Jay M

I just got back from the Dyno Shop today. I expected some loss between the chassis dyno and the engine dyno, but this is horrible!

Engine Dyno:


Chassis Dyno from today:


What went wrong??
My fist guess is that I need Headers, second guess is that the air cleaner might be a restriction. I didn't think to remove it for the second run.

I was expecting 390 HP at least. 303 is very dissapointing!

Any thoughts??

Thanks,
~Jay

1Bad69

what are you running if not headers? if you have stock exhuast manifolds on there, you are KILLING your motor....i have sidepipes with JCL baffles and when i uncapped the baffles i picked up 30hp at the wheels and about 25 torque...dont know what i gained from the baffles themselves as i did not have a dyyno done before them....
big blocks need to breathe otherwise you are choking them....

Jay M

I'm using the stock BB cast iron manifold. I was under the impression that they were not that bad. Perhaps I was wrong!!

~Jay

1Bad69

they may not be that bad, but headers are by far better....you should be making more hp than me...i pull 350hp at the wheels and 420 torque....junk those stock manifolds...

BB wowbagger

Well,the cast manifolds on a vette is better than any other cast manifold GM used.But it has a snowballs chance in Hell against a set of good headers.. :smash: :cheers:

zwede

"not that bad"? Think again. Here's my 454 with stock manifolds and then a set of headers.

MEAN72

:iagree: The single greatest improvement I made to my BB was installing a good set of headers. As the man said, these BB have to breath.

Is your engine stock of modified?

MEAN72

I didn't think BB were legal in CA. Iknow my '72 is not. :steering:

MotorHead

This is basically what I have been saying all along, 40% loss from engine dyno to chassis dyno. 500HP - 40% = 300 RWHP, nothing new here.

You can get closer to engine dyno results by adding/removing parts from the car to be in line with engine dyno setup. You are not going to do anything much about 20% drivetrain loss but add headers and remove afew other things ( electric water pump etc. ) you can play with the other 20 % . Your biggest gain right now would be headers. :D

GrandSportC3

Headers and open exhaust should add another 30 - 40 RWHP...

Even the best street mufflers cost you big HP..... I'm one of the few people on the forum that had good dyno runs and the secret is headers with big primary pipes and open exhaust.. (1 7/8 primary pipes and 4 inch open side exhaust)
You'll notice a significant horsepower difference if you'd upgrade your exhaust system...

I dynoed 365 RWHP/410 RWTQ on a 465 HP engine (383 small block)






[Modified by GrandSportC3, 6:28 PM 2/28/2004]

Chuck Harmon

Jay,

The factory Corvette exhaust manifolds are the best of factory series for that era; but, not very good compared to aftermarket headers. I wouldn't be surprised to see you add 100 horsepower with good headers. There is always the possibility that your throttle linkage was not opening your throttle all the way. This has happened to me and many others on this forum. But your graph is very similar in shape, if not power, to the engine dyno run. A partially open throttle will show a steeper fall of of power at the upper end compared to a run with true full throttle.

The good news is that if you thought you had a great running, powerful car before the chassis dyno run, look how much more there is just waiting to be unleashed!

I used a 13.6% correction factor for my L88 when I made 483rwhp, about 560 at the crank. I hope to break the 500 mark with the new solid roller cam.

Chuck

Fevre

:confused:

Think the only year Cali limited corvettes was 82 when they only allowed the 305 version, anyone know if you can register a non 305 82 in Cali now?

Stoge

RPO LG4 was 1980, not 1982

PRNDL

When your engine was dynoed out of the car did they put headers on it or did it still have your stock manifolds. I guess if I was an engine builder and dynoed the engine for my customer I would have headers in the shop that I would put on the engine. :)


I was a little disappointed with the improvement I got from headers. I guess Zwede had raised my expectations! :lol: I felt no noticeable difference while driving the car ( I expected it to feel like adding a supercharger) but I picked up about 2 mph at the dragstrip, which is what, 25hp? certainly not 60. A pleasant and unexpected benefit of the jet-hot coated headers is the engine runs cooler now.

