Alright guys here's the question. When you talk about your car and someone asks how much horsepower the GXP has what do you say, 275 or 300. I know we have the VIN Y motor that GM rates at 275 but with our factory tuned exhaust system I'm thinking in reality we're somewhere in the middle. People like a round number and even though 300 HP isn't quite what it used to be it still gets respect. So what do you say about your horsepower level to a layman and how do you feel about our cars possibly being under rated just a bit?

my answer always been 300 lol

i think John will be the only one with 400 :P

depends on if you want to run em, then you probably say its a stock six like i do

i assume the HP rating is SAE verified, in which gase GM would have had to print/state an accurate number

The HP~Ft/Lbs was certified http://archives.media.gm.com/us/powe...0LD8%20DTS.pdf 275HP@295 Ft/Lbs.

And people often misquote the certified specs for the L37, it was not the rounded 300. http://archives.media.gm.com/us/powe...0L37%20DTS.pdf It was 292HP@288Ft/Lbs

The LD8 motor's tuning profile wasn't actually "de-tuned" It was altered to provide slightly more torque then the L37. One of many cases of "it isn't the HP.... but what is done to deliver the most torque out of HP. A physics item hard to explain or rationalize to numbers oriented people. But the simple fact is more torque, faster car. A LD8 has an advantage over the L37 torque-wise and I've read that was the reason Pontiac's concept team went with it. Same price point really to them.

To bad they couldn't have swallowed some warranty worry and used the LD8's brother the LH2. Same engine with 10.5 to 1 compression (LD8 10 to 1) That half point takes the 4.6L to 320 hp @ 315 Ft/Lbs. A bit more than the GM Engineering's 305 max for the pricey (in Pontiac terms) 4T80e tranny.

I just state both numbers when people ask and sometimes add "up to 350ish HP" with spraying. I really don't use the nitrous much anymore and even though my kit has 75-100-150 HP add nozzles; the engine has stumbled on the 100 HP nozzles and caused me to back down.

The whole thing really doesn't bother me. I bought the car new and if I wanted sheer numbers/performance there was a nice black on black GTO sitting next to it with solid numbers. For less money. I bought the car because of it's room, style, and comfort along with a nice smooth Northstar. Unique to Pontiac as well as the GXP badging. Coming into this forum 5+ years ago gave me a Mod bite but it has faded. Still happy with my purchase and never looked back at the GTO. If I wanted a nice looking track car, it can be found for half the tradein value of what I now own. But it would not have the things that attracted me to the GXP in the first place. If I wanted raw muscle, with 30k cash in my hand, I wouldn't have been shopping at Pontiac in the 2000's. ;)

so the LD8 is rated at 295 torque? i always thought it was 300

There's a catch to auto figures like most things. It is rated and advertised @ 275HP/300FtLbs but they only pushed it to 292 for that cetification. And it was in a DTS. I find it interesting the torque fell off so quickly. If we had gotten the LH2 tune profile the car would be a different animal and most likely put the fat girl into the 13's stock.

the only difference between the LD8 and LH2 is the compression ratio?
so i guess even if they hack into the GXP's PCM it wouldnt change much tune wise, would it?

the LH2 has VVT.

And that compression increase had to come from stroke change. So it's got a few things going on different. I saw some items somewhere in the past about the valves and/or cams different on the L37 but no source to qualify either.

piston, combustion chamber or even head gasket thickness could have contributed to the compression ratio difference...

i may be able to pull cam specs for different years/motors. what do you want compared?

Just recent LD8/L37. If there was difference then a swap could change things. The LH2 was never made for tranverse mount. Don't see that swap happening.

i'm not very familiar with the N* generation, but IIRC, it's 93-99, 00-04 and 05-present?

i'm guessing you'll want the 05-up stuff?

04-05 is really all we have to deal with in this Section. I believe the changes were minor for 04 to 05. GM never changed the advertised power between the years and I don't know of any changes.

2004 Cadillac Seville with L37:

exhaust duration at .006: 246*
intake duration at .006: 251*
exhaust lobe lift: .2339"
intake lobe lift: .2421"
overlap at .006: 2.04*

cam event timing:

intake open: .3* ATDC
intake centerline: 122* ATDC
intake close: 246* ATDC
exhaust open: 229.3* BTDC
exhaust centerline: 110* BTDC
exhaust close: 11.2* ATDC

rocker ratio of 1.68:1

want spring rates and valve diameters as well? :lol:

2004 Seville with LD8:

exhaust duration at .006: 236*
intake duration at .006: 242*
exhaust lobe lift: .2339"
intake lobe lift: .2421"
overlap at .006: 1.98*

cam event timing:

intake open: 1.3* ATDC
intake centerline: 117* ATDC
intake close: 237.9* ATDC
exhaust open: 226.1* BTDC
exhaust centerline: 111* BTDC
exhaust close: 5.1* ATDC

rocker ratio of 1.68:1

Why Not ROFL! Obviously the cams are altered a bit. Wonder if they played with valve diameters.

04 Seville L37:

exhaust valve head diameter: 1.142"
intake valve head diameter: 1.426"

valve spring free length: 1.663"
valve spring thickness: .1618 X .1291"
valve spring ID: .7087"
valve spring OD: 1.0327"
spring height, valve closed: 1.378"
spring height, valve opened: .9646"
spring load, valve closed: 50lb
spring load, valve opened: 136lb
approx number of coils: 7



04 Seville LD8:

exhaust valve head diameter: 1.142"
intake valve head diameter: 1.426"

valve spring free length: 1.663"
valve spring thickness: .1618 X .1291"
valve spring ID: .7087"
valve spring OD: 1.0327"
spring height, valve closed: 1.378"
spring height, valve opened: .9646"
spring load, valve closed: 50lb
spring load, valve opened: 136lb
approx number of coils: 7

Well now we know. :thumbup2
Same valve setup and different cams.

