|10-18-2012 03:05 PM|
Yeah final drive has nothing to do with the cam. Its ratio in first gear for racing will have a large impact on 60 foot times.
If you want to bumble down the road 1500 rpm at 70 mph then you will need the right gear for that goal. Then if you have giant cam and cant get off the line hard enough at the strip you change your trans gear ratios to match up with the cam. Final dirve is much easier. But really not needed in most cases. If final is two low it will be annoying all the time. Not just the first part of the 1/4 mile.
4:56 gear in a street car sucks arse!
My poncho had a big *** cam .700+ lift 330 adv. it required 3000 stall. I put in a 1200 rpm stall. Its what i had on the shelf. It was fine. everyone asked if the low end torque went down. The only answer i could give them was. "When the tires stop spinning I will let you know." 71 gp 4000+ lbs It was a big engine but I know 350 guys with similar results.
No it was not dead in the power band at all times but it still had mad power. I put lower gears in it and went to the strip. ran 11:50 with 3:55 and felt twice as fast as the 3:08. only problem the 3:08 went 11:20's all day long. and felt smooth and gentle. Two weekends covered in smelly rear end oil only to finish with the same thing I started with. Well sep for money.
Hope this helps.
|10-18-2012 02:47 PM|
Basically you gain nothing and lose a lot by running a cam that is too big.
|10-18-2012 02:37 PM|
Howards Cams CL112591-08 - Howards Cams Hydraulic Flat Tappet Camshaft and Lifter Kits - Overview - SummitRacing.com How about that cam compared to xe274? who will be the best perfromer?
|10-18-2012 11:47 AM|
For the drag strip Fbird is right, for the street you're right. There's a huge difference between the two and gear selections are usually a compromise of something in the middle.
|10-18-2012 10:00 AM|
fbird,you are missing the point.The gears in the diff really have nothing to do with the engine.You cannot just say this cam needs this gear.What you can say is this cam works best at this RPM or RPM range.The rear gear ratio is tuned for application.If someone drives a lot at highway speeds,that application needs to incorporate a final drive ratio that is efficient,and that can vary alot.If someone wants to use a long duration cam(for w/e reason)then point out that the final drive and tire size will put the engine at a disadvantage because,,,then talk about cams and engine rpms and all the variables that contribute to w/e adverse effects that may be present.
NOTE:If I make peak torque at 3500 rpm,it doesnt mean I have to drive at peak anything,,,,lots of math rather than random numbers that have to match.
If I had a 283 in my corvette,I would still use 3.5 gears.Its the gearing I want/need for what it does.It just wouldnt do it as quickly. The car came with 2.73 gears and a whopping 160 horses.
A 195 horse 283 with 3.50 gears would match the 350 and 2.73 gears
|10-18-2012 09:30 AM|
Vinny yours works because you have a high CID to weight ratio. raw engine torque and a lot of gears to choose from (5 speed with steep 1st ratio)
if yours was a 350 not a 434CID you'd really want the gears.
Most street cars are heavier than yours too.
Ifr you had a 350 with that cam you'd want 4.10's (4.30-4.56 for drag racing)
especially with the .82 cruise ratio in 5th.
If your 350 had a auto trans and that cam you'd want a 3500 stall.
Crane used to have a chart based on cruisng rpm @60mph that matched up cam duration @.050" and gearing/tire diameter based on the average street car/engine. It worked pretty good for getting the basic gearing right for the cam/car/engine.
of course you can adjust that for a car with a high CID/weight ratio and or to optimize for your racing purpose.
And adjust for the 5 speed transmissions multiple gears range. 2.78 to .82.
If you look at your 3rd gear 1.28x 3.55 you get the same ratio I recomended for a 3 speed ( EG th350) car 4.56:1
A 350 with that 256° cam and a th-350 auto and say with a 10" 3500 stall would not be that happy with a 3.55 gear.
A 4.30 4.56 would run well.
I agree with you on the street tires. Most are pretty lame for straight line acceleration traction.
