I'm working on dialing in my Vette. It's first runs were using the 7+ year old 26" slicks and it did some low/mid 1.60's and had to walk it out of the hole.

New cam/header/trans combo along with 28" slicks netted a 1.55 60'. Overall gearing was about the same at the end taking new tires into account by changing trans ratios.

I've got several new changes going on that will allow suspension to work much better and I'm considering getting the 29.5's since I need some new slicks anyway. The 28's were borrowed.

I haven't dyno'd engine since new cam, but I expect peak Hp is around 6400-6700. Right now I'm crossing line right at 6500 or so.

The new tires will knock it down to the 6200-6300 range maybe, but hopefully will allow it to launch much harder and pull some low 1.40s or so...

So what experience have you guys had? My gut is that I'm better off getting better 60's.....

For reference, it's a pump gas 540" all motor deal with a 5 speed. It has 3.07 gears with a final drive ratio of 4.08 in 4th gear.

So far it's pulled a 10.04@139.96.....

I need a 9 sec pass bad!! I figure mph is in the game, so I'm not messing with engine...but the 60's are terrible. I figure that's where the most gain is.


JIM

If anybody's application called out for 29.5" tall tires - yours would be that car!

I would be confident that the longer footprint of the taller tires will quicken your 60' times. It will also put more of a load your engine earlier in the 1/4, which will draw more fuel and make more power. Distinctly possible that you will run more mph, even with the negative change in effective gearing.

I'm getting ready to move my axle further back to allow the use of 29" or 30" tall slicks, vs the 28" I currently have (the wheelwells on my old '65 are small, not helped by the 5" of lowering). I am expecting quicker 60' times.

Thomas

Very interesting topic, Jim!
I've recently discussed going to a 29.5" tall slick (from a 28") and was conserned with the reduction in final drive ratio...presently at 3.73 & a TH400.
I'll be following this one closely...

Bill, do you drive your Chevelle on the street much or is it strictly for the track? the one with the 540 in it :D I too am thinking about going to a 29" slick also,just to put a little more rubber on the ground. It seems to me that a 540 or in my case 505 would have enough torque to overcome the increase in tire diameter.

Jim, I'm going through this right now. I previously ran 28x10.5 ET drags and had run a best of 10.45@127.9 with a 1.492. I recently did a mini-tub and switched to a 29x10.5w Hoosier. Tonight I ran a 10.42@127.9 with a 60' of 1.454. The best 60 of the night was 1.448. Looks to me that the taller tire helped the 60' but no mph improvement and the 60' improvement translated to a 1:1 gain at the stripe. I'm gonna put some more gear in it to get the finish line rpm up. Now with the taller tire its crossing around 65-6600 and pk power with this motor is 6900. I'd like to see it crossing around 7200. At least now I've got some bite to work with when I change gears.

Hi Jim, I just got the corvette magazine with your car in it. The best idea would be to get a new set of shorter slicks as the attitude of the car will affect the 60' more than cutting back the gearing. Since it's not overgeared in fourth it would definately slow down markedly with the taller tires. You would also have trouble fitting the 29.5 tires into your wheelwells. When we geared my sons car back to 3.89s it lost over a tenth and it had about the same horsepower and torque as your car plus a torque converter to get it moving. The 10.5W x 28" E.T. Drags on a ten inch wheel ( Weld Alumina Star 2)are the best biting tire we have had on our car, period. The car now cuts low 1.3 - 60' times.

Originally posted by Rapid Robert:
Bill, do you drive your Chevelle on the street much or is it strictly for the track? the one with the 540 in it :D Bob,
The '70 is licensed, insured and is driven on the street very often. The car was built with this in mind...pump gas friendly.
It's been to more cruise nights than race days. ;)
You're right about tires, of course. I'm presently using ET Street radials when in street trim.

