aussiesteve

have a good 408ci th350 running 13.8@ 100mph first time raced.


changed to a 3.42 diff to get bottom end speed and couldnt go better than a 14.5 @ 95mph and over reving at 6000rpm end of 1/4 mile.
a BIG SHOCK as it felt like i ran a 12.98 or something close.


am running 255/60/15 BFG T/A and i feel the 400 engine is better @5500 no more..


i had no idea how much it effected the car going from 3.08 to 3.42


with the 27.3 inch tires 3.08 drops to 2.9?:1
and the 3.4:1 drops to 3.25:1..


i hope instaling a 3.23 diff will get me back to 3.08 overall with tire calculations and the torque of the 400 will be used instead of useless rpm,s,,
this is getting expensive,,not happy folks..


my aim is to run a 12.98 if i buy M/T street ET tires at 255/60/15

GeneralDisorder

iTrader: (1)

You fell past the peak of your power curve on RPM. Engine was making more power at the lower RPM of the 3.08. You need to dyno it and see what your performance curve is so you can tune your gearing and converter stall speed to your power curve. 342's will give better low end acceleration but if you fall off the end of your HP curve you'll be slower. The more power/rpm you have, generally the higher (numerically lower) you want the gearing, and the higher you want the stall speed to be.

Rick

larryjoe

I'd check everything because that's a hell of a fall off or try taller tires and see how it responds

QwkTrip

iTrader: (22)

I'd probably spend more time on the engine combo instead. You should be able to pull more than 100 mph without reaching the limits of the engine.

sofakingdom

iTrader: (1)

Sounds like your 400 has TBI heads, or a peanut cam, or stock exhaust manifolds, or some such. Something that utterly altogether totally strangles the motor at higher RPMs.

Street Lethal

iTrader: (16)

Your sixty foot will tell the real story, what were they? It sounds like you spun off the line...

redneckjoe

i wouldnt expect miracles out of those drag radials, especially being the same size you have. if your blowing the tires off on the line, you need bigger, taller, soft slicks. it will make a world of difference.

aussiesteve

Running a 400+060 bottom end hastings mellings clevite oil pressure 70lbs at idle ,,the engine is good,,
cam is a custom grind to suit compression ,engine size and intended,, rpm ,and gears to be used,,this is not off the shelf one size fits all...advertised duration 284,292
cam specs have a million numbers,,,lobe seperation 112


Comp cams pro lifters and magnum 1.52 rollers on L31 VORTEC heads,,
1 3/4 full length headers, "try that on an 82" 3inch single system.
weiand air gap duel plane and a 770 holley ultra avenger... the pro billet msd was re graphed and lighter springs fitted so it get full advance fast and it revs like mad.,,


the engine flys..


Th350 2500 stall,,extra clutches and bands and all steel internals and a big high flow gm oil pump fitted. 2500 stall..


This is not a drag car its a touring car with more power.


The TH350 has a full Sphone conversion kit and adjustable torque rod and Bilstein shocks, stiffer springs..with the 3.08 diff the car smoked the tires and would spin well into second and go sideways on gear changes if lost traction,,so engine is more than adequate..


The 3.08 diff with 27.3 inch tires brings the diff gear ratio down to 2.94
The 3.42 diff with 27.3 inch tires brings the diff rear ratio down to 3.24


when i ran the 13.8 @ 100 it crossed the line at 5400.. but had slow 60 foot times
when i ran the 14.5 @ 95 it crossed the line at 6000,,,and had simmilar 60 foot times.


i will get to a dyno,,not to tell all my mate after 6 beers how big my weaner is and how much power my poor old camaro has,, BUT i will use this as a guide to get engine rpm torque and rpm figures to work out where it makes power and where it drops off.


i think i can go to a 3.23 and with the eaton true trac fitted and a set of sticky tires it may run a 12.98..


i dont want to be over 5500 at the 1/4 but the dyno will tell.


I have counted my chickens and am close to buying a 434 Shafiroff unlimate pump gas special. Its $1500 delivered to me in Australia and i can use the 400 in a smaller car...
This Drag racing is an adrenalin rush for sure..

QwkTrip

iTrader: (22)

You're not going to gain a second in the 1/4 mile with a minor gear change. There is something wrong with your set up. Figure it out and you'll be a lot faster.

