I had my car dyno'd this weekend and was disappointed! I have a 67 RS w/4 speed with a ZZ3 (350 ci/345hp) and have added a hot cam kit that should have given me a 370 hp rating at the engine. When dyno'd I had numbers of 270 with 317 ft-lbs of torque. Any ideas why the numbers are lower than expected ( I thought about 300 assuming a 20% loss to the wheels)?

What brand of chassis dyno was it? Did they do any tuning? Was the car cooled down before the pull or just driven straight from the road onto the dyno and run?

Jody

The car was driven to the dynojet and it sat for about 20 minutes before it was loaded on the system. Here is a link to our site...

http://www.fattonyracing.com/dyno/

What ignition curve did you have.. did you check jetting??

Easy 30hp can be lost if both are not ideal.

Ignition read about 35 degrees total......jetting was stock. I have a 670 cfm street avenger.

I always thought the ZZ series engines were rated like the older Chevy engines were; few accessories, headers, and maybe open exhaust.

I assume you have headers; if not that's a huge chunk of the power. I also am not a fan of the vacuum secondary carbs; great for driveability on the street, but always seem noticeably slower as far as performance.

Another area I've seen is running a low profile, drop-base filter set-up with insufficient height; the lid is too close to the vents which can cause problems and the lid is also very close to the base if the filter is short, say 3" or less. I had a big block that would lose .7 in e.t. and 8 mph with a 3" drop-base filter over the 4-5" element in the same housing and base.

Jody

Actually I don't have headers they are stock cast iron, but flow into 2.5 inch tubing with Flowmasters. I also have the softer spring installed in the vac secondary. My plan was to replace the headers soon but not sure which ones to get that will fit my car.

the exhaust flow on a ZZ motor is crucial. There was a test of a ZZ3 kit on a third gen camaro. When running through the factory exhaust, the motor would only dyno at 308hp.

Looks like a good set of headers are in order. as far as the filter it is a 5inch K&N which can be seen on the website I have.

http://www.fattonyracing.com/CamaroRS.html

Filter is fine. Headers will probably get you the missing HP and torque. Those engines are rated with headers installed.

Jody

Some of my guys here said I might need to redo the heads that they might not be breathing right up top. Any thoughts? The engine has about 30,000 miles on it and little if any blow by.

Got to get headers. The old stock cast iron exhaust manifolds are plugging up your exhaust. I bet you get the 30-40 HP back simply by adding headers. Watch the carb jertting though. You may be lean with the better flowing exhaust.

I have contacted Thorley headers to see what they have to offer. I have been told that headers, although recommended for my car, don't always fit and some adjustments need to be made, i.e., hammer time!

This is Mister G's Son, the person you can see driving the Camaro on the Dyno.

The Dyno was a DynoJet. It was being used that day by South Bay F-Bodies. 50 bucks for 3 runs with Air/Fuel readings.

The car sat for about 20-30 minutes before being run. In the Shade.

While on the Dyno two large industrial fans which you can't see are blowing on the front of the car with the hood open.

1st and 2nd Video are a run in 2nd gear. Other video's are 3rd gear runs.

In the 3rd gear run the speedo went off the dial and WAY past 120 so I dunno what speed I reached.

Don't know if any of this helps.

Ron

Word for the day............HEADERS!!

Have fun!

Jody

Well this weekend I put a set of Doug Thorley headers on my car and a 750 double pumper. Took it over to the dyno place and got a woping 4 horsepower and 4 ft/lbs of torque increase. This is not what I expected. Any more ideas?

265 to 280 to the wheels is about right for that combo. I have seen a few ZZ motors pull those numbers. With traction you should go low 13's.

4 HP and 4 LB-FT increase? Something isn't right...

Hey Guy,

What kind of A/F numbers did you get with the dyno runs? Did you do any tuning after the swap?

