stall converter and gear ratio question for blown sbc

how much HP?

My bro in law runs one in his OT '71 chevelle

600 dyno hp natural aspirated 454,12 bolt 3.73's,28" tire and he's not very forgiving,he has some "fun" with it time to time

Loves it!! 112 LSA makes a difference also,less overlap,more eng vacuum

he runs a 2400 stall converter.

He had a TH350 before with a 3000 stall converter,scared the hell out of him 60mph at 3400 rpm's was too high.

they've really improved parts for the TH700 in the last couple of years to handle the HP and torque

 

i agree,you need to get the RPM's up there 4.10's would do it too with OD

 

26.5" tire and a blower, even I would probably go 3.73's, depending on how sticky the tires in question were. I drive around town a LOT more than I do on the freeway, but even if i was building a car that was going to see alot of freeway time, I'd go with 4 series gears and an OD like i am doing on my chevy II. There is just so much compromise with running a tall final drive. Not only does it make the car GUTLESS (by my manaical, crazed standards anyway) around town, but it restricts you in camshaft choice, and makes the car more prone to part-throttle detonation as well, which further restricts you. I just cant wrap my head around all the guys on here that want to run 29/30" tall tires with a 3.08 final drive. Sorry, you might be able to kid some people, but I know just how gutless a combo like that is. To me, modified cars are supposed to be FUN, like front seat of the roller coaster, ****erflies in the stomach, tighten the ol' sphincter fun, to drive. After 30 years as a crazed manaical street racer, thats just what I expect. Tall tires and 3.08s just aint gonna get you there, blower or not, as the OP has just found out.

 

I did not read all the responses but the shifts are being masked by the fact that you have a large 3000 stall converter and a huge rear gear. Until the rpm goes over the stall you won't feel hardly anything when it shifts. As for driving down the hiway you want to be over the stall of the converter to get any mileage at all. My Roadster has a 2500 stall and if I am under that it gets 13 MPG if I am over 2500 RPM I get 18. Still at 2500 rpm I still have 5 to 6 hundred flash at that rpm.

 

Guessing 600 to 650 hp on 10 psi. Seen similar built motors real close same cam 750 on 15 psi to crank

 

I know need to get it screaming, od is not an option now just looking to make it tolerable for short trips on the freeway with everything I have currently . Leaning towards 3.73 then I can always go bigger tires .

 

What about leaving the convertor and
gears "as is" and changing the blower
drive ratio to spin it a bit faster? That
would bring the boost in earlier - ie - at
a lower engine speed and give you more
low and mid-range torque.

Mart3406
================

 

I also read the tall gear is causing me to blow through the converter a bit on shifts when flat out because of the load on it . I know changing them should help dramatically .

 

Usually with cams that size gears are highly recommended by the manufacturer. I have 3.27's and an N/A motor (225, .477"@108lsa), 26" tires, and I'm looking to go with 3.73's soon. Mine weighs 3200lbs. With a 3 speed and 26" tires you should be perfect. Low-mid rpm power is where you're driving at MOST of the time. I'd gear it to respond in that 3-4k range.

 

I could it will push me past pump gas territory though , or I would need to put a boost retard system in it .

 

What will bigger tires do ?
They will lower your rpm for any mph.
They are effectively moving the rear gear back in the direction of the 2.73 gears .

 

i 've run 3.73 for years . they won't kill the motor. i've run stock 235 with 3speed and 4.11 gears alot of miles down the highway. just don't look at the tach. it get's in your head.

 

exactly if I do 3.73 say and Iam turning 3400 at 70 drop to 3100 slightly bigger tire . So what I am saying if need be I can make a small change with tires not as drastic as going to 3.42 gears .
I think 3.73 what Iam going to do any recommendations on gear manufacturer
should I go street or pro gear ?

 

Street. do not try to use 9310 gears in anything but extremely limited street use.

 

thanks What about strange they make pro street gears made from 8620

 

Totally wrong answer. The tall gear will hold the engine in the rpm range where part-throttle detonation is likely to occur for a longer time with a greater load on it. One of the benefits of running more gear is you can run more compression, as the engine will pull through past the torque peak much quicker with less load on it that a taller gear will allow.

 

I've been trying to tell you that your cam is for a driving range of 3000-6500 Rpms. This is where the engine was built to run. I didn't build it but that's where it wants to be and will give you everything you paid for. You see everything below that 3000ish rpm is a complete waste. It wants to run on the top end.

