Slowest Cobra on the Planet

[Russ Dickey]

Fellow members:
I just possibly own the slowest accelerating Cobra on the face of the Earth. At a recent exhibition event at the local dragstrip, my 289FIA could only muster a mere 15.02 elapsed time.

I am a pretty decent drag-racer, and have been down the 1320 many times in lots of different types of cars. In my Cobra, I launched at 3000rpm (with very little tire spin), and shifted at around 5800rpm (right where my engine stops "pulling").

My car is powered by a 351W with GT40 heads, with a very mild cam and a 750 Holley. Ignition is all MSD. Transmission is a Tremec 3550, and the rear-end is a 3.30:1 Jag. I don't know the specs on the cam, but I have sent an email to the previous owner to find out.

To say that I was disappointed with the performance of my new ride is a gross understatement. I knew that just from my "seat of the pants" , it wasn't as fast as I had hoped for, but I didn't think it would be this slow. I thought that even for as mild as my 351 is, it should be putting out close to 300hp. And since the car only weighs about 2450 with me in it, that I should be able to run high-13's fairly easily, even with what I consider to be a "highway gear" ratio of 3.30.

The car is not missing, cutting out, or blowing smoke. By all appearances, it looks and sounds to be running just fine.

So I guess I am asking your advice: where do I start to try and shake this thing down? Should I take it to the local chassis dyno first to establish a base line??? Any comments or help is greatly appreciated. Help a fellow Cobra brother try and prevent the embarrasment of getting my a$$ handed to me by the punk kids in the imports.....


Thanks,
Russ

[rdorman]

...... I would take it to a good dyno tuner and see what is up. Clutch wasn't slipping was it?
Rick

[Mr.Fixit]

Were they timing your slowdown too?

Change rearend gear to something more like a 3.73, you have OD on the tremec. Sounds like a wuss motor, maybe time for a performance rebuild.

[Clois Harlan]

Just for a reference, I first had a 302 in my Cobra, stock bore and stroke with a E 302 cam from Crane and 1.7:1 roller rockers with an Edelbrock Performer RPM manifold and a 650 carb. The only other thing that was done was just a little work on the heads and I had a MSD 6AL Ignition Box. My 1/4 mile times here in Tulsa and at the Run and Gun in St. Louis were consistantly in the 12.90's with my best time on street tires 12.86 in St. Louis. I was running 3.73 : 1 gears with a T-5 trans.

I think there is a lot more in the engine than you are getting.

Clois

[Excaliber]

The "basic" 351W was in the early days NOT considered a "worthy" engine. Low compression and VERY mild cam made it more of an "smog control" application than anything else. These motors CAN be made to perform very well indeed, but in their close to stock form they are far LESS worthy than a good 302.

You cannot assume a "bigger" motor is "better" than it's smaller cousin. It is well known a carefully built Chevy 327 will out run a "decent" 396 for instance. Another example, the K code 289 was WAY better than even the GT-350 302 of 1968 (which was about 250 hp ONLY).

I'm guessing a basically stock 351W is LESS than 250 horse AND takes longer to "spin up" due to the longer stroke. And "spin up time to rpm" is a big deal in drag racing!

As I recall when they were first introduced, nobody wanted a 351W, the 351C was the engine of choice in those days. It's not like the 351W got "better" as the years went by, it got worse. Few "up-grade" parts were available back then. That, over the years, has changed and these motors HAVE to have to up-grade parts!

Ernie

[HighPlainsDrifter]

Russ,
There a couple simple things to look at before you make any changes. Look down the carb with someone stepping on the gas pedal[engine off] and see if the secondaries open all the way. Also with a mild cam the power may die at 5000 rpm and you are wasting 3 or 4 tenths in every gear , I know my car runs quicker by short shifting the gears.
Good Luck,
Perry.

[Charlie]

Russ,
There is nothing wrong with the 351W engine as it is built today. Sure the olds ones of the 1970's were restricted breathers that were overshadowed by the Cleveland, but that all changed with the new heads, manifolds and cams available today. They certainly seem to be good enough for most of the Ford racers today! The GT-40 heads aren't the best available, but they are pretty damn good for regular street use.

There is something else wrong there, like timing, or carb setting, or restricted exhaust, or just plain lousy cam profile. I would check the first 2 first, just to eliminate those as variables. Then get yourself a better cam. That should wake that engine up. Get the cam that Ford SVO puts in their 385 hp 351 engine. That one works great on the street, has a nice aggressive lope and pulls quite well. You can get much better cams I'm sure, but you may give up something, like drivability. And if you emulate the entire Ford SVO engine setup, you can pretty much guarantee close to the same hp output.

I am running virtually the same settup you have, except for the engine apparently. What kind of pipes are you running? Could they be restrictive? A 3.7 or 3.9 gear would certainly help, but I would find out what is up with the engine first. I am still running a 3.3 final gear and mine pulls quite well regardless of the less-than-optimal ratio.
Charlie

[Mr.Fixit]

As stated earlier, check to make sure the carb is opening the throttle blades completely, I can't tell you how many times I have seen that one. If you have a vac secondary carb, only the front will open with the gas pedal, the rear needs a vacuum signal.

[xlr8or]

Have you done a compression test? What is the pressure?
Maybe the engine is just tired and compression ain't what it used to be.
I would look into the throttle opening properly first because if it's not getting the secondaries opening all the way it's kinda like running the restricter plate in Nascar and takes forever to build the power.