Gary Anderson

iTrader: (2)

I think you have a trans or converter problem. 100 mph with a 3.42 gear and 27" tire should be under 4500 rpm. Or a tachometer problem.

tylercamaro

iTrader: (1)

considering theres guys runnign 11's on stock vortecs on 350s and damn bnear same trans setups and gear ratios all over the place id say your engine trans isnt doing something up to snuff. you arent gonna loose what you did over a gear change.

sofakingdom

iTrader: (1)

I don't see the problem in the BOM for your combo; looks to me like it should continue to make power at the moderate RPMs that 3.42s would force it up into compared to the 3.08s.

The simple fact of the matter is, that for whatever reason, your engine's torque vs RPM curve (aka HP) falls off at a too low RPM to take advantage of the higher gear ratio.

If this is not due to mechanical properties (cam) or air flow (heads, exhaust, etc.) then the only remaining possible explanation is tuning.

But one way or another, you need to get more power out of it at the new higher RPMs, which on paper doesn't appear that it should be a problem.

A trip to the chassis dyno with a wideband O2 would be VERY useful. Use it as an opportunity to work on THE SHAPE of the torque curve, NOT on MAXIMIZING the absolute peak VALUE you can obtain (which is little more than bishop-buffing eye candy).

Your torque curve, based on what I can only guess would be your cam properties (correct me if I'm very far wrong, sounds like a flat tappet, maybe 230ish .050" duration on the intake and 238ish on the exhaust) should be at around 80% of peak at 2000 RPM, rise steadily to 95% of peak at about 3500, peak @ 4200, decline to 95% at around 5300, 90% @ 5600, 80% @ 6000. Peak HP should be at around 5200 RPM. I'd expect to a peak of see something in the range of 450 - 460 crank HP, or around 350 - 360 HP and 380 or so ft-lbs at the wheels. But don't worry about the absolute #: be looking at the shape of the curve, and verify that it roughly matches the percentages I gave you at those RPMs. Especially watch for it to fall off to rapidly once it passes through the peak, and be prepared to figure out why, preferably by experimentation (i.e. have a set of jets, a full range of power valves, and maybe springs & weights for the dist) to try out. If I were to guess I'd bet it will run best with a 10.5 pri PV and the jets set for about 12.8 A/F ratio at 2800 RPM on pri alone and the sec jets for about the same ratio at 5500 or so. Should run the fastest at the strip shifting at about 5300 - 5400 and trap near 6000, maybe 5800 or so, maybe 110 - 112 mph depending on exactly what the car weighs.

A drop base air cleaner might turn out to be the culprit... doesn't do too much good to put all that stuff under the hood, then force the air all go through a ½" wide crack on top of the carb from the lid being dropped right down onto the top of the air horn.

brettr81

Post pics of your setup, like the air cleaner you are running, also what is your TC and what stall?

aussiesteve

I am in Australia and will post as soon as i can...the engine guy i had a tune off has serious credentials and got this thing flying before it got hot in traffic with the lower gears and i may even have a blown head gasket or loss of cylinder pressure...he didnt build the motor..but before i run out and buy a 434 shafifoff for $15,000 i may pull this engine and get him to strip it and go right through cylinder pressures as the 1976 400,s were really not performance orientated or fitted with performance crank rods and pistons..i feel i can still get another life out of this engine...its +060 now and did have a tiny bit of corrosion in 1 cylinder and we used cast iron black rings to correct it..but in saying that the night i ran the 13.8 with lots of wheelspin into second it was flying and with slicks i may have run 12.98 or. 13.0 flat...i done my homework in selecting a setup and the cam was a custom based on comp ratio and gears running and intended Rpm.

redneckjoe

sounds to me like you were already having issues with street tires. the gear swap probably made getting traction much harder, thats all.
do you have 60' times like asked above? that might be the evidence right there?

