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power question


RichV

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I blew up the supposedly low mileage motor I bought after about 6 laps last weekend.

 

I have a line on a new built/balanced 306. Stock rebuild/CR/cam/etc. Internals are all stock for a Fox Mustang, pistons are forged, 20 over. I also have a possibility of GT40 heads from a 95 Cobra with 1.7 rockers, and I already purchased a 93 Cobra intake with 65mm T/B.

 

What if I make too much power? I just have a MAC prochamber, a crank underdrive, and an electric fan. My 86 with a similar setup (except BBK headers), but stock E7 heads, made 225/285.

 

Can I restictor plate a Mustang? Dumb question, but is it legal?

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Per 7.7.2, "cars may install a restrictor plate between the air filter and intake manifold to reduce horsepower and torque," so yes you can.

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i think most all Ford and 3rd gen guys pull timing to get power down.

some even play w/ fuel pressure.

Exactly, I pulled my timing back to a "conservative" number and then set fuel pressure and am at 229/278 with a very similar combo to what you described.

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I'm curious if power adjustments you make solely with fuel pressure are maintained? I've been told by several knowledgable tuners that the EEC-IV will pretty quickly relearn a change in fuel pressure and compensate for it, thus negating the change. I haven't tested this myself since my car has a stock non-adjustable pressure regulator.

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Not for sure on that Matt. But, raising FP will definitely get you more fuel at WOT. Lowering below stock levels can affect injector spray pattern and make the car run rough.

 

At WOT the EEC goes into a open loop mode and will just max out injector pulse and not adjust due to O2 readings. So I think the power can be affected up/down based on pressure.

 

But changing timing and fuel pressure will affect your HP/Tq curves, what is the optimal way to detune??

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...what is the optimal way to detune??

 

The best way I can think of is if you swap your 306 with the heart of "The Great Pumpkin".

 

If you only need small adjustments you could put the stock sized pulleys back on. After that I'd be inclined to retard the timing. If larger adjustments are needed...can you do a smaller throttle body? After that...restrictor plate.

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...what is the optimal way to detune??

 

The best way I can think of is if you swap your 306 with the heart of "The Great Pumpkin".

 

I'll swap you right now! But it's not the 306, it's the 6 lap clicker.

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  • 1 month later...

Update.

 

Dynod the new setup. Ended up with stock E7 heads, 1.7s, Cobra intake and TB.

 

Averaged 229.8HP and 274.5Tq on my 3 runs. Can I tune a little better for Tq? I'm running 15deg of timing and a non adj FPR.

 

Thanks!!

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The Cobra intake is probably hurting your torque numbers. My 5.0L makes 229/294 with E7s and a stock intake, stock 1.6 rockers and an HO cam. Ford revised the Cobra cam specifically to address lost low-end performance from the GT40 intake.

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Since CMC series rules aren't the subject here, I'd love to have a discussion related to what I'm about to suggest in another thread.

 

How about adding a 0.5" or 1" phenolic spacer between the upper and lower intake to ever so slightly lengthen the intake runners and gain a little low end torque? Would either fit under the stock hood?

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Matt, yea I figured as much on the intake. I think at this altitude I'd be hard pressed to make the HP #s with a stocker. When I dyno'd it was with the local Mustang Club and there were several Fox cars on the rollers.

93GT same mods as mine, but a trick flow intake, 210H/256t

89LX same basic mods, 212/261

89GT holley systemax kit, full exhaust 284/309

95GT systemax kit, exhaust, +?? 270/300

 

Al, I'm running the stock headers with a MAC off road H (the one with the single muffler in the middle) and the exhaust immediately turns and exits out the sides.

 

Scott, I think spacers are OK in CMC, I'd have to check. The other thing would be to offset cam/crank timing, but I don't think that's legal. I think a stock hood can fit 1/2-3/4", but I also have a 3 point strut bar, so it would have to clear that too.

 

http://s17.photobucket.com/albums/b99/myponyrocks/?action=view&current=MOV00100.flv vid on the rollers.

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If you are making max. power numbers on a dyno in Colorado, you will probably be quite a bit over the max. at a track like Mid-Ohio. I wouldn't be too concerned about being under power at altitude.

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If you are making max. power numbers on a dyno in Colorado, you will probably be quite a bit over the max. at a track like Mid-Ohio. I wouldn't be too concerned about being under power at altitude.

 

Except he has to deal with people who are at 230/300 limit at altitude.

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Simple. Start with an unrestricted bone-stock 260HP engine We just need to bring lot of restrictor plate choices when we come play you guys.

 

Or even with Rich's engine he's got 229.8, just can't find the torque.

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It's going to be interesting to see just how much effect the altitude really has on a dyno run.

 

And no - please - don't turn this into a physics lesson on the subject. I can always go over to corner-carvers and read some rants on the topic.

 

 

-chris

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If you are making max. power numbers on a dyno in Colorado, you will probably be quite a bit over the max. at a track like Mid-Ohio. I wouldn't be too concerned about being under power at altitude.

 

Yea, I've heard that as well.

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Simple. Start with an unrestricted bone-stock 260HP engine

We're talking about a stock 5.0L here, right? Your definition of "bone-stock" must be a little different than mine.

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It's going to be interesting to see just how much effect the altitude really has on a dyno run.

Ask James Griffith III.

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Simple. Start with an unrestricted bone-stock 260HP engine

We're talking about a stock 5.0L here, right? Your definition of "bone-stock" must be a little different than mine.

 

Right Matt, he must be running a SCAT crank, H beam rods and an internal balance crank. i bet it dont last him 1 race weekend.

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Simple. Start with an unrestricted bone-stock 260HP engine

We're talking about a stock 5.0L here, right? Your definition of "bone-stock" must be a little different than mine.

 

Right Matt, he must be running a SCAT crank, H beam rods and an internal balance crank. i bet it dont last him 1 race weekend.

 

A '98 4.6L SOHC would have been original to the car...or is this where the update/backdate rule is exercised?

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Boy, I'd be really interested to know how a legal CMC engine can make 230hp at 5000 feet!

 

But, the 230HP is corrected for all of us. The problem is the correction is a calculation. So your 230 at sea level is dead on, where my 230 at real sea level will have error.

 

Uncorrected, I'm sure were at 190ish.

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