SN17

I have a 91 RS 383 Stroked, Carbed, 9.7:1, holley 750, NOS 150 shot, TCI 3600 stall Streetfighter converter with a stock 700 R4. When I launch at the track I get great hole shots. I run low 12s at 106 to 108mph. I have noticed that when I race certain cars that I feel I should beat i blow them away off the line, but they catch me at the trap. It's as if the third gear has short legs. I am a good engine builder, but know little about transmissions. Would a turbo 350 or 400 have a taller third gear?
Thanks
Dave

dwkohout

T400, T350 and 700r4 all have the same 3rd gears ratio 1 to 1.

EvilCartman

iTrader: (1)

One reason why you're getting out on them at the start is the 1st gear of the 700R4 is 3.06 compaired to the TH350's 2.52 and the TH400's 2.48.

5678TA

just not enough hp.. even with a different gear, you still dont have the hp to run faster on the topend..

Pro Built Automatics

I have seen this many times before, the problem here is most likely the TCI 3600 stall. If the STR is to high or you have to much slip, the mph will be down as is in your case. If the motor is built right, and you are not running out of fuel, and the exhaust is not restricted, your mph should be a lot higher than what you have posted. The 3.06 first gear helps a little, but not as much as you might think. The TC has more to do with ET than the low first gear. I would try another TC such as a Vigilante, Edge, Yank, Pro Torque, etc. I am not a fan of TCI on 700R4's/4L60E's, they are ok on TH350/400's, but when it comes to lockup TC's I have not seen good results with them. A slippery TC will give good 60 foot times, and possibly a good ET, but the mph will be down. I would go with a STR of about 1.7-1.8 max. and a 2,800-3,000 rpm stall with the setup as mentioned. By the way what is the duration of your camshaft at .050" lift? and the lobe centerline?

SN17

OK, maybe my trans isn't the big problem. I have stock 350 heads and I have a Holley 750 that was fed by a Holley 88GPH (red) electric fuel pump. I have since changed to a Holley HP125gph because I had a lean condition with the old 88 pump and I would get a backfire through the carb in second gear while spraying 150 shot. I have not sprayed with the new fuel pump yet, but Holley tech and several other more experienced racers said it was likely a lean condition, that the old pump just could not keep up with the carb and the 150 shot at the same time. Also My exhaust is two Edlebrock shorty headers going to a 3" Y pipe, to a 2.25" pipe for two feet then into the cat and out to a 3" pipe to the muffler and out to two 3" pipes. It's an edlebrock system, but the guy who installed my sub frames had to re-rout the pipe and that is where it skinnies down to 2.25" before the cat. That could also be holding me back. I'm begining to wonder if my heads, combined with my micky mouse exhaust is choking the engine back a bit. I have a 3.73 rear gear and 26 inch MTs and a 5100 chip in my shift light. I am running an MSD Billit Dist and Digital 6 box with a 38 degree advance curve. And ya know, I have no idea what a resonable redline on this engine should be.

Here is my last time sheets with the old fuel pump:

Spraying 150, NOS Power Shot Wet System
R/T .031
60' 1.618
330' 5.048
1/8 7.907
MPH 86.78
1/4 12.456
MPH 107.53


Motor Only, No Spray
R/T .119
60' 1.741
330' 5.533
1/8 8.743
MPH 76.85
1/4 13.873
MPH 97.44

Last, here are my cam specs:
Part Number: 113841 Grind Number: F-278-2 (REPLACES CC-278-2)
Engine Identification:
Start Yr. End Yr. Make Cyl Description
1957 1987 CHEVROLET 8 FAIR IDLE, MODERATE PERFORMANCE USAGE, GOOD MID-RANGE HP, BRACKET RACING, 3400-3800 CRUISE RPM, 10.0 TO 11.5 COMPRESSION RATIO ADVISED. BASIC RPM 3000-6500
Engine Size Configuration
262-400 C.I. V
Valve Setting: Intake .022 Exhaust .022 HOT
Lift: Intake @Cam 320 @Valve 480 All Lifts are based
on zero lash and theoretical rocker arm ratios.
Exhaust @ Cam 3334 @Valve 500
Rocker Arm Ratio 1.50
Cam Timing: TAPPET @.018
Lift: Opens Closes ADV Duration
Intake 29.0 BTDC 69.0 ABDC 278 °
Exhaust 82.0 BBDC 26.0 ATDC 288 °
Spring Requirements: Triple Dual Outer Inner
Part Number 96877
Loads Closed 126 LBS @ 1.850 or 1 27/32
Open 304 LBS @ 1.400

Recommended RPM range with matching components
Minimum RPM 3000
Maximum RPM 6800
Valve Float 7400
Cam Timing: TAPPET @.050
Lift: Opens Closes Max Lift Duration
Intake 10.0 BTDC 48.0 ABDC 109 238 °
Exhaust 63.0 BBDC 5.0 ATDC 119 248 °

ps, I will totally understand if this gets moved to a different forum now.

