[Birddog1970]

Got my car back from the Dyno Tune. 70 396 with stock intake, Qjet, stock exhaust manifolds w/flowmaster exhaust, minor head work to the stock heads (bigger valves, ported, Roller tip rockers), 10:1, mild cam all back by M-20 and stock 3:31 gears. Im also at 5000 Ft Altitude.

First run I was at 305 HP @ 5000 RPM and 396 Torque @ 3300 RPM at the rear wheels. After Recurving distributor and playing with the Qjet I'm at 364 HP @ 5200 RPM and 426 Torque @ 3500 RPM. The dark line is first pull, the thin line (hard to see) is the last pull.

What would you guesstimate HP at the Flywheel (M-20 and Mustang Dyno used)? I would like to bump up the gears, any thoughts based on the chart if 3:73's or 3:56's would be better?

Thanks Guys,

Dave

 

[jeff swisher]

you decide how many R's you want to turn on your daily commute.
I like 325's for a good daily driver work horse. and for kicking a$$ i go straight to the 456's..411's arent bad...
math for you: 336this is a given to make the problem work.
336 X gear ratio X MPH, divided by tire diameter = RPM

I use this a lot of times to determin what tire and gear would best work for a combo...now if you have a loose converter you must take that into account,,as the equation is only for Zero slippage

Not a bunch of difference in the 2 gears you meantioned...

 

[JamesL0822]

66 402 with M21 very similar build I'm at a lower compression ratio (9.3:1) and I changed my 308 rear gear to 373 posi and I wish I would have went with 331s or 342s rpms are way to high for highway cruising

 

[KMR]

WOW!!! 60 HP from tuning. I'm jealous

 

[Twins Fan]

Those are impressive numbers from a mild cammed 396 with a stock intake and stock exhaust manifolds in CO air. Almost unbelievable. If they're correct though, that puts you at about 450 flywheel HP.

 

[Tom Mobley]

especially impressive since it's Colorado. There ain't no air up there....

 

[FRYNTYR]

Those numbers should run easy 12's in your chevelle.

 

[Buzzbomb]

Not bad! So what timing numbers did you end up with? Did you have the bushing to limit the advance?

What did that place say was up with your carb? How did they calibrate it? I'm assuming the bog is gone..

I sort of remember the other posts, but not in total detail..

 

[mr 4 speed]

Based on the fact you made 364 HP at 5200 RPM (very impressive BTW) you don't need any more gear...the 3.31's are perfect.If your HP peak was at a higher RPM then you would need more gear.
FWIW,I have 3.31 gears and cross the stripe at 5000 rpms going 108 MPH in the 1/4 (with an auto)

 

[Birddog1970]

Not bad! So what timing numbers did you end up with? Did you have the bushing to limit the advance?

What did that place say was up with your carb? How did they calibrate it? I'm assuming the bog is gone..

I sort of remember the other posts, but not in total detail..

I originally set the total timing at 39 deg, but the dyno showed that the timing kept climbing past 4K (which I didn't realize). He recurved the distributor and now it comes in full at 39 deg at 2500 RPM. We aren't using the vacuum advance can anymore.

The carb issue I had where it would have a flat spot was actually my accelerator pump. My pump wasn't bad but it was a little too big for the hole so it wasn't a smooth pump and was creating vacuum. We had to go through 4 different pumps until we found one that would seat nice and not binding up. Bog is gone now

I'm really happy with the performance now, the car is very responsive. The Dyno guy said if he had some more time we could fine tune some more by playing with the carb and maybe squeeze out a few more HP but I'm good with the results considering all the limitations I have on the motor.

Thanks for the advice on the gears Mr. 4-Speed, I dont want to over gear the car ... I did that on my old 66 Chevelle and didn't like it. I'll just put a posi unit in there and keep the gear ratio for now.

What % loss from the Flywheel to Rear Wheels is avg when running a 4-Speed? I thought around 15%....

