Mark 89Formula

Anyone have data for the cams in the post title that's compatible with Dyno 2000? I already know the duration @ .050, lift, and LCA. The data I'm looking for is the seat timing specs (seat duration or IVO/IVC/EVO/EVC) and the intake centerline in crank degrees. I think I can make some good estimates but wondered if someone else has already done this homework and would be willing to share. Thanks.

88IROCs

DYNO2000 specs for: <u>ZZ3 camshaft</u>

Cam Specs @: Seat to Seat
Int Lift @ Valve: 0.474"
Exh Lift @ Valve: 0.510"

Lobe Center: 113.8
Valve Overlap: 50.0
Int Duration: 275.0
Exh Duration: 280.0

IVO(BTDC): 23.0
IVC(ABDC): 72.0
EVO(BBDC): 73.0
EVC(ATDC): 27.0

When selecting the type of lifter, choose "Hydraulic Flat-Tappet Lifters". Dyno2000 is extremely "optimistic" in it's power projections when "Roller" lifter is selected. Choosing "Hydraulic Flat-Tappet Lifters" will yield more realistic projections.

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He who hesitates,... is lost!

Mark 89Formula

Thanks for the info. It was close to my assumed values. You're right about the flat tappet setting giving more realistic results than the roller lifters setting.

One question. You list the lobe center for the ZZ3 as 113.8 degs. All my GMPP catalogs show a lobe centerline of 112 degs. Why the difference in values?

88IROCs

I checked with the GMPP catalog, and you are correct: the LCA was wrong. I can't remember where I got the .cam file, so I can't credit or correct the author. I have though corrected it on my version.

Just for the sake of trivia, I plugged the ZZ3 into my L98 file, using both LCA's to see what the difference would be:

'88 L98(all stock)
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330 lbs/ft @ 3000
235 hp @ 4000

'88 L98 w/ZZ3 cam(LCA = 113.8)
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322 lbs/ft @ 3500
248 hp @ 4500

'88 L98 w/ZZ3 cam(LCA = 112.0)
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320 lbs/ft @ 3500
250 hp @ 4500

If these spec's are anywhere near accurate, the ZZ3 would not be on my list of swap candidates for a TPI engine. Comp Cams Xtreme rollers do show a fair bit of promise, but I think a head swap would/should come before getting rid of the L98's bumpstick.

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He who hesitates,... is lost!

[This message has been edited by 88IROCs (edited July 30, 2000).]

Mark 89Formula

We must be using some different modeling assumptions. My results were:

89 350 w/small tube headers
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265 HP @ 4000 RPM, 384 lbs/ft @ 2000

89 350, headers, ZZ3 cam
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309 HP @ 5000 RPM, 373 lbs/ft @ 3500

The baseline run with headers correlates well with my dragstrip and Dynojet results so it's in the ballpark.

I ran both of these engines in Dragstrip 2000 and found a .40 sec improvement in ET and 4 MPH increase in trap speed with the ZZ3 IF you raised the shift point from 5200 to 5900 RPM. I have been finding larger than expected gains in ET/trap speed by going to a healthier cam FWIW. The XTREME series do look good as do many of Lunati's EFI grinds.

I think the best compromise is... don't. Swap the heads and cam at the same time!

88IROCs

Possible reasons for our variance:

1. I have no airflow data for the cast-iron L98 heads, so I use the sim's default data.

2. I tend to avoid using 'headers' as the output seems overly optimistic. I find using 'high-perf manifolds and mufflers' to be more representative of the gains that can be found with real-world headers and cat-back.

3. When choosing 'TPI' for the intake manifold, I limit airflow to a max of 650 cfm. The individual components(plenum, runners, and lower base) may support higher flow when measured seperately, but in combination this would be their max flow without some serious porting(this, of course, assumes you are using stock LTR's. An aftermarket base and runners could boost this up to around 700 cfm).

4. I tend to adjust the cam timing to find the best torque value, which as a consequence tends to lower max h.p.

5. Do you have seat to seat timing values for the stock '88 - '89 L98 cam. All my values are based on the published 0.050" specs(which tends to lower output 2 - 5%).

6. I tend towards conservative options, while avoiding radical parts. This seems to better simulate real-world expectations, rather than outrageous 'dream-motor' numbers. I also tend to focus on the 3000 - 4500 rpm output, as this is the best operating range for a stock, LTR TPI motor.

7. I made a trip to the chassis dyno in June, and got a best of 261 rwhp @ 4600 rpm. I simulated my motor in Dyno2000 two weeks later, and came up with 309 hp(flywheel) @ 4500. I think this validates the conservative approach when using the sim. However, there was significant variance between my actual torque peak values(Dyno2000 tends to be very optimistic with TPI torque predictions).
I also think that the best use for Dyno2000 is as a comparitive tool, but when using conservative specs, it can sometimes generate surprisingly accurate numbers.

8. Based on the comparitive gains, the Comp Cams XR258 would seem to be the ideal for a mild(like mine) street-driven 5.7 TPI.

9. Hopefully, Dyno2001 will allow adjustments to the spark and fuel curves, as these are key to optimizing a TPI setup(or any motor for that matter). Would be nice if it could sim the effect of chip-swapping with popular aftermarket PROM's too.

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He who hesitates,... is lost!

Mark 89Formula

Quite a comprehensive and informative response you made there. I'll follow your lead.

1. I'm using the airflow data from the L98 AL heads. Our stock heads are basically iron copies. Both CHP and GMHTP have published flow figures for the AL heads. The flow characteristics are different from the default Dyno 2000 figures. I would be happy to send this file to you if interested. BTW I'm using a compression ratio of 9:1 even though the published value is a bit higher.

2. The headers option seems to work best with the stock L98 I've created. The high perf setting kills too much power and the stock manifolds result in a flywheel output that's less than my rear wheel HP values. I'll play with this setting as I get more experience with the program.

3. I'm using an airflow value of 500 CFM @ 1.5 in-HG for my simulations. Like yourself I want to be conservative. The poor intake air must follow a winding path through the airbox, filter, a 90 deg bend, MAF, another 90 deg bend, TB, plenum, runners, and manifold before reaching the heads. Data from the TPIS Insider Hints books also guided me on this choice.

4. If I don't know the cam manufacturers recommended cam phasing I usually select either straight up or 2 degs advanced. This is not an optimization, just a simulation assumption.

5. I've never seen seat to seat values for stock GM cams and I'm too lazy to measure them myself, so I built my own cam file.

The Seat to Seat specs are:
Int duration/lift: 255 degs, 0.415"
Exh duration/lift: 264 degs, 0.430"
Lobe CL: 117 degs
Intake CL: 115 degs (builds low RPM torque at expense of higher RPM power)

Using the 0.050 specs of 207/213 in my theoretical engine yields 10 more peak HP and reduces peak torque by 9 lb-ft FWIW.

6. Couldn't agree more about being conservative. My optimizations are for the 3500-4500 RPM range since I have a relatively loose converter. Iterator still says I should get a big cam.

7. Dynojet showed 230 RWHP at 4400 RPM. This compares favorably with the predicted 265 flywheel HP posted above. Definitely agree that the software's strongest benefit is as a comparitive tool rather than a highly precise qualitative prediction.

8. I respect your cam choice. I'm going to go with more int/exh duration than the XR258 and a lobe seperation angle between 113-114 degs.

9. Altering spark timing and A/F ratio would be cool. Sounds like a good input back to the developers.

Mark 89Formula

BTT... continuing conversation after short 45 day coffee break.