[DAVID GAGNARD]

Russ;

Just as a comparison,I have a 350 hp,351-W in my 65 Fastback,running a Tremec also,3.00 rear gear in a 9" with stock Posi Trac,26" tall Wal Mart tires approx. 7" wide,leaving the line at idle,shifting at 5,500 each gear,I generally run 13.10 to 13.20 with a best time on a cool night of 12.95..... With me in the car at the track it weights in at 3200 lbs.

It is a 1972 351-W with the 72 iron heads,the heads have been ported/polished/gasket matched,running an Edelbrock Performer RPM intake and a Holley 600 double pumper,cam is a Crane Cam with 484 lift and 272 duration,idles at 750 rpms all day at 180 degrees water temp. This motor is fairly mild by most standards but runs well and has a lot of low end "grunt"...

A 351-W with GT-40 heads and a "mild" cam should easily put out 300hp. I think they were rated at 225hp from the factory,the heads and cam and of course headers should be worth at least the other 75 hp....

I would first check the carb out and make sure the 4-v is working properly then check compression and timing.....Seems a 3000rpm launch would or should just smoke the tires,could it be the cam was not installled "straight up" possibly retarded or advanced too much????

Even with a bone stock 351-W and a Tremec and your rear gear my guess is you should run high to mid 13's.... I have seen FFR's with stock 302 GT motor run high to mid 13's on pure street tires....

Something seems way out of whack here for you to run those times,sorry I can not be of more help,but your car should do a lot better,hope you find the problem..

David

[wilf leek]

You have nothing to worry about.

The slowest Cobra on the planet is my own.

That is when the wife is riding as passenger.

[got snake?]

Russ,
I'm sorry to tell you this but your just gonna have to rebuild it. Its not worth your time trying to fiddle with it...just get a stroker kit and be done with it.

GS

[blykins]

Some other things you might wanna look at...fuel pressure and ignition timing.

One of the other members made a good point about a slipping clutch. Oh, another thing...I don't know anything about Kansas City...the altitude isn't high out there is it?

[decooney]

Hey Russ,

You're not the slowest right now... Your car is faster than the Volkswagon powered Cobra I saw last year at the NorCal Kit Car show last year, and definitely faster than than all those unfinished kits sitting out there in people's garages right now.

Don't be too hard on yourself, hey, at least you own one. We are all lucky to be able to own one, I believe. Good Luck.

[Excaliber]

5800 rpm is pretty high for a "stock" 351W, 4800 was more like it. SO, if indeed it IS "still pulling" up to 5800 the cam is not anywhere near stock. Might be "timed" incorrectly to the crank as mentioned. The stock 351W 4V heads weren't "that bad" I wouldn't think the GT-40 heads would make a huge difference.

I would do the "basics" as recommended befor going in to deep. Throttle plates, cam/ignition timing, compression check (wondering what the C.R. is by the way?).

15 sec do sound TO slow all right. Gotta be something wrong (assuming it's NOT a stock 351W). Remember, it's not about a single component, it's about how ALL the parts come together. Cam matches carb matches intake matches exhaust, all that.

Ernie

[Russ Dickey]

Thanks guys for all the information and support. I now have a "task list" of some of the things to start looking at. To answer a few of the questions that have been posted:

1. Clutch doesn't feel like it's slipping, but maybe it was.

2. I am running the "stock pipes" that Unique supplies with their 289FIA car.

3. I haven't done a compression test yet, but I will, and I'll post my findings.

4. Altitude in KC is..I have no idea. I'll have to check into that.

5. I think my CR is 9.5:1.

Anyway, I'm headed to Canada for my yearly fishing trip. The Cobra will have to wait for a week. Thanks again, you guys!

Russ

[RICK LAKE]

Russ Dickey Hi Russ First thing I would start with is the side pipes. They can cost you 20-60 hp racing. I you want to know if they are causing too much back pressure, tap a small hole on the inside of the pipe, buy an Cat Convertor tester. You only need the high temp hose and gauge. Take the car out for a drive and do a wide open throttle with SOMEONE watching the gauge Your reading should be no more than a 1 3/4 pound pressure. If more you have too much back pressure. The exhaust is designed for the street not racing. I would go get the car dynoed to find out the power output. You can do 1/4 mile runs on the dyno and tune it up. You did not say gear ratio your trans has. Your rear should have 3.55 to 4.10 depending on what you want to do with the car, cruising,autocross,1/4 mile, or roadracing. The cobra can do it all with the right set up. Change the pipes and dyno the car. You will know where the power band is, Torque is more important than HP to me. I have 340 hp and 428 tork. I can break the tire loose in 3 gears with a 3.31 rear. I run my car easy at the 1/4 mile for brackets and run 14.1 with two gear shifts. Your motor may need a LITTLE bigger cam to go with the intake and heads. 9.3 is not bad for racing. Valve springs could also hurt the performance of the motor. If weak, they will float the valve at a lower rpm, nopower. Start with the exhaust than go to the dyno. Good luck Let us know what happened. Rick Lake

[JWheaton]

Where are all the Big Block comments?


Wilf,

What are you implying about your wife? You may need to duck and cover if she reads that post.

[RICK LAKE]

J Wheaton Big Blocks don't need to comment. You already know what was said. When are you getting your car done. Rick Lake

[bobl]

Russ.... I have good news and I have GREAT news.

The good news' name is Ron Golden. The GREAT news is that he is in KC as well. Call him at 816-436-6108.

Ron will check the distributor, check the carb, interrogate you thouroughly and then tell you EXACTLY what needs to be done. He is a terrific gentleman and no more knowledgeable soul exists to help you.

And, no, we're NOT related!! Whatever he charges you will be WELL worth it.

All the best....... Bob