What axle ratio are you running? Believe it or not, lower gears (i.e. 4.11 vs a 3.42) will result in lower numbers in RWHP even though the real world performance is improved. On our dyno days we have seen members RWHP drop after nothing but a gear change. It wasn't a huge difference, maybe 5 - 10 RWHP, so that wouldn't explain everything but it may contribute. There still may be something else wrong. I would suspect jetting. You may need to fatten up the secondaries. Improved flow / headers will make you run lean and negate some of the gain from the headers. Contact Holley's tech line for a jetting / vac spring recommendation. What kind of ignition system do you have? At what RPM did your peak HP occur? My HEI on my '79 wouldn't rev past 5100 RPM, even though total timing advance was o.k. With nothing more than a swap to a Mallory, I can rev to 5800 RPM. I haven't put it on a dyno, but there is a significant difference. Good luck.

[ 08-06-2003, 10:33 AM: Message edited by: need-for-speed ]

Now you need to tune. Those headers are worth 20+ ft. lbs over the exhaust manifolds and probably about the same in HP. Knowing the A/F is critical. Are the secondaries opening? Too stiff of a spring is not uncommon, they make kits with an assortment of them for tuning. Also, what is your full timing and at what rpm? There's more power in there, guaranteed. You just need to find it in your tuning.

Jody

Assuming 20% drivetrain loss, 270 rwhp equals 337.5 hp at the flywheel. 338hp is pretty close to the advertised 345hp, but I agree you should be making a few more hp with the HOT cam.

Sorry for the delay in getting back. Business called me away. For one, I did not do any tuning just put the headers on ran it down to the muffler shop to get the mufflers welded back on and took it to the dyno test which was scheduled for Saturday morning. The gear ratio I have is 3.07. The A/F graph shows just a shade under 12 as an average. The H/P never seemed to max. It climbed to 260 at 4500 and then 275 at 5600 and stayed there until we hit 6200. I will have the graph posted on our site as soon as my son can get it scanned and updated.
Thanks again for the feedback,
Guy

That 750 DP is going to be rich on your 350. Its on the big side for a 350 IMO --- if its not too late take it back and get a 650 DP instead. Your AF readings were "under 12" which confirms you are really rich. IMO you want to be closer to 13.0:1 for max power, maybe even a little leaner than that.

The other question is what do you have for the rest of your exhaust system? size of pipe, mufflers, crossover, etc? A restrictive exhaust system will negate any benefits from the headers and make your AF mix rich at the same time. IMO you should have dual 2-1/2" pipes (preferably mandrel bent) with either an H or an X pipe and good flowing mufflers like Dynomax Ultraflows, Flowmasters, Borla's, etc.

Thanks for the info. The dual exhaust system is 2.5 inches into some flowmaster mufflers with an H cross pipe. They are pretty good. I feel part of my problem is in the timing and as you say running to rich. I got the 750 as a trade for an Avenger 670 as it was not worth a damn. Probably to big as you say and I may try something a little smaller when the funds are available.

I had a zz1 backed up by a T350 working to a 4.11 rear in a 3100lb 1969 Camaro. I, at sea level ran 13.90's at 99 or 100mph graemlins/boring.gif . To me, that was crap Figuring stock LT1 camaros do the same with more weight. I was to say the least, disappointed with the zz1. The main thing wrong with them is the heads. Although they are aluminum, the suck. The flow terribly. If I were you, Id start looking for a pair of AFR's or get some GM Fast Burns. That would add at least 50hp. :cool:

I just dynoed (Engine dyno) a friends FB 385 that was going in his 81 Corvette. Just for comparisons sake we tried the stock cast iron exhaust and Hooker Supercomp 1-3/4" headers. We lost 70HP!!! with the stock manifolds. The ZZ1 heads aren't the same as fast burns, but It gives you an idea what headers (properly sized) will do for good flowing heads. :eek:
Jim

Mr.G
If your'e thinking of better heads, (Fast burns or AFR) hang on to the 750 carb. It won't be too big then!
Jim