So far my best et is 15.7 with the following...
1987 IROC 305 TPI HO automatic 700R4
Flowmaster Exhaust
Hypertech Streetrunner Chip
K & N's
2:73 gears

This week the following is being done....
New rear with 3:73's
SLP Headers
MSD 6AL ignition
Airfoil
New Moroso wires
Bosch +4 Platinums
cat. converter removed and a straight pipe installed

How much do you think my ET's will improve??

[This message has been edited by Hurst (edited July 17, 2001).]

 

I have an '89 IROC-Z with the Borg Warnner rear with 2.77:1 gears. It is a 350 TPI automatic with 62K miles on it. It has the following mods: SLP 1 3/4 headers, no cat, Hooker catback, ported plenum, gutted MAF, gutted airbox, no smog equipment, AFPR set at 47psi, MSD coil, Taylor wires, ARAP custom PROM, 180 degree stat, cool fan turn on settings, TB bypass, and K&N filters. Unfortunately it has 2.77:1 gears in the BW 9-bolt rear.

I just went to the track last Friday the 13th and ran a 14.0 at 98.87MPH with a 2.16 60ft time. The track is at about 700ft above sea level and the time is NOT corrected, although I dont believe in corrected times if your that close to sea level anyway. I was running on Eagle GS-C street tires. The weather was nice but more humid than I would have liked. The trans was also shifting a little too high, 5500RPMs.

 

Al,

Whatever you do, do not have any expectations when you run after your mods. If you do, you're only setting yourself up for a disappointment. I learned this the hard way. Almost every time I ran at the track after a mod or two, I did not gain what I thought I would (typcally less). Just do the best you can, then evaluate.

Also, keep in mind that weather conditions play a major factor.

You are right. NHRA's Altitude Correction Tables for stock and super stock does not list any correction factors under 1,200 feet.

------------------
Willie

Supercharged 1987 305 IROC-Z, Daily-Driver, Emissions-Legal.
Former Paxton (6-psig) with 50-hp nitrous: 12.043 @ 112.86 mph.
ATI D1SC (10-psig): 12.056 @ 116.62 mph.
All stats are altitude corrected for 3,100 feet using NHRA's Altitude Correction Table.

http://willie.camaro-firebird.org/

1987 "20th Anniversary Commemorative Edition" Z28 Convertible -- Super Chevy Show Class Winner, 1998.

[This message has been edited by Willie (edited July 18, 2001).]

 

I agree with Willie!
He is right about setting yourself up for disappointment.

Go to the track and do the best you can. Alot of things depend on your times.
One major thing is the 60' time and with the 3.73 gears you are going to spin alot and may have times as high as 2.4X!
If you can reduce your 60' time by 0.1 second then your overall time (1/4 mile) will decrease by about 0.2 seconds and vice a versa.
So practice on your launches with those new gears.
You got a base time before the mods so that is good so now go and have fun!

------------------
89 IROC 350 Auto
MSD 6AL
Custom DUAL Exhaust
Edelbrock Performer 6085 Aluminum Heads
ZZ9 Cam
TPIS Level 5 Chip
And Free mods.
(stock intake, runners and suspension)

13.879 @ 98.90 mph (with 2.77 gears!)


Moderator of http://www.iroczone.com

Member of JFA Crew

 

Having fun on the track is not a problem.

My 60' times now (before the mods) are 2.2.
I know that without slicks I will have a problem with wheel spin. I am in the process of trying to get a pair.

I know about disappointment at the track. My first run of 16.3 was very humbling to say the least. Getting down to 15.7 is not too shabby for what I did. The main reason was changing the rpm at which I shifted (4500-5-5300).

You have to admit though, with GOOD traction and those new gears alone, will account for a decent decrease in my times. It would have to. Going from 2:73's to 3:73's should account for more than a .2 decrease.

I know that there are other variables such as temp. etc. but I anticipate with all the mods to lose a minimum of .5 off my et's. With slicks and NO wheel spin (or at least an insignificant amount) I should be looking at .7 or .8.

I saw a drag tire test and switching to a drag tire the test car's et's decreased by .9!! They tested many, many tires.

This may be overly optimistic but I can't help it. It is all in fun and dissapointment makes me even more motivated to overcome an obsticle.

My favorite saying...."The truth is in the time slips"!--Al

[This message has been edited by Hurst (edited July 18, 2001).]

 

Cars with stock (or close to stock) engines will not see a decrease in E/T's with lower gears. Although it will "feel" stronger, what you gain on the low end will be made up by lack of power on the high end.

