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View Full Version : Ways to increase horsepower for L18?


jdl xstar
11-26-2009, 12:45 PM
Are there affordable ways to boost horsepower- specifically for the L18? Is it possible to replace the cast iron exhaust manifolds with an aftermarket header? Here is a picture of a header kit i saw online. It is way to expensive to consider - appr $4,000- but the idea intrigued me.

53358

JimN
11-26-2009, 02:51 PM
Are there affordable ways to boost horsepower- specifically for the L18? Is it possible to replace the cast iron exhaust manifolds with an aftermarket header? Here is a picture of a header kit i saw online. It is way to expensive to consider - appr $4,000- but the idea intrigued me.

53358

How would you cool the exhaust gases and how would you keep the headers from melting everything in the engine compartment? Your manifolds are probably flow about as freely as any header out there.

03 35th Anniversary
11-26-2009, 07:47 PM
SuperCharger!!!! :D

jdl xstar
11-26-2009, 08:01 PM
How would you cool the exhaust gases and how would you keep the headers from melting everything in the engine compartment? Your manifolds are probably flow about as freely as any header out there.

How do other set ups with those types of headers not have an overheating situation in the engine compartment?

jdl xstar
11-26-2009, 08:08 PM
SuperCharger!!!! :D

Your boat has a supercharger on it??? How much of a difference does it make? That must be pretty sweet!

TEAL98
11-26-2009, 08:27 PM
Not sure what engine the L18 would be, but I would reccomend a bigger bumpstick. It's probably the cheapest way to efficiently gain a noticeable amount of power. The only downside is, it's hard to go big without losing anything on the low end. My '98 feels like it could pull a brick sh()thouse down, so I wouldn't hesitate to throw a nice-size cam in it, if I didn't have my LS1 car to toy with. Besides, you don't have to worry about producing enough vaccum to assist power brakes or power steering. And if you've already got the Vortec engine, you don't have to buy an expensive set of heads, because the Vortec heads flow damn well to begin with. I'm a Gen III SBC guy, MC enthusiast, but don't know much about the marine engine setup. Perhaps Harold, Jim, or someone else can assist with this.

TEAL98
11-26-2009, 08:38 PM
Take a close look at this picture for instance. I've got that one peice sittin on the passenger seat, with a portable toolbox and a little blue bottle in the background:D:D:D

Jerseydave
11-26-2009, 10:14 PM
Are there affordable ways to boost horsepower- specifically for the L18? Is it possible to replace the cast iron exhaust manifolds with an aftermarket header? Here is a picture of a header kit i saw online. It is way to expensive to consider - appr $4,000- but the idea intrigued me.

53358

JD, you already have 450 horses............maybe you have the wrong prop?
(I knew I should have met up with you last weekend to "evaluate" your boat!) Haha! :D

vision
11-26-2009, 10:34 PM
I have to agree with njskier.

You have an L18 and you need more HP? Damn! I have the little MCX in the same boat and have zero issues pulling doubles with a loaded boat.

Are you pulling another boat behind your Xstar, and then the rider behind the second boat? 8p

If you do make the modification, let us know how it works.

scott023
11-26-2009, 11:37 PM
Take a close look at this picture for instance. I've got that one peice sittin on the passenger seat, with a portable toolbox and a little blue bottle in the background:D:D:D

Don't tell me you has NOS on the boat...

DooSPX
11-27-2009, 12:23 AM
scott, please do not use NOS as a generic term for Nitrous Oxide. :rolleyes:8p NOS is a brand from Holley... Damn them fast and furious movies!!! :D8p just messing with you!

Teal, I myself am a major GenIII, LT1/first gen Vortec 350' and Gen1 geek as well. built several LS1 vettes and F-bodys, trucks, LT1's and many Gen1 stuff from street to Pro Stock drag SBC.

OP, I think you have the wrong prop for your application. You need to contact OJ and talk to Eric about what prop you need.

