Just got back from the Dyno and am wondering if my output is right.

Could someone help with the desktop dyno to see if it is the same.

I built a conservative engine but was hoping for about 390HP

I am not sure what Desktop Dyno variables are needed

I have a 427 with stock oval port heads and 9.6:1 compression
Camshaft XE268H-10 Duration @ 0.006" 268 / 280 Duration @ 0.050" 224 / 230 Lobe Separation 110. Carb is a well tuned QJET with 13:1 mixture during dyno. Exhaust has stock manifolds, 2.5 inch duals to Dynomax mufflers. Ignition is stock points setup. YEA I know but I was into the numbers matchine thing.

Thanks in advance for any help and recommendations
:smash:

 

Without consulting custom cam files (I lost them) I'm coming up with 319 hp at 5000 and 395 lb ft. of torque at 3000, at the flywheel.

Large tube headers with mufflers jumps it to 378 hp at 5000 and 446 lb/ft at 3500.

Fully ported, rectangular port heads (again, generic file) brings the juice to 496hp at 6000 and 490 lb/ft at 4000.

I'll save the file, and if I find the cam files, I'll redo it for you.

So what were your numbers?

 

So where is the HP ? What were the dyno numbers ? :D


[Modified by MotorHead, 10:21 PM 9/30/2002]

 

WOW - Maybe I should not be complaining - I have 311 hp at about 5000 and 389 ft lbs about 3600 to the ground. It was about 85F that day.

I have the cam card - lift is .515 int and .520exh with the 1.7 roller tip rocker I have.

What percentage can I use to get the crank number (20%)?

kos


[Modified by kostutsman, 10:30 PM 9/30/2002]


[Modified by kostutsman, 10:32 PM 9/30/2002]

 

I believe 15-20% is the rule of thumb.

I found the head and cam files, but nothing that fits your setup.

I ran my combo through the Desktop Dyno, and I came up with 351 hp / 396. I chose my combo after reading what a bunch of the magazines did with it. They came up with anything from 400 to 415 (at the crank). So I don't know what the deal is.

Tweaking your exhaust a bit (going from stock manifold and mufflers to high power manifolds and mufflers) brings big gains. Messing with the cam, does very little. I think the lack of exhaust choices with the Desktop Dyno explains the variance. Switching the exhaust components to high performance yields 409 hp at 5500 and 442 lb/ft at 4000.

I think the software is accurate enough, that if you could hand input exact numbers, it would return stats that were within 10-15%.

Hope this helps.


[Modified by joeveto, 10:48 PM 9/30/2002]

 

Here is the way I do it. On DD I use the lowest restriction exhaust which is either large tube open headers or stepped headers. I believe this will give you a pretty accurate GROSS HP number. We have to be careful what we are asking for here as the numbers can change 10 - 25% between GROSS and NET HP.

If you want to know what the NET HP is then figure out what kind of exhaust, mufflers and accessories you will be running and subtract another 10- 25% off the GROSS number you got with the open headers on DD.

If you then want the RWHP numbers subtract another 20% ( especially on older Vettes ) and viola you get some numbers that you aren't happy with.

Here are some facts to back up my theory in 1971 a LT-1 was rated by GM as 330 Gross HP and 275 Net HP a loss of 10 % and a LS-6 was 425 Gross HP and 325 Net HP a reduction of 23.5%. You take another 20 % off the LS-6 and you end up with 260 RWHP. Bummer :eek:

This is the major reason why a lot of people freak when the actually go to chassis dyno, sure the engine builder built you a 450 HP motor but don't be suprised if it pulls less than 300 RWHP.

One more thing, 300 RWHP is nothing to take lightly either, that is where I am and I pretty near pull the front wheels off the ground off the line :D






[Modified by MotorHead, 8:28 AM 10/1/2002]

 

You did better than me.
I have an almost identical setup except for the well tuned carb and mufflers.
I think I came in at 290Hp and 370Tq.
I plan to dyno again after some tuning, but I think you did pretty good.

 

Pat,

Thanks for the input maybe another difference between our cars is that I have a 3.70 rear and no power steering.

Joveto and Motorhead,

- I appreciate all of your work and research - I think since it is fall here it is time to stop working on it and drive it! I feel much better now esp Motorhead's comments - thanks guys.

Karl

 

Karl, great shot of a beautiful car!! I don't know what it is.... but the 68 bigblock convertible is just the best looking vette ever made! :) yours is a great example. It even looks great in RED!!! :lol: Take your vette to the dragstrip and get a better idea of realworld hp by your trap speed. MJ