Cam choice for LS3 - being used in a jet boat
 

Hi there,

After some advice on a couple of points with regards to swapping up the cam on an LS3, and what other supporting modifications are required (springs / rockers etc) given that the RPM usage in a jet boat application will be much lower (but arguably higher load - being that it will be held at load for longer) than an automotive application.

Context: (Feel free to skip over) Boat is a 5m alloy hull. Boat best described as a sports boat, almost entirely for lake use; though it could do river work. Jet unit is a HJ212. I want to run with the 3.4kw impeller for hole shot; which in turn governs power input levels at given RPMS - as the given power to spin the impeller at certain speeds to achieve certain thrust (without cavitation risk) and certain elevation losses are all known parameters. Over laying engine power delivery over these parameters helps to calculate the best combination - with regards to efficiency. Efficiency unfortunately in this application has some irregularities, due to the fixed nature of the impeller pitch - for example, too much power does not increase speed (impeller and/or jet choke) which would lead to higher fuel burn for the same speed, despite having (say an LSA) working easier than an LS3 would be. For what I'm wanting to achieve, an LS7 is the ideal choice, followed by an LS3. Given the price difference between the two engines, the fuel burn efficiency difference is not enough to justify the difference in the motors. However, after some investigation on this forum and others, it's entirely feasible to increase an LS3's torque by ~10% where I need to - that being 2400 - 4400rpm. The cost of doing this is far less than the LS7 premium, and is worth doing.

TL;DR - I want to cam an LS3, focusing purely on 2400 - 4400rpm. And also, know what supporting modifications I should be doing to maintain OEM levels of reliability.

I had decided on a cam with the following specs:
222/226 0.575,0.575 LSA 114

However, when talking to the camshaft manufacturer, they pointed out that they have already designed a cam for previous customers in this situation, who had essentially the same goals. They've suggested the following specs:
226/232 0.600,0.600 LSA 110

My concern with their suggestion is how rowdy it's going to be. They've assured me it will only be rough at idle, and will be smooth well before 2000rpm. Given that its a jet boat, spending almost no time at idle.I shouldn't really care. But, I do - as I want the whole thing to be buttery smooth.

They've suggested making the cam with their specs, but with a LSA of 114, to give the smoother idle. I realise that doing so will reduce some of the performance gained from having the LSA at 110.

Apparently, I'm in the 1% of customers where they are talking me into a more aggressive cam; instead of talking me out of an aggressive cam.

I'm still undecided on the cam selection. On the one hand, I know what I want out of the setup; on the other I know to listen to those "in the know". Given the relatively low cost of the cam I'll likely not further think the selection to death and buy both - and see first hand which I prefer.

One question I do have - which is difficult to answer via previous posts, is whether I'll need to upgrade any of the valvetrain in support of swapping the cam. Typically, the answer is yes. However, given the motor would never see 6500 or even 6000rpm (and would only ever see 5200rpm if I swapped out the impeller - which I'm unlikely to do) then is it necessary do change / upgrade anything? Preempting that it's likely a case of just doing springs anyway - for the peace of mind. What about rockers? (This whole pushrod thing is new to me, I'm more experienced with OHC)

Appreciate any thoughts or comments on suggested other mods, and / or the cam selection. Thanks.

You definitely want the higher lift smooth lobes for this. I have zero jet boat experience but that second cam looks decent. I wouldnt recommend the 7.0L for any boat application, ever so your making a wise choice sticking with the LS3 head imo. Be sure to get some good quality valve springs and run stock rockers too would be my suggestion.

Jet Boat Pump RPM
 

Hi Diss7, I worked with John Drake, the Drake Pumps.
The 4400 RPM I understand, with exception of the Grate Design ? (not provided?)

I would ASK FIRST, you have the HendricK head ?

I would specify the LS-1/2 "CATH" head with the truck "TBSS" intake manifold.
I would fit the L-92 VVT assembly.