No matter what boat you have and what your pulling, you shouldn't need more than the 8.1L. Your torque is outrages all ready. Prop it right and you have a different boat.

scott023
11-27-2009, 01:26 AM
scott, please do not use NOS as a generic term for Nitrous Oxide. :rolleyes:8p NOS is a brand from Holley... Damn them fast and furious movies!!! :D8p just messing with you!

Teal, I myself am a major GenIII, LT1/first gen Vortec 350' and Gen1 geek as well. built several LS1 vettes and F-bodys, trucks, LT1's and many Gen1 stuff from street to Pro Stock drag SBC.

OP, I think you have the wrong prop for your application. You need to contact OJ and talk to Eric about what prop you need.

No matter what boat you have and what your pulling, you shouldn't need more than the 8.1L. Your torque is outrages all ready. Prop it right and you have a different boat.

I wasn't using it as a generic term... that's a NOS bottle in the backround. Had one im my Mustang.

DooSPX
11-27-2009, 09:39 AM
I wasn't using it as a generic term... that's a NOS bottle in the backround. Had one im my Mustang.

Oh, sorry about that. I was mostly joking anyway. Yes, that is a nos bottle. I have had NOS, NX and Compucar.

TEAL98
11-27-2009, 09:49 AM
lol, i was just messin' with ya'll. I'd be more than an idiot than I already am, if I were to throw the juice to my little indmar 350. I'm not that dumb;) Gen IIIs are the sheeet, I love 'em, I'm on my 6th LS powered fbody and I'm sure it won't be my last. Now if I could just afford to get an LS powered MC:cool:

DooSPX
11-27-2009, 01:33 PM
I would love to have an LQ9 or LY6 PS190....

but, that said... the LT1 in the MC's have one of the sweetest curves for our boats of any motor.

TEAL98
11-27-2009, 02:07 PM
For the gas that the LQ9 chugs, you may as well have the LS1... but that's my personal preference and opinion

jdl xstar
11-27-2009, 02:58 PM
JD, you already have 450 horses............maybe you have the wrong prop?
(I knew I should have met up with you last weekend to "evaluate" your boat!) Haha! :D

True- plenty of power already. I wasn't sure if there was a part or two at autozone to throw onto the engine.

I do need a new prop for sure. I'll get whats recommended for the L18 - 14.75 x 17.5 - and I know that will make a big difference. Just wish they didn't cost so much!

DooSPX
11-27-2009, 03:00 PM
Teal, I agree with that. but you have to look at the curve of the engine. I'm sure you are aware, but LS1's dont even make peak torque in till after 4K. every dyno I have of my LS1's and my LM7, the torque is above 4K at peak. Also, Peak is not what you want in a tow boat either. thats why with the exception of the LT1, all the motors that MC and CC use are based off of truck platforms. Its a better platform to start with for the tow boats. Now, I know that the LS1 as more torque on a dyno than a LT1 in a car, but the power curve for the LT1 best suited this industry.
Not to mention BU tried the LS1, but it proved to not be reliable in the marine application as it is in the automotive world.
the famous piston slap that hardly affects anyone with a car, killed many LS1's in the BU. I would think it has to do with the load that a boat has compared to a car. even at high rpm.
Water friction causes A TON more drag than air, no overdrive,etc. and as far as GPH usage, in a tow boat with tons of wetted surface, etc. even the LS1 is not going to be anywhere near as fuel efficient as it is in a car.

TEAL98
11-27-2009, 03:34 PM
Teal, I agree with that. but you have to look at the curve of the engine. I'm sure you are aware, but LS1's dont even make peak torque in till after 4K. every dyno I have of my LS1's and my LM7, the torque is above 4K at peak. Also, Peak is not what you want in a tow boat either. thats why with the exception of the LT1, all the motors that MC and CC use are based off of truck platforms. Its a better platform to start with for the tow boats. Now, I know that the LS1 as more torque on a dyno than a LT1 in a car, but the power curve for the LT1 best suited this industry.
Not to mention BU tried the LS1, but it proved to not be reliable in the marine application as it is in the automotive world.
the famous piston slap that hardly affects anyone with a car, killed many LS1's in the BU. I would think it has to do with the load that a boat has compared to a car. even at high rpm.
Water friction causes A TON more drag than air, no overdrive,etc. and as far as GPH usage, in a tow boat with tons of wetted surface, etc. even the LS1 is not going to be anywhere near as fuel efficient as it is in a car.