This is interesting, wish I had a few sets of wheels/tires to try. When I talk to Super Stocker Vette guys..who are nailing high 1.30's/lo 1.40's and running mid 10's...all the way out to some 8 sec guys with IRS setups...there really isn't much that they do to make them work overall. Most run 28-30" tires..not wide...just tall as possible. They limit rear travel and let control arms go solid against adjustable snubbers, they use a stout rear spring and some adjustable shocks and that's about it. They even say that they just jack it up as high as needed to fit bigger tires even if it looks dorky I guess!

I have too much travel on rear suspension and my car goes through some pretty wild gyrations in first gear as it loads/unloads suspension. It settles down when I grab second gear (gets 4-6" of air in second gear under both front tires) and goes great from then on.

I'm going to extend snubbers, change shocks along with new slicks. I spoke with M/T and they said that a stiff sidewall deal would help. They said it was basically the same construction as an ET Street. Not sure with the IRS setup how it would effect it. If I set snubbers to hit, the added cushion of a regular tire might help.

I have suspension designed to minimize camber change on launch, so that's working well.just gotta cut the bouncing down some!

Since I'm definitely not overgeared in high gear, I'm concerend about what you said Harold. Without a converter to help...it's going to have to really work hard without a gear change. I'm not worried about the first gear mutiplication....I can always adjust launch with the "variable stall speed" option the clutch allows! The fact that you guys have that Chevelle running like it does on a 28" tire is amazing.

It's intersting that Mike didn't change mph much even though the taller tire really has you going through traps way below peak. Wonder what will happen with more gear to let it get there a little easier? The added gear might let you use the taller tire better too.

If I keep pulling rpm back, I'm going to have to re-look at whole combo..right now it stays in the 6500-6700 range at the most. Hopefully helps parts life!


JIM

Jim........sounds like my kinda ride :cool: where can I see some pics?

On stick cars you want to go thru the traps at approx 300-500 rpm above where your motor makes peak horse power, So seems like you need a deeper gear and with 29.5 tires and new gears your e.t. will come down you should hit 9's...mike

Ok......we have something going here :D How about a 9.85@136.10....with a motor that leaked water like Niagra Falls......71 nova 355,5speed. :cool: BTW,14-32s with a 3.05 low and 5.43 final drive smile.gif

69 Rally Green..tell me about your car. Sounds like my kind of stuff!


JIM

graemlins/clonk.gif

Originally posted by 540Hotrod:
69 Rally Green..tell me about your car. Sounds like my kind of stuff!


JIM Jim if i had your car i would put a 5.00 gear or better in the rear, 29.5 tires, Thats what your cars calling for, and then you will see deep 9's if you can shift it, I have a hard time shifting, And im thinking about an automatic and some nos if i keep it on the track, Then ill see 9's, Im thinking of a little more street now, My dad helped me pick the combo, he was running 9's in the 70's. Its a 460,4 inch callies crank lunati 6.385 rods CP pistons 12.6 compression ratio solid cam good aluminum heads m22 four speed and a 4.88 gear 29.5 tires, nothing like your set up though, car looks like an old super stocker, Its jacked up in the front to, I am in the middle of tuning it down for some street cruzing, Im going to change the gear intake and some retuning so i can enjoy it more, Let me know if you need any more info...mike

Originally posted by 69ralleygreen:
On stick cars you want to go thru the traps at approx 300-500 rpm above where your motor makes peak horse power, So seems like you need a deeper gear and with 29.5 tires and new gears your e.t. will come down you should hit 9's...mike Also you need 5 inches of travel in your front end to hook!! I use global west bushings ...mike

I gotta keep the 3.07's for "Viper Hunting" as needed! Trying to do "best of both worlds" stuff you know?

I have G-Force trans...no synchro's, straight cut gear etc..shifts great. Much better than old Doug Nash. It was fine until HP and RPM's really got up there.

It's no lightweight either..it's 3600 lbs with me in it...sure be nice if it was a few hundred pounds lighter!

I think the 60's will definitely like the 29.5's,,,,just not sure about actual acceleration through the rrest of the track. Maybe some header extensions would help it pull back some RPM?

