best gearing for carbed 3rd gen?

[C4RACER]

I am in the process of switching from a locked rear to a T2R, and while I'm in there I have the opportunity to switch gearing.

 

Car is the #82 Kevin Hall carbed 3rd gen Camaro. The motor currently makes ~200rwhp and maybe with a few tweaks I can get another 10-20hp out of it. So far I've tested at BW and THill, but I am not going fast enough with the car yet to know what gearing it wants.

 

Current gear is a 3.42. Would the car benefit from a swap to 3.73's?

 

I may switch to a TPI motor at some point, but plan to run the carbed motor for all of 2007 assuming it stays alive.

 

Any tips from you carbed 3rd gen folk? The few, the proud? (or something) Hey - we are more like a NASCAR ride!! (or something)

 

Scott

[Tony G]

Carson and John can answer this best, but I would use the 3.73 gear.

The 3.42 was great in a TPI car though.

Tony

[Lady in Nomex]

I second what Tony said!

[Carson]

Greetings Scott , good to see the ole red,white and blue 3rd gen back at the track .. the 3:73 's are the best to use . I bought yukon gears from Randy's ring + pinion ( 800-347-1188) for $187 plus install kit $ 90..

give me a call for more info 805-344-5901

[Richard Pryor1548534703]

It all depends on your redline....if you're not going over 5800 I'd use the 3.42's...if you can regularly pull 6500 I'd definitely use the 3.73s...that's what we just put in our new build carb CMC car...and we're up to 228 rwhp and use a 6800 redline...we just did a shakedown run and played with the shocks...this thing is a rocketship...did a drag race with a TPI CMC Camaro we're fine tuning for a customer and this car screams from 4500 to 6500 rpm and left the TPI in the dust...watch out for 2007...this is the car that is going to win...and of course it's for sale.

[King Matt1548534716]

A 6800-rpm redline? That's just one more reason the carbed Ford 5.0Ls need to have a spec flat-tappet camshaft option like the GMs do. A roller cam 5.0L is lucky to hit 6200 without floating the valves, and the stock flat-tappet cams are done making power by 5 grand. Maybe Santa granted my Christmas camshaft wish in the 07 rules.

[C4RACER]

My motor seems done by 5500rpm.

[Richard Pryor1548534703]

Nah, Matt, he left you a lump of coal...blue, of course.

[jeffburch]

Where are my waders ?

 

Look at your dyno sheet.

 

 

3:42's for an experienced driver.

73's for a Novice.

 

 

jb

[fastjohn]

We use the 3.73 gear. Seems to be a good match. The cam you have in that motor is only good for making power to 5500 rpm's then it will start falling on it's face. Carson's and our car with the cam you have make about 221-224 hp and 270-274 ftlbs of torque. At Infineon the car ran a 1:58 and carson's car with Nick Steel driving ran a 2:06. I could only get a 2:07. I've driven around the # 82 and the 3.42 difently hurt it in acceleration. We usually shift between 5500 and 5700 and we have a memory tach to verify this. Hope this helps.

[Carson]

NOTE... Nick Steel turned that 2:06 in my 3rd gen firebird @ Thunderhill during our one and only cmc enduro

[GT4Point6]

NOTE... Nick Steel turned that 2:06 in my 3rd gen firebird @ Thunderhill during our one and only cmc enduro

 

In which the Ford Mustang of Margetta/Guaglione/Sciuto WON! with stock 3.27's.

[Tony G]

Geez Kevin, just think how much MORE we would have beaten them if we had some 3.73's!!

Tony Guaglione

[Richard Pryor1548534703]

Scott...and other carb Camaro/Firebirds...yes, you're going to fall in the 220/275 range unless......you do as we did and spend around 8 hours on the dyno and the lift working with exhaust....the secret to 10-15hp and more torque (especially the torque over the racing band) is in the exhaust...spend the time working it out and you'll get to the max and have a real broad hp and torque curve....or you can buy our system and bolt it on for at least 10hp/15 torque over ANY system now running in CMC...the way CMC keeps getting faster is exploiting all the details...build a car to the full extent of the rules and keep developing certain areas, such as exhaust, and you'll get there....we've been doing this for seventeen years with F bodies...we've learned a bit....check out our current build Camaro for sale in the classified section...or spend 5 years learning everything we learned to set it up right..RP

[Carson]

Hey Bubba, i guess that makes youes da..... exhausted rooster...

sign me up for da " winter tune up"

great web site ..by da way...

[C4RACER]

BTW - 6800 rpm richard? Out of a 305 running stock heads and a 2102 cam? Seems far fetched to me from everything I've seen on these motors. Or was that a typo and you meant 5800rpm? that makes a bunch more sense.

