Greetings. I lurked for all of ten minutes before i just had to register. This looks like a fun site. So, excuse the yet another 'how much power does my engine make?' question. If it helps, the car is really neat, it's owner is slant six for life (despite us big-block guys trying to corrupt him...).
We've got a 225 out of a 71 Demon with some fun stuff done to it, it's in a 2800lb Valiant and this thing just rips! Nobody out here has any experience with these engines (aside from pushing them off tailgates into landfills/engine blow-up contests, etc) so NOBODY can even venture a guess as to how much power we're making.
-The thing is .030 over, $15 cast pistons (new)
-Deck and head are shaved lots ('as much as the machinist dared', over .100 total but i'm guessing, i wasn't there)
-Compression remains a mystery though it still runs fine on 92 octane. It's much higher than stock.
-Head was ported (bowls, ports cleaned up/not hogged out, polished exh)
-Comp 264S cam (264/264adv. 220/220@.050 .440lift 110LSA) Comp springs/hdware
-Clifford alum 4bbl manifold
-Holley 390 vacuum secondary
-MP electronic ignition, MSD Blaster coil, MSD wires, etc.
-MP 6 into 1 header (shudder... ugly header, VERY temporary)
-2.5" single exh w 2.5" Borla XS
Lets see, what else; elect. fuel pump, 4 blade steel fan, K&N filter...
Engine was balanced and is very smooth all the way up to 5300RPM, it sounds quite heathy and the car seems quite fast despite a rotten 904 (no stall) and 3.21 gears. It is somewhat disappointing in that it doesn't really come alive until 3500RPM, cant quite pull down low 15 second imports and gets TERRIBLE gas mileage (2 mpg better than my 3700lb Charger with it's rotten 440 Magnum and the same gears!) I didn't know you could suck that much fuel through a 390... I would like to see a better cam (i dont like Comp Cams for Mopars, maybe we'll go custom or?) and it does seem to want a bigger carb (we're thinking 525 Demon or 570 Holley Avenger). We're definately getting a better header, possibly a custom with duals.
So there you have it. Apologize for the epic but we've been guessing from day one on this. Anyone have any idea what kind of power this contraption puts out? It'll be some time before the car sees the track as the owner is broke (wonder why...) so the MPH equation is out. Anyone got any ideas? Anyone still awake...? If this thing gets any cooler i may just stop bugging him about the big-block...

J

Welcome to the site. I have a 74 Dart set up very simmiller and have ask the same ? My best ges would be 180-200 HP. I would love to have a chasse Dyno close to Columbus.

I'm with Jim, probably in the 180-200 range... you'll get your mileage back when you dial in the timing curve on the distributor and if you take the time to play with your jetting and springs on the Holley...the build up will want more carb (my 'milder' build likes the 390, but accelerates better with the 600 cfm on it...). Probably stall convertor and checking your rear ratio would help performance.

Next time you have it apart, take some measurements, if the machinist 'chickened' out you might only be running 9:1 compression, and he thought he knocked it up to 10:1....


If you have some buddies who are serious about 'tuning' or have a few $$ check out getting a G-tech Accelerometer, set it up,plug it in, and find a nice flat road the cops don't patrol, and make some 1/4 mile runs, then you can compute a 'ball park' HP/torque number...I have the $200 version and it will plot your power curves and power vs. time ratios and you can use the software to look at various runs and 'tuning' changes v.s previous ones...A very useful tool.

-D.Idiot

Weigh the car with you in it. Run it at the track and see what the MPH in the quater is. The result you get will be more accurate than any dyno because no car not once ever in the history of the world ever ran faster than it had HP to push it. There are several progams around that do a good job. I believe comp cams had one called cam select that had this program in it. Figures were very close to actual perfomance so i tend to trust it.
As to the bad mileage here is what i found out when we had a had /6 in our 66 Baracuda. Offy manifold fuel distribution with a four barrel is terrible. Front have runs rich and back end runs lean execpt at WOT (wide open throttle) I played with jetting but still a lot of dissatisfaction so one fine day I took the fourhole section off the manifold and opened it up to one big sort of square hole then I bought a 2bbl to 4bbl adapter (wiend makes these for one and they are still available . (Saw one in the auto store yesterday)
I installed it upside down so it was a 4 bbl to 2 bbl adapter and installed a 500 Holley 2 bbl.
From the git go it was a totally different car. We drove it for several years and took it to Florida twice (1500 miles one way) 25 MPG was normal (Canadian Gallon (Imp 160 oz) .
My wife raced it on weekends in the powder puff class at the local drags.(She still has her winners trophy.) I still have the time tickets (This was in the 1970s)It ran a best of 15.84 at 87 MPH .
I would highly recommend this mod. For those who would poo poo it "don't knock it if you havent tried it" You will be very surprised at the improvement. I know i was.
Car is on my website . (Search "Don's Dodges" should get you there.)
Don
BTW the previous tip on advance curve mods is also "Right on!"