detune an engine?

cavboy78 · Jan 15, 2009

I have a 1970 Sportsroof with the stock 302, a T5 conversion, and a Ford 8" rear. I have a line on a 347 stroker built by a friend of mine that makes around 415hp/415ft-lbs. It is almost too good a deal to pass on, but I don't want to crush my tranny and rear end with the power. What is a common sense/cheap/easy way to detune this to a more manageable power level until i can afford to upgrade the tranny and rear end, while not doing any damage to the engine itself? Things i am thinking of now would be some sort of restrictor plate, a smaller carb, retarding the timing...Unfortunately, my right foot is not reliable enough.

mrmustangman357 · Jan 15, 2009

just stay out of it. maybe a smaller cam or go less ratio on the rocker arms?

rbohm · Jan 15, 2009

best way is a smaller cam.

57fairlane · Jan 15, 2009

415rwhp? Thats a nice 347 right there.

The 8" should hang in there, obviously if you put slicks on it and launch then no.
The t5 should also take that for awhile unless you like powershifting.

Basically if you just cruise around it and get on it from a roll then they should both hang in there.
I would imagine the t5 would let go before the 8" from just normal driving abuse.

cavboy78 · Jan 15, 2009

it should be around 415 at the flywheel...my plan isn't to hit the strip so much as it would be a daily/weekend driver with trips to the track.

Hack · Jan 15, 2009

I agree that the best way is a smaller cam, but you have to know what the compression is. If an engine is built for high performance the compression ratio may be as high as possible for pump gas. When you change the cam it changes the effective compression (known as "dynamic compression"). In other words, there is less bleed off from the combustion chamber with a small cam that doesn't have as much overlap, so the cylinder pressures are higher at low RPM than they would be with a bigger cam. This may cause the engine to detonate with the smaller cam. There may be some relatively simple things you can do to reduce the C.R., such as thicker head gaskets.

Just something to think about before you make the purchase. Figure out whether the CR is ok with a small cam and the gas you want to run.

Another method to make sure you don't hurt the trans or rear end is to make sure you keep small tires that aren't too sticky on the car. You may hurt the tires, though!

ForceFed70 · Jan 15, 2009

Why not just go with some skinnier rear tires? All of the power in the world won't break the T5 adn 8" if you don't have traction...

D.Hearne · Jan 15, 2009

Hack said:
I agree that the best way is a smaller cam, but you have to know what the compression is. If an engine is built for high performance the compression ratio may be as high as possible for pump gas. When you change the cam it changes the effective compression (known as "dynamic compression"). In other words, there is less bleed off from the combustion chamber with a small cam that doesn't have as much overlap, so the cylinder pressures are higher at low RPM than they would be with a bigger cam. This may cause the engine to detonate with the smaller cam. There may be some relatively simple things you can do to reduce the C.R., such as thicker head gaskets.

Just something to think about before you make the purchase. Figure out whether the CR is ok with a small cam and the gas you want to run.

Another method to make sure you don't hurt the trans or rear end is to make sure you keep small tires that aren't too sticky on the car. You may hurt the tires, though!

Hack's on the right track here. You could also limit the carb by means of a throttle stop and/or discinnecting the secondaries (if it's a 4 bbl carb)

RUSTYNUT · Jan 15, 2009

Why not just keep your current engine in the car, store the stroker and wait to put it in until you score the other upgrades. Don't forget to have brakes that can stop the car.

Hack · Jan 17, 2009

D.Hearne said:
Hack's on the right track here. You could also limit the carb by means of a throttle stop and/or discinnecting the secondaries (if it's a 4 bbl carb)

Thanks for the props! Means a lot coming from you.

The carb mods are a great idea - way to think out of the box!

D.Hearne · Jan 17, 2009

Hack said:
Thanks for the props! Means a lot coming from you.

The carb mods are a great idea - way to think out of the box!

That was good thinking pointing out the compression ratio factor. That's the one thing that people seem to overlook in engine buildups. Especially in SBF's

phutch11 · Jan 18, 2009

Lift your right foot...

