gator's 99TA

iTrader: (2)

Ok PLEASE HELP ME HERE. in kansas city there is a site called www.mogmhp.com - a mainly f-body local internet board. many members here are on that local board and is very strong, BUT there are some there (the owner/admin) that believes to his grave that given teh same stalled, geared, etc ls1 with stock heads, a 216 duration low lift cam will be faster and more powerful than compared to over 230+ duration cams (like the big thunder racing 230, X1, Futral, comp xe-r, LGM G5x-2 or whatever cams). he also says that hardly ever will a properly setup ls1 car with a cam spend its time over 5500 rpms.

he says "Most cars spend the far majority of their time below 5500."

is this true? i dont see it at all. in fact either with a std yank/vig convertor, the shift extension, even with stock gearing, wont drop below 5500 or so anyways. also in 4.10 geared 6 speeds, i dont see you spending much time below 5500 rpms compared to over it (lets assume a good slick launch).

lastly, he posts Even with a 4000 stall, if you log it, you'll find out you spend more of your time at 5500 or below. Considering that at most you want to shift 200rpm past your peak and it takes 200-300rpm for an automatic to complete the shift the cam has to have peaked by 6100. At 6300 the shift starts and completes by 6500 and drops you back down to 4000-4500 after the shift. All of a sudden that 1000rpms has turned to 600rpms. You just don't spend any time there.

maybe i am wrong, maybe i need more info, but i HATE MISINFORMATION spreading so let me know if i need to learn more. we are not talking all out race cars, but true std dynos and street-strip cars. i hate to say it but the big cams SEEM to be making more power and tq than the small 216 duration type cams esp if matched with a proper convertor, gearing, etc setup.

TIA

by the way, i run a 230/230 comp grind on stock heads and have run a best of 116.8 mph in midwest crap spring air at over 3500 lbs.

gator's 99TA

iTrader: (2)

here is the post by the way. direct link.

http://www.mogmhp.com/forums/viewtopic.php?t=9258

soundengineer

iTrader: (16)

just read the part that 383ss said...his bigger cam made more power everywhere except below 3200 rpm...in a race setup...below 3200 rpm doesnt exist...and he even attributed it to bein a little leaner there....this was a tried and dyno'd setup...not some stupic computer generated program...that isnt accurate untill you put in a lot more data than he did(way more data)(you gotta be a designer to know that much data)

BTW....
Hello John...

Damian

iTrader: (89)

Well, considering that 5 yrs ago, when everyone was scared to run anything over a 221 duration cam, LS1's were barely getting into the low 12's with heads/cam. Now, LS1's are running 10's on stock bottoms, with these so-called "slower" big cams.

Some people just need to give up. This guy is definately one of them if he truely believes that.


Josh

gator's 99TA

iTrader: (2)

hello soundenginer.

ok here is my thought. when an mn6 car launches, he is launching at a high rpm and even thought tha first gear he might be below 5500 rpms for a bit of time (not if you launch off of et streets!) after you shift at 6500 rpms or where ever, you dont drop below 5500 rpms with a slight geared car(say 3.73 or 4.10s) at all so how could you possibly spend MORE time UNDER 5500 rpms? now, lets talk convertors - shift extention brings you over 5500 rpms in nearly all convertors.......

qqwqeqwrqwqtq

FWIW, a 6-speed car shifted at 6,500 will drop to approx 4,400 shifting into 2nd, 4,700 shifting into 3rd, and 5000 shifting into 4th.

Rearend gears have no effect on the RPM drop, it is determined by the trans gearing. (2.66,1.78,1.30,1.0)

gator's 99TA

iTrader: (2)

ok good info. so bigger rear gears still get you out of that lower rpm range still faster right? i am pretty sure of that. so still we are talking 4700 and 5000 rpms in 2-3 and 3-4 shift. i was close

also can we talk about power to the ground as well? is it even a discussion? i know small cams can make some nice power but we are talking comparing std setups. will the small cam make more average power than the bigger cams like i mentioned? the only thing i can use is a dynojet dyno to compare power. mph is more setup, air, weight, etc.

Cal

iTrader: (1)

Actually, rearend gearing does change how much RPM drop you have between each gear. This is because you are running through both the transmission ratios and the rear end ratio at the same time, so they do both have an influence on the final drive ratio. The final drive ratio is the product of the gear you are in and the rear end ratio. As rear end ratios get larger, the trans ratio becomes a smaller percentage of the overall gear reduction. If you swap out your stock 3.42 gears for 4.11's as I did, you will notice quite a difference; the gears will seem much closer than before. This actually helps out in a race situation, keeping the engine more in it's power band.