JIM

Viper hunting (i love that) well you have to compromise sometimes you cant have your cake and eat it to, But what about a little nos that will bring your rpm higher and then the viper hunting will be more fun, But to get the most out of the car for 1/4 mile you need to change that gear for it to cross 300-500 rpm over hp range thats the trick, Or just add a small 100 shot thats all it would need and you dont have to touch the timing either, Thats the compromise NOS...mike

Before our Chevelle ran nitrous we tried the 10.5 x 29.5 M/T E.T. Drags on our car and they just never worked nearly as well as the shorter tires. I suspect the side wall is stiffer on the 28" "W" tires as well as having slightly wider tread (11") vs. (10.5"). This particular tire will put 3-4 feet of daylight under the front tires if you jack up the N2O hit up to the 200 H.P. level, but comes down kinda hard. Whatever you use, get a wheel that is nearly as wide as the tire. We have ours on a 10" Weld Aluma Star and this setup works great. I believe if you get a snubber that will cut out the unwanted suspension travel after the initial leave your nine should be pretty easy to get as you have plenty of power to get you there. The last cam change seems to have matched the powerband to the gearing much better. Six MPH is nothing to sneeze at. Now to go out and humiliate some vipers. A 150 shot of juice and you could use fifth gear.

540,

I'm curious as to what your first gear ratio is as well as the type of clutch you are using and how it's set up?
I have a family member that has a 66 vette that runs 9.40's at sea level and he's still tuning.

But before I give any ideas, I'd like to know more about your combo?

Trans ratios?
Clutch type / setup?
Peak torque RPM ?
Does your car have a rear-end traction bar?
Launch RPM?

MSFR.....

Oh yeah..make me give it up first huh? :)

No problem....I don't have any secrets...I just do this stuff for fun.

Trans...3.25/2.22/1.65/1.33/1.00
Clutch- Mcleod Street Twin- Dual Disc- 1600# static
Peak TQ rpm- Don't want to lie...not sure....old cam was 5300 rpm on dyno..I expect this one is right at 5000 maybe.
Traction Bar- No...I have a custom built Dana 60 that was made into an IRS setup. 3.5" halfshafts/1480 joints etc. I added a small "wing" on the rear of the "sombrero" crossmember mount that is attached to the welded in crossmember behind diff. When diff tries to rotate, it "pulls" down on the wing that is attached. Works well holding diff still.
Launch rpm- tried several different approaches. Usually only around 4000-4300. Really needs to be higher but traction isn't good enough yet. Plus I probably need to go to a softer slipper type clutch so it won't hit tires so hard.

So tell me about the one you knopw of...any help is good! Saves me some trouble..I don't get to track that often, so I like to make it count!


JIM

540,

Here's my .02 for what it's worth. Take the good and throw out the trash if it's not something you would agree with.

Changing your tire size to get a larger footprint is a good thing, but all the numbers being equal, your 60ft time will slow down with that larger tire. Like running a taller gear, which I'm sure you already know.

If your 60's improve with that new tire, I feel that it's covering up another problem. If it's traction, then that needs to be solved first. "Loading the motor" to make it deliver more fuel, hence more power is fiction. BSFC on your dyno sheet will show what your motor is doing with the fuel. Lower RPM on a load will not help. Look at an under-powered car going up hill in too high off a gear.

Your clutch is a big limitimg factor in your setup. I know that you want to chase vipers, but 1600 lbs static is (most likely) what's causing your car to hop off the starting line. Your clutch is grabbing so hard that it bogs the motor and then unloads the chassis. (My Camaro did it with a street clutch also. Took 2 years to figure out how clutches work and by that time I was ready for an automatic.) So your just waiting for the car to settle down and the motor to recover some RPM before it can get power to the tires and track.

If you talk to the Stk/SStk crowd, most of them are setting up (single)sintered iron discs with 300-700lbs static load and then allowing the weights in the pressure plate to increase the pressure as the RPMs increase. Their clutches are just on the edge of slipping in high gear. Most of the time.