I honestly can't argue too much with your points in case, because all of my experience with these engines have been in the automotive field (but that is plenty, I can assure you). I'm not a big fan of the LT1, I've had 2, thinking that my first was just a dog, the second never proved to be much of a front runner either. Just like the L98, the LT1 was nothing but a torque monster. Which is why you're case proves to be legit. However, while the LS1 (fbody) doesn't hit its peak torque of around 345 until well after 4k, it does flex a little more than 70% of it just over 1500RPMs. And as far as this whole "piston slap" deal goes... well, i'll keep my mouth shut on that one. We can go back and forth discussing the pros and cons of both, but MC and the others did what they did for a reason. I'm still stuck with the ole' 350 and it's not either the LT1 NOR the LS1:(

1redTA
11-27-2009, 03:51 PM
It's amazing, no matter what forum I go to, it is always some lt1 versus ls1 argument ( lt1's are awesome ).

TEAL98
11-27-2009, 04:05 PM
LS1s are awesome damnit!!!:rolleyes::D Even the dirty ones!:cool:

Jerseydave
11-27-2009, 05:31 PM
True- plenty of power already. I wasn't sure if there was a part or two at autozone to throw onto the engine.

I do need a new prop for sure. I'll get whats recommended for the L18 - 14.75 x 17.5 - and I know that will make a big difference. Just wish they didn't cost so much!

What prop are you running now? My MCX powered x-star now has the 14.75 X 15.5 which is an awesome prop for my needs. Great holeshot and still hits 41-42 mph on the top end. Might be too much prop for your L-18, but you could pull cyprus trees out of the ground with that one. :D

DooSPX
11-27-2009, 06:36 PM
I honestly can't argue too much with your points in case, because all of my experience with these engines have been in the automotive field (but that is plenty, I can assure you). I'm not a big fan of the LT1, I've had 2, thinking that my first was just a dog, the second never proved to be much of a front runner either. Just like the L98, the LT1 was nothing but a torque monster. Which is why you're case proves to be legit. However, while the LS1 (fbody) doesn't hit its peak torque of around 345 until well after 4k, it does flex a little more than 70% of it just over 1500RPMs. And as far as this whole "piston slap" deal goes... well, i'll keep my mouth shut on that one. We can go back and forth discussing the pros and cons of both, but MC and the others did what they did for a reason. I'm still stuck with the ole' 350 and it's not either the LT1 NOR the LS1:(

