My Dyno Experience

[Roscoe]

Well last week I decided to put my Cobra on a dyno and just see all those four-hundred and yadda yadda horses I've been bragging about. Just like talking to a new date, we tend to embellish things.

Now my engine certainly has the potential for power: 351W bored +40, TRW forged pistons, Edlebrock performer plus cam and timing setup, 58cc AFR alum heads with Harland Sharpe Roller Rockers, Edelbrock Performer intake, 650 Speed Demon, etc. and running 93-94 octane.

I was really disappointed when I saw my hp at 267 and torque at 330. I really thought that I would be more powerful than that. Hey, with a 2600 lb car that will still propel it down the highway at tremendous velocity but, still, I should be getting more…right? Even allowing for 18% power loss through the drivetrain that is still only 315 hp at the crank.

Well I faxed the dyno sheet down to the Demon tech guys. They were very helpful and I made the following changes:

1) Replace the progressive linkage to one-to-one
2) Raise the throttle cable on the carb to the big 1/2" hole to allow for full stroke of the linkage and better leverage.
3) Rejet down 2#'s from 70/78 to 68/76
4) Replace my 1/2" open spacer with a 1" 4 hole spacer.

Well I did all this, at very little cost, and took another run on the dyno yesterday.

I made three runs and all were about the same: 291 hp at the wheels and 365 lbs of torque!! What an improvement!! This is almost 350 hp at the crank and there is still room for improvement.

I just faxed the results down to Demon for more suggestions.

Anyway, I guess the point is that we all tend to talk up our cars but you never really know what you have, or where you need to tweek it, until you get it on a dyno. I certainly had the potential but was not tuned properly.

By the time I get done I should be in the 320-325 hp at the wheels and in the very high 300's at the crank. Certainly a big difference over last week.

Roscoe

[Dominik]

Roscoe,

we all should do this, even if the dynos are said to vary +/- 15%.
So it's okay for back to back testing and better than nothing.

If the dyno reads 300 hp, how would you know if this was at the upper level of the tolerance or lower or the real value?

Or if your engine had 300 hp that could show either 345 hp or 255 hp on the dyno.

So your reading maybe 345 hp one day. But as you do not know if this was the upper value (it could be the lower reading also: minus 15% of the real value).

Than your engine may produce 85% = 345 hp: 100% = 405.8 hp.

That is quite in interesting mathematical game, but you may get the picture ...

The drivetrain loss is more with automatic, or in any other gear than 4th (direct) of a manual. The sum is more like 12%, but I thought the dyno calculates this during the "coast down"?

Now, you dyno people: yell at me!
I am at least six hours of flight time away from you
And I am no fan of this "put your rear wheels in the roll and dyno" to find accurate numbers.

Dominik

[Brownyard]

Gents--

I recently took delivery of my new motor from Southern Automotive, a 347 cube motor with solid lifters, single plane intake, 780 cfm holley and twisted wedge heads among other things. I was hoping for 400-410 horses at the rear wheels.

After tweaking the jets, pushing the timing and dialing the motor in, (about 3 hours of dyno time and worth every minute) I was showing 339 horses at the rear wheels and 325pounds of torque. The technician advised me that the above equated, with my gears and driveline3 settup, to approximately 422 horses at the flywheel. Allowing for some reasonable tolerance, I feel that I have gotten a very strong small block for my money and I am extremely pleased with Southern Automotive. The time on the Dyno yielded about 30 horses over the as-delivered power, but this is understandable as initial tuning and settup was "seat of the pants" and I am known as a numb a$$. My first small block only achieved 224 horses at the rear wheels, so this is a great improvement.

We all talk about these big-horse numbers, but its really interresting to see what happens when the rubber meets the rollers

Rick

[CobraEd]

I was dissapointed with my numbers on the dyno at the DVSF. Turned out that my timing was way too advanced. The ring on my harmonic damper had slipped (since I have owned the car) and I had no way to time it other than by seat of the pants and listening for detonation. Well, I kept advancing it and advancing it always with better throttle response. I kept waiting to hear some pinging but it never came. I am told that this was because the new aluminum heads are very resistant to pinging due to the material and combustion chamber design.

Anyway, I went home, found TDC and marked the dampner. Now the timing is set right and the car hauls ass. Just as an aside, check this out. The clutches in my posi rear were all worn out, and I was completely blowing away the right rear tire. The simple short term solution was to buy the BFGoodrich Drag Radials which I put on. Recently, I rebuilt the posi rear with all new clutch packs. Now the car consistantly spins both rear tires equally. So I figured, now that I have the posi all fixed, I will take off the sticky drag radials and put the regular Radial T/As back on. Well check this out, . . my little low torque 302 (but almost 400hp) completely blows BOTH tires away now at any speed rolling along in first gear. The thing goes right to readline. It's like driving on ice. So, the moral of this story is, that if I had not had my car dynoed, I never would have known there was a problem and I never would have gotten the car where it is today. BTW, the drag radials are going back on this weekend!!! I don't know how you guys with large displacement engines get any traction at all??

ED IS HAPPY!!!

[Roscoe]

Dom,

I guess you find out if you are varying on the tolerance by doing multiple runs and look for consistancy. We made three runs yesterday and the hp varied about 1hp, torque the same.

Just heard from Barry Grant. After reviewing my dyno runs recommended I jet down 2 more numbers.

Roscoe

[427sharpe]

I.m happy to see some reality creep into figures! Dont let motor brokers con with this 800 HP crap--it aint gonna happen. As far as dyno variance--if your dyno is off by 15% get someone who knows how to set one up and try again! While HP and torque readings will vary--a dyno should be one hell of a lot more precise than +/- 15% if set up properly!

