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Discussion Starter · #1 ·
I picked up my friends 68 mustang today so I can detail it for him tomorrow. He has recently rebuilt the engine (500 miles), added a new 4bbl Holley (600cfm I think he said), port & polished the heads, mild cam, new duel exhaust & mufflers. C4 tranny has less than 100 miles on it, and believe it or not... I can get a quicker 60'ft. time on my 18 speed mountain bike!

I mean, you start this car up, and it sounds as if it's going to eat you alive. It's sounds fantastic with the slight lope of the cam, and the throaty duel exhaust!!! But that's where it stops. Yes everything else is stock, but my bone stock 289 in my 67 will break the tires loose until I take my foot off of the gas pedal.

What gives? Is the carb just not dialed in?
 

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timing could help
 

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Discussion Starter · #4 ·
Wouldn't you be able to tell if the firing order was off since it would be missing pretty bad? This thing runs smooth, I imagine the timing could be a tad off as shagg mentioned, but it fires right up on first try, and runs pretty smooth going through the motion, just gutless. I will check the fire order though tomorrow just to make sure.

I'm guessing since it's a new carb, that maybe he just stuck it on top with out making any adjustments. He's playing @ HAN's right now or I would ask him. Hmmm! I guess I will be playing more with it tomorrow than I expected /forums/images/icons/smile.gif
 
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sounds like the rebuild wasnt balanced. throaty cam doesnt equal performance. Hard to say whats wrong,need more details of his rebuild/combo. His rear end could be problem or his intake? sounds like a slap dash rebuild. imo
 

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Discussion Starter · #6 ·
Not a slap dash rebuild, This guy knows his stuff, his race car does low 9's without the aid of Nitrous or a blower, so I think we can count out shoddy work. It wasn't built for performance, but basically just a stock rebuild. He has hardly driven the car, so I'm sure he isn't aware of it. The cam is pretty mild, and that was a "throaty" exhaust that I mentioned! His rearend is probably stock 2.80:1 or 3.00:1, but so is mine, so I don't buy it being the rearend, since it seems it should at least be able to stay up with my 67 289 and stock rearend. And I don't think the cam, head work or exhaust would have deterred the performance, but instead a slight gain I would of thought? At least with my experience in the past changing to a mild cam, and allowing the engine to breath a little easier has always gained me at least 20hp.
 

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Nothing wipes out bottom end on a stocker like a cam and dual exhausts..even a mild cam will feel like a dog with stock rear gears..he may be slow for the first 60 feet, but I would guess once he winds up..the car will come alive.. a stock cam will feel quicker off the line in every instance..most people make this mistake..he needs to dial in the timing perfectly and change out the rear gears..probably go to at least 3:25's..better yet 3:50's..it will feel like a totally different car..been there done that
 

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HE probably knew you had a lead foot and backed off the timing 10 or 15 degrees. /forums/images/icons/cool.gif
 

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My first guess is timing. The mechanical or vacuum advance isn't right. If you advance a car too much it will ping. The vacuum advance may be comming on too hard and it keeps pushing it into ping, then stumbles a little. Try unplugging the vacuum advance from the distributor and cap the vacuum line to prevent a leak and try it again.

Holley carburetors are also the devils play thing, especially the ones with mechanical secondaries. Then there tuned in they give great power, but if you don't have it tuned in there very easy to run too rich or lean.
 

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You did mention ported and polished heads right?

Sometimes opening the ports up too much will take that low end torque away like you wouldn't believe.......

Sounds like he slowed the port velocity down.....which is very easy to do when porting....

tell your friend to try another set of unported heads and go from there......he should pick up some good torque

porting should be limited to slightly massaging the ports and smoothing the bowls behind the valves....any other work beyond this should be done by a specialist.

regards
Roberto
 

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did he brainfart on the cam timing?

that, the carb, and ignition timing/advance
 

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Anyone that can make a SBF run 9's knows exactly what he's doing...only way I could do that was in a FED (9.20's)...

I think he's messin' with you...

How does the engine run at, say, 6K rpm? (100 miles should be enough to try that out *G*)

I still think it's the new carb

So, what kind of carb?
 

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Discussion Starter · #19 ·
Actually the race car is an FE running low 9's /forums/images/icons/tongue.gif

It runs ok at around 6k, but not what you would expect! Just got back from taking it across town this morning, parked it for about an hour, got back in to start it, and got a backfire through the carb. Tried again and it fired up but just didn't sound right, as I pulled out of the parking lot, it would die with it in gear and foot on the brake, just slowly die as it wasn't getting enough gas? I would stick it in neutral, and it would idle just fine, but still sounded like it wasn't firing on all cylinders? I had taken it to Bob's last night, and it ran fine with the exception of no umph! Today after it back fired through the carb, it just didn't sound the same when idling. Once you got up to speed, there was no other problems. Got home and quickly checked the plug wires, and evertyhing was on.

So basically this wasn't just me thinking there was something wrong, it has proven there is. Anyway, I'm going to pull it in the garage and take a look.

btw, the #s show the holley as a 80457-2 3400 which is what, a 4160 600cfm?
 

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Don't know which Holley that is...number sounds wonky...didn't show up in Holley's database...maybe OEM?

You coulda popped a power valve...

Put one of your carbs on it and see what happens..
 
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