USE the Yellow or Blue Valve Spring. (OEM)

My method is to fit a LS-2 with a 4.1 Crankshaft LS-416.
This is a common practice by my customer Riddle Marine on the Snake River.

You may not be happy with your stated camshaft choice.

Lance

Neat strategy to pump cubes and run cathedrals. Would be sweet in that 4500 range for sure. This thread makes me think of FormulaZR ( havent heard from that dude in eosn, wow ) anyways hes a member here who LS swapped his Liberator jet with a forged 383 LS1 based build using cathedral heads. Cam was 230/232 iirc on XE lobes or something like that. Totally different boat than yours here, but its a jet and it sure goes good, check it out

The cams that have been suggested to you have too much duration for 2400-
4400 RPM.

For that RPM range, what you need is a 216/224 on 111+4 with about .595" lift. I work for Cam Motion Camshafts. If you would like me to make this camshaft for you, just give us a call and ask for Steven.

Jet Boat Pump RPM
 

Hi All, I too followed the given advice here by using Performance Trends EAP. (Engine Analyzer Professional)

The LS-3 OEM Spec with users camshaft specification was the base.

The Torque request at 2500 = 378 ft.lb with MAX HP at 5500 = 519 is the report
The change of heads (C's) and intake (TBSS/Truck) is next.
The Torque at 2500 = 390 with MAX HP now at 5000 = 593 is the report.
The crankshaft change with the C heads/TBSS to a 4.1 stroke, the last.
The Torque at 2500 = 466 with MAX HP at 5000 = 608 with torque of 640 ft.lb.

This finding is mostly related to the LONGER RUNNERS and HIGHER PORT AIR SPEED.

At the very least, I would fit the L-92 Truck intake as on my 2007 Escalade.

Lance

I do this for fun. I use my memory mostly and compare experiences both personal and builds I've supported. Only two elements we found with the square port heads; low lift cams suck, and cams up to 220/230 improve torque in all areas under the curve over stock. While what Lance is offering is a FAR more concise approach targeting a specific RPM range swapping to cathedral heads and adding cubes pumping up huge torque gains over the initial cam, square port head and 6.2L displacement use in the first post. That said I am not sure the cam you picked would be a bad choice for stock cubes with square heads, but I like that spec Tigger posted, it would probably work great but I wonder how much torque differeence there would be between that and the second cam you posted about OP at 4500 RPM? My guess is not a lot

Its all about dough vs testing. How far you want to take the process, totally up to you OP.

Fun thread, informative, thanks for the input fellas I learn every day

Cam / Head / Intake
 

Hi Cam, I did YOUR EAP model request (same time) and found the report was your guess = No Change.

That report has little merit, thus not a reason to post results.

I did find the OP's first cam choice was best for the Head/Intake changed to "Cs + Truck Intake".

Lance

Thanks for sharing that Lance, very helpful. I have pondered a little on this jet application since this thread and I wonder what the peak impeller efficiency range is vs intake cavitation? 4500 RPM is sort of standard boat RPM logic but with LS engines higher, smooth, consistent RPM and flat torque curves if there isnt a better way to skin the cat here?

Target 5500RPM impeller range and utilize the torque gains? Or am I off base? Just a thought

How much does the boat weigh ?

Pump Impeller RPM
 

Hi Cam, this problem is NOT related to engine, it is PUMP RPM related.

Sure, the Pump RPM can be raised by a "cut back" impeller with MAJOR low RPM output loss in thrust.
Most will spend time on grate modifications to increase inlet water flow.

Lance

I see. I dont have any jet experience, only prop. Was flying blind on that last guess

If it was me doing this I'll have a cam spec to my boat weight speed prop and purpose is only 40. and you can have the best cam for the purpose on your first try.

https://www.guerragroup.com/camshaft-help

If you want to get the right camshaft for your boat, it is wise to do business with people who have experience succeeding with boats. We have extensive experience making all types of boat cams from air boats, to jet boats to off shore boats. We have won countless championships with our boat cams.

This was a post I made from my personal account. This is the camshaft that I would recommend.