A properly set up clutch WILL slip on the starting line. Your trying to maintain RPM on the launch and if the clutch doesn't slip then it pulls the motor out of the powerband and if it grabs that hard, something has to give and it's usually the tire(loss of traction) or drivetrain parts. Sticks are very hard on cars which I'm sure your wallet has seen in days past. If you've ever seen a playback tach in an auto car, you'll notice that when the convertor flashes, the RPMs stay there and then continue up. It "slips" until torque multiplication takes over. That's why you see a lot of cars go quicker with an auto trans. It's usually due to a poor or mis-matched clutch setup. So see what you can do there first. Call clutch people to figure out exactly what you need or want. Maybe yours is adjustable.

Reguardless of what clutch, you need to launch much higher. Stick cars do "pull" the RPMs down so you really need to be above your torque peak on the launch. Whaen the clutch grabs, ideally you would like to be no more than a couple hundred RPM below your peak. Thats when the car will 60 ft the best. If yours is 5300, try launching at 5800. If your skitish of that much RPM, at least launch at peak torque. I launched at 6000 and my motor only made about 550ft lbs at about 4700 RPM and it still pulled my motor down to 4200-4400 with a mis-match clutch.

One other thing while I'm rambling. Your trans gears in your G-force are making your car think it's got a tall rear-end gear. So the taller tire will compound that. A VERY GENERAL rule of thumb is that your first gear final drive ratio should be about 12/13:1 for a bigblock/stock eliminator tired car. Larger tires can affect where this number wants to be also. Your's is only 9.98:1.

G-Force can help you out there if that's an option you wish to consider other gear choices and still retain that 3.07 rear.

My Uncle's vette has a 4.06 first gear and a 3.07 rear gear and still keeps his RPMs reasonable on the street. G-Force worked with him extensively to get the right ratio percentages to run on the street and the strip to optimise his combo.

Hopefully this rambling will help out, but do some research on that clutch first.

Rob

Jim, I think Rob is right on about the clutch. I have an old stick shift Chevelle and never did get the clutch thing right, but going up over the torque peak did improve the leave. The M/T 28"W tire will outperform the 29.5" tire and the 28" has a stiffer sidewall so it wont "grow" downtrack and get into your wheelwells (this Will be a problem with the 29.5 tires). Again the shorter (28 inch tires on a 10" Aluma star 2 wheel) will stand your vette on it's bumper if the pressure is right. This tire is like nothing we've had on our car before. 1.315 - 60'

Thanks a lot!

You've pretty much confirmed the stuff I knew. When I got the Street Twin from Mcleod..we had lots of tech discussions about it. Pretty much circled around "how much was street...how much was track?" type stuff. Since it really is more of a street car that only sees track a couple of times a year at best, I went with other clutch. It's really not adjustable to the point of a Soft Lok or something like that.I've used "hockey puck" clutches on the street before with great success, but not a pure sintered iron one. I know lots of folks are using them and I'm working on changing it over now. I live in Houston and the real possibility of getting stuck in traffic is good. Most folks I know of with them go through flywheels as much as anything, but I suppose that's the cost to play huh? I have friends with one in a low 9 sec LS-1 Camaro (high 1.20's 60's) that has lasted 4+ years so far. Mcleod says they aren't slipping it enough!

I went through lots of combo's with G-Force when I ordered mine. Surprised to see someone else using one with 3.07's. Anything more you can tell me about car? Someone else as sick as me? Is it an all motor car? N20? Boost? Any info on rear end setup?

Mine makes lots of TQ--700 ft lbs or so..that's where G-force figured they would give up some first gear. How is your uncle's trans set up? Is it clutch type or clutchless? Does he use any type of interupter to stutter engine on shifts, use clutch or just pull it?

Thanks for the info....anything more you're willing to help with is appreciated. If you want to do it off line that's great too!


