PCM torque curves...

[tdc_worm]

...why do you think they dont post them? i would bet the torque curves of the 330 and the zr6 are pretty stinking close, with the zr6 just marginaly edging the 330 because of its $6k, .3L displacement advantage... it doesnt appear that Indmar or Mercruiser want to talk about their torque numbers, either...

[78LS2]

RE: PCM torque curves...

Just curious, why do you want to see the curves?


My guess is that they curves depend on fuel mapping, ECM settings etc, which are proprietary.

[tdc_worm]

RE: PCM torque curves...

why do i want to see the curves? it actually has to do with justification of upselling an engine. while the curves may depend on those variables, showing me a curve on a graph reveals nothing about where those variables actually lie, thus revealing nothing proprietary.

it was more of a rhetorical question. my gut feeling is that they dont show you those curves because (or even a max torque spec like they do in the auto industry) they would lose every upsell to a bigger engine. the HP number is all smoke and mirrors. in the case of PCM, the next step up from the 330 Excalibur is a $6k jump to the ZR6.

the horsepower number they show is garbage...when it comes to towing. even a 3.5L nissan Z makes 306hp, but only makes a paltry 268lb ft of tq. there is no replacement for displacement, so i cannot imagine that the 6.0L ZR6 makes a significant amount more tq than the 330 with just a .3L advantage...

the other reason is that if the arrive at an ungodly number for the torque in one short spike at 6000 rpms, then that number is useless, also...

[78LS2]

RE: PCM torque curves...

I wasn't asking you to be a dick. I used to do business with Indmar and PCM, and finding a published torque curve was impossible.

The ls1 (5.7) put out 365 ft pounds and the ls2 (6.0) puts out 400. I don't know what is "significant" but 35 ft lbs is decent. Assuming the Zr6 offers a similiar advantage over the Exaclibur, the question becomes is it worth 6k... not to me.

The best way to tell when one engine makes way more torque than another is the transmission. When one gets a bigger transmission, and/or a larger cooler, it is processing more torque.

[tdc_worm]

Re: RE: PCM torque curves...

I wasn't asking you to be a dick.

the one thing i love about message boards and texting on phones, is no matter how much try to come across one way, the reader always takes it another way, hahaha. i was trying to be articulate, not an ace. everyone (including myself) always takes message boards and texts too seriously or as a personal assault... i often find myself apologizing for a perception that was not intended...so here goes again: i am sorry for coming across as an ace with my inablity to express myself in a civilized manner online! probably offended somebody else now, hahaha!

anywho, 35 ft-lbs of torque difference may seem like a lot on the surface, it is nearly 10%. it may be a lot, but depending on the curve, that peak difference may happen 1k rpms higher in the zr6 than the 330, which may render it useless for the non-barefooter...

i did notice that they post a torque number at the prop (whatever in the heck that is supposed to mean) on their website. for the 5.7L it is 430, and for the zr6 it is 492. these numbers are contingent upon being equipped with the power plus tranny...

[78LS2]

RE: Re: RE: PCM torque curves...

you took that the wrong way! I meant it as I was not asking you just to give you a hard time, aka me just being a dick. LOL way to read it and take it another way bonehead. hahaha

the torque at the prop is equal to the engine torque multiplied by the reduction gear ratio. So to get engine torque, divide 492 and 430 by 1.23. That comes out to 400 and 350.

[tdc_worm]

RE: Re: RE: PCM torque curves...

hahaha. yup, i suck. i figured that is how they arrived at those numbers. that 350 number for the 5.7L is interesting in that you said the ls1 is supposed to make 365 lb ft or torque... something screwy is going on here...

[78LS2]

RE: Re: RE: PCM torque curves...

Well, the excal might not be the ls1. it could be an LT1, or another setup.

I am pretty sure that the ZR6 is based on the LS2 though, as it weighs less than the Excal, and the LS2 is all Al. block is probably not AL though.

[78LS2]

RE: Re: RE: PCM torque curves...