aussiesteve

I also found i had the car in my garage at home while i got the diff gears in it and bilstein shocks on the car...this car seems to need the spark plugs pulled and cleaned if its left sitting...i was told by an extremely good engine guy.that the fuel we have now..our premium unleaded is designed to be sprayed or atomized under pressure.( EFI fuel injection) and when an EFI injected car is turned off the fuel stops imediately..nothing sits in the intake manifold as it only deliveres air in an EFI injected car.... When we run this fuel in out carburetored cars like mine and we drive as normal and when we turn the engine off when we get home and put the car away for a period...the fuel stops when the engine is shut off but there is still a little fuel in the intake manifold...edelbrock rpm...victor...weiand dart intake etc etc etc...whatever...our holley,,or carburetor and manifold still has fuel residue that over TIME WILL TRICKLE INTO CYLINDERS..and eventually foul plugs...it may take 1 month ..it may take 6 weeks...it may take 2 weeks but it will foul a plug or 2 or 3....OVER TIME.. I drove this car the day before i drove to the strip and it had backfire and banging and poping in a few cylinders..so i drove it for 1 hour and it cleared itself....i feel the night i ran the car needed the plugs pulled and thouroughly cleaned or ever drit blasted to clean them up....this has happened before 3 or 4 times and i feel NOW THAT COULD WELL BE THE BIGGEST ISSUE,,,, I also feel because the car reved easily and it ran to 6000rpm all night i looked at other issues. .The time difference in Australia makes my entry on this sute 12 hours behind you guys and i will post 60 foot times tonight and the car is booked in the check the Torque at given RPM on An advanved O2 dyno after easter....i will pull the plugs today and just see whats going on...i will run a basic compression test...this car should run 12.7 or better as is....
thank you for all the advise..keep it comming please
steve in Australia

sofakingdom

iTrader: (1)

I don't believe a word of that crap about gasoline. Doesn't make it "true" or "false"; just, there's WAAAAAAAAAAAAAYYYY too many people with carbed cars that run JUST FINE on it, for that to be the jump-to-the-conclusion culprit, to the exclusion of all else. Not to mention, that has NOTHING to do with a motor running out of steam at higher RPMs.

How far is your air cleaner lid from your air horn?

aussiesteve

Thanks for nothin....and thank you for the engineering brilliance and reasoning..

there are thousands of cars here running od PETROL..UNLEADED AND NO ISSUES you live there..i live here and the fuel is changing all the time to accomodate the newer cars...our older carby cars will eventually come across issuea regarding fuel..weather its shelf life or its compression issues and timing related issues that we didnt have 20 years ago..all associated with the available fuel....yes i have had good fuel and i also have had days where the thing wont go like it did last week sobto speak and i have had to pull the plugs and clean them of unburnt fuel and carbon deposits that can effect everything.....

one guy told me i had a peanut cam and crap heads without even knowing what i had...thats the sort of garbage that does nobody good and shooting from the hip and firing blanks does no good..thanks to the good constructive reply,s and its a simple thing that i will get fixed

sofakingdom

iTrader: (1)

Any time.

How far is your air cleaner lid from your air horn?

QwkTrip

iTrader: (22)

Sounds like your engine really needs a good tune up. Probably has never been tuned well yet. Make sure your dyno time comes with a competent person that will get your engine to run right. Keep in mind that a dyno is only a tuning tool. Getting a sheet that says you make 270 RWHP isn't money well spent. Driving away with the engine tuned and running really well is money well spent.

All the dyno time I have paid for was to tune the engine (idle, acceleration enrichment, full throttle, some driveability). The paper sheet you get is just a little bonus at the end but not the goal.

QwkTrip

iTrader: (22)

Also, your engine speed (RPM) and ground speed (MPH) don't add up, at least the way you describe things. The dyno will tell you how much slip you have in the drivetrain and if that is part of the problem.

aussiesteve

I thank you guys with credible scenario,s..this wasnt supposed to be a drag strip special once a month but its looking like its got potential...yes the tune on the car WAS REALLY GOOD AT IT FLEW the night i ran 13.8 with wheelspin..but it simply got slower and it ran hot one day...i dont trust the brand new gauges either...NVU gauges...bad decision @$1000 a set.... Delivered.......anyway the dyno will show me where it makes power and where.my fuel and air is at what Rpm....i would expect this thing is good from 3500 to 5500.. However with the 3.4 diff and that engine Was advancing fast real fast it was over reving in every gear and costing time....the tune is good..i will see how i go after the machine checks everything AND I CLEAN THE PLUGS AGAIN....WHAT A CRAPPY JOB...THE CAR IS ROGHT HAND DRIVE..FULL 1 3/4 HEADERS AND ITS TIGHT....