But seriously, if you've got an aftermarket ignition system why not a rev limiter?

That 347 probably has to spin pretty high to see 400 ponies - limit it to say 5000 and you ought to be safe.

Good luck...

Posted via Mobile Device

VTStang66 · Jan 19, 2009

phutch11 said:
Lift your right foot...

But seriously, if you've got an aftermarket ignition system why not a rev limiter?

That 347 probably has to spin pretty high to see 400 ponies - limit it to say 5000 and you ought to be safe.

Good luck...

Posted via Mobile Device

I wouldn't think the car would be much fun to drive if you have an engine designed to run at high RPM and you're driving around at low RPM. Odds are that engine is peaky and driving it like grandma will be frustrating and less fun than just keeping the engine you have.

I agree that you should either change the cam and be mindful of the CR or just store it until you have the rest of the drivetrain together. Or just go ahead and break something...."if it broke it needed to be replaced anyway."

cavboy78 · Jan 20, 2009

Hack,

I appreciate the feedback...i learned something new.

Rustynut,

Important point indeed. I do recognize the need to stop if i go. I already installed the vintage venom kit with the '04 cobra brakes on all four corners.

I have decided to get the engine and am looking at some choices for smaller cams. I like the idea of thicker head gaskets coupled with disconnecting the secondaries. Once i get that built up, I'll dyno again to measure the effectiveness. Thanks everyone for the input!

Rusty67 · Jan 21, 2009

I don't often say something like this but, just slap that bad boy in there and drive it until something brakes. You can get a Gforce or Astro T5 that will handle the power no problem and a built 8" will take that kind of power as long as yer not drag racing all the time. What kind of tires you got in the back ?

brianj5600 · Jan 21, 2009

HP numbers are a lot like golf scores...optimistic or even overstated. Not to mention corrected. If you are not at sea level with cool, dry air and a high pressure system, you are already giving up some HP. If the motor is not in perfect tune there is some more. A couple degrees of timing will kill some power with out hurting the motor. I would not sweat it. T5's can live if shifted nice. There are guys with way more than 415hp drag racing them, but they are not gorrilla shifting them. Buy it, run it and smile! A motor not used is a useless motor!

cavboy78 · Jan 21, 2009

Due to the 13" rotors on the front, i needed to put 17" rims on the car for proper clearance. As such, I am running 17x9s on the rear with 275/40/17 Kumho summer tires.
I was already considering the g-force option if the t5 doesn't make it. I don't want to upgrade to a tko because of all the tunnel mods and additional parts required to install.
As for the rear, I was going to contact currie to see what they could build for me. I know the 9" would be nice, but i would have to get a small bearing rear end due to the vintage venom kit. I would think that a built 8" would suffice based on how i would drive and how much money i can afford.
Brianj5600, you also bring up a good point with the altitude as i will be moving to colorado this summer.

68RCodeConv · Jan 21, 2009

If you try putting a mild cam in a motor in which all other components are set up for a big cam (big carb, single plane intake, free flowing heads) you are liable to make a complete dog that will not get out of its own way.

As long as you don't "shock" the drivetrain by putting on slicks or speed shifting you should be fine.

SadbutTrue · Jan 21, 2009

cavboy78 said:
I have a 1970 Sportsroof with the stock 302, a T5 conversion, and a Ford 8" rear. I have a line on a 347 stroker built by a friend of mine that makes around 415hp/415ft-lbs. It is almost too good a deal to pass on, but I don't want to crush my tranny and rear end with the power. What is a common sense/cheap/easy way to detune this to a more manageable power level until i can afford to upgrade the tranny and rear end, while not doing any damage to the engine itself? Things i am thinking of now would be some sort of restrictor plate, a smaller carb, retarding the timing...Unfortunately, my right foot is not reliable enough.

If its a smoking deal, just retard the timing some, lean the carb, etc. Maybe put some stiffer springs on the throttle and a block under the pedal so its harder for you to slam it

And start saving the pennies you save on gas with the leaner carb for a T5z and 9".

detune an engine?

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