Camin00

My buddy has a ski boat with an old school 350 carb motor. We need more tq for barefoot skiing.

He has an Lq4 and we were thinking about putting the 5.3L truck heads on it to bump compression and trade top end hp for bottom end tq with the smaller runners. What do yall think?

Since the boat has one gear, what rpms would yall have the lq4 run to wide open. I think 6000 is way to much haha was thinking around 4500ish

I have the tool kit to align the motor correctly so no issues there, but I dont know whether we can run the truck ecu some how or if we need to look into some type of msd system.

BLKSSLTT

iTrader: (12)

which cooling system are you gonna be using? Im not familiar with the ls series into a boat but I have seen the crate motors being sold. I would contact mercruiser and see what they use for their ls swaps.

726.0chevelle

iTrader: (17)

I don't see why you couldn't use the truck computer with a motor only harness but I think you should a get custom specd cam that will peak early

Vortec350ss

iTrader: (20)

I don't know that I would swap to untouched 5.3 heads. They will help off idle, but that power gap would soon dissappear.

As far as a WOT RPM max I would think that 5500 or so on a stock LQ4 would be totally fine. How often do you cruise with it pegged?? And if you do why? If you want to cruise at 4500 RPM then back the throttle off.

If youre looking to bump compression then get the 243 heads and maintain the flow characteristics of the heads that are on there. As stated before you should also look into a mild custom cam. Something that will make great power right off idle.

I'm curious how high the RPM's would flash from a stand still in the water like that.

Camin00

You think the 5.3L heads would choke the 6.0 that much? Is it due to the smaller valve or runners, or both? Definitely keeping the truck intake and a diy port job on the tb cable driven. He is trying to do this on a budget. And the new Mercrusier motors cost 8K+ which is worth more than the boat.

The 6.2L MerCruser cam specs are 214/220 .481/.496 112Lsa 107ICL the lift numbers are with 1.6 ratio rockers

.452/.465 is the lift with 1.5 ratio rockers

I was surprised when I found the cam specs. Didn't think the cam would be so similar to our truck cams minus.

What is a general rule of thumb for lift? more lift means more top end hp?

I found the run the old school raw water cooling system or a brass sea pump with some type of radiator with antifreeze. Would like to go the radiator route to not have to buy expensive water flowing manifolds. Would like to create a lontube system that doesn't allow water to flow up the exhaust and flood the motor. haha

Camin00

I totally agree with you on not running it at 5500 lol usually we crusie to ski spots at 25-30mph which is roughly 2500-3000rpms ski about 40-45mph which is 4500 rpms again the biggest factor to this is the prop.

My dad and I have a barefoot natique that has a new prop. Increase our top end speed to 50mph from 43pmh and takes off to 50 almost a whole second faster than the stock prop