Cam change

[Jack Houpe]

For some time I've griped about having two much HP, this summer I plan on going over the car in preparation for the up coming 50th anniversary event and plan on a cam swap, not to make more HP but decrease it, I've ridden in many GT40s but really enjoyed riding in Richards car which I think is 450 HP and very manageable. Here is the dyno specs on my engine when new with weber carbs, now has 4 TWM throttle bodies with EFI, I would like to see somewhere in the 400-450 HP range at the crank. Its a solid rocker roller motor with the rev limit set at 6500 now so hydraulic rollers is not a problem for me. The car and engine have 13k miles. Here are a few pictures with carbs and then throttle bodies.

This is a person preference, I'm to old for surprises.

Please post your ideas and comments.

Sorry forgot to upload

 

[Sean]

Jack

I would say your issue is torque more than Hp, going for a milder cam can give you even more Tq. Also from prior posts did you not say you had a 4.22 rear end ratio, that would make any motor kinda hair trigger vicious.

If it were me, I would look for a taller rear, something like the stock 3.78, that will blunt the power surge and make it all more manaegable. Then a milder can with hydarulics. But pulling a hipo 427 down to 450 hp does not seem like a great or too feasible plan, then you will have a truck motor and all that TQ and short gearing will not feel terribly different.

Alternatively there is a world of great 302 based motors of 450-500hp for $10-15K. You could pull the twm off your current motor, sell the motor and install the twm on a 302 based motor. Something with less tq and more revy woudl probably work better with your gearing.

 

[Jim Craik]

Jack,

Changing to a 302 would give you a chance to change out that pressure plate that is so hard on your left leg

I'm very happy with my 302 based motor, 450hp, 425tq, smaller, lighter, cooler quieter....

 

[Jack Houpe]

Jack

I would say your issue is torque more than Hp, going for a milder cam can give you even more Tq. Also from prior posts did you not say you had a 4.22 rear end ratio, that would make any motor kinda hair trigger vicious.

If it were me, I would look for a taller rear, something like the stock 3.78, that will blunt the power surge and make it all more manaegable. Then a milder can with hydarulics. But pulling a hipo 427 down to 450 hp does not seem like a great or too feasible plan, then you will have a truck motor and all that TQ and short gearing will not feel terribly different.

Alternatively there is a world of great 302 based motors of 450-500hp for $10-15K. You could pull the twm off your current motor, sell the motor and install the twm on a 302 based motor. Something with less tq and more revy woudl probably work better with your gearing.

Gearing was my first thought, they are pricey and at one time could have had a higher ratio as you mentioned for just under $3k but had already put over six figures into the car and ruled the added expense out. The small block swap has also entered the equation but I would have to purchase a set of headers for 302 Windsor as I have 351 now. I was hoping for a cam change with less expense.

Thanks for the input!

 

[Jack Houpe]

Jack,

Changing to a 302 would give you a chance to change out that pressure plate that is so hard on your left leg

I'm very happy with my 302 based motor, 450hp, 425tq, smaller, lighter, cooler quieter....

Absolutely Jim, if the motor comes out so does that pressure plate! I'm using Richards car as a base to get to, his car is comfortable and seems easy to control, his intentions was not a tract car but a GT40 with street manors, sort of what you have also. Richard runs a ZFQ and not sure of the ring and pinion but would be its higher geared than mine.

 

[David Briggs]

My car is a 347 with webers and a ZF with 4.22 ring gear and it makes about 450 hp. The car is very fast and very driveable, the only 427 cars that I have worked on and driven had a 3.70 gear and that kept the torgue down but they were not any faster at the speeds most of us drive at, even on the track the smaller motor and 4.22 gear do very well.
Dave

 

[Mike Drew]

Jack--just remove a couple of spark plugs and wires. That should do the trick! :laugh:

 

[Jack Houpe]

Yea dude, that will do it.

 

[Cliff Beer]

Jack, a 331 with the go fast bits on it a great engine - roughly 450/450 tq/hp, nice and compact. An alloy block 331 is particularly sweet. The 331 will rev like a 302 because the piston skirt isn't hanging out the bottom of the bore too much at BDC. Smaller and lighter engine overall, good for handling.

450 hp/tq is plenty for a 2,500lb GT40...your transaxle will thank you as well!

 

[Steve]

Wow, that's a big freakin' cam. I'm surprised a cam was spec'd with lobe separation that low for a Weber setup. Webers usually need 110 degrees at least. Did it spit like crazy? That cam is actually for oval course 1/2 mile racing with an RPM range of 5800-7800. If you're rev limiting at 6500 you're barely getting into the area where this cam works. Since your power is dropping off at 6k I will bet the heads aren't built for high flow at high rpm but rather more for torque (you have a broad torque curve that comes in very low). This probably means your heads and cam are a poor match. I think you're right that you can do far better with just a cam change. It might be worth talking with a comp cams camshaft specialist to spec a cam for exactly what you're looking for. When I spec'd mine they requested gearing, weight, use (some road course but still streetable for me), as well as all of the details about the engine. You should be able to knock 100hp and nearly that much torque off, keep a broad torque range as long as your valves/runners aren't too big. Based on the fact your power drops off before the cam gets into it's power range I'd bet your heads aren't too big and this can be accomplished along with improved idle and streetability.

