79 Spider on a dyno - The Sequel - Alfa Romeo Bulletin Board & Forums
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post #1 of 23 (permalink) Old 03-14-2019, 12:05 PM Thread Starter
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79 Spider on a dyno - The Sequel

It is almost 5 years since I started https://www.alfabb.com/bb/forums/spi...ider-dyno.html

I just got home from 2 days with Al Mitchell and his dyno in Smithfield Virginia where we tested my rebuilt 2L engine. I am pleased with the results - 155.1 RWHP and 135.5 RW ft-lb, a nice improvement on the previous build. We did not record AFR's because of a lack of a suitable interface to my wideband and I just kept an eye on the readout and we made adjustments from that.
The peak torque is not much higher than before but now it is much broader. It is over 130 ft-lb from 4800 to 6300 rpm and over 120 ft-lb from 3800 to 6700 rpm.
The AFR's were good above 6000 rpm but they were too low (rich) from 3500 to 5500 rpm. There is an opportunity to get more torque in that range if I can find a better main jet/air corrector combination.
My sole good data point for converting RWHP to engine HP is from a GTV race car motor that made 215 on Jim Steck's engine dyno and two weeks later made 175 RWHP on a Mustang dyno in Birmingham Alabama. Applying that factor to my motor gives 192 HP and 166 ft-lb at the flywheel.
I can add some more data in another post but brief engine specs are
Stock & unmodified block, crankshaft and rods.
85 mm Arias pistons from Jim Steck
Motronic cylinder head prepared by Jim Steck
RJ575 intake cam and RJ457 exhaust cam from Richard Jemison
45DCOE152 Webers and an AR plenum "ported" and matched by Richard Jemison + modified AR air box.
Shankle headers into a 2.25" collector with a 2.25" Borla muffler
123ignition distributor with MSD Blaster 2 coil.
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Ed Prytherch
79 Spider
85 GTV6 3L
76 Suzuki GT500
2011 Jaguar XKR

A little government and a little luck are necessary in life, but only a fool trusts either of them. - P.J. O'Rourke

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post #2 of 23 (permalink) Old 03-14-2019, 02:46 PM
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Very nice, very nice. I am looking to build a second motor with some HP mods. Nice to hear you can leave the bottom end alone and get good HP and torque gains from head work, valves, cams, and some well tuned carbs. I would be swapping engines every 2 years for reasons left unsaid here...... thanks for the info!
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post #3 of 23 (permalink) Old 03-15-2019, 07:00 AM Thread Starter
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Air Filter performance

Towards the end of the session we did back to back pulls with and without the UNI filter (from Centerline). You can see from the charts that the curves are almost identical. There is a fraction of a HP loss at high rpm with the filter but there is also a little torque boost with the filter at 4900 rpm. This is most likely a function of my Carburetor jetting,
I modified the stock air box by cutting off the intake horn and diverter flapper and replacing them with a short length of 3" exhaust tube. The inner tube of the box is gone and there is unrestricted air flow to the inside of the UNI filter.
Removing the whole air box makes the motor run lean because it collects and recycles fuel laden air that is discharged into it from the Webers during reversion.
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Ed Prytherch
79 Spider
85 GTV6 3L
76 Suzuki GT500
2011 Jaguar XKR

A little government and a little luck are necessary in life, but only a fool trusts either of them. - P.J. O'Rourke

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post #4 of 23 (permalink) Old 03-16-2019, 05:25 PM Thread Starter
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Intake valve timing

We started the dyno pulls with the RJ575 intake and RJ785 exhaust and then switched to a RJ457 exhaust - more about that later. After moving the exhaust LC around we settled on the sweet spot and moved the intake. The effect of this was greater than moving the exhaust. We started at a nominal 104 then advanced to 101 and made more torque and power then advanced to 98 and again made more torque and power. 98 is as far as I can go with this cam and piston combination. 101 was the limit with the old motor with Venolia pistons. The attached chart shows 104 vs 98. I talked to Jim Steck about the results and he said that the improved performance is due to closing the intake valve earlier which makes less reversion and a longer compression stroke. Most of the discussion about valve timing seems to center around overlap which might lead you to expect the opposite of what we observed.
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Ed Prytherch
79 Spider
85 GTV6 3L
76 Suzuki GT500
2011 Jaguar XKR

A little government and a little luck are necessary in life, but only a fool trusts either of them. - P.J. O'Rourke

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post #5 of 23 (permalink) Old 03-16-2019, 05:28 PM
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Sure pays to have a good engine man..... and a dyno. Only a couple around me and it costs an arm and a leg to use it, if you can get scheduled.
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post #6 of 23 (permalink) Old 03-16-2019, 05:56 PM Thread Starter
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I am fortunate to have a friend with a dyno, even though he is over 5 hours away. My experiences with my local dyno operator have been mixed.