A guy I knew with a relatively stock 350 in his '89 Formula lost about 0.3 seconds going from 2.73's to 3.73's (and no other change). Another friend of mine went from 3.08's to 3.73's in his nearly stock 5.0 Mustang. He saw no change in E/T's.

Willie

 

Willie,

The lack of top end power is constant with 2:73's or 3:73's. I should be getting into drive much earlier than compared to staying in second gear for almost the whole 1/4 mi.

Traction is everything. It was a slight problem before and will be worse now. With slicks I should harness that power to the ground and launch much better with better 60' times.

You are the first person out of many that has said this. I hope your wrong. No offense but I want to decrease my times.

Maybe I am missing something here but I can't see how 3:73's would not decrease my times significantly.

Again, the times slips will prove what the new gears will do or not do.--Al

 

Yes, you are right BUT what happens after your car shifts into third gear? With 3.73's this will occur much sooner and there will be more "track" to cover to the traps. A near stock TPI will run out of top end power around 4,500 rpm. You probably won't reach this point with 2.73's, but you definitely will with 3.73's. This being the case, what will you do? The choice is to keep revving the engine which will rev higher, but it won't produce any power. The alternative is to shift into overdrive -- don't want to do this when racing. It's like being stuck between a rock and a hard place.

First, I have seen the disppointment in the faces of my friends after running with 3.73's for the first time. They both expected good things, only to be shot down.

Secondly, Tim and I have simulated runs with Desktop Dragster with different rear axle ratios. This software confirms what I'm saying. On a nearly stock TPI, you won't gain anything. That's because TPI's are not designed for high rpm operation, but low end torque.

None taken. And of course we all want to decrease our times. What I can tell you is that as you modify your engine, thereby effectively raising the usable rpm range, the lower gear ratio WILL have a much more profound effect than 2.73's. So it is a good thing to go with a lower ratio. It just will not produce positive results.... yet.

Willie



[This message has been edited by Willie (edited July 18, 2001).]

 

What other mods will be suitable to take of advantage of the new rear and gears? You don't have to go into heavy detail just the basic info......
Thanks.

 

What would be the ideal gear set for stock TPI then? And doesn't it depend on the engine? 305 vs 350?

Just wondering because my car is basically stock, with the 9 bolt 3.27 gears. However, I am no where near the top end of the power band when I go through the traps. The car will pull right up to 120 MPH in third, and I am only hitting 92-94 MPH at the end of the 1/4. Wouldn't this indicate that lower gears would help?
Right now my car shifts into 3rd at 4750 RPM.. a little over peak HP. It was dynoed, and shows peak to be at 4575. So it seems like it's shifting right.

 

Willie,

This is what you said would happen with my mods...

"Cars with stock (or close to stock) engines will not see a decrease in E/T's with lower gears. Although it will "feel" stronger, what you gain on the low end will be made up by lack of power on the high end."

"A guy I knew with a relatively stock 350 in his '89 Formula lost about 0.3 seconds going from 2.73's to 3.73's (and no other change). Another friend of mine went from 3.08's to 3.73's in his nearly stock 5.0 Mustang. He saw no change in E/T's."


I ended up installing another cat. converter on my car instead of going with the straight pipe. I did nothing with the ignition. The only thing I did was change the gears from 2:73's to 3:73's and add headers and new plug wires.

The new gears and headers did help my times.

My best before the mods was 15.75 in 55 degree weather and NO humidity. On weather just like what it was today at the track, I was running 15.9's.

Today with HIGH humidity and the temp. in the mid 80's, I ran a 15.37.

My fans are not kicking on hardly at all. They are doing absolutely nothing to bring down the temps. My car temp gauge was running just shy of the red mark. My traction was lousy and I had not yet practiced with the new setup. My driving left little to be desired. I went to the track with no intentions of racing. I had 2/3's tank of gas and about 50lbs. or so of extra weight in the car. Between the gas and the extra weight, that probably added a tenth or so. If not then real close.

Those new gears and headers helped my times big time! Wait until I learn how to drive it again and they will surely increase by another tenth or two. Advance the timing, and I am in the 14's. I would bet on it.

I have a fan problem that is seriously robbing hp's and my times still decreased drastically. 14's are just around the bend!

[This message has been edited by Hurst (edited August 04, 2001).]

[This message has been edited by Hurst (edited August 04, 2001).]

 

Yeah you need to get that fan situation figured out quick.
I replaced my radiator and thermostat on my car, which dropped the temp big time because the old radiator was getting plugged up.
I went from a best of 14.7 running @ 220* to a best of 14.4 @ 170-180*

 

Wow! That is a big difference. I am going to get that figured out today. Thanks.