philofab

So, I am building a LQ4 for my jet boat. Been reading searching all I can but I still have questions. Mainly cam and valve springs. Here is my plan so far:

99 LQ4 block and crank
Eagle H beam rods
Wiseco forged pistons
317 heads
LS7 valley pan with PCV
eBay stainless v-band turbo headers
eBay sheetmetal intake
eBay v-band to T4 elbows
eBay T4 "GT35" turbos
truck coils
Microsquirt 24x
Meth injection
91 octane
liquid to air intercooler with 50 degree river water
Home made oil / water heat exchanger
Good head bolts ARP?
102 mm TB (fits intake)

What valve springs should I run? GM? Pac Springs?

What cam should I go for? I have the stock LQ4 cam and a pile of LS3 cams already.

Goal is 700 hp which seems very doable. Any problems with my setup other than the chinese element? Most of the parts are intended to look nice in a open engine compartment.

JRENIGAR

iTrader: (37)

What is its intended use IE: racing, or just crusing the local party coves and sitting anchored out? If mostly racing, what RPM is it gonna be run at?

rkreigh

just like in a car, where you match the cam with the turbo and torq conv in a boat you want to consider the RPM range and prop characteristics.

I would say for the budget build the LS9 or LS3 cams would be a good choice.

especially if you have them already.

what are the specs on the LS3 cam?

you likely want good low end torq to get the boat on plane and a very "forgiving" cam and springs that is easy valve train for sustained 5k plus croozing

with only wanting 700 hp you can save money on the cam IMHO and use some stock stuff

philofab

It's a small 18' boat so 300 hp would get it on plane. I don't plan on racing it, it will just be for fun. 6500 max should put me at mid 90s mph, will probably only run at that speed for short busts ~1 minute.

The LS3 cam is a factory crate LS3 pullout. They come out of GMPP LS3 crate engines when they are brand new.

Like anyone, I wouldn't mind making more horsepower... lol.

mkvamso

iTrader: (2)

I'm using the same turbos on a 5.3 with an ls6 cam and they light off pretty quick
Theyre at full boost at less than 3k rpm

I think if you put too big of a cam in that 6.0 it'll start to choke those turbos up top
I'd use something pretty small in duration with a wide lsa to try and keep it pulling up top.

I'm using pac beehives with my little ls6 cam, more seat and open pressure than a factory spring but not nearly as much as a most dual springs

philofab

Wow, really? What heads and how much PSI are you running? I have not purchased heads yet so I could go to the GT45 but those things seemed huge! I'd was afraid the GT35s might be a little large.

I think I'll try the LS3 cam to start off with. They cams are so easy to change it won't be a big deal if I don't like it.

mkvamso

iTrader: (2)

I'm using 243s, wastegate pressure is 8psi
I've ran it up to 18-19 lbs so far, think they'll go a little farther before they run out of steam

Genuine garret gt35s seem to be a lot better breathing than the ebay replicas

Friend of mine has twin Garret's on an ls3 and it's making over 1100 wheel
I doubt mine will go passed 750 maxing these out

philofab

I agree that the real garrett stuff is wayyyy better. I just don't want to spend that much on this engine.

I have the choice on a few different turbos...

" GT35" Compressor .70 A/R, Turbine .68 A/R, compressor wheel size 61.3/82 mm turbine Wheel size 62/67.8 mm

"GT45" (same cold side?) Compressor .70 A/R, Turbine 1.00 A/R, compressor wheel size 61.4/81.2 mm turbine Wheel size 64.5/73.6 mm

Seems like the GT45s would be less likely to choke at 6500rpm? I think there is another turbo that is even larger... like 1.15 A/R on the turbine but I know that is too big. I'm not really worried about lag as it's boat, no shifting, and it will be under heavy load. I will be running external wastegates on the T4 adapter flange elbow. They should flow well there.

mkvamso

iTrader: (2)

I'm using these cx flange/elbows. They're 3 inch vband to a non divided t4 and a vband for the wastegate
Working well so far.

I think the bigger gt35s they sell would probably work, twin gt45s might be a bit big without a pretty good sized cam to help them.

It's kind of hard to judge what would work best in a boat
There's a lot of load from pushing it through the water and like you said, no gearing, just rpm dependant.

fastbarry

i think that a lot of people on here dont really understand the dynamics of a jet boat. you dont need low end response and torque to get moving. the jet pump is just like a VERY loose converter.

what pump and impeller are you using?

a cammed near stock lq4 should turn a berkeley A imp to 5000 rpm or so pretty easy. that means you can spool damn near anything and spooling before 4000 is unnecessary. a turbo that spools at 2500-3000 is completely wasted on a jet boat.

i wouldnt start with anything less than a pair of the 68mm ebay gt45's. they will still easily spool before you need them to.

same goes for the cam as the turbos, small high torque cams are not needed. you want that motor to really breathe above 4000.

Torqueshaft

Yep....

What he said.

You need to design your engine combo around the pump and impeller you plan on using.

Oh...And since I am around your neck of the woods I call "shotgun" for one of your banzai river runs....

Should be a fun ride...

philofab

Berkeley JE pump with a split bowl, loader, inducer, place diverter, and a AA impeller. Tune/optimize it once it's together.

I have a local turbo shop in Havasu, and they built a TD06-20G-14cm for me back in the day for my Syclone. Going to see what they can do before I pull the trigger on ebay turbos.

Jumping out of the hole is cool but most races and what not happen from a rolling start. IE 30 mph. Standard boat engines are all huge big block with tunnel rams and giant carbs. Think 750 and 850 holleys on the small engines.

lq4151

I am running a lq4 2500 series chev in Jetboat it is a 4.5 meter alloy hull built for river use the engine is stock it goes great pulling 5500rmp with a speed of 87 kms the jetunit it is a Hamilton jet 753. leave it stock as nothing worst than being up a river broken down miles from the ramp.

philofab

I'm looking for about twice that speed. I think a Hamilton is a mixed flow pump so it's a bit different than what I have.

In the mean time I had a piston melt in the 396 in my other jet boat so I am throwing a 5.3 in it real quick to get back out on the water and then I'll be back on this one.