In any case I am happy to share what I have learned.

Ed Prytherch
79 Spider
85 GTV6 3L
76 Suzuki GT500
2011 Jaguar XKR

A little government and a little luck are necessary in life, but only a fool trusts either of them. - P.J. O'Rourke
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post #7 of 23 (permalink) Old 03-17-2019, 08:53 AM
Richard Jemison
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Ed`s cam timing actually is most likely 98 intake and 108 exhaust, as the head I sent to Jim for Ed`s build is a 86/87 Bosch version that the exhaust cam caps factory LC is 108, and the cam is timed at that mark. I can understand that the power is very good (with smooth idle) as the LSA is 103 and the combined cams are advanced center wise which moves the power stroke lower in the RPM range.

This same cam pairing in Hayes Flynns race engine made 215 HP with no power drop with a 7500 RPM cut.
The power decrease above 6K is a result of the "Advanced" cam timing. (Imagine a single cam with both intake and exhaust lobes on the same stick, timed by advancing the cam 3 degrees)
His Low end drivability is as good as any. With this power curve it would make a great race engine as set up regardless of the 10.6 CR. Torque not HP wins races. And this with a full length exhaust system on pump gas.
Below are a couple of emails received today;

Quote:
In a message dated 3/17/2019 10:18:10 AM Central Standard Time, [email protected] writes:

I drove the Spider on my favorite country roads this morning and it was very good. The top end acceleration is terrific and it drives nicely at any speed. I was able to drive at 2100 – 2200 rpm in 4th gear with no problems, even up inclines and it pulls away smoothly. I made a set of 150 air correctors and installed them with 150 mains (was 200 AC, 155 MJ). The low dip moved from 10.8 to 10.9 and it did not go over 13.0 anywhere. I found an undersize Chinese 1/16” drill that is 1.56 mm and I now have a set of 156 AC’s and I will give them a try next week.Thanks for helping me get here. I doubt that anyone has a nicer Nord Street motor.Ed

From: [email protected]: [email protected]: [email protected]t: 3/17/2019 10:23:16 AM Central Standard TimeSubject: Re: Spider

Make at least 160 AC. The effect of the ACs is 1/3 the same change in main jets. A true 1/16 drill is 1.59mm

Richard Jemison
RJR Racing

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post #8 of 23 (permalink) Old 03-17-2019, 11:35 AM Thread Starter
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I checked the exhaust mark against the Shankle template and it is indeed at 108. There is some data that suggests 102 for S4 Spiders but I think this head is an S3.5 - in the transition when S3 Spiders got Motronic heads.

Ed Prytherch
79 Spider
85 GTV6 3L
76 Suzuki GT500
2011 Jaguar XKR

A little government and a little luck are necessary in life, but only a fool trusts either of them. - P.J. O'Rourke
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post #9 of 23 (permalink) Old 03-17-2019, 03:53 PM
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Congrats Ed, happy for you that you're back on the road and the car is running strong!

The numbers are impressive but I gotta ask...how does it sound??

Greg East
Loveland, CO USA
'74 Alfa Romeo Spider
'87 Porsche 944 turbo
'93 BMW 740i
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post #10 of 23 (permalink) Old 03-17-2019, 04:18 PM Thread Starter
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It is LOUD. I wore noise cancelling headphones for the Virginia trip and again yesterday when I met some of the AROC guys in Charlotte. I plan to have a little glass pack installed in the tailpipe. It would be cool if you were around here sometime so that you could give it a blast.

