Dyno results of 408 falcon today

Originally Posted by dennis111

IMHO, his build looks like it would be in the neighborhood of 500 or so hp at the flywheel. At the wheels will certainly be less. One of the major contributors could be the transmission. The build sheet says C6 flexplate and a C6 will rob more power than a C4.

It does look like Frdnut is on to something about the valve springs possibly falling out at higher RPM.

Irregardless, the dyno that was used is a chassis dyno and this one could be stingy. There are just too many variables and differences between readings. Do what Melissa does and run it down the track a few times if you want a more accurate measurement of HP.

You should know that about 5 months ago I put a professional built c-4 with manual valve body and appropriate flex plate in the car. The build sheet is 4 years old now. Thankyou.

james comet/falcon

Wow...what a nice looking car and ya gotta love the 260 emblems. I think you may have another 25 HP hidden somewhere.

I'm with Dennis... it certainly looks like a healthy build on paper. However, right off the bat I would think it could use more carb than your 750. What size headers and exhaust do you have on the car?
For me a throttle linkage adjustment, degreeing the cam properly, and a 3" exhaust got me from 357RWHP/383RWTQ to 419RWHP/418RWTQ running through an AOD. Just going from a 2.5" to a 3" exhaust alone was worth 19RWHP and 13RWTQ.
Are you planning to run it down the track? As Dennis indicated, that would really tell you where you're are.

Originally Posted by kgordonl

I'm with Dennis... it certainly looks like a healthy build on paper. However, right off the bat I would think it could use more carb than your 750. What size headers and exhaust do you have on the car?
For me a throttle linkage adjustment, degreeing the cam properly, and a 3" exhaust got me from 357RWHP/383RWTQ to 419RWHP/418RWTQ running through an AOD. Just going from a 2.5" to a 3" exhaust alone was worth 19RWHP and 13RWTQ.
Are you planning to run it down the track? As Dennis indicated, that would really tell you where you're are.

I'm going to have everything checked out on Friday and especially the linkage. When I put my gas pedal to the floor the carb does not open up all the way. It's about an inch short from being fully opened and there is some slack. I to have 2.5" exhaust. As well I forgot to mention that I have a Holley blue electric fuel pump. Anyway, I will know more on Friday and thanks to everybody for their help.

james comet/falcon

If you want all the power the engine has to offer... full throttle opening and 3" exhaust with mandrel bent pipe. THEN, you can start tuning. Until then, you're peeing into a strong wind.

You can use 3" pipe back to 3" STRAIGHT THROUGH mufflers. (Magnaflow)
Weld 3" header rings to the muffler outlets.
Mount 2.5" tailpipes using header reducers to make them removable.

This provides the best of all worlds.
The tailpipes can be installed for quiet cruising.
The tailpipes can be taken off and dumps installed for "thumping" around at full 3" power.

Plus, the removable tailpipes make the entire exhaust system easy to remove for trans work, etc. It's truly the best of all worlds.

Think about it!

Oh... NICE CAR!!!!

Good Luck!

Originally Posted by jamescomet

When I put my gas pedal to the floor the carb does not open up all the way. It's about an inch short from being fully opened and there is some slack.

I can tell you that my linkage was leaving the carb about an inch short from being fully open on my first trip to the dyno. Just fixing that and no other changes, mine went from 357RWHP/383RWTQ to 376RWHP/405RWTQ. So for me, that alone was worth 19RWHP and 22RWTQ.
Then the exhaust upgrade was worth an additional 19RWHP and 13RWTQ. You never said what kind/size headers you have. If they have small tubes, that could be holding you back quite a bit at 5000rpm up.

Good luck, and let us know what you find out!
.

IMO, the valve springs seem pretty light for a solid roller.

I've seen lighter springs on similar cams, on Pontiac motors (which have MUCH more mass in their valvetrains) without problem.

My 425 is VERY similar in spec (1 degree more intake, 3 exhaust) and a tad more compression. With a small carb, my motor made 557hp at the flywheel. Picked up 1.5mph with a larger carb, so flywheel hp should be at least 10 higher now. Your lash may be screwed up, too, as mine is not noticable at all.

At the rear wheels, though, best pull has been 428.

FPA 1.75" headers into 3" X-pipe to 3" Goerlich mufflers, then to 2.5" tailpipes out the back. Fuel system has been upgraded to 1/2" hard line inside the tank to -8 to the regulator.

At a 3790# race weight and 3.50 gears I've gone 7.302 in the 1/8 mile. Still more tuning to do, I've found .09 seconds on JUST tuning the squirters.

Lee

Originally Posted by kgordonl

I'm with Dennis... it certainly looks like a healthy build on paper. However, right off the bat I would think it could use more carb than your 750. What size headers and exhaust do you have on the car?
For me a throttle linkage adjustment, degreeing the cam properly, and a 3" exhaust got me from 357RWHP/383RWTQ to 419RWHP/418RWTQ running through an AOD. Just going from a 2.5" to a 3" exhaust alone was worth 19RWHP and 13RWTQ.
Are you planning to run it down the track? As Dennis indicated, that would really tell you where you're are.

Ok I got the car checked out today and the first thing that needed fixing was my carb linkage. Two springs were added and they were added in a different hole on the carb because it was short in opening up all the way.

***Secondily, I have shorty headers which are an 1"5/8's and the exhaust pipes are only 2'1/4" with some bends in them. I knew I already had the magnaflow mufflers. Now, the thing about the headers is the fact that I have a set of Crites which are a lot bigger including the collectors. This engine was originally going into my 71 mercury comet gt and then I found the falcon and put the engine in it. The crites headers will not fit in the falcon so in order to get the maximum power I would have to have someone make me special headers which is very expensive. The mechanic said he knew somebody but it would cost around 2,500 dollars.

***The other thing that is robbing me of hp is the elevation of las vegas nv which is over 2000 ft above sea level which can also have an effect on my 10:4/1 compression. So the bottom line is the headers and exhaust pipe situation. My mechanic who drove the car said he would not even mess with getting special built headers because the car is already "scary" fast the way it is. In any event, I really appreciate everybodys help. ThankYou.

james comet/falcon

Yikes! 1 5/8 shorty headers and 2.25" pipes really have to be choking it. You are probably losing 50+ RWHP from that alone which sort of defeats the purpose of that big stroker. I'm sure 375 RWHP feels very fast in that light car, but imagine what it would feel like if it were "uncorked!"
However, if you are happy with it then it is a beautiful car regardless.