the old engine.

Or Less...

 

[mkast]

Re: 1990 larson senza 210lx

Or Less...

I'll admit to being a little optimistic, I don't think he'll believe me anyway, we ARE talking a 90 horsepower increase.

 

[fuzzybob]

Re: 1990 larson senza 210lx

Speednut, welcome to iboats.
You can go to Larsons web site and click on the archives section and probably get the data sheet for that hull and power package.
As for what you'll gain with the repower there's too many varibles for me. Mabe one of the other members will chime in with an informed guess.
Good luck and let us know how it works out.

 

[180shabah]

Re: 1990 larson senza 210lx

we ARE talking a 90 horsepower increase.

Are we?

The 260hp was a measured rating, at the prop. The 350hp is estimated - most likely a crank rating, at what RPM?

We KNOW, that a stock vortec 350 with 4bbl puts about 290hp to the prop (or approx 320 at the crank). Just don't see him getting another 60hp out of of with just a cam and possibly an intake manifold, AND keeping the RPMs down to 5k.

 

[mkast]

Re: 1990 larson senza 210lx

Are we?

The 260hp was a measured rating, at the prop. The 350hp is estimated - most likely a crank rating, at what RPM?

We KNOW, that a stock vortec 350 with 4bbl puts about 290hp to the prop (or approx 320 at the crank). Just don't see him getting another 60hp out of of with just a cam and possibly an intake manifold, AND keeping the RPMs down to 5k.

The numbers stated weren't mine.
But, I remember the hundred horsepower headers in the sixties.

 

[John_S]

Re: 1990 larson senza 210lx

I checked the GM ramjet specs, and it looks like it uses the standard mercruiser roller cam. It does have 1.6 rockers which may cause a problem. The torque/hp graph did not have any detail on the set-up, but it was probably with the fuel injection and headers.

http://www.gmperformanceparts.com/E...350&engine=Ram Jet 350&sku=12499120&engCat=sb

Changing to 1.5 rockers and a dual plane carb set-up, put you in the 280-290HP at the prop range.

 

[bspeednut]

Re: 1990 larson senza 210lx

Ok i very grateful for all the input. thanks alot i just joined iboats a few days ago.
I will say i am not looking to get alot of more performance out of the boat from what it was stock. I am merely wanting to make the engine i go back with a little more durable and hopefully as a side effect get more performance. if not thats ok too.
My hp rating is not as acurate as i made it seem - i realise that now.
Yes the factory engine or powerplant ETC states its 260 hp. i dont know where thats measured. i do know that a ramjet engine is rated at 350 hp - i also do not know where that is measured - i think someone had the formula earlier with the 40 hp gain as apposed to the 90 hp gain-- after the formula is figured in .
I do know the ramjet cam is the exact same as comp cams marine roller cam or at the very least it is super similar.
I do know that i am going from a flat tappet cam to a roller cam and from the old style gm heads to the better flowing vortec heads.
reusing the same carb and intake assy.Also the bottom end is now a 4 bolt main wheras the engine i took out had an only 2 bolt main.Oh and the exhaust will be through hull now instead of the lower unit
If the boat runs 50mph i will be tickeld to death.

Oh can someone chime in on the duoprop system. for this aplication ??
was it factory and does it add any exta to the boat or not.
Thank you guys so much.
I will say i am a gearhead of sorts i was a Transmission Rebuilder for 14 years an now i sell cars for a living. I have done alot of fuel injection in streetrods and sand drag cars but never the boat thing. I have found that what i knew about cars doesnt mean NADDA when it come to boats.

 

[John_S]

Re: 1990 larson senza 210lx

reusing the same carb and intake assy.

Vortec heads require a vortec intake manifold and gasket set. Carb may need rejetting.


Through-hull exhaust buys you allot more noise and maybe 10hp.

A 250/260hp at prop is a very typical spec from a 1990 4brl 350.

 

[bspeednut]

Re: 1990 larson senza 210lx

Yes i was figuring on having to have the carb rejet done
however the intake i had completely overlooked. I have a vortec intake in my race trailer that inever used i got it on a trade at the local dirttrack. I dont use vortec heads on anything but i was using them on this bc i just wanted some stock hp with durability. I have a dirt modified that is a constant maintainance issue for the engine in it is a small block 406 with all kinds of crazy will stuff . I dont know all thatlingo but i just wanted to make a vortec 350 to fit in my larson and make it dependable.
so i will have the intake and engine done and all i need to do is rejet the carb.
Sound easy enough. thanks guys for your input.

Oh do i have a rare item with this duoprop bc i have yet to hear anyone chime in on the prop setup.

 

[180shabah]

Re: 1990 larson senza 210lx

Duoprop is not really rare, just got overlooked with all the hp talk. It is one of the best drives you can get. The down side - if your new power requires a prop change, you're talking 1k or more.

 

[captmello]

Re: 1990 larson senza 210lx

Duo prop outdrives are not rare. They are known for great hole shot and maneuverability. They are also a step slower, 1-2 mph, than a single prop. I would switch to a DP in a heartbeat if someone left on on my doorstep.

 

[Don S]

Re: 1990 larson senza 210lx

Oh and i have never driven nor owned a boat with the duoprop system
anyone have the pros and cons for this setup.

You now have the best outdrive stuck behind a 350.
I had a 27' Bayliner that did 20 with the single prop, 30 when I changed it over to a DP.

They are also a step slower, 1-2 mph, than a single prop.

I agree, but only after 50 to 55 mph. Up till then, top speed increases also, it doesn't go down. See comment above about my old boat.

What is your original engines Volvo serial number or full model number?

Before you go through a bunch of "I wants" on the engine HP, why don't you just take it for a run and see how it actually works and what speed you actually get, how to trim it (if you have trim) etc. Then go from there.

You are putting the cart before the horse here.

 

[bspeednut]

Re: 1990 larson senza 210lx

well i bought the boat with no horse so to speak. I would love to have taken it out when i bought it but the previous owner did not winterise the boat therefor the block is busted and that is the reason for the powerplant update to begine with.. as i stated b4 if the boat runs 50 mph i will be very happy with it.
I was thinking about the prop change when i started my quest here - I am lucky in the sense that the previous owner also [purchased a prop setup that he installed and then removed because he said he could not get enough rpm with it on the boat. It hadf good holeshot but no rpm so he had to change back- I hope if i have more hp now that the other prop will do the trick if not i am going to be a little under budget to start with so if i have to get another prop setup I hope i can get it for around 600 - 1k is alot - hell 600 is alot -

Man thank you guys for all your input.