Ed Prytherch
79 Spider
85 GTV6 3L
76 Suzuki GT500
2011 Jaguar XKR

A little government and a little luck are necessary in life, but only a fool trusts either of them. - P.J. O'Rourke
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post #11 of 23 (permalink) Old 03-17-2019, 06:37 PM
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From what I see posted . emulsion tubes or air correctors could be off for the midrange richness... not the main jets..IMHO..

The older I get.. the faster I was....
Tom

Last edited by Tom Frasca; 03-17-2019 at 06:43 PM. Reason: content
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post #12 of 23 (permalink) Old 03-17-2019, 06:53 PM Thread Starter
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I have experimented with emulsion tubes in these carbs on a similar engine and F16's work best. For any engine there will be more than 1 main jet-air corrector combination that will give optimum AFR in the peak power rpm range but they will give different AFR's in other parts of the range. I posted a lot of test data in another thread a few years ago. Both main jets and air correctors influence the AFR throughout the main range but main jets have more influence in the mid range and air correctors have more influence at the top. I started out the dyno testing with 145 MJ/220 AC then when we made another change that made more power but it went very lean and we had coolant coming out of the tail pipe. Detonation blew out the head gasket. After replacing the gasket we ran with 155 main jets and 200 AC's made the best power but it is richer than I would like in the mid range. We tried going down to 150 MJ with 170 AC's the smallest that I had and I aborted the run when I saw 14 point something on the wideband. Now I am trying 150's again with smaller AC's and I am making progress.

Here is the Weber/wideband thread: https://www.alfabb.com/bb/forums/car...da-sensor.html

Ed Prytherch
79 Spider
85 GTV6 3L
76 Suzuki GT500
2011 Jaguar XKR

A little government and a little luck are necessary in life, but only a fool trusts either of them. - P.J. O'Rourke

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post #13 of 23 (permalink) Old 03-18-2019, 01:16 PM Thread Starter
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Exhaust cams

One of our objectives was to compare exhaust cams. I have been using Richard's RJ785 cam for many years with good results but I wanted to try his newer RJ457. We started with the 785 timed at 108 degrees, got the timing and carburation sorted out and recorded a run. We then switched to the 457 also timed at 108 and recorded a second run with no other changes. You can see from the charts that they are very similar. The 785 made a bit more torque below 5200 rpm and the 457 made a bit more at higher rpm. I decided to leave the 457 in for the remainder of the tests.
The 457 has 20 degrees less off the seat duration but the two cams are similar at .040" lift and the charts reflect that similarity. The 457 has more duration at high lift.
The car had much better driveability at the end of the dyno session than before we started and I think that the 457 contributed to that. So the 457 may be a better choice for a street motor.
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Ed Prytherch
79 Spider
85 GTV6 3L
76 Suzuki GT500
2011 Jaguar XKR

A little government and a little luck are necessary in life, but only a fool trusts either of them. - P.J. O'Rourke
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post #14 of 23 (permalink) Old 03-18-2019, 05:01 PM
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Quote:
Originally Posted by alfaparticle View Post
It would be cool if you were around here sometime so that you could give it a blast.
Sounds like a plan, good chance my wife lands a consulting gig in the neighborhood and I'll tag along.

Greg East
Loveland, CO USA
'74 Alfa Romeo Spider
'87 Porsche 944 turbo
'93 BMW 740i
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post #15 of 23 (permalink) Old 03-19-2019, 02:14 PM Thread Starter
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Pistons

The pistons are 85 mm Arias prepared by Jim Steck. Measured compression ratio is 10.7 to 1. I have lost my notes from when I weighed them but I remember that they are about 100 gm lighter than Motronics and they are balanced to 0.1 gm. It has a Napier ring in the second groove.
Pistons for #2 and #3 cylinders are interchangeable, cylinders #1 and #4 must have the matched piston.

The shoulders of the pistons closely match the curvature of the combustion chambers and there is a small clearance. The combustion volume is concentrated around the valves and the spark plug which gives a short flame path. The tight clearance around the shoulders creates a squish band which in turn increases turbulence in the combustion volume.

Here are two pictures of #4 piston plus a comparison with one of my ex-Alan Ward Venolias that have a similar compression ratio.
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Ed Prytherch
79 Spider
85 GTV6 3L
76 Suzuki GT500
2011 Jaguar XKR

A little government and a little luck are necessary in life, but only a fool trusts either of them. - P.J. O'Rourke
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