QwkTrip

iTrader: (22)

Ya, we get it.... you don't have to keep repeating yourself over and over and over again that the engine is a monster. Honestly, 90% of your content is useless info to the people trying to help you.

One of the few useful pieces of info is the carbon fouled spark plugs. The engine is running way too rich (too much fuel) when driving. Likely so rich that the entire combustion chamber is loaded with carbon and that will hurt performance. It can keep valves from closing all the way and cause pre-detonation (engine knock). If you remove a cylinder head then you would probably be appalled at what you see. Also, spark plugs with special coatings on the tip (such as platinum) will be ruined if you rub it down to clean it. This will exacerbate the problem by promoting poor burn of the fuel.... and wet spark plugs. Basically, you might be experiencing a snowball effect where things just get worse and worse over time, but it all began with a really bad tune. You really need to get a professional to help you with this because frankly you are clueless. You know, sometimes our strength is knowing what is our weakness and letting somebody else do the work.

13.8 seconds is no slouch but it is not tremendously quick either. You should have no trouble finding time to move a shifter just 2 times and even sip on a drink in the last half of the track. You just need more seat time (experience) to get used to it. Probably just a month of driving and everything will feel "normal" to you.

Don't equate tire spin to being fast. There are a lot of slow 15 second muscle cars that will shred tires. A lot of the spinning will stop if you make some adjustments to suspension and/or get better tires. Part of the reason the tires spin so aggressively is because you have such shallow gears for freeway cruising. Once you break loose you can generate tons of wheel speed for a huge, smokey burnout. The 3.42 gears will give you more control of the wheel speed so you can drive better on the edge of traction. I guarantee the car is faster with 3.42 gears, you just need to sort out the problems with the car and become a better driver.

sprojam

poor guy following eyes still burning and probally still can taste the gas

sprojam

still no 60 foot times bench racer.

aussiesteve

The car had 3.08 gears and 255x60x15 tires @27 inch BFG T/A Radial Brand New on 8 inch rims


Left line at 1500Rpm with 2000 Stall TH/350 drove car manually changed at 5800 and panicked all the way..chasing the other guy who ran 12.98....i wasnt watching my Tach too much and just glad to do it first time up.


60 foot 2.089
330,, 5.892
1/8,,,8.970
mph,,,80.56
1000 foot mark 11.617
1/4 mile 100.87mph
13.853 time 1/4 mile ET


put the 3.42 gears in it and it felt like the engine was great but thinking back it wouldn,t pull but reved like mad to 6100,,6200,,


i thought i was going to run a 12.98 or faster but got a rude shock.

aussiesteve

The engine is not a monster and its not my idea or a hot rod,, its basicly garbage and i will get it out over winter... but i am in Australia and we cant drive 5 miles down the road and pick up 10 more blocks for $200 each like you guys can,,so i work with the garbage i have and the Air Fuel Tune Guy can see where its at. Thank you. the 60 foot times are below,,thanks again

sprojam

good stuff keep us posted.

pancherj

I think you have either a fuel delivery issue (running out of fuel in the higher RPM's) or you are floating the valves at higher RPM. Your 60' wasn't too bad for street tires. You went 80.56MPH in the 1/8 mile, but only went 100.87 in the 1/4. The 20MPH gain in the back half is not great. This engine should get you into the 12's. I had a similar 406 in a 1975 nova. It would pull about 82MPH in the 1/8 and 108 in the 1/4. It went very low 12's (12.10 I think). I had 3.73 gears and a 28" tire and it definitely needed more gear! I was crossing the stripe at something well below 6000RPM.