JIM

540,

What is your car?

I'll try to give you a briefing on my uncle's car. Hopefully I'm not giving anything away that he doesn't want anyone to know and he made so many changes last year to run at the Hot Rod pump gas drags I'm not sure if I'm up to date anymore. We used to wrench on it quite a bit together until he did all this new stuff and now he's had to leave it in the hands of pros.

-66 Vette
-Dart Big M block
-Short stoke 480CI
-Dart plus 2 heads? worked and reworked and so on
-Roller cam-don't know the specs(265 @.050)700 lift I'm guessing
-N/A motor 746HP on the dyno, haven't tried the new intake and the 1050 carb yet. That I do know.
-G-Force 5spd-clutch type, reworked so he doesn't have to but he's too chicken to pull w/o the clutch :)
-Sintered iron (McCleod?) set up by a very well known SS racer (still working out the bugs)
-Custom CNC'd billet alum rearend, IRS retained
-Went through approximately 6 sets(no kidding) of wheels to find the perfect fitting 28" tire (custom Bogarts/Lambs/Monocoques)? 10" rim 11.5 tire and it just barely fits but it works. Who knows maybe a new set that I'm not aware of now:)

Launches off a plain old 2 step at 6800 I think, shifts at about 7000, traps at 7200-7500 depending on the elevation.
9.70 at the pump gas drags on a shake down run, but had to pass on the other 2 runs. Broke a throwout bearing or something?

750lbs static pressure and drives it on the street with no problems. One thing the clutch guys told him was to not feather the clutch like you would in a normal street car at a stoplight. He kind of has to just "let it out" when the light turns green. (Be ready to go) I've driven it and after about the 3rd stoplight you get it figured out and it's a piece of cake. Tranny sure is noise with those straight cut gears though.

Rob

One thing I might add is about Harold's post. He's right about the a 28" tire working just as well if not better than the larger one, but I need to add that with the IRS I think my uncle found that the regular slick worked better than the stiff side wall. Since an IRS doesn't typically work as well as a solid rearend car he used the softer sidewall as part of the suspension.

Hoosier makes a great tire for 16" wheels and 28" tall if that's an option.

Rob

That's got to be the gorgeous black coupe huh? I've been really hoping that Hot Rod would run some more features on it. Not often you see a stick shift big block midyear running 9's!! It was a bummer to hear he had clutch troubles.

The 480" engine is generally a high rpm screamer....sounds like fun!

One of the issues the Mcleod guys told me that swayed me a little, was that *if* I was running around at relatively low rpm and nailed it, the clutch was going to slip a good bit until rpm got up there...think "Viper Hunting
again from a 40 mph roll or so.....I guess best thing is to rev it to the moon and sidestep it from a roll to get it going huh?

Is the IRS based on a Heidts type 9" deal?

What kind of MPH does it usually go? Weight? I need to find folks that have been messing with one of these...we're pretty rare!

I sent in entry for PGD's...but they were pretty clear that my "lack of NHRA" type equipment was going to keep me out. Didn't like a convertible without a cage doing this stuff!


JIM

Thanks for the tire info. That was another question. When I spoke with M/T the other day, they said all indications would be to try a stiff sidewall tire due to wieght, stick and HP. But I was figuring same deal that with IRS going essentially solid against snubbers, that a little sidewall action would be needed to help cushion it all.

They said the stiff sidewall tire was basically an ET street construction.

JIM

540,
Yes it is the black one in the magazine. brand new paint job. He hates that huge hood though.

You are correct about nailing it at low RPM. I thinks that's where his clutch problems started. They definitely like heat. I think if you met up with a challenger on the street, your right about either beating him at a rolling start(cruising) by re-dumping the clutch or just nailing it at a stoplight, but for cruising it works great.

The rearend is a one off that I believe uses 12 bolt parts(more efficient) and that's truely all I know about that part. It was cut from a 300lb billet aluminum block.