 

[Buzzbomb]

70 396 with stock intake, Qjet, stock exhaust manifolds w/flowmaster exhaust, minor head work to the stock heads (bigger valves, ported, Roller tip rockers), 10:1, mild cam ...at 5000 Ft Altitude..............

..........We aren't using the vacuum advance can anymore.

Why can't a mildly built engine use a vacuum advance? At 5000 ft, I'd bet you can easily tolerate at least a 15 degree can on PORTED vacuum..You aren't gaining any timing at idle by using the vac advance on a PORTED source, but you are giving up economy and perhaps throttle response at part throttle cruise, not to mention that a disconnected or non-functional vacuum advance can sometimes cause hot running for cars that actually get driven..

This is something you could easily fiddle with yourself by either getting a new can better suited to your app or by trying to dial in 15 degrees or so with your current adjustable can. This is very easy and well worth the effort.

That's interesting about the accelerator pump..

Not sure about the HP loss from a manual, but an auto is generally thought of as a 20% loss, so one would guess that a manual would be less than that.

 

[mr 4 speed]

Dave..install that posi in there as you mentioned and you'll have a blast driving it :thumbsup:
What your dyno numbers translate into is throttle reponse.I bet its very snappy.
Your HP peak is 364 @ 5200 and thats where HP and TQ are equal,on any motor at that rpm..pretty cool IMHO
Again,you'll be happy with those 3.31 gears as is
What camshaft is in there?

 

[Birddog1970]

I can mess around with the vacuum advance can to see if I get a better response. Just got it back the other day and haven't had a chance to play with it too much.

Attached is the Cam Specs, its a Melling Select Hyd cam. I'm using 1.6 roller tip rockers vs 1.7 so the valve lift will be alittle lower.

 

[Winston Wolf]

Pretty nice numbers, especially for a Mustang Dyno. I've had a couple of my cars on them.

One that's a stick had 384 HP at the flywheel and did 302 HP on the Mustang rollers, so that's 21% loss.

Not to get your hopes up, but I had another that did 328 on a Mustang/364 on a Dynojet. That car ran low 12's at 3600 lbs.

I would get an adjustable vac advance and set it for 10 deg advance, with it coming off at maybe 10" to start with. That will help it to idle better and drive better in general.

 

[Buzzbomb]

I can mess around with the vacuum advance can to see if I get a better response. Just got it back the other day and haven't had a chance to play with it too much.

Attached is the Cam Specs, its a Melling Select Hyd cam. I'm using 1.6 roller tip rockers vs 1.7 so the valve lift will be alittle lower.

I know this may not be the most popular opinion here, BUT...If you have your car idling just fine now at a decent rpm on the initial timing you are running, I wouldn't put the can on manifold vacuum. Put the can on a ported source and adjust it for 10 or 15 degrees max. You'll get this only under cruise conditions. Higher altitudes means you can use more timing. Perhaps the dyno shop just gave you a power tune? In any case, you can improve overall drivability by using your vacuum advance. You don't have a full on race car where vac advance is a waste, but it must be running pretty nice to put down those numbers. No need to throw manifold vacuum in the mix at idle and having to retool idle speed/etc. if it isn't necessary. Just keep your ears open for any pinging, which at 5000 ft, you probably won't get with a reasonable amount of timing from the advance can and 39 total. Just IMHO..

 

[mr 4 speed]

Dave...I wasn't aware that 1.6 rockers where available for a BBC
In any event,I would install 1.7 rockers and get you all you can,and besides..thats the factory ratio. BBC heads love lift.
Again..congrats on the numbers :thumbsup:

 

[Birddog1970]

Dave...I wasn't aware that 1.6 rockers where available for a BBC
In any event,I would install 1.7 rockers and get you all you can,and besides..thats the factory ratio. BBC heads love lift.
Again..congrats on the numbers :thumbsup:

That does seem strange. I just went back and looked at my specs of the build, he did use Comp Cams Magnum Steel Roller Tip Rocker Arms 1.7.

I think early on the build discussions we were talking about clearance issues with the stock valve covers and thought he said he would go with 1.6's .. guess I was wrong.

Dave