I do recall that the 71 LS6 engine which we all know as "425 hp" which is a gross rating, was also rated at 325 hp net. So you have to figure 325 hp net could not be more than 300 hp at the rear wheels. That's how you would go from a 425 hp engine to less than 300 at the rear wheels.

MJ

your dyno run actually looks a lot like mine... this was before the headers:




[Modified by MNJack, 8:52 PM 2/28/2004]

thevetterisbetter

I heard there is less of a loss with a manual than an automatic? Is this true, someone told me to calculate 20% drivetrain loss for my dyno results of 420hp and 424 lbs-ft of torque.
What my question is, cars that advertise today saying they are getting 250-275 hp, is that at the flywheel and is it net or gross?

427Hotrod

Definitely need headers. Your engine seems to like 6000+ rpm so those manifolds are killing you.

The Flowmaster 50 series and 2.5" pipes aren't helping much either. When I had a 427 in mine, it made 423 RWHP through 40 series mufflers and 2.5" pipes. Uncapping didn't help much at the track, but I didn't try it at dyno.

The 540 in it lost literally 50 RWHP through 3" pipes and 40 series Flowmasters when capped up. Uncapped it came alive. I'm running 3" race Bullet mufflers now, but they are a little loud. :blueangel:


JIM

Jay M

Thanks for all the replies,

Headers are now going to be a top priority for me. I actually have a brand new pair of Jet-Hot coated Thorley headers on my front porch. I didn't use them because the shop couldn't get them to fit. I think I will call Thorley and see if they can do the install, and modify them if needed.

Doug Thorley headers aren't very popular around here, maybe because they don't fit very well. I searched the internet for thorley+corvette+fit and found the BB from hell artical. They used Thorley headers and had to grind and dimple a little bit to get them to fit.

Marcus-
While I was at the dyno shop your dyno results came to mind, I remember reading about your dyno testing on your website. Hopefully I will be able to get headers installed within the next few weeks and I can post the results. I don't want to spend another summer working on the car!! I want to spend the summer driving it.

YES! I see this as a good thing! As long as it doesn't cost me too much :banghead:

The main purpose for the engine dyno was to tune the engine and see what his design could produce. Therefore he used huge headers, and no accessories. It may have been helpful to bolt on the stock manifolds while the engine was on the dyno, but at that time I wasn't planning on using them.

Well, financially I am stuck with 2.5" pipes. I already hate the Flowmaster 50s. TOO Noisey!!

How much will 2.5" system really hurt a 490HP 5700rpm engine?
Is there some quiet muffler that is better flowing than the Flowmasters?
With the Flowmasters, it's not so much the noise as it is the resonance at cruising speed- It makes my fillings rattle!

I'll also make sure the carb is opening all the way.

My wife would kiil me if I put side pipes on the car! Maybe a valve so I can run open headers at the track and quiet mufflers on the street would work?

thanks,
~Jay

zwede

Jay, I also tried flowmaster 50's on my 454. Think they were on there for about a week. Resonance was horrible. I recently installed a set of Borlas and like them. No resonance, good sound. I used PN 40665, 2.5" in/out, 19" long.

Shark Racer

According to a little CFM chart I have, the flowmaster 50s flow 362 CFM.
Dynomax Super Turbos, which are VERY QUIET compared to Flow 50s, flow 410 CFM.

Dynomax Ultra Flows flow 1133 CFM. (Wow!) That's what I'm going with. I'd probably recommend that to you, too. If you're going for undercar, you could order the WLK-17219 mufflers from Summit for $66 ea. That's offset inlet center outlet.

-Steve

PRNDL

OK, that explains a lot of the discrepency !! :)


Sure! They are called "cutouts" if you look up "exhaust cutouts" on Summit website or even JC Whitney you will see a pic.

I actually like my flowmaster 50s.... no accounting for taste! :) MJ


[Modified by MNJack, 10:10 PM 2/29/2004]