Greetings all,
I finally decided to try running down the track. WOW, what a blast that was! It seems like this sport could get addicting (and expensive). It was the last test and tune for the year at Maple Grove Raceway in Reading, PA, and it was packed. There was only time to get 3 runs in. Here's the car info:
'81 with 383 stroker with Dart Iron Eagle heads, Isky 280 Mega hydraulic cam, Holly 750 DP, hooker 1.75" headers, custom dual 3" exhaust with X-pipe, non-lockup TH350, 2400 stall converter, 2.78:1 rear WOO-HOO, radial T/A 225/70/r15s



First run I shifted (held in gear longer) at 5500 RPMs, second run at about 6000 RPMs, and the third run at 6500 RPMs (never shifted into 3rd gear!). It looks like 6K was the best run, but there could have been other factors. My RT was horrible on the first run, second was red, third was good. Any comments, please.
I think the first 2 obvious improvements would be tires and rear end? How easy (cheap) is it to change the rear end?

 

Yes it is addicting...............and can be expensive depending on how fast you want to go.

Glad you had a good time.....13's aren't bad for your combo.

 

Better 60' time every run, keep it up!

 

Fun, aye....

and only one red light.

 

Well done mate.
Good times for first up, especially with that tall diff ratio.

I guess you don't need to do that math calc now.
You need to make a decision which way you want to go with further mods.... building a car to go fast on the track has it's rewards, and its drawbacks..... biggest one being funding.

Does the 81 have an overdrive auto box?
If yes, and you want to optimise your strip times, you should aim for a diff ratio which will get you over the line in 3rd gear approaching your peak horsepower.... at a guess, I'd say 3.7:1 ratio.

In saying that, it will compromise your highway touring fuel usage... but heck, what did you put a 383 in it for.... performance I'd guess.

tom

 

.....since 60' times will greatly-effect your ET (typically, .01 improvement in 60' = .02 in the 1/4-mile ), break-down your runs incrementally, to see how well the car was running on the track, with your various shift-points:
I have done-so below, 1st run in GRAY, 2nd run in RED, and 3rd run in BLUE -

0060-0330 : 3.722/3.685/3.729
0330-0660 : 3.053/3.007/3.008
0660-1000 : 2.641/2.588/2.597
1000-1320 : 2.259/2.196/2.196

Note how the far-superior 60'-time on Run #2 effected even the 60'-330' increment, a full .04-quicker than either of your 2 runs.

I am not-aware of the details of that Isky 280 cam, but guess it to be about 280* advertised (duh! ), 228*-236* @ .050"-lift, and .480"-.490" lift (? ), and would think that might-not be enough cam to effectively turn 6500 RPM, 'specially in a 383" SBC, and those airplane-gears out back.

You DO realize that RT has no-effect on ET, correct?


The 2.87s are probably KILLING any chance of the car going much-quicker:
3.73s would put you at about 5200 RPM while trapping 102.5 MPH, and if you can find a ring/pinion set to work in your Series-2 carrier, 4.11s would be 5700 RPM.

The 2.87s give you a very high MPH for such a relatively-'slow' ET, because the car is so-lazy of the line (again, relatively-speaking ), then it runs like a raped-ape the 2nd-half of the track:
(I think we spoke about this last week..... ET x MPH is optimal at 1320..... get this number into the 1350-range for a street-driven/tire'd car, and you're doing good! )
it's possible that a switch to 3.73s would show an ET of 13-teens with no-increase in trap-speed, if traction is maintained.

A gear-swap would greatly effect your ET..... I have gone 2.11 short-times with a stock Miss-Fire and 3.73s, yet I have probably 1/2 the power you do:
not-only will it help your 60' times, it'll allow the motor to 'wind-up' quicker (2500-6000 RPM ) in all gears, too, allowing you to apply the power you have effeciently in 1320'

A switch to shorter & wider 255/60R-15 would help the over-all gearing (I believe 225s are 27.4" tall, while 255s are 27.0" ? ), and give you a wider foot-print on-launch:
when I had the 2.87-to-3.73 swap done, my buddy who did the switch STRONGLY-SUGGESTED (read-as WARNED ) that I not use a set of sticky-street tires with the Dana-44 rear-end (even-with my box-stock Cease-Fire! ), as it is fairly weak.

