OK this is for a Ford, but the question is for all cars. My buddies Mustang(Shelby) has 351W (8.0 to 1)stock with a Comp 280H cam in it.Shelby dual plane intake with a 600 Holley,shory headers, 21/2" dual exhaust, 4speed and a 456 gear in the rear end.It's probably making 300 to 325hp The car runs decent, but just doesn't rev like it should. We've been chasing the ignition and carb trying to figure out whats going on. But the more I think about it, I wonder if the rear gear is just loading the engine too much. In other words it's not making enough torque to turn that tall of a gear.He says it ran better with the 325 gear in it before the resto. Any ideas?????....Thanks!!!

I am not good with a lot of the powertrain figuring, but, that does sound a little extreme for 300-325HP. Might not be enough power to turn the powertrain.

4.56 gear in a street car with a small block making 300-350 HP is a little over the top IMHO..fun,but over the top..

Chris,
That's just it. You'd think the thing would break the tires loose at the drop of a hat. But it doesn't. The drive train just seems tight to me.

my aunt's 73 with a 351w made 264 h.p. it broke the tires easily. i think you've gone the way of the tractor. you have too steep a gear in the rear. i bet your 0-30 is neck braking, but after that the engine has overrun the gears. for instance my harley is 1:1 final drive. now if i beef the engine, it gets there alot quicker, but it still has approx. the same top speed. get some higher gears in there and you won't have that pull off the line, but it will have a better top end. it's a fine balance. i'm sure one of these bright guys will give you a web to go to (i've heard of it, but can't think of the name). you go in there tell them your mods, and they give you the gears to run. good luck.

How did you know I was at DTS today? :D

the cam is a bit too big for the compression too. how many rpms does it pull to? a smaller cam and 3.50 gears would probably really wake it up. that motor isn't going to rev like a 302, it's much more of a torque motor, especially if it has stock windsor heads on it.

Cam is too big with the low compression and stock wussy little heads.If the car had a higher gear (3:50)in this current setup it likely would be even more doggy.

Wow! Have to agree that gears are way to big along with the cam and low compression. Looked in Comps and they recommend 268 cam for 8-9 compression. You said yourself the 325 gear ran better-well thats the ticket for your application or you need to build an engine! Goodluck! :D

I'd say boost that compression up if possible. Any smaller gear, numberically that is, should make the car more dogish. Sounds like these guys are right about the compression and cam choice.

My thought is that there is something mechanically wrong with the drivetrain, the gears are going to let the car accelerate quicker.

Could be something wrong with the engine, other then the obvious mis-match of parts, did he degree the cam, if so, what ICL?

A little more info is needed.

As stated earlier, 351w's are torque motors. I have had excellent results with quite tall gearing behind them (2.75 to 3.50 range). The compression is obviously too low for that cam, but the big killer is the heads. Even the so called "good" '69-'70 heads have totally pathetic exhaust ports. A little pocket porting and short side radius blending makes a HUGE difference in the way the 351w's run with the stock heads. Put the 3.25's back in, and drop the .050 duration about 10-15 degrees...the difference will be quite substantial even with the weak stock heads.

Agree with Brian, something's amiss..... 56s should light up a 4 speed car...

Are Ford motors that wussy? tongue.gif

I think you can go too far the other way. Fords expecially seem to react this way to a lot of gear. My old high school buddy has a '46 ford truck with a cobra spec 289 (306hp) and a 3 speed stick out of some old ford truck. We figured the rear end ratio at about 5.10-1 :eek: You could side step the clutch at 3500 rpms and stomp it...it would just barely squeek the tires, slam your head back against the back window, and then almost immediately slam it forward because it revved so fast that it would almost immediately get to a point it would quit pulling. 95mph top speed at 7K :eek: On the other hand, the last 351w I built was in a 4500+ pound '77 ford 1/2 ton truck. pocket ported and short side work on a set of '69 351w heads, 9.0-1, 272 crane energizer (216@.050, .484 lift), '69 iron 4bbl intake with a 600 holley, stock '69 mustang exhaust manifolds, and dual exhaust. With a stock convertor in a C4 tranny and 2.75 gears, it would incinerate a set of 31x10.50x15's like there was no tomorrow. It also fell flat on its butt at 5K. Brutal torque for such a mild engine, but no real hp.

IMHO,the cam isn't too big..a friend of mine has a 71 Mustang fastback,with a .030 302 with cast rebuilder dish pistons w/a .030 piston/deck height,and 54 cc chamber heads..compression is 8.5 at best..and it has a Crane 226 @ .050,108 LSA hydraulic cam...car runs low 14's with a 4 speed and a 3.70 9" locker..this car has no problem breaking the tires loose either..

no the cam isn't too big to work, but i'd bet money a little smaller one would work better. i've run a Comp 280 with an 8.5 to 1 350 and it ran much better later after i swapped in a .442/.465 Wolverine cam. BTw, how much do those 71 Fastbacks weigh?

I don't think that it's the gears. That thing should go like hell up to about 75 mph and then run out of steam.I think you have other mechanical problems.