QwkTrip

iTrader: (22)

Gosh, now don't swing hard in the opposite direction either! You don't have to defend it or trash on it. Just stay on topic with the issues that you are experiencing and things will get sorted. It is actually pretty impressive that you went 13's with the horrendously sucky gearing you have (3.08 gears and 27" tall tire). You're about to go a lot faster after tweaking a few things.

antman89iroc

My experience has been that mild gear changes don't make drastic ET differences. 1/8th mile anyway. I went from 3.27 to 3.7 and picked up .05-.10. (faster, lower et) I then went from 3.70 to 3.50 and couldn't really tell a difference (directly related to gear anyway) I can also share that my car seems to vary quite a bit depending on conditions and my "driving". I do run a stick which is more hit or miss but there's probably a real .2-.3 difference due to temp, humidity etc.
You can look at my sig but similar size engine and it runs about 8 flat at 88 in the 1/8th with 1.80 60ft's.
Tune then traction before I would change gears again.

aussiesteve

Thank you sir...this is the sort of thing i need to hear..my problem is i havent had a car like this since the 1970,s... The car will be on a dyno that maps fuel air ratio across the entire range..it can give us spark plug sellection and changes. And fuel issues and a compression test will be done on that day after easter..yes i agree with the gear change you mentioned thats why i sellected the 3.42 to begin with.steve

aussiesteve

Thank you sir...this is the sort of thing i need to hear..my problem is i havent had a car like this since the 1970,s... The car will be on a dyno that maps fuel air ratio across the entire range..it can give us spark plug sellection and changes. And fuel issues and a compression test will be done on that day after easter..yes i agree with the gear change you mentioned thats why i sellected the 3.42 to begin with.steve

antman89iroc

I would look for something limiting power on the top end, 35-4000+. Possibly too much timing coming in or a fuel problem on the top end. My guess is it was there before but the lower gear, and higher rpm, helped unmask the problem. Of course there could be converter/trans problems or possibly the rear was still "stiff" from the rebuild if new bearings were installed and it was set up tight. I just built a rear and put over 1000 miles on it before going to the track.
Or maybe you accidentally popped the shoot at the 1000' mark.

aussiesteve

The rar end only had 300 to 400 miles on it on that day i ran bad.


I am getting an O2 sensor fitted to the exhaust before the cat and it will be driven on a dyno and monitored and we will illiminate all the gueswork and check fuel pressure at RPM and air fuel ratio sorted and possible valve spring binding at high rpm or valve bouncing,,i run stock vortec springs and we will see how we go after easter,,on paper this car should run 12,s even with the crappy stock bottom end and 8.5 compression.....it revs fast but has no torque or power like it had, AND its rich and on the night it had 2 wet plugs but no missing..we will sort it out and todays tune up gear can find the issues and we go from there.


I am confident of a low 12 and my last run i wasnt panicking and took in all the important surrounds,,the first time i run a 13.8 i knew i could get a lot better and the whole thing wasnt a freak out world series home run type feeling.

NoEmissions84TA

iTrader: (1)

LOGIC says the problem is whatever you touched last right before you ran slower.
And that would be the installation of the 3.42 gears. You definitely should have run
faster with the gear change. Something is dragging in the rear end.

86White_T/A305

No doubt your issues are going to stem from more than just a gear change. From what I see..the gear change is just opening your eyes to the other underlying issues that need attention.

It doesnt matter what the engine was built for..drag racing..cruising etc..if the engine isnt setup to run right..and the trans/stall not setup to match..the car as a whole just want feel or perform right period.

I think that motor with a proper stall with the 3.08 gears couldve still had a better time if everything worked in harmony than your best 13.8et,the gear change shouldve only helped you your et..nothing crazy..but helped for sure.

My opinion, you should tackle 1 thing at a time.making a car happy that will make you happy will take a level head in chassing down problems. Dont jump all over the place and expect the car to just work perfectly. If you know the car isnt running great..have it tuned/fixed as best you can. Then dig into that th350 and the converter..i think your issue is really in here also for transferring the engines power at the right time and staying in the power band is hurting you.once that is buttoned down..look at the rearend..and suspension. Are you hazing tires too easy..might be time to get better tires..when the car hooks..and everything infront of the tires work well together..that cruiser of a 408ci..might just surprise you! Trust me..i used to just rush into problems and throw parts at the car and hope it would go faster..it only costs me more money and time wasted. Solve 1 problem at a time and it will all come together..get the engine right..checked that the trans/stall are setup for that engine,try some stickier tires or practice launching the car and not spinning like crazy..record everything you can about each pass at the track.Your rpms for launch..tires pressure..shifting points etc..all this will only help you in the long run.

sprojam

you will get there takes time sounds like you are on the right track

aussiesteve

I allways thought this car ran extremely rich and it was never put on an o2 machine to map whats going on,,i feel i ran with wet plugs second night with the 3.42 and the 3.42:1 with 27.3 inch tires like i have brings the rear end to 3.29:1 wich is moderate.
the 3.08:1 diff i had with 27.3 inch tires like i have took the diff to 2.96:1,,thats the reason i took it down a little..


i feel its geared well and has a really top Th350 built by a fellow here thats been doing GM auto,s since the 1960,s and never had 1 fail and 99% are used in hot rods and modified cars that race,,a one man outfit that i known since 1975.