Now briefly explain to me why you want to drive it in the idle to 3100 range ?
That rpm is not where it will do any good !
You won't be happy !
You aren't getting what you paid for !

You could easily change the cam and have the engine perform its best at 1500 to 5000 rpm.

 

From a drag race perspective, which is where my experience is, I agree with everything 31 Vicky with a hemi has said.....He is spot on

 

I would agree with 31vicky. If you want more street response you'll need more of a street cam. Not to mention large ports on a small block can kill responsiveness at low rpm. If the cam comes in at 3k and you have big ports and valves, without enough boost to pick up the lack in cubes you'll be waiting for higher Rpms to make power.
With N/A stuff port velocity is key. With blowers you'll need more boost with less blower rpms to avoid hot intake air (prone to detonate). Is your blower under driven or over driven?
Also, you may be able to run a few more degrees timing, maybe 30*. 28* is safe but with 7.**** compression you may have some wiggle room.
Check the cam card and calculate valve overlap. Too much overlap can ruin otherwise good duration numbers.
The cam is the at***ude of the engine. It wants what it wants.
Lots of factors here, mainly seems like a strip/street engine in a street/strip car.

 

Really, these guys are right. Why run a blower at all? Just gut the case and put a 600 vacuum inside, the noise comes from the belt anyway. Does a street rod really NEED more than 300hp? As long as it LOOKS like its quick, does the rest of it really matter?

 

Iam 14 % under driven 9 psi full boost 7.84 static compression . I do understand what every one is saying , I am Not changing the cam really 3.42 or 3.73 are going to get me over 3k cruising . Main question at this point do I go 3.42 try to save my self a few rpm which is probably not worth loss in holy **** factor around town or let it eat with 3.73 be 300 rpm higher on the highway .

 

Yes do need 600 + on the street I like to keep it interesting and scare myself a bit .

 

I'd go with 3.73's. should be great seat-of-the-pants feel.
-Plus: You can go with a ~28" tire to adjust your cruise rpm after you destroy the old ones.

You could try advancing the cam 4* if you have enough piston-to-valve clearance and a timing set that allows It. That'll pick up low rpm power

 

Where's the dyno sheet on this engine ?

 

I was actually poking fun at the "street rodders" on this thread telling you to castrate your combo. The 8620 gears will be fine, Richmond and pretty much everyone else uses 8620, its the "standard" alloy that everyone makes high performance gear sets from. As you say, most of your driving is around town. The 9310's are very soft to withstand really high shock loadings, but they do not respond well to repeated thermal cycling and will not last in regular street use.
Go for the 3.73s and let that dog eat. If you are going to a taller tire, I would seriously consider 3.90s or 4.10s, especially if you are running a sticky tire that will hook the car. You have already tried the tall gear that 90% of these old ladies will INSIST that you should be running, and you have found it wanting.
If you really find you cant handle the rpm on the highway, pull the 3.73s, replace them with 4.56s, and put a 200R4 in it.

 

Yukon gears are just as quiet as OEM,Richmond (if you can find them) are noisy and hard to setup a pattern,Motive are good too

what i would choose:
1. Factory GM (easy to setup,quiet)
2.Yukon (quiet like OEM,easier to find)
3.Motive (a little noisier)
4.Richmond (company has been sold,might be hard to find them,Noisy,hard to setup,but very strong)

 

Thanks I should I will check with machine shop see if they set it straight up to begin with . I am going to go 3.73 then go from there .

 

My father in law owned a '68 SS Nova with a 350Hp 327 prepped by Warren Johnson (yes THEE Warren Johnson) he was friends with him in the late 60's,anyways he ran 4.56's in that car and drove it on the highway with an M21 4 speed...he said that thing would scream at 4000 down the highway cruising normally and he never even gave it a second thought about rpm's...There's a point where you just have to man up and put your balls on the table!RUN THE *****! don't be afraid for christ's sake!!.Didn't that '55 chevy in two lane blacktop run 4.56's w/an M22?? and they ran it cross country for filming? I think you are on the caution side enough running 3.73's w/your combination
you could even run 4.10's/w a taller tire in effect get the same results,but better 60ft times at the track...

 

Seems no matter how perfect things are someone has always got **** to say and always knows more . I know eventually I am going to have to change the trans I dont see it holding up . Its basically stock th350 with shift kit. thanks

 

Didnt put it on an engine dyno and just got the motor in and tuned enough to run it and check air fuel. This is very close copy of another motor that made 750 on 15 psi