Well it looks like the jury is still out. I talked with him some more and the only difference in the car before the resto is the following. The gears 3:25 to 4:56. MSD ignition and distributor to a stock style distributor and a pytronics module. Hooker long tube headers to BBK shorties. The cam in it before was a Crane 280 dur cam to the Comp 280. No head work was done other than knurled guides, seals etc.
So There are a couple other changes, but nothing that was radical. He still has the old ring and pinion, sothat could be swapped in to see what happens. Also the MSD and distributor. So maybe we can step back and see if this thing can wake up a little. Thanks for the replys and if anybody has any ther suggestions let me know!

Jblack-

This not a joke and is in no way neant to be taken as offensive.

An engine is an engine is an engine.It doesn't know what the name is on the outside,it only knows what it has to work with.

The thing we have bean preaching about matching the compression and the cam is for "ALL ENGINES" no matter what brand of manufacturer.You need cylinder pressure to produce torque.

Here is another tip;

THIS IS CHEVY SITE!
Would you go to a Mopar site to ask Chevy advice tongue.gif

Didn't think so smile.gif

If you want good Ford advice look here
http://www.mustangsandmore.com/cgi-bin/forumdisplay.cgi?action=topics&forum=Ford+Racing&number=12&DaysPrune=1000&LastLogin=

If a guy called Moneymaker responds pay attention,he is a smart cokie and holds many records in Super Stock,he has for years so he knows what he is talking about ;)

Because of the greater gear multiplication the 4.56s will actually make a motor rev easier than a set of 3.50s. Something is wrong. If it is used as a race car it can run out of RPM before the end of the track but should not have a problem reving.

Originally posted by Jblack:
MSD ignition and distributor to a stock style distributor and a pytronics module . Hooker long tube headers to BBK shorties. The cam in it before was a Crane 280 dur cam to the Comp 280.
The highlighted areas are the areas in which i'm concerned.
Shortie headers are great for clearance, but horrible on the power range.
Why was the msd module and distributor removed for a stock distributor and pertronix?

Was the Cam ICL degreed in? if so, what degree is it?

The header swap could be a factor in why its down in power...and the ignition (pertronix) could be the reason why it isnt running right, not revving quickly, ect, as well as being a factor in the power loss.

Does he have alot of experience in changing rear gears? Some people scan over directions and read 20 Inch lbs as 20 foot lbs.

I'm leaning towards a mechanical problem in one of these areas.
Investigate and let us know what you find.

Whew...What a combination...

As others have said too much cam and not enough compression...shorty headers are nothing but glorified exhaust manifolds...ect.

A couple things come to mind.

Says he has a 600 Holley...If this is a vacuume secondary carb what sec spring is in there...Second concern about the Holley..If he switched from a 3.23 to a 4.56 gear he has increased the RPM per second and as such likely increased his demand for fuel...has he done any jetting changes ?

Even when dialed in properly a really low geared car " generally " is easier to get the tires lit up but harder to keep them lit up as the gears blast you past the torque peak too quickly...a 3.55 gear set will lite them forever as it keeps the engine in a torque mode longer !

well for me guys this seems to be pretty easy...........he went in and changed cams.....and what did he do? he went with a bigger cam......so he just killed the power there even worse with the low compression motor...........the crane cam is smaller then the comp 280........

then he took the long tube headers off and slammed on those junk shorty headers.....they do nothig for torque........so there is another step backwards........

next took off the better ignition system..........another step in the wrong direction.......

now the gears on the other hand would make great for a around town kinda car........these should provide all kinds of tire smoke even in the weakest of motors..........

to me the best thing to do is put the motor back into the state he started with........every move he made to the motor killed the torque and hp.....and was just plane wrong moves.........

either that or it is time to rethink what he wants out of the car and time to start matching the combination.

butt as he sits now......the combination is way wrong and there in no ONE single fix.

what did you expect out of a over cammed (under compression however you see it ) none flowing exhaust, choked up head combination........

I'm assuming the car has a 9" rear...so changing the gear/pumpkin isn't too hard.71 Fastback was 3540 w/o driver,1/2 tank of gas

First off guys, thanks for all the help and ideas.Thrasher, no offense taken. smile.gif The reason I asked here is I've been around for a few years (just haven't re-uped for this year) and I know the knowledge around here goes way beyond Chevelles and Chevy's. So that why I didn't think the question was out of line.
Brian, (motor martyr) The changes wer made because he wanted to try and make it as stock as possible.This is a VERY nice GT350 car. He had put manifolds back on, but switched to shorties The cam wasn't degree'd, just lined up the marks.
He had an Autolite carb on the car, but had leakage issues with it so he switched to the holley. I can find out what jets are in it.

It looks like it's a combination of a few things that are leading to the problem. So I'm going to suggest changing one thing at a time and look for improvements. Some thing won't be changed as this car is going to be sold this summer and he doesn't want to molest the car too much.But I will suggest looking at the ignition and carb. And also look at changing the gear back.

Once again the folks here at Team Chevelle have helped out. graemlins/hurray.gif I've said it many times before and you've helped me with two Chevelle projects so far. So on that note I will get my flag flying again!!!! graemlins/thumbsup.gif