ZR6 torque curves here:
http://www.gm.com/explore/technology...LY6_Marine.pdf

Excal torque curves here:
http://www.gm.com/explore/technology...700_Marine.pdf

Notice those sheets state that actual numbers vary due to calibration and application

[tdc_worm]

RE: Re: RE: PCM torque curves...

good find. i am gonna do a little interpolation here from those links you posted.

where the ZR6 makes its money as far as numbers go, is at least 1000 RPMs higher than the Excal for both HP an TQ. i never run WOT, and i rarely go above 3500 to get out of the hole (06 220, loaded w/ @ 2k lbs above stock, 1234 prop). boarding speed is around 3200 RPMs, give or take. by looking at those curves and rated numbers, it seems that the benefits of the ZR6 happen in a range that i do not run my boat. 2nd point of interest is that at 3200 RPMs the ZR6 is making about the same torque as the Excal (according to their unreliable graphs). I picked 3200 because that is where the Excal hits its max TQ and it is around where my typical boarding speed registers.

so what's my point? nothing really, other than you dont see the benefits of the ZR6 unless you are barefooter or just really enjoy rapping the heck out of your boat...

[NCH2oSki]

RE: Re: RE: PCM torque curves...

I never realized boarding rpm is 3200 RPM. With my old 99' ski (gt-40) and an acme 422 at 3200 your running around 31 mph, if I remember correctly. I cant imagine the excaliber is much different.

[DanielC]

It's just numbers, folks. Does anybody remember the late 1990's hp wars, when engine and boat manufactures were claiming that thier engine made a few hp more than the other guy's engine? 285,290, 300, 310, 315, and so on? Then PCM brought out the 502 Python, and ended it all, with 430 HP.
If you buy a boat with a "Corvette" engine in it, rest assured it does not have the same hp, or torque curve as Corvette. The requirements for a boat engine are vastly different than for a car.
If you do not know what engine you want, test drive boats with the same equipment, weight, and see what you need. Speed costs money. How fast do you want to go?
The big advantage I see in the 6 liter engine is variable valve timing, and a longer stroke. The stroke has an influence on the torque curve, the variable valve timing makes the torque curve broader. The 6 liter engine is assembled in USA, the 5.7 was assembled in Mexico. Maybe that is important to you, maybe it is not.
It is your money, and your boat. Educate yourself, and make a wise choice.

[tdc_worm]

Re: RE: Re: RE: PCM torque curves...

I never realized boarding rpm is 3200 RPM. With my old 99' ski (gt-40) and an acme 422 at 3200 your running around 31 mph, if I remember correctly. I cant imagine the excaliber is much different.

there are a lot of relative variables: gear reduction, boat weight, speed, prop, etc. i am running a 14.25 pitch prop.

[tdc_worm]

It's just numbers, folks. Does anybody remember the late 1990's hp wars, when engine and boat manufactures were claiming that thier engine made a few hp more than the other guy's engine? 285,290, 300, 310, 315, and so on? Then PCM brought out the 502 Python, and ended it all, with 430 HP.
If you buy a boat with a "Corvette" engine in it, rest assured it does not have the same hp, or torque curve as Corvette. The requirements for a boat engine are vastly different than for a car.
If you do not know what engine you want, test drive boats with the same equipment, weight, and see what you need. Speed costs money. How fast do you want to go?
The big advantage I see in the 6 liter engine is variable valve timing, and a longer stroke. The stroke has an influence on the torque curve, the variable valve timing makes the torque curve broader. The 6 liter engine is assembled in USA, the 5.7 was assembled in Mexico. Maybe that is important to you, maybe it is not.
It is your money, and your boat. Educate yourself, and make a wise choice.

i am just having fun with numbers. right now, i have the zr6...my next boat will not. the tq curve on the excal from GMs website looks pretty good to me, and the tq (where i use it) appears to be nearly the same as the zr6...and all i want to do is get 6000+ lbs on plane and run 24.5 mph...

[AirTool]

Not to stir the pot....but one word of caution with respect to hp and torque curves....These curves are usually determined at wide open throttle and STEADY STATE CONDITIONS. That means that the torque value at the low speeds like 2k rpm were measured at wide open throttle and the engine NOT ACCELERATING. In other words, the engine was connected to an electric generator or water pump or something and was allowed to reach redline...then the load was increased as the throttle positioned to wide open...then again the load increased incrementally until the engine stalled or reached the low speed limit. The data values obtained were then plotted to form the curve.

So my point is, how often in a ski boat or any vehicle for that matter does a person hold the engine at WOT and a heavy load is applied to keep the engine bogged down to 2k rpm? Never...The curves as presented really do not have much value.

There is a lot of analysis that could be done to try to calculate which engine "better". But it is not worth. Someone else suggest match up two boats and test them. I agree. Then each person can make the personal decision as to the economics.