 

Basically if the TPI motors like a 3.42 gear, those pretty much die at 5000rpm - I know that engine very well, I had a '89 IROC track car for 9 years that I also did autox with. So 5500rpm in a carbed motor is another 10%, meaning they should be able to use ~10% more gear going the same speeds. So 3.73 seems about right for that equation.

 

BTW - if you really had a 6800rpm motor that made power up there it would neen a 4:10-4:30 gear to make it work unless you are running much faster speeds than the top TPI and 4th gen cars and Mustangs. You would also be making a lot more power than 230rwhp if you could get a 305 to make peak power at 6000rpm, which is what it would take to spin to 6800.

 

thanks for the info guys.

 

I plan to look at the exhaust pretty close on my car and do some testing on some combos - I hope that and going from a flex fan to a elec fan will get me into the 220hp / 270tq range which is about +20 from where the car now sits.

 

BTW - I picked up a 3.73 gear - found a new GM gearset on the frrax board for a good price so I grabbed it.

[Richard Pryor1548534703]

Nope, the 6800 rpm redline is not a misprint, however, the shift point in optimum conditions is 6300 rpm...the extra 500 rpm allows you to keep it in gear going into a corner that otherwise would require a shift up/shift down, such as Laguna's T6...you can pick up .1 second per lap minimum by not having to make that shift...the max power in the carb engine is at 5800 rpm which when shifted at 6300 rpm gives a nice power up/peak/down curve over a select rpm to keep in the power band to optimize lap times..we use the same "over rev redline" philosophy on our TPI cars and use a 5800 rpm redline on them with the shift point at 5400 rpm...we've done lap and sector times to find the quickest way to drive with the different engine/rear/redline/power combos....just going to a race weekend and thinking you can discern the difference is pure fantasy...it takes hours and hours of testing of minute changes to try and optimize ALL components of the car including the driver...data acquisitions really pay off here for test days...CMC hasn't reached the intense development that is possible under the rules...but I believe it is coming as the series continues to grow...you are going to have more and more professional approaches to this series...it won't change the fun attitude that permeates CMC but it will widen the gap between the weekend warriors and those that bring a 100% racing program to the series...wait until someone puts together a program equal to the effort made by Joe Aquilante's Phoenix Racing in SCCA T1, AS, SSB and T3...there's a reason they've won all those National Championships...with NASA creeping onto the National Championship stage and attracting more media and participant interest those "pro" teams will not be far behind...one of these years you'll see a CMC car win at the NASA Championships that has a driver like Boris Said piloting the car with an engine built and developed by Rebello and the chassis engineered by Protofab and developed on a GM shaker rig...fantasy? nope, it's already happening in SCCA "amateur" racing....disabuse yourself of what you think CMC is....that image is going to change and those that want to race at the front are going to have to step up their programs...no matter how tight the rules are, the more money, expertise and time you have, you can extract that last percent or two of advantage that wins races and championships...CMC is at a crossroads of a making of its own success...it's going to be an interesting ride...err, race.....rp

[King Matt1548534716]

Richard, I think there are a lot of people here who will question a CMC engine built under the current rules that can regularly turn 6800 in extended use, let alone be making enough power that high for it to actually be useful. You must have some pretty good valvesprings and retainers to do that. Did that stuff come "stock" on a 305? Even the 5800 power peak is a big advantage over the carbed Ford engines, which is why I submitted a rules request this year for a spec cam option for the carbed Fords.

[Richard Pryor1548534703]

Matt...well, I never said how long it would live at revving it to 6800 rpm...at 6000-6300 we'll be replacing the valve springs every two race weekends...but that's what it takes to run the engines at the edge...big advantage, you bet...are the Fords in need of some revision to equal the GM's..you bet...right now they're at a definate disadvantage in my view (sort of the opposite of the AS stuff we've been watching)...the carb Fords need parity with the carb GMs and hopefully will get it in 2007...it's tricky getting the playing field level but I'm betting the Directors come through...rp

[supermac]

Engine was just rebuilt from pan to carb and is ready for years of CMC racing with only oil changes.

 

I'm not saying.....

[C4RACER]

I toasted a stock TPI 350 motor reving it to 6000 for only a couple events - this was in my '91 vette race car. The motor made power to 6K, but it had headers and a TPIS miniram intake. And it still probably made peak HP around 5000-5200 but could be reved to 6000 no problem. But the stock valvetrain wasn't up to that abuse for very long. Major valvetrain event happened and bent about half the studs, maybe toasted the cam and timing chain too. 6800 on stock LG4 valve-train? I am also not buying that is really a CMC legal engine you are describing.

