351 b & s, what would you do?

[tom pritchett]

I have a delima. I have a CAV, bored and stroked 351 to 427, 48 ida's, with zf. I really want to track this car, but have had challenges three times in a row. First time out the outboard cv exploded at turn 1 at Pacific Raceways in the Seattle area. Second time out, I broke the ring and pinion in the ZF. On the third time out, I broke a rod cap, not the rod once again turn 1. The builder of this engine and transmission combination claim 700hp. I did a dyno tune before my last event to make sure the 48 ida's were tuned right and ran out of time for a hp run. I am thinking that I may destroke this engine to a stock configuration to remove torque and maybe get more reliability. I just want to run the car. Any thoughts?

 

[Jac Mac]

Yes , if your builders up to speed the 351 cu in should be able to make 700hp albeit a bit further up the RPM range and a lot softer on the torque curve. Valve train will have to be good to extend the RPM etc. Wont be a user friendly street combo though, still cant have cake and eat it too.

 

[DBLDREW]

Well you’re going to have to increase the transaxle strength or de-crease the power of the motor.

I believe the Porsche 930 4 speed have been said to handle 700hp, or you are going to have to go with a racing straight cut box to get it to handle that power.

 

[tom pritchett]

I just had the ZF rebuilt and don't want to do it again. This combo just is not driver friendly or reliable. That is why I am thinking of destroking it, chromemoly rods and light weight pistons. I appreciate your replies.

 

[Jac Mac]

I just had the ZF rebuilt and don't want to do it again. This combo just is not driver friendly or reliable. That is why I am thinking of destroking it, chromemoly rods and light weight pistons. I appreciate your replies.

Tom, Now I remember you from about 20 posts ago, Sounds like you need to quit that ZF while your ahead, looks like plenty of others will take it off your hands!

Your usage and repeat failures to date suggest that you need something stronger!!!

 

[Cliff Beer]

Tom, the ZF should be fine with sub-500hp and no drop clutch starts. It should also be able to handle a few laps around SIR with that same hp. 500hp in a CAV is a LOT of hp - that will match or beat a ferrari 430 in a straight line for example. The 427 GT40s at Lemans in the day weren't more than 500hp due to weaker ignition systems and poor flowing heads and cams.

It sounds like you have a decent sized budget. If I was you, I'd go with something like an all aluminum 347 with IDAs/IDFs. You should be able to save 75lbs going with an all aluminum block. The less weight, the less hp you need to accelerate the car quickly, the less strain on the transaxle. 450hp out of an all aluminum SBF will rocket your CAV down the straight at SIR past just about anything else out there except the odd F5000 or Enzo. I'm looking into this engine set up for my CAV right now.

If you've fallen out of love with the ZF due to the recent troubles then you might take a look at the mendeola box which seems to be imminent.

 

[Randy V]

What the others have said all make good sense..

I would stick with the 351W myself as the headers and all other plumbing etc is sorted..

 

[Russ Noble]

So why did the cap break? Can't be that hard to build a 427W to stay together at that power level. Ford ditched the ZF when they went to <600HP 427. You should do the same.

Guys pay a fortune for ZF's! What you get for a freshly rebuilt ZF you can put into a rebuilt 930 with all the bells and whistles and that will take everything you can throw at it. IMHO.

We still haven't heard of any 930 failures on this forum, the same can't be said for ZFs. Even Ross Nicol mentioned some time ago that his new ZF now needs 2nd gear synchros renewed! ZFs appear to wear out rapidly and destroy themselves when pushed too hard.

 

[tom pritchett]

I really appreciate everyones input into this question. I am leaning to detune the engine to save the power trane because the crank needs to be turned anyway. I also have alot of torque steer in the car as well. All of the suspension is tight and checked over. Is this common with this car?

 

[Ron Earp]

I also have alot of torque steer in the car as well. All of the suspension is tight and checked over. Is this common with this car?

Torque Steer?????? :huh2:

 

[chuck smith]

torque steer is a product of front wheel drive. As far as the motor, I doubt you are anywhere close to 700 hp. My roush 427 makes 530 or so and it is a beast, to get 700 hp out of a stroked 351 and get it to idle at all seems unlikely especially with webers that do not like big cams. I do agree that the combo has not been favorable to you. I would think an easier route would be to use a smaller cam or change the heads and this should drop the power and torque. many people seem use a ZF on the track with good success.

 

[Jac Mac]

Torque steer in a rear drive is usually a diff set up with too much preload if a clutch type or if a detroit locker its always there and increases with power,engine torque applys more weight to one side and traction increase to that side will make car veer to opposite side. Boss Mustangs/GTHO XY Falcons both have this feature with detroit lockers. Depends on type of suspension being used . You also might have some deflection in your rear suspension that is causing a rear steer effect under power or even some front bump steer in acceleration, cannot remember if you put pics up when you first broke CV etc, but it might pay you to have a hard look at all your cars rear end geometry. While many on this forum seem to accept longer plunge dimensions with half shafts, the cold hard fact is when using a lot of power its really critical to keep it to a minimum, this might mean relocating the engine/trans assy to do so.

 

[Russ Noble]

It's torque that kills transmissions, not power. Listen to Jac Mac, you need to cam it up to reduce the mid range torque, not detune it and have it produce more. You need to fix the problem, not alleviate the symptoms. Also the Mendeola trans suggested by Cliff could be worth looking at.

By torque steer do you mean the ability to change the line of the car by changing the throttle opening? I'd say thats pretty normal in most cars. Unless its excessive.....

 

[tom pritchett]

What I feel under hard acceleration is the right rear of the car shifting over to the right a few inches. On hard deceleration, it flips to the left and when not paying attention, it could mean a lane change. I think Jack Mac is on to something with the deferential. I have a jeep with a locker in it and it acts alot the same. Its been a long time since I have driven it and just didn't make the connection. Being this should be a clutch diferential, the clutches may be new or just too tight.

When I was at the dyno tune, the tech called the engine builder to get some specs. It runs really rich(did) at an idle and it needs to for the cam. We did not adjust the carbs for the idle and on load at 3500 the mixture was right on. I was told that it needs to run rich at an idle or it just won't run. I have actually thought of getting the fuel injection system that looks like the ida's, but I can't seem to want to sell the carb set up. It is just cool.

Chuck, how does your car act with 530 hp? Do you track your car? I am trying to dial in to a hp that is fun, reliable, and still fast.

Thanks for your input Cliff. Its been a long time since we talked. Now you know why after getting my car fixed last time that we didn't get together. I will sort this thing out and then maybe we can have a day at XXX Issaquah.

tom

 

[Jac Mac]

Tom, If it is only the diff causing the problem I would suggest a change to a Quaife or Torque Sensing type unit. Other than that more seat time will help, after a while it becomes second nature to apply a bit of corrective steering lock under acceleration.

The Torque Sensing units get some bad press from the 4wd types since they dont work properly in reverse or in the front diff where the rotation is sometimes reversed. This may be why if in the Jeep the reaction is worse when you lift off the throttle. To work under power and going fwd in that combo the skew gears need to be swapped from side to side.

 

[Cliff Beer]

Tom, JacMac is likely right on with the differential line of inquiry. In parallel it might be wise (as JacMac also suggested) to look at the rear suspension for directional deflection where that much hp is being applied. This is tough to do in a static garage environment obviously, however, I wouldn't be suprised at all to see a couple degrees of deflection with that much hp. Your whole suspension is probably rose jointed rather than rubber bushed so it's not easy to pin point where such deflection might be occuring, however, you could try going to the next size up rose joints, and, welding in some support brackets to the reverse lower wishbone. Just an idea.