gearheadgene

I've read through a lot of the post, here and around the web on these 2 cams. The tech at Lunati and I went back and forth - but I can't make up my mind. Lunati seems to lean towards the bigger cam, I lean towards the smaller one.

Here's the setup:

1986 Firebird
350, .030 over
10:1 compression (roughly)
vortec heads with comp cams beehive springs
edelbrock vortec Performer intake
Factory QJet, setup from Jet
T5 5-speed.
3.42 rear gears (coming soon, 2.73 now)
Pete Jackson gear drive (removing it though - way too loud)


Power brakes - definitely
AC - probably, just not yet.

It'll never run on the track. I want this car for really good fun around town, be able to run 30 miles to work, and there's always the possibility it'll get stuck in traffic. Oh yeah, and I want respectable gas mileage, particularly on the highway.

I have a hot rod (1969 chevell ss), that thing is a beast, not the same sort of ride as the bird. So you see, the bird is really for everyday fun. So, I want to build loads of torque

Admittedly, the 60103 sounds great at idle. If I were choosing on idle sound alone, it gets the thumbs up. But, I think it's just too much for daily driver. Am I wrong?

Attached is a plot of RPM vs MPH, one curve for each gear. 5th gear is just about at 2000 RPM. The 60102 is running above it's listed minimum (1400 RPM) but if it were the 60103, it's just barely above it's posted minimum (1800 RPM). Actually looks like a little more rear gear would be nice - just a thought, but I don't want to get too large (like 3.73).

So I really think the 60102 is better. It's got a little bit of chop in the idle, and all the other specs seem to line up with my needs. But - that 60103 sure does sound good - and the guy at lunati says it'd be a good match here.

I can't decide

Any help?

regards,

gene

gearheadgene

The prior graph was for rear gear =3.42.

Changing to 3.73 instead doesn't seem so bad. The RPM for 1-4 gear moves into the power band a little bit more. The 5th gear cruise changes by a couple of hundred RPM,but not bad. So cruising at 60 MPH, the motor is just humming along at 2000 RPM. That seems pretty easy on gas to me

So I want to throw this question to the group as well - are 3.73 gears a good compromise? Or are the 3.42 gear set better all around choice?

86LG4Bird

iTrader: (1)

The 60102 would be a no-brainer for me.
As far as gears, you'll have to help me out here, as I have never had a T5. Unless it has an OD 5th significantly longer (less numerically) than .70, I'd go with 3.42's. I have 3.73's with the 700R4, and would really prefer 3.42's for all-around driving. Mine has more low-end grunt than street tires can handle in low gear.
I wouldn't even consider the 60103 cam and the 3.73 gears since you say you won't be tracking it. The 60102 cam will have a VERY noticeable idle to it. Even my little ZZ3 cam (208/221/112), tuned smooth as I can get it and with a very mellow exhaust, would never be mistaken for a stock cam to any trained ear.

DeltaElite121

3.42's will be stronger than 3.73's in a 7.5". The actual casting quality won't be different, but the teeth will be thicker and you need every bit of it under a modified car with a 7.5" still under it.

gearheadgene

My graphs account for tire size, rear-gear, and all 5 gears from the T5. I'm not 100% sure about the ratios in the T5, but it's close. Again, I think 5th is 0.68. Cruising the highway with 3.42 at 60 MPH puts the motor around 1800 RPM. The 3.73 moves it up to 2000. Small difference,really - but those 2 cams don't see it quite the same, seems to me.

After I posted that 2nd plot, I got to thinking there's 2 good combinations here:
1) 3.42 rear and 60102 or
2) 3.73 and the 60103.

The tech's a Lunati (good guy, btw) was leaning to the bigger cam. The guys at comp cams also leaned bigger. Maybe they want to build race cars?

So yeah, I think I agree with you, 86LG4Bird.

I'm more interested in building a Ferrari,not a pro-stock. But that big cam sure sounds cool

1991sleeper

iTrader: (-3)

Go 3.73.... I got 4:10's and with a 28" tire its like running a 3.73 ... All gear ratios are based on a 26" tall tire

91' bird 305 TBI T-5, trick flow 175 cc heads, 4.10 gears, lots of suspension upgrades. 24mpg @ 2500rpm hwy. 8.80@ 84mph 1/8th on street tires... 8.000's soon

Fast355

iTrader: (2)

T-5 does not have as deep of a first gear as the 700r4. Go with the 3.73s and the bigger cam.

gearheadgene

You didn't say how fast your car goes at 2500, so I plugged your specs into my program. I estimate your car goes about 70 MPH in overdrive at 2500 RPM

Is that close?

I don't really want to be at that RPM - a little too high.
My estimate for the 3.42 gear, at 60 MPH, is 1813 RPM
My estimate for the 3.73 gear, at 60 MPH, is 1977 RPM

Eyeballing the chart I made for your setup is around 2300 RPM.

So your setup would isn't an exact match to my tire and gear setup. In my case, it looks like I will be running a lower RPM than you across the board.

Orr89RocZ

iTrader: (20)

For your setup, 60102.

gearheadgene

and 3.42?

Orr89RocZ

iTrader: (20)

Either would be fine. More highway i would go 3.42

Confuzed1

iTrader: (4)

With a stock T5 and 3.73's, I use to run closer to 2800 RPM's doing 70ish MPH on the freeway. It was up too far in the rpm range to get any type of decent gas milage. If you can get 2500 or under with the 3.42's doing 70, that might be ideal IMO because, let's face it….most people run at least 5 mph over posted speed limits…I do 70 in posted 65 mph zones regularly to keep up with traffic….close to 80 in posted 70 mph zones….you get the idea.

-I will tell you, 1st gear in my car is nearly useless. I catch myself shifting into 2nd gear before I even get across an intersection. I can lope around town doing 35-40 mph in 5th gear. For everyday street use, the 3.42's are the best compromise with a T5 IMO. The smaller cam will be easier to tune around, easier on the valve train and most likely a bit better on gas overall.

gearheadgene

Sounds about right. Mathematically, the 3.73 @ 70 MPH is around 2500 RPM, assuming P230/60R15 tires. Maybe your tires were slightly smaller? But close enough for gov't work

The 3.42 @ 70 MPH looks like 2200 (I can plug into the program later for an exact number).

I'm not 100% sure on the 1st gear ratio in the T5, I found a lot of reported variation in the tranny, although I believe it is World Class version, am not sure which 1st gear it has. Anyway, your description sounds on the money. The graphs predict it runs out of engine at 20 MPH ~

gearheadgene

I am leaning towards the 3.42 and 60102. Maybe give it a couple of days to sink in before ordering the parts.

cuisinartvette

With the intake and heads you have x 2 on the 60102.
Its a strong running cam for its size. Youll know it has something in there but it wont chop (doesnt matter). It will pull hard though through the entire range. Sure woke up a TPI did a few yrs back. Basic 10-1 shortblock box stock performer heads and headers and a crappy 2.73 gear youd swear it had a 383 in it and would light them up soon as you hit passing gear. Not spinning them some but smoking them hard.