 

I came to CMC to run a grass-roots low cost series that did not require car prep like Richard is suggesting to be competitive. I have a long way to go in driver development before I need to worry at all about the car prep, so right now I'm not too worried about it. I hope things don't go that direction or I could see a lot of the people who are now racing the series leave it for something else. Time will tell.

 

Scott

[C4RACER]

I also will say I do not for a second believe that is a CMC legal 305 carb motor if it is really making peak power at 5800rpm. Car craft built up a LG4 305 a few years ago. Details can be found here:

http://www.goingfaster.com/spo/325_horsepower_305_cid_chevrolet.html

 

Using the stock heads and a bigger cam than the 2101, plus headers, they found peak HP was 270 at 5100 rpm. That is with a cam with 218deg duration at .050, where the spec CMC cam has 204. Even adding a much better flowing set of heads, the World Products S/R and staying with that very healthy cam the motor made peak power of 298hp at 5500rpm. It makes no sense that a stock LG4 headed 305 with a performer 2102 cam would have a peak power up at 5800rpm. This completely defies all logic and everything I know about chevy engines, which I have beed building for 30+ years now....

 

I ran some numbers through an engine analyzer program that I have that has been pretty good at predicting performance - or at least good at predicting the peak HP and TQ points of the motors I've built in the past. I didn't spend much time but I threw together a 305 with 9:1 CR and a set of stock 350 heads and the performer cam and intake combo that is spec'ed in CMC. Peak power showed ~290 at 5250rpm. This was a bit of a best case scenario, but that translates into somewhere around 240rwhp which is over the spec limit but we'll use it as a baseline. I see no way to shift peak HP up to 5800rpm without improving airflow in the heads and also increasing HP a good bit. I added a set of L98 vette heads and it bumped the hp up to 310 and the peak RPM up to ~5600rpm or so. Of course that is going to be well over the 230rwhp limit of CMC, such a motor should pull 250-260rwhp. So I just do not see how a 230rwhp 305 motor could come in at a 5800rpm peak - simply not possible in my opinion.

 

Now, one thing I did see that was interesting to me is the HP curve is pretty flat up near the peak. With the stock heads it held within a few hp of peak from 5000-5500 and then dropped off only slightly past that point. So I can definately see the point you are making Richard which is extending the RPM limit of the carbed combo will have some benefits if it prevents a shift because the power doesn't drop off too much at all. But then again how you control the valves with stock valvetrain is another matter. I have not read the rules - maybe stock valvetrain isn't required??

[C4RACER]

rules clearly state that the valveprings that come in the Edelbrock performer kit must be used. I checked and they spec a seat pressure of 74-84lbs - they are a single spring 1.22" OD. I cannot see how this spring will alow operation over 6000rpm for even a single event w/o causing a failure. If this is truly the spring you are running, you are flirting with disaster every time you rev that motor past 6000 IMHO.

[Lady in Nomex]

Don't worry Scott, CMC will never become A-sedan. BTW I ran a CMC legal carb L69 305 in my '84 Trans-Am for many years. It had a mild top end rebuild - I finally replaced the tired motor after it started smoking a bit too much! I shifted about 5500-5600 normally.

[Richard Pryor1548534703]

OK, I give...I'm taking my tongue out of my cheek and admitting the first posting at 6800 was a typo...that's the A Sedan Rebello engine specs...with nothing else going on I couldn't help stirring up the pot....and kept the joke going (sorry, Matt, I knew I could count on you)...at the urging of an unnamed person who knows my skewed sense of humor too well, I am coming clean so as to not get newbies to CMC into an uproar and also get a false sense of what it takes to compete in CMC....yep, the car engine turns to 5800 and runs out of air there...just like the TPI at 800 rpm less...and it will run forever at those revs, requiring neither rebuilds or valve springs...that's the beauty of CMC right now...it is cheap and designed for a "spec" series...so, sorry for the misleading posts...but..and this is a big one...the coming of "pro" teams is real...CMC and NASA are gaining stature and numbers and anyone that believes what happened in SCCA won't happen here is hiding their head in the sand...A sedan had it's own set of problems with rules creep...but the coming of "pro" teams like Phoenix didn't depend on the rules in T1 etc...they had a manufacturer that wanted wins and they build to the full extent of the rules and used a top driver in John Heinricy...I firmly believe it will come to CMC and CMC2 (especially with the new body style Mustangs) soon...will this affect Scott and other newbies? no, keep concentrating on your driving and car prep...the neat thing about CMC is there is always someone to race with whereever you are in the field...but if you expect to win; it's going to be harder and harder and more and more expensive...there's a reason we built the new CMC motor from pan to carb and spent hours on the chassis dyno working on the exhaust, etc.....it pays off in lap times and wins with the right driver or it moves the mid-pack driver further up the grid...RP