JF WS6

I don't know how someone can deny the higher HP and TQ outputs that some of these bigger cammed cars are getting not equaling better track times. Just look in the latest issue of GMHTP the 30th anniversary TA. Before: G5 cam (224/230) 409RWHP & low 11's. After: G5X2 (232/240) 435RWHP and 10.80's. There have been several examples such as this. This guy needs to have a look around at what's going on and what other people are doing, his argument just doesn't hold up at all.

gator's 99TA

iTrader: (2)

what is surprising is even if you wanted to talk tq, look at the big traditional split cams too like g5x2 cam. they make MORE tq all across the band including down low in the 3000 rpm range compared to the smaller cams! so there goes that arguement. only the big cams are making easily over 410 rwtq on 346" motors from what i have seen.

sbrown99TA

I agree. The smaller cams have now been proven to be insufficent for most aggressive setups. I'm looking to upgrade from my TR224 for that very reason.

JF WS6

Gator,

Yup you're exactly right. The point the guy is missing is that the bigger cams are making more HP and TQ through most of the range (maybe not all), not just from 5500 up.... some crappy simulated computer program is not accurate to what really happens in reality obviously.

In my own personal experience going from a 224ish cam to a 230+ duration cam, I did notice a SOTP drop in low RPM TQ going to the bigger cam, but 4000-redline the cam is noticeably stronger as well, so it's a tradeoff. Personally I don't mind the slight loss of low RPM grunt because before it was way too easy to blow the tires away, now it's easier to roll into the power on the street and I still have the upper RPM power to dump the clutch at high RPM's on slicks at the track.

qqwqeqwrqwqtq

If you shift at 6,500, 2nd will drop to 4,400, 3rd to 4,700, and 4th to 5,000.

This will happen whether you have 4.56's or 2.73's.

Shorter gears like 4.10's will have more torque multiplication in each gear, making the drop less noticeable, but nonetheless it is still the same.

Hitman#1

iTrader: (1)

The sensation of the gears seeming closer is just that, they SEEM closer, but they actually aren't. It's merely an illusion brought about by the quicker engine revs due to the higher (numerical) gear ratio. I ran it through a simulation program, and there is virtually no difference in RPM drop between a 3.42, 3.73, 4.10, and a 4.56. All together, there is maybe 50/60 RPM variance. Not enough to worry about.

Hitman#1

iTrader: (1)

LOL,INTMD8, you and I posted virtually the same answer at the same time. Great minds think alike, eh?

dug

iTrader: (10)

Youre right but youre forgetting about the energy from the flywheel. It accelerates the car a couple of mph between shifts. The flywheel contains more energy at 6500rpms than it does at 4500rpms. When you shift some of it turned into heat in the clutch and the rest accelerates the car.

When you run higher numerical gears the shifts occur at lower mph. KE = 1/2 mv^2. The faster you go the more energy it takes to go faster. The energy released from the flywheel during shift is relatively constant. So with the higher gears the car accelerates more mph from the flywheel energy between shifts. This is why rpms drop less between shifts with higher gears.

Larry

iTrader: (4)

He did not say what headers or exhaust the car had. Maybe I didn't read close enough but if he had stock headers, stock catback and a stock air filter housing, then that 216 cam just might make more hp/tq than the larger cam. You can certainly over cam a restrictive engine. Even though a cam would make more hp/tq on one engine does not mean it will on another.

I don't believe an LS1 engine spends more time blow 5500 rpm during a 1/4 pass. My engine does drops to about 5100 on the 1-2 shift with my PI 3600 converter. It quickly gets above 5500 however. When I had my stock converter it dropped to about 3700 rpm on that shift and just maybe it did spend more time below 5500 than above at the time.

Under his conditions the guy just might be right.

CHRISPY

With an A4 and 4000-4400stall shift extension is around 5400-5700rpm. When I had the 200R in my car I wouldnt drop below 5500rpm.

I think with the tuning advances from LS1edit and peoples experience with it bigger cams just dont seem that big anymore. My cam feels tame now (230/230 112LSA XE-R)

Cal

iTrader: (1)

Guys, big cams and deeper rear end gears go together. Sure, if you shift at the same rpm with the stock gears vs. 4.11s, the rpm drop is the same. But but normally you put in a bigger cam with the deeper gears so you are shifting at a higher rpm. For example, with the stock cam and stock gears (3.42) shifting from 1st to 2nd, you drop from 5500 rpm to 3656 rpm. But with my TR224 and 4.11 gears, I drop from 6500 rpm to 4346 rpm, keeping the engine much higher in the power band. The deeper gears make up for lost low rpm torque with the bigger cam, but you don't loose speed because the motor peaks at a higher rpm than it did with the stock cam.

soundengineer

iTrader: (16)

the question doesnt involve gears....
Its only asking about the cam....
I have an X1 from MTI (230/227 .591/.571 112lsa)
thats a pretty healthy cam...
and I have no plans on gears...ever....
maybe a 12bolt...but I'm gonna stay with the 3.42 for my daily driver...
gears dont make a difference in power...they make a different ratio....
at a 1:1 ratio you still make the same power and torque with any ratio combo....so leave the gears out of this one....

I belive the question applies to dyno with 1:1 gearing