Okay, recently purchased a nice third-gen that was previously a drag-car for several years. The set-up is a carbed 350 (vortec heads, edelbrock carb and intake, good headers and exhaust) with a Turbo 350 tranny with a 3.73 rear end ratio. I'm not sure what kind of cam is installed.

Right now you can tell the car is set-up for a quarter mile. At 55 MPH I'm running every bit of 4500RPM (and probably 5 miles per gallon... lol). 75 MPH is about as fast as I'm willing to take the car for any duration, I don't even think I've taken the car over 80 yet. To make a long story short, this car sold almost all of its top-end for acceleration.

My question is, how can I change that without loosing all of my acceleration? I really do enjoy getting up to 70 in a hurry, but this lack of top end speed is killing me. I'd like to be able to take the car to atleast a hundred and ten without fear of blowing the motor.

I've been told that changing my rear-end to something more 'streetable' (ala 3.23) will fix it, but will that kill my acceleration? I've also heard changing to a new cam would allow me to keep my current rear end ratio while getting more top end speed.

What can you guys recommend?

 

The answer to your problem is a good 700-R4, with a moderate converter (2500-2800 RPM).

I would leave the gear alone. In fact, that's what I have in my car; just that stock one like yours. Works fine. Worked fine for a LONG time with a T-5 (similar OD to a 700), and works fine now with a T-56, except that it's kind of low. It could really stand to go up to 4.10. But that's just my setup; yours is a bit different, being an auto car.

Since you know what heads, gear, converter, weight, exhaust, and so forth are there, pick a cam that suits YOU and the way YOU want to use the car. Cams are CHEEEEEP, even the very best. Especially compared to the amount of fuel a poorly chosen one can waste, or to your continued frustration trying to overcome a wrong one (no matter how low its purchase price was... those couple of pennies disappear into the overall noise level REAL QUICK), or to other parts you might buy to try to "compensate" somehow for a wrong one.

From your description, I'd suggest a Comp XE262.

I'm not a big fan of those Edelbrock (Carter) carbs, myself. They're "OK", but that's about it. They can be made to run "OK", and get "OK" fuel mileage and decent driveability, and "OK" power; but they are a very poor fit to our cars. The fuel line arrangement is pitiful, the linkage isn't great, etc. You might want to consider replacing that with either a Holley 6210 (650 CFM spreadbore man sec), or a good old Q-Jet.

 

55 mph with a th350 and a 3.73 is no where near 4500rpm. Are you in second gear? Are those gears not 3.73? look around your setup more closely.

 

Right: it's ACTUALLY about 3000-3200 RPM.

That "4500 RPM", was that the factory tach?

Not that it matters too much, except just to get the numbers straight.

 

The car's at the family mechanic's house getting a tune-up right now, but when I drove it down last night the Tach was reading 4500RPM at about 55-65 MPH. I can't really say how accurate the Tachometer is though. Seems to be fairly accurate to me, at least when it's idling. Though I don't know alot about Transmissions..

As for the Edelbrock Carb, I'm not a terrible fan either. But its working pretty good now, no complaints yet. Would it actually be worthwhile to ditch a working Edelbrock for a new Holley?

The engine and tranny I know, but I'm not sure about the converter in my car. Perhaps my mechanic will be able to figure out which variety I have in it.
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Nope, after market. My mechanic told me its a fairly high dollar tach. But that doesn't necessarily mean its set right. heh

 

I'm going to do my research on the 700-R4, thanks for that tip!

Is it a significant increase over the Turbo 350?

 

Hmmmm, would the XE 262 be aggressive enough for a 350 with vortec heads?

I'm hoping to be able to improve on my top-end without doing a complete transmission swap.

 

Well, "significant" is in the eye of the beholder.... but, the 700 has overdrive, and a torque converter lockup clutch; and the 350 has neither.

 

Well, I know what Overdrive is and does, but the Torque converter eludes me... I thought all transmissions had such..

 

Right; all automatic transmissions since the early 60s have had those. Before that, they had a "fluid coupling" (no stator).That however is a different matter. It's a clutch that couples the 2 halves of the converter together, thereby eliminating losses in the fluid. They first appeared in the late 70s; and became pretty much standard by the 80s. They're good for another mile or 2 per gallon, and a couple hundred RPM lower on the highway, in most setups.

 

Second question; is the 700-R4 robust enough to support the horsepower my engine produces? I'm looking at 250 right now, and maybe 300 in the future?

I thought the 700-R4 was for less horsepower heavy applications and the TH350 was for more "hardcore" applications?

 

Well, look at it this way:

The trans behind the LS1, LS6, etc. is the 4L60E. That model is IDENTICAL to the 700, except it has solenoid valves to tell it what gear to be in instead of hydraulic control. Same clutches, same shafts, same gears, same EVERYTHING, as far as power transmission and strength is concerned.

Those cars put more power than that little bit you're talking about TO THE WHEELS, off the showroom floor. And then people mod them and get even more. And the trans still holds up fine.

Eh? Does it sound like enough?