Added fresh bottomend (306), ported intake, and longtubes...gained just .8 mph...why?

Speeds8erM-1 said:

Probably didnt pick up as much just on the account of it being a new engine, older engines can run just fine (not always) and new engines generally take awhile to loosen up. The 4 cubic inch gain can just as easiely be offset by tighter clearances, tighter ring gap, ect ect. Who's to say the car really picks up much with the ported intake or that it's working within your desired RPM range? Or that the stock tach is even getting you in the rpm range you need.

I think it's all that making fun of the 5.0 finally catching up with you.

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Speeds8erM-1 said:

Who's to say the old engine was really that worn out? Did you do a compression test? You can easily lose some power with tighter tolerances and tighter ring gaps. The 306 should make a few more hp all else being equal but it might not be equal until it gets some miles on it.

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04sleeper said:

What kind of control arms do you have David?

Have you checked your torque boxes?

Sounds like something is off.....

Your driveshaft shouldn't rub anything.

I have seen mufflers rub against the driveshaft before by not being adjusted right but not the driveshaft hitting the car.

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04sleeper said:

Hmmm.

Saggy rear shocks would not cause the driveshaft to hit or rub anything. It might cause the tires to rub but thats about it.

All of my Fox's had aluminum driveshafts and were lowered. I never had the drivshaft hitting anything.

It sounds like your control arm bushings are whipped.

If your bushings were worn then it could cause your rear to twist rearward when you get on it.


How are your tranny and motor mounts?

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25thmustang said:

I will add my .02 here...

Number one, your motor could very well still be tight. A 160,000 mile motor although starting to lose compression, and burn oil, is broken in, loose and running hard. Loose is fast, anyone can tell you that. Knowing this, your bottem end may not have helped at all. The 308 compared to 302 CI is next to nothing, and unless you bumped compression with a better piston, will probably only help in the tq area. Now a good bottem end, offset ground crank, and loose, with flat tops, would have helped you out a lot, but a 308 rebuild with stock stuff, isnt going to gain much.

Number 2, although I say LTs helped my car a ton, you and I know it was just my case for some reason. I do know they make more power, but how much is more or less a toss up. Youd never know what they did without running shorties, then running the LTs.

Number 3, it sounds like an issue my dads car had. We found out it wanted to be reved. Car wanted to see 5800-6000 RPM, and with his tach (even his autometer) it was off and we were shifting it at 5400-5500. Needless to say we set the light for 6000, and the car gained a few mph (109-110 and now 110-112). Id say get a shift light and experiment.

Number 4, the numbers arent bad. I did an 8.4 @ 86 in the 1/8th which was a 12.9 @ 108 or so in the 1/4. Your cars probably hitting 12.7 @ 109 which makes for a nice street car. Id say shift it higher, and you could be in the low 8s.

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Speeds8erM-1 said:

It's hard to make changes like that and come out and make a big different right off the bat. Look at it this way, how many times had you ran before you got your BEST? Comparing your BEST before to your first time out is kind of hard. You almost picked up almost 1 mph in the 1/8, thats a big gain for the 1/8, might have done more in the 1/4.

You will probably need some passes before you nail that BIG number like you did with your old setup. You might even need to shift it up higher than before with the ported intake.

I do belive a 306 can make more power, all else being equal, more cubes, although not but but you also get the valves unshrouded more. You wont see factory stock cars running standard bore and for good reason, you need all you can get. In this case though, you might need to get some more miles on the new bottom end before it's equal power wise with your old one. That is weird though since the other one lost compression, it should have been weaker.

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jjd975 said:

If you build the exact same motor and ones a 302 and the other is a 306 your looking to gain close to nothing, maybe 4 HP for the extra cubes.

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DMAN302 said:

Not sure wether I buy into the 'will loosen up', I wonder if maybe your old mill just ran well for the miles logged. Second I might want to get the car on a dyno..perhaps your running fat and need to lean her up a bit, or get a bit more aggressive with the timing...just some thoughts.

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