disappointed...need advice

Hi all, i'm new to the forum and i have a 65 fastback that i use primarily for open track/drivers school road course events. I had the car dynoed today and things didn't work out so great. For one, halfway through the second pull the water pump toasted itself. I was also a little disappointed in the first run. It pulled a shade under 290 hp and the same torque at the wheels. The thing is, peak hp was at about 5500 rpm. For my combination this power seems low as does the rpm. Also, i'm running a wilwood disc brake setup with dual master cylinders that uses 2 lb residual pressure valves on the brakes. I think this might be part of my low rear wheel numbers but the rpm is really puzzling me.
311 cu in
edelbrock performer aluminum heads with 1.9 intake 1.6 exhaust
about 9.8 compression
Victor jr manifold
650cfm mighty demon
isky solid lifter 240 duration at .050 with .512 lift
tri y headers with original shelby style glasspack side exit exhaust
canton oil pan and windage tray
full msd ignition

i feel like i should be getting peak power at more like 6500+ rpm rather than 5500 given my cam and manifold. The only thing i can think of is maybe the exhaust is choking it up...

The headers need to be 1 5/8" min and 2.5" dual exhaust. I'm not sure how the side exhaust is laid out but I doubt it is very straight at all. Also make sure the entire exhaust has all mandrel bends(no kinks) as it flows 50-85% more than standard muffler shop bends.




To see if the exhaust is a prob, unhook it and run open headers. You'll lose a bit of lowend torque but it will defenitely flow well.

<font size=-1>[ This Message was edited by: 1 Bad 88 GT on 9/20/03 4:11pm ]</font>

thanks for the reply...the exhaust is not mandrel bent although it is pretty straight with 1 bend of about 70 or so degrees to come out in front of the rear tires. If my memory serves me it's 2 1/4 inch. The headers are tri y's that are small tube, i think less than 1 1/2 inches. How much do you think this could be costing me, and do you think it is the source of the low rpm peak power?

Put some Hooker Super Comps on the thing, along with a larger, preferably mandrel bent exhaust system.
[addsig]

anything else you guys can see that might be a problem except for the exhaust?

You will want a bigger carb when you get that better exhaust, like a 750.

Also double check your valve lash and make sure its not too loose. Are you valves floating at 5500? Did a professional set up you head springs or are they stock edelbrock?

About the brake drag thing, if you can jack up the car and spin the tire freely without drag noises its fine. If it only turns a couple revs and stops, I'd have it re-adjusted. My 408w picked up 30rwhp at the dyno after breaking in the rear drums on my drag car, the stang's emergency cables were too short for the LTD arms/drums and made horrible drag/grinding sounds and didn't spin too freely at fist install.

Maybe wrong but that combo should be around 400 hp at the flywheel (with) a bigger carb and 1 5/8 headers.Lift on the cam seems a bit short but duration looks about right.Simple things you do can produce big gains.Just changing the purple spring to a long yellow one in my 750 vac holley is worth .48 in the quarter.
[addsig]

the carb is not too small for the engine. i consulted many hours with summit, barry grant and others on 650 over 750, even found an article in one of the magazines about a 500hp 302 at a dyno where they switched between a 650 mighty demon and a 750...there was no difference other than a drop in low end torque with the addition of the 750. The lift is short on the cam because of piston to valve clearence issues. But yes, i was expecting around 400 at the flywheel at somewhere around 6500 to 7000 rpm. Are the 1.5 inch diameter tri y's the best explaination for peak horsepower at under 5500 rpm?

Where is your timing and what was the A/F ratio?

I know you only got in a couple of runs, but not having a good tune can cost you power also.

If you post the dyno graph, some of the more experienced here might be able to spot something.

Also, what kind of chassis dyno was it?

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<font size=-1>[ This Message was edited by: mstngjoe on 9/21/03 9:57pm ]</font>

What pistons??? The Victor Jr may be costing you a little vs. a Performer RPM.. Hate to say it but the Tri-Y's aren't big H.P. producers. At least step up to a set of Hooker-Comp's... Super-Comp's are better because the tubes are equal length. What's your tune-up???? ie. plugs, timing etc. What springs are on the heads???? If the are the stock Edelbrock ones you are probably a little short on spring pressure and floating the valves... The Rpm range on that cam is from 2500 to 6500.... I ran about the same combo with 68gt cast cylinder heads and a dished piston @ 9.5 to 1 with a simular Crower solid cam and a Torker11 with a 700Dp and made 375 hp @ 5800rpms[img]/phpBB/images/smiles/icon_confused.gif[/img]

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Todd
1971 Maverick Grabber
306 cu in
10.71 @ 124 best to date

<font size=-1>[ This Message was edited by: Teasme on 9/21/03 11:35pm ]</font>