Thread: Just dynoed my 396 BBC...how to get more HP?

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So I just came back from my first dyno run on the 396 that I built. I'm running a th350 tranny in a 1969 El Camino. 3400lbs, 3550 with driver. I tuned it somewhat on the street before I went...the thing pulled 355HP to the wheels at 5800 RPM. It made over 350HP from 5400rpm to 5800rpm. I believe I let off at 5800rpm because it dropped like a rock after that. It made 350 Torque from 4400rpm to 5000rpm. Very flat. The mixture at full throttle was at 12.42-1. At idle it was at 10-1...way too rich. Anyways...Does this HP # sound right? If my engine is pulling all the way to 6000 RPM shouldn't it be making more power than this? I believe I set the timing a couple months ago to 34 deg. total advance.


Shouldn't my car be making more HP with RPM's this high?
Anybody know what this car would run in the 1/4 mile?

Thanks.

Also...if this dyno is right, that would mean that my big block is making 400hp/400tq at the flywheel(approximately). To me, this sounds like it is at least 50HP and 50 TQ Low... What do you guys think?

1 hp/ci is quite respectable... How much CR and what cam? You will get more power with a leaner mix around 13.5:1 you don't want to go much leaner than that. Maybe can stand more timing lead... The plugs will tell you... Look for the heat line on the ground strap, you want it about the middle of the bend or a little further... More lead pushes the blue line further down the strap to the base... That's too far. What fuel are you running? With a little tuning you could see a couple dozen more horses... What do you have for intake and exhaust?

-Chris

Calculator says you should see 12.37 @ 108 in the 1/4 mile

Thanks. The cranking compression reads at 160psi, I believe I measured that cold. A little low, but still runs great. It's a new motor... The cam is a fairly big solid flat tappet with 240 deg. @ .050. on a 108 LSA. .530 lift. Desktop Dyno's have said this motor to push at least 450HP to upwards of about 500HP and about the same Torque. The Heads have been ported and polished and tested at 271cfm at .500lift @28in. 1.75" primary tubes and 3" collector doug thorley headers. The exhaust is just a set of 3" Purple Horny glasspack mufflers.(They weren't too happy when I brought it in to dyno) Performer RPM Air Gap Intake. 750cfm pumper carb. The jets are 73/82's right now.

And I would have believed the HP numbers because that is respectable considering I didn't use a dyno to tune it, but the torque being only 350tq? That's what made me wonder... A mild small block 350 could put out those numbers...

Oh and I put chevron 91 octane in it. And just for the hell of it I threw 5 gallons of 100 octane VPRacing StreetBlaze to 1/2 of a tank of gas.

i would run an 850 carb cam somewhere in the .550 lift range bit more duration

Dyno's don't always tell the true story,great great tools for tuning but nothing more.10 different dyno's will give 10 different results. Engine builder dyno's always show big numbers. Theres a guy here in St.Louis that calls his dyno the Humbler, he swears he gets more realistic numbers than anybody and delights in putting so called big name,big buck,big horse
motors on it

I knew dyno's were off but I didn't realize they would be off by that much...I guess the track is the only way to really tell how much hp you have. Does anybody know what 160PSI cranking compression would be? I'm thinking maybe my compression is a little low for the camshaft...maybe I could try a wider LSA like a 112 and more duration and lift on the exhaust

if anything I'd guess your compression is on the high side... At 160, you have about 10.9:1 dynamic compression at sea level 70F... Probably putting your static cr north of 12:1... Do you know what the actual SCR is? You really should know these things in building a motor and picking a cam... Do you have any ping? Cr that high you probably want to use 110 octane or straight 100 at the very least... What heads? Iron or aluminum? My 402 had 540 lift and that required relief in the bore for the intake side with closed chamber heads so you probably can't go much higher on the lift but if your cr is as high as I think you want quite a bit more duration.... How can you get reasonable numbers out of desktop dyno if you don't even know your cr? Who built your motor?

Sorry if I'm ruffling any feathers but this don't add up

-Chris

160 PSI is not 10.9 dynamic compression. My engine would have blown up running 91 octane for the past 5 months. I can't remember who posted it, but I remember seeing something posted that anything less than about 185-190PSI was able to run on pump gas. The engine is right around 9:1 static compression which is a little low. I just wanted to confirm if that matched up with 160PSI. And I built the engine myself. Closed Chamber Oval port heads 96.4cc chamber with a piston that measures -1cc. Between the very small dome and the valve reliefs it is basically a flattop piston. There was no detenation detected on the dyno...

So maybe the big camshaft and lower compression ratio is hurting the torque numbers? Or is the dyno WAY off on HP and Torque numbers? This thing pulls hard, it doesn't feel like a small block with 400lb. of torque. My friend says it's faster than his 69 chevelle with a 468, milder cam and large oval port heads when it was running... Even with 2.73 gears it gets up to 100mph in what feels like under 10 seconds.

Also, since I had 2.73 gears...the guy recommended that I run on the dyno in 2nd gear...would that affect the dyno #'s? Because I know you're supposed to run in the 1:1 gear ratio, but he said since my gears are so high that it would work better? So instead of running in 3rd gear I ran it in 2nd...

Well, in short standard atmospheric pressure at sea level is 14.7 psi so if your cranking compression is 160psi your dcr is 160/14.7=10.88:1... Just math... So it seems one of these numbers ain't right... That's why I mentioned it because you would be detonating with pump gas... I would expect a normal cranking compression to be in the 120-130psi range for a hot street motor... If your scr is closer to 9:1 you should be around the bottom of that range... I would also be very surprised if you could get 1.25 hp/ci out of a 9:1 motor... If you can post all the motor specs I can run it through desktop dyno for you but it sounds you've already done that... Keep in mind dd won't account for accesory drive (water pump alternator etc) which can amount to about 20hp... I'm not trying to beat you up or anything... The numbers just don't sound right.

-Chris