373 to 4.1 or 4.5 for my combo?

fstarocka

Member
Feb 1, 2013
75
Seattle
Thoughts on this cam/combo - currently 373, i dont care too much for economy as that is currently non existent anyway. Built this for a high-ish revving street toy, nothing more. I have a 2004r with excellent gearing.

373 are :nice" but im done with nice, i want brutal.. with 4.5s 65 cruise rpm is 2300 which is still great for me.. the street fun factor is what im all about on this one-

Im considering either 4.1 or 4.56 gears to experience more punch.. street raidals out back 175/60/15 nittos..


11:1, 200/64cc alu heads, 5.7 rods. 850 dbl pumper holley brawler, Vic JR, 1-3/4 LT headers into 3 inch collector and 2.5 true duals. 373 posi, 2004R, 3k stall, comp 288HR cam straight up-
Rips but sucks fuel like the tank is leaking.. 8 inches vac at idle.. sounds mean but sometimes at prt throttle seems a bit lazy/soggy when accelerating. off the line pretty awesome-
Im leaning towards 4.10 gears or one more.. 28" tire-

18-20 initial, vac adv disconnected ..
 

G72Zed

Veteran Member
Sep 8, 2015
4,228
Canada
To give a good "thought" I'd have to ask a few questions first.
1- What's the crank stroke, what's the cubic inch
2- What's the weight of the car with driver
3- What rpm is the max HP attained
4- What is the max HP if dyno tested, or educated guess

I'll assume you meant 275/60/15's for rear tire size.
 

rotinrob

Veteran Member
Oct 2, 2018
312
My Monte Carlo has 4:56 gears, TH 400 w 10" converter and the original BF Goodrich drag radials in 275/60/15 28" tall tires. Not a great highway car but when I built it it was meant for in town cruising as well as the occasional run down Milan dragway (I would drive the 30 miles there). Actually works well with the engine combination with the in town driving as it keeps the revs up and I'm not driving around in 2nd gear all of the time. Would be nice to have an OD for the occasional highway run as the car is in a different town now (less than a mile to the nearest freeway and about 10 miles to Martin dragway) and a cruise through this town takes like 3 minutes. If you can live with that much gear I say go for it, you will like it around town. Also I would have put 4:30ish gears in it if they were available when I built the car a nice compromise between the 4:11 and the 4:56 gears. I see Richmond has 4:33 available.
As always have fun.

rotin
 

fstarocka

Member
Feb 1, 2013
75
Seattle
3.750 stroke, weight with driver 3450lbs estimated, not sure about max hp as yet, est around 6000 for the cam (rough guess)


To give a good "thought" I'd have to ask a few questions first.
1- What's the crank stroke, what's the cubic inch
2- What's the weight of the car with driver
3- What rpm is the max HP attained
4- What is the max HP if dyno tested, or educated guess

I'll assume you meant 275/60/15's for rear tire size.
 

G72Zed

Veteran Member
Sep 8, 2015
4,228
Canada
My "cheat sheet" states a 10.25 O/A 1st gear ratio with a 3,500# vehicle and a 3.750 stroke. That 2004R with the 2.27 1st and 3.73 gives you a 10.22 O/A 1st gear, right in that sweet spot.

But, it's that big 42.7% second gear drop that hurts you (shift recovery). If it was a TH350, it would be 4.07, so 4.10, and th400 it would be 4.23, so 4.30's.
 
Last edited:

pooch400

Member
Feb 21, 2012
40
waterbury
Thoughts on this cam/combo - currently 373, i dont care too much for economy as that is currently non existent anyway. Built this for a high-ish revving street toy, nothing more. I have a 2004r with excellent gearing.

373 are :nice" but im done with nice, i want brutal.. with 4.5s 65 cruise rpm is 2300 which is still great for me.. the street fun factor is what im all about on this one-

Im considering either 4.1 or 4.56 gears to experience more punch.. street raidals out back 175/60/15 nittos..


11:1, 200/64cc alu heads, 5.7 rods. 850 dbl pumper holley brawler, Vic JR, 1-3/4 LT headers into 3 inch collector and 2.5 true duals. 373 posi, 2004R, 3k stall, comp 288HR cam straight up-
Rips but sucks fuel like the tank is leaking.. 8 inches vac at idle.. sounds mean but sometimes at prt throttle seems a bit lazy/soggy when accelerating. off the line pretty awesome-
Im leaning towards 4.10 gears or one more.. 28" tire-

18-20 initial, vac adv disconnected ..
The laziness at part throttle acceleration is caused by the carburetor, intake and header sizing. Those parts are for turning 7k-8k rpm’s Your cam operates between 2,500-6k rpm’s. The intake is rated at 3,500-7k. A Performer RPM intake, 600 cfm carburetor, and 1 5/8 headers will really wake up your combination. With 11:1, 288HR cam, 3k stall converter, and 3.73 gears it should have awesome throttle response everywhere. I’d try those things, an adjustable vacuum advance, and heavy advance springs before changing the gears. You may not want to afterwards. You’ll notice an improvement in idle vacuum and fuel consumption.
 

G72Zed

Veteran Member
Sep 8, 2015
4,228
Canada
I'll assume it's in the "383" cube range with that 3.750 stroke.

I agree with pooch400 above for the most part. But, the right parts combination and tune, you can use a 200cc runner head and open plenum intake with ease.

I would first remove that 850 Holley and go down to a 750, or even 650 if you are in the 450-525hp range. If you could borrow one, it would tell you right away. Open plenums are carb cfm size sensitive, dual planes not as much.

Your explanation points to low port speed/booster signal, and perhaps atomization fallout, especially on shift recovery and the lazy 2-3 gearing. Sucking fuel like the tank is leaking + fuel washing the cylinders and taking the life right out of the it.
 

1978 Z/28

Veteran Member
Jul 17, 2017
595
New Brunswick
A 850 is a big carb. You need a very heavy breathing engine to run that size carb, I have only used a 750 and it has served me well. Worked fine with 3.73s and 4.56s with 355 that reved 7500. Now I have a 385 450 hp 480 ft/lbs with 3.42s and and 275-60-15 tires pulls good. no stumble.
I had a friend that ran a 850 but it was on a 355, using GM 2nd design Off-Road Cam, 12 to 1 CR, and 4.88s in a street driven 68 SS Camaro that ran 10s on a 9 inch slick
I think you are oversized on carb do you have access to something closer to a 750 to try
with a 750 your cam and 4.56s it will be fun to drive
I loved the 4.56s

 

fstarocka

Member
Feb 1, 2013
75
Seattle
i think the big question is what torque does the engine produce after tire sizes have been calculated.. getting this cam over 3000 is key, the 383 does have an advantage over a 350 but sure the big blocks can run 342 etc.. the small blocks need a little more help.. im considering buying a 410 as well and comparing all 3.. but will try some fixes first, ie 750 carb and some tuning with the afr gauge..

tranny went out on me at about 200 miles of hard street driving - 2004R, followed chris book and the tolerances are so darn tight and pictures are too few for a noob.. drives ok when cold but once hot car wont move.. i know the 200 is known for fwd clutches getting fried if tolerances are not in spec.. might be that-

or could the TC have burned up prematurely?
 

1980RS

Veteran Member
Jun 17, 2006
6,550
MN
You will not notice much gain at the track with either 4.10 or 4.56, I would leave the 3.73's and add a super good converter. Also dump the Vic Jr. and put an Air gap on the car it's a better intake. I tested both, the Air Gap won hands down.
 




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