Im stuck with a 351W ford in my 91!
its a good motor though.
My LT1's have always ran good. my A4 96 WS6 T/A ran 13.3x with NT555Rs, Borla CB and a hyper crap 3. a 97 T/A M6 ran 12.5's with headers, cutout, NT555R's and a custom cam in the 21x/22x on a 111LSA. a 96 Z with LE heads, baby custom cam with MT DR's and a vig 3000 run 11's. You have to look at the limiting factors of the LT1. the heads are still cast from the Gen1 port and valve design just with reverse cooling to help aid in cooling because of high comp. and the computer is very very slow. Though on that note, the LT1/Vortec heads are the best of all factory 23* heads. The vortec head has the same ports as the LT1, they modeled that head off of the LT1 just with standard flow. Hell, I had a 92 L98 run 14.5x-14.6 stock. not shabby for that old motor that is crapped by 4K.Put a LS1 computer on the LT1 and its a whole new world for that motor. The LS1 makes most of its power from the new head design and the computer is very fast. 04's having the fastest of all GenIII computers. now, the efficiency of the LS1 is mostly due to a different firing order, PCM and the heads.
The Indmar LT1 has the northstar ignition for obvious reasons and is also rated for more than the Automotive LT1 ever was some even more than the LT4's 330. The Indmar LT1 is one of the most sought after Indmar in used MC's
I have had a few fast LS1's too. ;):cool: 02 SS M6 with a lid, and the factory CME on 555R's running 12.5-6's, 00 T/A run 12.0's with lid, LT's, CB, 4000 stall, MT DR's, and rear suspension. its all in the setup. I am a believer that setup beats big heads and big cam everytime. I have proved it with the cars I have done.
anyway, I would never want a LS1/6, LS2 or LS3 in a boat. it was not designed to handle the load of a boat. I would love to see the L92 6.2 in a MC :love:
to tell you the truth, all of the new fancy engines i have done, i still love the good ol' Gen1 SBCs. had a few favorite 350's and a 400.
man, I ditched my EGR and AIR in all the pre 01 LS1's about a month. LOL just messing with ya!

DooSPX
11-27-2009, 06:41 PM
ANYWAY back on topic, I think you need a new prop, you will think you have a new boat.

KHall
11-27-2009, 06:47 PM
My Predator TBI pulls up damn quick. Thats with 2,000lbs ballast and a 14.75 X 15.5 prop. Prop is probably a much better way to go then adding horsepower.

TallRedRider
11-27-2009, 07:52 PM
I think you have probably seen the threads about my experience with a new prop. The Prop OJ recommended for you really made my boat come alive. Even with about 2K ballast, my 45 really leaps out of the water.

I cannot understand the concept of having more horsepower with that engine. Ok, I barely understand. Er, uh, I mean it is plenty OK for our needs, and I am sure getting more out of it would be way expensive.

jdl xstar
11-27-2009, 10:29 PM
What prop are you running now? My MCX powered x-star now has the 14.75 X 15.5 which is an awesome prop for my needs. Great holeshot and still hits 41-42 mph on the top end. Might be too much prop for your L-18, but you could pull cyprus trees out of the ground with that one. :D

I'm running the 13.7 x 19.5. I'm not hitting the rpm's I should be at WOT. Not quite making 4900 rpm's. Manual says 5000 to 5400. The 14.75x 15.5 could work but I think an ideal comprimise for good hole shot/good top end would be the 17.5.

ANYWAY back on topic, I think you need a new prop, you will think you have a new boat.

True dat!

I think you have probably seen the threads about my experience with a new prop. The Prop OJ recommended for you really made my boat come alive. Even with about 2K ballast, my 45 really leaps out of the water.

I cannot understand the concept of having more horsepower with that engine. Ok, I barely understand. Er, uh, I mean it is plenty OK for our needs, and I am sure getting more out of it would be way expensive.

From my understanding, OJ Eric made the 14.75 x 17.5 for the L18.

You're right that it doesn't need more HP, but I was curious what it could do with a little aftermarket help!

1redTA
11-27-2009, 10:41 PM
If you really NEEDED more you could swap the cam and port the heads. If you think that won't be enough put a Maggie on it and put the meth to it

DooSPX
11-28-2009, 12:05 AM
If you really NEEDED more you could swap the cam and port the heads. If you think that won't be enough put a Maggie on it and put the meth to it

on the 8.1, I think the TVS 2300 is the best bet. an original maggie would choke, even a 122.

03 35th Anniversary
12-07-2009, 09:39 PM
Supercharger!!!!!

trickskier
12-07-2009, 09:58 PM
Supercharger!!!!!

Not everyone has deep pockets like yours.......................:D;)

trickskier
12-07-2009, 10:00 PM
JD..................Props is the answer for a lot less MONEY!!!:D

CottagerGreg
12-09-2009, 12:09 AM
Just spray er out of the hole! Instant 50,75,100,150 hp on a button!