Is it safe to run a 305 to 3500-4000 rpms before shifting?

 

it all depends on the motor and how it is bulit. I run a roller one to 5700 rpm in the elky !!

 

Yes the engine depending on the engine max power is made at 4000-4800. To produce optimal speed and fast time it is proper to shift so that the shift occurs the engine is at peak torque, which is 2400-3200. It all depends on what engine, transmission and rear gears your talking about though.

 

Wont do anything to it. Probably shifting at or over 4500 with a stock setup would provide the best performance

 

Ummm yeah....

 

I wouldnt worry too much about where you shift it regarding engine reliability when the motor is at WOT. A stock LO3 would have a hard time getting within spitting distance of its mechanical redline inder any sort of load, youd have plenty of time to shift it. Probably speeds up to around 5.5-6k would be fine if you had decent parts on the shortblock. 4500 rpm shiftpoint is just about right for your car, if your trying to get performance out of it. If your jsut driving around tehn theres not much need to take it over 3000 rpm.

 

Well I think after about 3500 it starts losing torque and would be better to shift way before 5000. I like to wind it up in first sometimes cause it sounds so sweet, but i was afraid I might blow it.

This is just a stock motor..

 

If we are talking about your 89 LO3, then it has 150hp @ 4000 and 240 ft-lbs @ 2400 rpm. So i would shift at your max hp rpm of 4000rpm.

 

Actually it has 170 hp and 255 tq, but anyways, I would shift much higher. When I was bone stock, not one single modification, I gained 5 tenths and almost 4 mph shifting at 5,000 rather than the stock 4400. You want to shift at the rpm where you get your max AVERAGE hp, not peak.

 

I could be wrong, thats what my Chiltons says, we all know how good those are.

 

DP

 

Guess that makes sense with a 700-R4. Carrying first out a bit longer would help put the engine right around its peak torque area in second. Wish they could ahve made second a bit closer to first with those trans'.

 

Actually you want to shift so that the rpm drop occurs at maximum torque, where the most work is done.

 

I don't agree, and I have time slips to prove that theory wrong.

 

The torque is what actually moves the car (torque x angular rotation = work) and its hard to say if its wrong to assume that since with a 700 there is a large disparity between first and second so shifting higher past the point of peak horsepower in first would help get the motor a bit higher in its powerband in second.

 

Is your car stock? Do you actually know where your engine is making maximum torque, like did you have it dynoed? Let me go lookup the gear ratios for T5 and th700 trannys and i will get back to you.

 

I think for a 700 the ratios are:

3.08
1.63
1.00
0.70

 

I'm basing this off both my 305 tbi and my LS1. The 700r4/4L60E has a 3.06,1.63,1,.7 gearing. Let me go find some dyno graphs of the LS1.

EDIT: might be a 3.08 first, I can't remember.

 

3.06 first is correct.

 

How high do you carry the LS1 before you shift?

 

currently shifting at 6,400, but I may reprogam it to shift at around 6,600 or later.

 

Ok i found 3.06, 1.62, 1.00, 0.70.

So you would want to shift at 4533 in first, and 3888 in second so that the rpm drop falls to 2400 where the max torque occurs according to my Chiltons.

But there is really know way to know where peak torque occurs without a dyno because GM does crazy things with thier motor ratings. So i don't really doubt that you ran faster shifting at higher rpm. Also it is really hard to just compare two different timeslips if they are not back to back, and even then.

 

they were back to back. First run let it shift by itself at around 4400 and got a whopping 16.8@79 mph, lol, second run, shifted manually at 5,000 and was able to run a 16.3@83 mph. Identical 60 foots as well. I believe if I had held second longer and not shifted to third I would have been close to 15's bone stock. I am a firm believer in shifting where you get your highest average hp.

 

That doesn't make any sense, how can you have an average at one point or rpm?

 

6400? damn... what is the mechanical redline of an LS1?

If you really wanted to find out where to shift, you could dyno the car in each gear and obtain a RW torque curve for each plotted against rpms (maybe speed would be better). At the point where the torque at the wheels in the present gear falls below the torque that can be made in the next gear at your present speed is the point where you would shift.

EDIT: You coudl jsut use a standard torque curve for the motor itself but inertial effects would be left out. But then again on a dyno the actual inertial effects that would be seen when the car is actaully accelerating on the road would probably be obscured.

 

maybe I didn't say it right. I meant shift at the point which keeps you in your highest average part of your power band. It's hard to explain without a graph.

EDIT: Here is a good calculator to help explain my theory

http://www.bgsoflex.com/shifter.html

 

So are you saying to shift so that after the rpm drop from that point to redline the average hp is maximum?

 

Could you try to explain what you mean a little better, I'm the one confused now.

 

I always hated thinking about things in terms of horsepower since its jsut a function of something else.

 

To add to my above statement the easiest way would be to multpily the engines torque at each point by the overall drive ratio of each gear and plot them with respect to speed. The point where the torque of the previous gear meets and then falls below the torque of the next would be the ideal place to shift.

 

So after the shift occurs and the rpm drops, you want the hp from that rpm to the next shift rpm or redline to have the maximum average hp. Is this what your saying? Sorry if this is confusing but im trying to understand what you mean.

I will agree that the car will be fastest when it uses the highest amount of average hp, throughout the run.

 

yes, exactly

 

Yep, i totally agree thats kinda what i was talking about in my last post at the bottom.

 

Good so now we all agree and are on the same page. It is really a very complicated subject and there are many different theories about how to calculate the maximum hp actually used.

 

my best times ahve been shifting my 89 with the 700r4 at 5000 every gear

 

So far, my best times have been when I shift at 7,000 Gotta get a couple things worked out to make this silly thing go quicker.