Sorry about the hijack Matt, :D
Seems this thread took a hard left turn.

you forgot to add sucks theres nothin you can do about it cause "I'm the BOSS!"

thanks for the info Rob!

Hey I wasn't the only hand on the wheel.........hehehe

I guess I'll forgive you.....this time. ;-)

But I would agree with some of the posts, after almost a year of owing my GXP I've started divorcing in mind the concept of these cars as all out performance machines. It seems more and more cars can put up the same performance figures and in some cases surpass our big Pontiac by a mile. The looks, comfort, and performance of the GXP's make them an attractive package. I do think the next auto purchase for me will be a CTS-V, looks. comfort, and OBSCENE performance.

By the way, as the mileage has been added on our cars, has the mid 14 second quarter mile become more accepted figure? I know the flame wars of 2004-2006 were pegging the GXP's at low to mid 15's. (and now I've hijacked my own thread)

FWIW:

http://www.mpt.org/motorweek/reviews/rt2351a.shtml

Thats one "version" Robert. There are alot of them 14's to 16. I believe Intense Racing owners stock best was 15.1

Motor Trends 1/4 mile testing when the car was new was 14.6. The old staff here said "they couldn't be trusted" and "they cater to Manufacturers". Maybe. This was nearly replicated by a forum member who submitted a valid track receipt (and posted here) So for me mid 14's is the benchmark. Being an engine that's lean on delivering low end torque and a FWD config, I'm sure technique and experience with FWD has alot to do with it. The member who ran the time had gutted the airbox out and had alot of "performance drive time" with his car. So I say, the GXP is capable of doing upper 14's, not does.

It's been decided here long ago that rather than continue the argument, either go out and prove it right or wrong. I haven't any further patience redigging past flames on the matter.

and 14.6 is completely believable. back in 1993, motorweek tested a 93 eldorado ETC and pulled a 14.8@98 weighing a bit over 3700 lbs...

some cars ARE factory freaks and break the general trends by up to a whole second, all other factors reamining the same.

Sorry, didn't mean to open old wounds. I was suggesting most of the benchmarks were from when the motors of the cars were still tight. I just wondered if a more accurate figure was derived. Mid 15s always seemed a bit slow with all things considered.

you can always just check, i have one of the gtech accelerometers and you can go out on a back road and check what you got. it says my monte is still at 7.9s 0-60 which is right on most of the listings. i weighed my car and with accurate weight it gives hp and all that pretty accurately.

i have two scanners at home i might go out tonight and see what it would run in a 1/4 mile

ops, nevermind

i just remembered i wont have my car for couple of weeks
it just went into the bodyshop to have the front bumper skin replaced and repainted

The only thing I have as far as a GTech goes is an iPhone app that uses the phones accelerometer. Probably not the most accurate. Maybe this spring I'll go to the drag strip and see what she'll do. The only problem is the local track is 1/8 mile.

As far as "tight", one of the Northstar'ss attributes is it's taking forever to get tight, worn in. And the reason some many resort to the "Italian tuneup" LOL. Ya an 1/8 mile I imagine is going to show somewhat slow to it's 1/4 time. The engine would just start breathing. As the GXP gets a little older I am sure we will see more times posted. It's easy for someone with a say 90's Bonneville to quip in the forum, "well why haven't you taken the car to the track" back in the flame war days....."Maybe because I just paid pennies under $40,000 for it???" I think was on most owners mind.

i doubt i'll ever track mine, its not even worth the embarrassment.
6:15:00 PM Track update:
"Oh look at that V8 on the 1/4 mile! it just took off like a bat!!!"
9:16:15 PM Track update:
"WOW! that was a new 1/4 mile world record!!!! gp1"


but you guys had it lucky back in 04 & 05 for the GXP being high 30s
here in Canada they were going for high high 40s if not few pennies over 50k

its fine, theres lots of slow cars at the track. i took my 88 olds cutlass coupe with a 2.8 down one night cause there was something wrong with my bird and there was actually a woman with a 4dr early 90's cs and we ended up racing a few times. at the places ive gone theres usually trucks and ricers, the gxp would be faster than all those normal cars.

whats an Italian tuneup?

i'd take the MC...

with all 160HP/180TQ and 3300 lbs of heft plus me, it should pull a high 16 assuming i don't kill the tires.

it's about fun, not ETs.

essentially, beating on the car just a little bit...

generally, WOT throughout all of second gear should do it, preferably where it is legal and somewhat acceptable to do so(freeway on-ramp is a good one, especially if it's uphill).

depending on your shift points, that should net you somewhere between 70-90MPH at the end of second.

thats actually kind of funny because there is a guy who drives like that at work takes on ramps at speeds where the 4 tires are howlin, and hes very Italian. its funny to me cause he thinks hes a displaced racecar driver and hes had a intrepid and now hes got a vibe.

"The Italian Tuneup"
When it was first mentioned years ago (after it became apparent it worked) was to take the car our on the highway and drop it back into second, put the throttle to the floor until nearing the rev limiter (or recommended RPM max) NorthStars have a reputation (more so in older days) of the rings having taking an extended time of seating, and the combustion chamber carbon fouling when driven around like a granny. To me that's a bit hard on a car/transmission. The alternative (my choice) is just find places to start from a standstill and WOT through the gears a couple times. And feel it "breath" a little better afterwards.

ive only owned my 05' gxp for about a month and a half, but i have to tell you i think its a sexy, sleek, fast full-sized car. and after putting on a pair of flow masters the BEST sounding car ive heard in awhile.