I like to run a high traction tire. Like the M/T Sportsman Pro. They work pretty good on the street.
You get to actually use the engine power. My torquey 406 vortec SB w 4.10's is all over the road with a normal street radial
but the M/T Sportsman pro's hook real good. Tires make a BIG difference. Reguardless, I do my racing at the track.
|10-17-2012 09:51 PM|
forgot to mention 5th gear is .82,,,
also on street tires I can break the tires loose at almost any rpm in first gear,if I hammer it in 2nd at 35 mph,the tires break loose.road racers dont usually power shift.
|10-17-2012 09:46 PM|
addressed directly to f bird,Ill help you out here.using my car as an example,engine peak power on dyno was 6470 rpm,so call it 6500,,,3.50 gears,2.78 1st gear= 55mph,2nd gear 1.89 = 81 mph,3rd gear 1.28= 120 mph,4th gear 1= 153 mph. I used 27.7 for tire height.
This would make my car shift into 4th at the end of a 1/4 mile drag strip,if I raced 1/4 miles.
NOTE: not everyone races 1/4 mile,Im more interested in road racing. A straight offers more than a 1/4 mile and you enter off a corner,plus you need to slow down for the next corner.If I had 4.56 gears the 1st gear would be useless even coming out of a hair pin.
I guarantee my car accelerate very quickly.It weighs about 3300 pounds.There is noway my car could use 4.56 gears with any street tire except drag radials and believe me,I havent found too many cars that accelerate faster from 10 mph that are driven on street tires.
also,theres noway I want to drive on the freeway with my tach sitting at 3200 rpm.I can drive very nice at 2200 rpm and thats 63 mph,which is a common speed limit here
|10-17-2012 09:26 PM|
Its not the best thing for a strip only car but it works fine for a car that sees street time- especially freeway time.
|10-17-2012 08:42 PM|
|10-17-2012 02:16 PM|
On the street you will have sluggish initial acceleration with a big cam and no gear. ( assuming typical car wight and HP to weight ratio).
You will also be "on the converter" for a long time when you rug it.
Inefficient, creates converter heat. Long wait for the power band to hit.
Bad choice when a high stall converter is used (unless the power to weight ratio is very high)
Unless your car is very light weight or your don't care about acceleration.
Of course if you have no tires traction It won't matter much.
You average camaro malibu muscle car #3200-3600# with a 350 and a 256° cam and 28" tall tires wiill want a 4.30 to 4.56 gear It wil alos want 10:1 to 10.5:1 cr (for pump gas)( if you want strong acceleration.)
The motor will want to cruise at 60MPH at around 3200-3400rpm in Drive (1:1)
At the track you would be way under geared with 3.50:1 gears. Your ET will be 4 to 8 th's slower than what It could be with the right gears.
You can run what ever gear you want in your car. Its your car. But don't expect stong acceleration performance with a big cammed 350 and hiway gears in a typical weight car or even worse in a heavy truck) and a stock low stall converter. All the torque power will be at higher rpm ...very high vehicle speed. Initial Acceleration will be lame untill the rpm gets up to where
the cam makes power. 3000+++ 3500++rpm for a racey 256° cam.
Unless you got 5 or 6 transmission speeds (with a low 1st and 2nd ratio) to work with. Not the typical 3 forward gears and a 2.5:1 first gear as in most cars.
If you want to optimize it to break the land speed record thats a different thing.
|10-17-2012 08:48 AM|
AP72,you are correct"They aren't related directly"
most cars and trucks have multi gear transmissions,to say a car with a flat tappet hydraulic cam "needs" 4.30 or 4.56 gears?
Im trying not to correct or call out anyone,but,,,,,,,?lets think about gear choices and applications.I use 3.5 gears and my cam is 256/264@50 with valve lift over 600,is my gear choice wrong?
|10-17-2012 08:34 AM|
Changing gears is not totally necessary but in most cases it enables the driver to make the best use of the new found power at the higher RPM ranges.
|10-17-2012 08:31 AM|
|10-17-2012 07:29 AM|
Cam for a Vortec 355
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