If that doesn't work, next up would be the gearing...

 

[Rich E.]

Jack,

I'm with you. The cheapest way to change the behavior and power level is to do a cam change, fatten up the fuel tables, and adjust the timing abit. It'll probably run cooler too. As far as re gearing and spinning the tires off under hard acceleration, maybe a taller stickier tire can solve both?

.02
Rich.

 

[Terry Oxandale]

Or, a warmed over 351W, keep everything else and wow...look at the lift on that cam!

 

[Jim Craik]

Jack--just remove a couple of spark plugs and wires. That should do the trick! :laugh:

I remember hearing the story, that Team McLaren tried that at the Laguna Seca Can Am, the one that John Canon won in the pouring rain. The story goes that they removed a couple of plug wires to try and lower the torque as the cars were undrivable in the rain.......

I'm not too sure if this is true, I was there that day and I sure don't remember the McLarens sounding "flat"....and although "drivable" they were obviously a handfull!

Jack, sorry for the drift...

 

[Glenn M]

Richard runs a ZFQ and not sure of the ring and pinion but would be its higher geared than mine.

Jack, The ZFQ has a final drive ratio of 3.75

Glenn

 

[Jack Houpe]

Cliff that is the engine Richard has to spec, he had his engine built by Keith Craft, I've offered to trade him, I think he thought I was kidding.

I agree Rich, changing the Cam the most affordable solution for this engine, I'm running really fat on the top end now just for protection, AFR 11, I might go full sequential with this mod or swap, I'm running an old TEC2 unit now which is only batch fired, but have a motec in the box here in my office which will really smooth out the low end. Did you tell me your running FAST system or is my dementia kicking in?

Steve I have AFR 225 heads, and I'm looking for for a smother torque curve, more than likely when the time comes I will be calling up comp cams, I really don't have a clue to what it should be, I'm more of a electronic tech than engine builder, most the engines I mess with came from Italy.

Terry, I thought of swapping to a almost stock 351 and putting the 427 in my office as a coffee table, better than in the coffin with me. Don't get me wrong, I really like this engine, its the 70 mph blow outs in 3rd that I don't like, cold days its far more common, it would be perfect in an old muscle car that weights 2000 lbs more than the 40. I like driving my car, its almost clicking 13k miles, would like to see as many miles as Richard and Jim. Richard has over 35k miles on his car, Jim how many do you have? 40k? These are old guys like me who just want to cruise in a cool car. HAHA!

Thanks Glen, I think Richards fifth gear is .654 too?

 

[Sean]

Or you could change the cam and destroke it. Go for a stock 351 crank. You have pretty short gearing, so a revy motor is always going to be more fun and relevant. The 351/427 is a pretty stroked motor, a stock stroke crank is going to be much smoother, softer down low and then at your option you woud still have punch if you went up the rev range.

Or you could sell the motor you have now, and just get that 302 style motor you really want, life is short. But me thinks you also like fiddling, so try the cam and motec.

As to gearing, comparissons to the RBT and ZFQ final drive ratio are misleading. The ZFQ has taller final ratio but shorter gears in the box, plus what gears do you have in your RBT. If they are the standard GT40 gears, then other than 4th and 5th they are pretty short to begin with, add in the 4.22 final and there are issues.

All of which is to say that if you are running a 4.22 final a big camy engine as you have now is probably close to undriveable because the power cannot be put down. That type of gear train would work far better with a 302 that can spin, and thta is another type of enjoyment. If the gears stay then try destroke thge motor and go with a different cam, the race 351's seem to come out at 377 and they can spin. Gordon levy racing seems to make some of these motors and KC seems to understand them well too.

 

[Dave P]

Jack:
For what it is worth with the cubic inches you have. I think you would be very happy with a gearing change. With a 4.22 you are really mulitplying the heck out of the torque your producing. Had a 455 Pontiac GTO years ago. It had 3.08 gears with 301/313 duration cam with Rhodes lifters very drivable. Your cam specs are not that far from what I had in it. After blowing the rear diff I put 3.70 gears and it was unbelievable. Could not imagine a 4.22 gear

 

[Rich E.]

I'm running a Holley HP EFI in my Ls7 powered M3. Davis technologies makes a traction control box as an add on. I haven't bought the TC yet but I love my Holley system. I'm assuming by Motec you're referring to an M48 box? If so aren't they already equipped to identify wheel slip. Might be an opportunity to fab up a set of hall affect rings and sensors or modify an existing set of abs rings/sensors to control slip. Just a thought.

 

[Jack Houpe]

Sorry Rich, my mistake, its bosch MS3, really a nice efi system with all the whistles and bells. I do like the idea of traction control and actually bought a drive by wire set up for GM, I guess the Davis unit comes with the a the computer and throttle motor?

I have mixed emotions, buy a 302w and make this 427 a coffee table or change cam, and add traction control, change ring and pinion, heck it all cost money. Sell this 427 and start over, decisions, decisions decisions. I could be sacrilegious and put an LS motor in it.

 

[Rick Muck- Mark IV]

I could be sacrilegious and put an LS motor in it.

And we would hunt you down and you will suffer the torments of Hell if you do! Plus you will be on you own for headers......