He fitted one of the GM high pressure oil pumps and it changes extremely well and the harder you run the motor the harder she changes.


The car has a full Spohn suspension and crossmember kit and i will double check the pinion angle that is at 1%


To be honest the Tune up fellow is old school carby older guy who has asked me to get an o2 sensor fitted and take it to him and he said we will get results on the day.


Anyway enjoy the Aussie racing below

aussiesteve

Took my Carby to an old school Carby guy who works from home.
He first looked at the car and the cam specs etc and general condition of the problem.
Fouled plugs regular.
He looked at my carbs and told me to bring my near new street HP 750DP that got no choke housing to his place and let him go through the idle circuit and modify the carb for MY MOTOR..


He also adjusted the entire thing and more or less blueprinted it for MY ENGINE ALONE.
I was asked to have an o2 sensor plug welded into the exhaust y pipe and we took the car to an Advanced Dyno and ran the car.
it needed big changes in the linkages,,the throttle cable and it was running out of fuel at 5400rpm.
Fitted a Carter 110Gal Pump with a return line setup to keep a constant 6 lb at wide open throttle and all times.
The carb was pulled apart 2 or 3 times to get it setup perfect and it took all up 1 1/2 hours.
Took it to the drags and ran 13.3 @106mph on street tires.
and the dyno showed the engine @ 405hp with real good torque.
i changed gears at 5500rpm and still spun the tires into 2nd and crossed the line at 6100rpm and it was movin fast.


a set of good tires will i think get me into the 12,s with no more fouled plugs,,,EVER.
thanks guys and we DRAG ON.
steve in Australia

Z28FAST1

Looks like you are getting it sorted out. What's your 60 fts?

Orr89RocZ

iTrader: (20)

I was gonna say a good condition 400 with vortec heads and that cam should trap way over 100! 100 is bolt on L98 350 numbers. I still think 106 seems slightly low unless way heavy of a car, like 3600 lbs heavy. But it definitely is alot better than previous numbers.

aussiesteve

I ran 41 times and thought i was at gas pedal to the metal,,,flat out,,,,3rd run i noticed i still had 1/4 throttle left and it ran real good and last run ran over 107mph but i am running 3.42 gears ,,i feel i should be ar 3.23:1 and M/T street Slicks could help the wheel spin.

aussiesteve

I meant to say i ran 4 times not 41 times

aussiesteve

60 foot 2.058
330 foot 5.703
660 foot 8.669
1000 foot 11.238
ET 13.372
mph 106.67


street tires, BFG T/A,, 255/60/15,
3/4 tank fuel,
cold,windy night

QwkTrip

iTrader: (22)

You are still in 2nd gear at the end of the drag strip, aren't you?

Your car will be a lot faster if you put numerically higher gear in the axle.

aussiesteve

I am well and trully in 3rd.
it has the MSD setup to advance fast and it revs fast and gets moving quickly.
i am crossing in 3rd and at 5800 to 6100.

aussiesteve

the distributor guy changed the springs to get full advance fast at wide open throttle and it revs fast


the distributor guy and carb guy i used set up the front runners in that road racing video i posted,,very good guys who get great results.
my car is basicly not what they do but its got potential

newbvetteguy

Folks,

If Steve's HP peak is at 5,500 how much could he move that up by retarding the cam 3-6 degrees? Would that help his the ETs?


Adam

aussiesteve

the engine seems to. rev well past 6200..i didnt ask the dyno guys where it starts to drop off in hp numbers but i will ring today...he did give me sheets with praphs frpm my tune but they are not the ones i think i need....it had 1600 torque 309 rear wheel hp but no mention at what rpm on the graph..and 1600 torque?? i need ft lbs to become familliar with what i am accoustomed to.