3100lbs w/driver and he's trying to get to that elusive 140mph mark.

You still didn't say what your car was?

Rob

540,

I lied. My uncle's running a hoosier 16" radial, not stiff sidewall(DOT Street?). The reason I remember is that his tire pressure is about 18-22lbs in the rear.

Rob

mfsr, Jim's is the cover car on the February, 2005 issue of Corvette Enthusiast and is a metallic blue, '67 convertible. It has a 540 Big Block making about 825 H.P. (story starting on page 33). In my opinion this is the best looking Corvette ever built be it convertible or coupe. The pump gas drags were neet but i noticed all the cars slowed way down on the third pass, probably was a running out of nitrous thing. A couple of other cars would have won if they hadn't had glitches. The '68 Corvette would have won if his ignition box hadn't overheated on that drive thing. I don't know of any fast car that doesn't require tuning so the closed hood thing was stupid since the gas tanks were sealed anyways. The white Chevy II's, (#13), roll bar was only Legal down to 10.0 since it didn't have a halo an the extra down legs at the dash so the whole premise of safety rules was kind of phoney anyways. If you know the writers of the magazine they kind of change the safety rules. By the way, your Uncle's vette is neet.

Harold,

I heard about some of the tech stories. "Got a helmet? O.K. your good to go" kind of stuff. My uncle took every safety measure that NHRA has just short of a 7.50 certification and he was rather disappointed in the lack of safety checks there.

Yeah there were a lot of if's. My uncle's car doesn't have nitrous and I think his one pass was a 9.70ish and he did exactly what the McCleod guys said to avoid. Not enough heat in the clutch and then got on it and burned it up enough not to make all three runs. Had everyone been in top form I would still have hoped that he would have been in the top 10-15. Pretty good with no juice.

I thought I herd that they were being hot lapped so that's why they may have slowed on the last pass, not sure though.
Is there a place on the web to see Jim's car. Sounds like a nice one. Allthough I am partial to black when they're painted right. :)

Rob

I think someone posted the Magazine Cover picture on this board somewhere. The guy who got picked from here didn't have any juice either, Mel Graham, # 8 and was the fastest motor only car. We never see him out here at the strip as i'm sure he doesn't want to get thumped by some of the faster machinery that occasionly comes to the midnights. The Vega that does drive the streets here regularly was probably the fastest real street car in Tulsa, but was passed over by Hot Rod. The N2O probably wouldn't have lasted three runs if only one bottle was used and this is why i think everybody slowed so much or the track had dew falling from moist air that might have caused traction problems. mfsr - I found the post about the magazine article on Jim's car and it is a few posts up.

Thanks Harold for putting up the link again. I've been off-line for a few days doing the Christmas thing...

Rob...sorry I missed your question on what kind of car it is....

I've had quite a few of the "life in the slow lane" cars with tons of gear, converter, two stages N20, etc etc. This time around I really wanted to keep it something we could jump in and drive around abywhere we wanted. Has to be pump gas even at the track, no bottle etc. Plus wife has to be able to cruise in it if she wants to! I've had several mid year Vette's before and got convertible fever a few years back and had to build this one. But you know how it goes..they all start out simple....when I first put it together I used a nice little oval port 427 I had with a Doug Nash. Ran 11.20's@123 through 2.5" pipes. That was with stock rear stuff that scattered regularly. If I had the rear end setup I have now I'm sure it could have made a high 10 sec pass.

Just like always, I find myself tweeking them until they get further from real street use, so I'm trying to keep myself from doing that this time. We drove it the 2000 mile round trip from Houston to Bowling Green Ky (where magazine stuff was shot) with no issues. We're going to go again this May. It's a lot of fun to actually drive this stuff..and if I can nail a 9 sec timeslip before then, I'll be a happy camper!

Man, I gotta put mine on a serious diet if he has his down to 3100# with driver! 500# off mine would be hard to come by without lots of digging....I better start looking! Better cut back on some of that holiday food too!


JIM