Ok guys, my desktop dyno has me really puzzled. I ran the set up for my motor now as it is:

360 ci
9.0:1
stock 416 heads
600 cfm carb on a performer intake
long tube headers
summit 1103 cam

and came out with 269 hp, which is exactly what i expected. But then for sh*ts and giggles i put on a set of 882 heads with 2.02 1.60 valves and knocked the compression down to 8.5:1 to compensate for the larger chambers. But left everything else the same. I came out of it with 360 hp! I checked the flow numbers, they are only a little more than the 416's (195@.500) and 205@.500 for the 882's. still very reasonable.

What is up with this? I thought these heads were supposed to be crappy???

I can get a set of these heads ported for next to nothing from a guy I know... got me thinking about a poor college kid's winter project.

 

They are crappy, where did you get your headflow files? The compression with 76cc 882 heads will be way less when you have 9:1 with 58cc 416's.

 

i have a lot of head flow files on the desktop dyno that I have. (downloaded from the internet) The 416 files match exactly what i've seen posted on this board many a time.

 

anywhere in particular you get those head numbers??

 

His flow numbers are correct for the 416's CHP has the 882's listed at 210 @.500. Your setup has to have more than 270hp to put you in the mid 8's in the 1/8. Your track times are way better than I would think with that combo, are your 416's completely stock(stock 1.84 and 1.5 valves)?

 

Those are some pretty good times. Must hook good because you rmph is pretty low.

 

The car hooks pretty well most of the time. I can usually pull 1.90-1.88 60 ft's

The 416's are completely stock, they even have the stock stamped rockers sitting on top of them.

The car is light, it weighs 3100lbs with me in it (i weigh 200lbs)

All of the flow files were part of the desktop dyno i downloaded, it also had around 100 cam files, and mine was in there, it was dead on what my cam numbers were.

 

How did you get it down to 2900lbs? Thats pretty light for one of these cars.

 

Yeah please explain, i have nothing in my car except the front interior, seats, and dash. I also have a SMC hood, which weighs 10#'s or something. Under the hood i only have an engine, alternator, and ps pump. My car weighs 3180 with 1/4 tank of gas.

 

There is no interior, i have it all stripped down to the metal. I have 2 summit race seats, and a gutted out dash (the shell is there) no center console. No heater. No front sway bar, no power steering (s10 manual rack), no stock exhaust or heat shielding for the stock exhaust. Th350 is lighter. umm i dont know what else, there just isnt much there. The weight is correct because my dad owns/operates a grain elevator and I used his scale which has to be certified by the state of Iowa every year.

The car is going to be getting lighter yet, i'm ditching the set of stock steel wheels for weld's with skinnies in the front during the next week or so.

I'm at college right now and the only time slip i have is an 8.59 one... if anybody wants to see it, i can scan it for you.

But kinda back to the main point... is desktop dyno lying to me?

 

I believe you. That is a real good time for your mods. Those 4.10s probably help in the 1/8th a lot. Probably hurt you in the 1/4 though.

I have ran some things through desktop dyno and I have decided its a crock...numbers always seem WAY to high.

 

yeah.. they do hurt some in the 1/4. The only time i've ran at a 1/4 mile track i couldn't hook up for anything, best time in the 1/4 is a 13.66@98.8

 

Couple of things.....

LOW LIFT FLOW NUMBERS are what make power in an engine like that. What they flow at .500 or higher is practially meaningless. Don't beleive me? Plug in 150 CFM for the intake ONLY at .500. Then plug in 250 CFM for the intake ONLY at .500, making no other changes. Doesn't make much difference in power, does it? THAT IS REAL WORLD, TOO. Wanna make power with a mild cam? Concentrate your efforts on flow in the .150-.400 range.

I bet the flow numbers in that range are significantly different from eachother between the 2 files.

Also, when you up the size of the valves DD AUTOMATICALLY does a flow extrapolation from the original (smaller) valve size that you plugged in to benchmark their flow. If your hypothetical 882s flow 205 on the intake with a 2.02 valve installed then you MUST tell DD that those flow numbers were tested already with a 2.02 valve installed, not a 1.94 or it will take your already large flow numbers and extrapolate them even bigger.

In short- watch that valve size related to the flow numbers- that's an easy one to get all hosed up over.

DD is only as good as the data you plug into it. When I plug in "real world" numbers it spits out fairly "real world" answers. In other words, you gotta stay conservative. Your carb flows 700 cfm, but does the whole intake system including the air cleaner? Better plug in 600 CFM instead. Does you exhaust REALLY work as well as a race-tuned open header system? Better select a more real-world exhaust choice if you want it to tell you the truth. Do you REALLY have 10:1 compression or is it maybe a little lower than that because of your choice of head gaskets or more deck clearance than you think you have? Better plug in 9.5:1. DD nails my engines withing about 10HP every time, at least in the 300-500HP range. Can't say it's accurate above that level becuase I haven't built anything that strong since I got it.

The only thing it doesn't do well (at least in my version and my limited experience with it) is model a roots-type blower. Don't know who programmed in those models but they didn't know their butt from a hole in the ground.

 

Since DD is intended for racing engines, it's always best to underestimate your exhaust. By the definition in the manual, there are pretty much no "large primary" headers on the market for a thirdgen. Small primary shorties would probably be modelled best as "Hi Perf Manifolds".

 

ok, i ran a very conservative set up through DD just now:
882 heads
1.94 1.60 valves
8.5:1 compression
500 cfm carb (mine is a 600)
small tube headers with mufflers (i have long tubes with open exhaust)

and the thing still spit out 327 hp thats almost a 60 hp gain changing nothing but the heads which i can get dirt cheap including port work. the more i look at this the more i want to get some track numbers out of these heads, maybe they aren't as terrible as everyone on here says. I know they get some race use around here in circle track applications.

 

Damon: The DDyno works up to 600hp with proven consistency. I have all the "needed" numbers when I was building this 388 and gave the dd a shot for fun and the thing said 598hp and ???tq, in the mid 500 range cant remeber right now.

But I'll agree, junk in-junk out. The more you know the better the real world result. Just wish the Itinerary(sp) testing on the DDrag could exp[lain how to get me into the 10.5's like it says I could run.