Van Steel offers kits to 'back-date' the Dana-44 to '79-and-earlier specs, using stronger units, with heavier pieces through-out to withstand 850 HP, but it might not be cost-effective for you, unless you are determined to build an ultra quick/fast IRS-equipped car:
it's possible that a local chassis shop in your area, such-as Carpenter, Ed Quay, Vanishing Point, or S&W, can hang a solid-axle/short 4-link set-up in your car for the same money, which'll never break, and effectively 'plant' the tires on every run.

Forum-member Jamie Jamison races a 12-second '80 Corvette at Moroso Motorsports Park, in West Palm Beach, Florida, with slicks, so you may want to contact him about advice on making the Dana-44 survive:
I believe he told me he has replaced/upgraded pieces as they've broken, and he might be a good source of information.

Lastly, I think BKbroiler is running 12.80s with a 383" SBC & 3.73 gears..... he may offer advice on what rear tires he uses to run those times, shift-points, etc.

 

Yeah, I guess I was stressing out about how bad I was going to do. Mid 13's makes me feel better than the math was.

Originally mine didn't, but I had a different tranny put in anyway (non-lockup and still no O/D).
If I change the rear end, I'll probably split the difference in what you listed as optimum and something a little more highway friendly. My whole life I've driven overdrive vehicles, so even this running 3000 at 75 MPH seems like a lot of unnecessary revving. I can't even imagine revving over 4K. This is a 90% street 10% strip car. That's why the mild cam and extra torque from the 383. I now wish it would have been quite a bit more cubes with a similar mild cam, but that will be well down the road.

 

Good numbers for your first time to the track.
For comparison, my car has different parts but overall its a mild 383, auto and street tires (see my sig.) But the big difference is in gearing, 3.73, and converter, 3,000 stall - I assume yours is stock. I cut 5 tenths off my time switching from 3.08. My tires are BFG 255/60/15 TA Radials.
I'm posting a timeslip from my best run, ET wise, so you can see how 60 time affects ET while our mph numbers are close (left lane on time slip).

 

Yes, but it's yet another thing to have fun trying to excel in. Besides, the last 2 runs I was side by side with a good friend of mine driving an Evo, which by the way has 2.0 L compared to my 6 L and weighs only a hundred or so less. The second run which was my best, was also his all-time best and he's been racing all summer. Since he's about a second quicker, getting a jump at the line gives me a chance to win the race. Winning was more important yesterday than beating myself because of bragging rights. Low and behold, the 3rd run he missed a gear and ran his 1/4 mile quicker than me by only .4 sec, but I won the race because I had a .8 sec RT. His RTs are terrible, but that's because he is concentrating on his ETs like he should be.

I babied the gas on the first run and got progressively more loading on the converter every run. The second run stuck or possibly slipped only a fraction of a second. The third run I spun for about half a second which like you said, killed every time after it.

.485 lift, 280 adv duration, 232 .050 duration, 108 degree lobe center and using a 1.5 roller rocker. I don't know what any of this stuff means

I definitely will be changing to wider wheels/tires and doing the offset T/A upgrade and yes, I had heard that I may have problems with my rear. That's probably going to be an expensive upgrade. I will also make sure the new tires are slightly smaller effectively giving me a lower speed rear.

To me, now the big question/decision is this: Which is better, to spend the money to get .5 or so seconds quicker with the same power, or spend the money to get more power and get the same .5 seconds quicker just from barrelling-*** down the second half of the strip? Remember, this is mostly a street car, so that launch won't mean much to me for 90% of its use.

 

WOW! That's 6 tenths quicker than me with almost identical trap speed. And with radials??? They are wider than mine, but geez. Are you doing a burnout with them?

About the converter - I forgot to mention that in the specs up top. No, it's not stock. It's a 2400 stall.

 

I wouldn't want to guess how-much more HP you'd need to 'walk' off the line as-is, then rip-n-tear from 330'-onward, just to pick-up half a second:
(your trap-speed doing this would be astronomical, and I'm not-sure how effecient, or streetable a combination like that would truly-be..... )
I think BK has a very versatile set-up that runs very-good for what it is, and I'm guessing it is fairly streetable, too (? )

 

I do a fairly long rolling burnout just before staging.
Then I hold it against the brakes at about 1,200 rpm, then nail the gas pedal. Sometimes it hooks, and sometimes it doesn't.