AlkyIROC

Back when my car was roughly still stockish, I had a TH350 with a 3800 stall converter. 26" tall tires and 3.27 gears. I managed low 12 seconds but at 117 mph. The car was a real slug out of the hole but near the end of the track it started to pull really hard. It wasn't geared properly. Chances are it would top out at 3/8 of a mile or maybe a little higher but at the end of a 1/4 mile, you shut it down.

My competition running the same ET would get a huge jump on me off the line. At the end of the 1/4, they were topped out and I was still accelerating for the big MPH. They soon learned that when they looked over into the other lane after the 1000' and I wasn't there, I could come up fast and pass them by the 1/4 mile mark.

If geared properly no matter what tranny you use, you should be at or just over you shift point at the finish line. Any combination of shift points, tranny gears, diff gear and tire size that gets you to the finish line at the engine's peak is what you're trying to do. A car geared for high highway mph will run out of track before it runs out of gears on the 1/4 mile. A vehicle geared too low such as a 4x4 will run out of gears before the 1/4 mile.

Your mph is about right for your ET. A normal low 12 second car can be anywhere from 106-112 mph. If it feels like you're running out of steam on the top end when you know it should be making more power, you're probably running out of fuel.

Do a breakdown of the run.
60' time
Time it takes to go from 60' to 1/8 mile
Time it takes to go from 1/8 mile to 1000'
Time it takes to go from 1000' to 1/4 mile.

With the 1/4 mile run broken down into sections, you can see where you gain or lose time as you do adjustment.

All vehicles should have very close to a 1.19 ratio from 1000' to 1320. Take your 1/4 mile ET and divide it by the 1000' ET. If the number is much lower then you're really dropping off after the 1000' mark. By the 1000' mark, the car should be just about maxed out. Between 1000' and 1320', you're not gaining any more in speed because torque is so low at the high rpms.

Multi gear trannys have the extra gears to get the vehicle's weight moving through torque multiplication. The 700R4's very low first gear increases torque much more than a TH350 or TH400 however the gear spread between first and second gear is too wide apart. Using a TH350 will probably be a little slower off the line but with a better gear ratios and the tranny's lighter weight, you should probably run a quicker ET.

Your cam card says the cam makes power up to 6500 rpm but you have your shift light coming on at 5100. You're short shifting the engine. If you can't make power to 6500 rpm then you have issues with parts of the engine like induction, heads, exhaust etc that are holding you back. Even when everything seems right it could be something like timing, jetting, weak valve springs etc holding you back. You shouldn't be crossing the finish line in OD so raise the shift point higher to keep it in each gear longer.

Here, go read this on HP and torque and how they affect a car's performance.
www.hardtail.com/techtips/hpandtorque.html

SN17

Thanks Stephen, That makes alot of sense and I learned a lot from you comments. I am carefully reading the link you posted. I will also pull all my time sheets together and do a break down as you suggested. I also have a dyno pull report that was don last summer. The only difference is that when it was done i had an HEI (stock) ignition system and was not spraying (motor only) and now I have an MSD Digital 6 box. Can you help me inturprate these results. Thanks again Dave

AlkyIROC

Those dyno sheets don't tell much without knowing the rpms.

SN17

Whoops, Sorry, I didn't realize I cut off the bottom with the Rs. See above, I edited it. Also, the car ran 13.7 at 98 MPH when that dyno run was taken. As I said I have not done a dyno pull when spraying. But when I spry the car runs 12.4 at 107 mph.
Thanks
Dave

AlkyIROC

The HP curve is absolutely flat from 4000-6000 rpm. I'd say, bump that shift point closer to 6000 and try again. It's still well below the operating range of your cam.

SN17

Will do. Thanks again and I will post my results. But I must say that I was expecting the torque and HP to be higher based on my engine specs. I wonder if my heads are constricting me a bit. But then again I think the dyno sheet is measuring rear wheel HP and that is less than HP at the crank. I think. Or am I getting ahead of my self? Just for fun here is a pic of the car.