[dscott]

I agree with the +/- 15% on the dyno. That would make it impossible to tune anything. I have an engine dyno in shop and we build alot of circle track engines and do testing on the dyno. Some of the small 4 cylinder engines we build can run up to 200hp. We are always looking for that extra 1 or 2 hp with cam, carb, header, timing. The runs on the dyno need to be consistant or we couldn't tune at all. The computer does compensate for air temp, barometer, and humidity. We have to be very careful with each run to make sure it's identical to the last for comparison. Engine temp is a big hp killer. So if someone's dyno is off that far on each run I'd look for a new place to dyno. I have seen dyno sheets from other shops and they do vary from shop to shop but not by that much if it's setup properly. I wouldn't think the chassis dyno would behave any different as far as consistancy from the engine dyno.

[Brownyard]

I'd add that over the years I have found that a properly maintained dyno with an operator that understands how to set it up and run it consistantly should never demonstrate anything like a 15% error factor.

If you want to get a feel for the effect that your tweaks are having, then you need to do one change at a time and then do a pull. Last week we did a series of 19 pulls to get my car where I wanted it, but watching how each change affected the power curve really gave me a feel for the process. The results we achieved wer right where we calculated the engine would be, so I am confident that the error factor was minimal.

Rick

[MY 401K]

GUYS,
I have a 392 stroker crate engine with a 650 Speed Demon , with a 1/2" carb spacer hooked up to a Tremec TKO with a 3.88 rear. Everything came out of the cartons with no mods at all. My Snake had 2200 miles on it and I took it to Mustang Magic in Deer Park, NY to get it Dyno'd. I was more than happy with the results. The Torque was 390.3 and the HP was 378.8 at 5600. The timing at full advance is 34 degrees. My Snake runs terrific but I'm still entertaining the thought of AFR heads. They say you can realize an additional 75 HP. Maybe a winter project.
Later........John

[JAM1775]

I have a 351W crate (385) motor which dynoed numerous times at a consistent 337 rwhp (405 flywheel) @ 5800 rpm and 336 rwtq at 4300 rpm. I swapped the Victor for a Weiand stealth before the dyno which explains the stronger mid range than advertised. I am running a 650 race demon. This past winter I ported/milled the crate GT40X heads, port matched the intake and added a 3/4" spacer. With the mods the motor dynoed at 378rwhp @6000 rpm and 360rwtq@4600rpm. The second dyno sessions also reflected the motor producing 330rwtq@3000 and 330rwtq at 5600 rpm. I was very satisfied with the width and flatness of that curve . Roscoe..if you feel you have more power potential try calling AFR and advise them of your cam and motor specs. They may better advise you than BG.

[Roscoe]

Jam1775,
So far BG has given me excellent advice. Once I get that down pat I'm going to start with timing and AFR. One thing at a time.
Roscoe

[leadfoot]

I have never understood people that spend $1000's of dollars on an engine, and never spend the $100 for a few dyno runs. If done properly, you will most surely gain another 10-25 hp with the tuning on the dyno.

Perhaps everyone is afraid of the reality that we can't take a stock block, snap on a few pieces and end up with 800hp.

[Dominik]

My friends,

dont' be confused. I am talking about a 15% "error" for a chassis dyno. I do not have one, but that is what the chassis dyno people / engine builder use (here in Germany) to tell you to give the car owner a better feeling = "more" horsepower.

We, no my buddy, dynos his engines on an engine dyno before he puts the engine into the car.

That serves for the run-in procedure, as well as to verify that the engine runs correct. As a side effect he optimizes the torque curve and measures that. That takes about 2 days most of the time.

His cars / engines, mainly race engines, wander to the races and nothing would be more frustrating than having a leaking engine 1000 miles away from home.

As you said before, the chassis dyno is a good tuning tool, better than doing it on the street. Especially when you're not allowed to travel much beyond 60 mph. And it shouln't be 15% off! Go there!

800 hp = crap, indeed.

My buddy's 520 + cui almost reaches that values, but we are talking big money here.
No, I am not posting a picture from his Can-Am McLaren again.

Only if you insist.

No, I am not Mr. Dyno or Mr. Engine in our forum. I built about 10 to 15 engines (one all-aluminum, three times) and five Cobras and watched the rest.

Don't be mad with me, but I always hated that "four-hundred and yadda yadda horses talk".

BTW, my car had 552 Hp. That has been calculated by the coast down / accelerating method described elsewhere. GM over here does it all the time on the Autobahn with big engined cars.

This car went like h***, just ask the big-bikes in my neighborhood. And it had more potential. Lift was only 0.600" at the valve.

Dominik

[ERA535]

Domenick:

How about a picture of your car!

I would love to see a shot of your engine - it sounds really nasty!

Pat

[JAM1775]

Roscoe...BG's tech line is awesome ! I have called them many, many times. They are extremely helpful and patient which is important with my "fussy" DR demon. If anyone has every called the Holley tech line they would LOVE those BG guys ! Good luck with your inquiries and please keep us posted ?

[Dominik]

Pat,

my car is posted here:
Superformance dealer in South Africa

My buddy's Can-Am here (he could have won this season, but wasn't registered for all events in spring not knowing if the car will hold together. It's mostly a one man show. He's 62...):

Dom

My intend is not overloading this server. The Can-Am was shown before, but I don't not remember where.

http://www.supersportscup.com/