Alfa Romeo Forums banner

1 - 17 of 17 Posts

·
Registered
Joined
·
16 Posts
Discussion Starter #1
Greetings everyone. I bought a 1988 Spider QF in August. The car now has 35,700 original miles, and I wanted to get a baseline dyno measurement of the engine performance. It is stock to my knowledge except I put a K&N air filter in a week ago. I tried to start each of the 3 runs just over 2,000 RPM and tried to end at 6,200. The runs were done at WOT. The graphs below are for the middle run, all three were within 1-2 hp. I think the graph stops just before 6,000 because my tach may not be accurate.

I plan to put in a pair of performance cams from RG, the stock exhaust manifold from a '74 GTV, and the Centerline/Magnaflow performance exhaust system. May also recurve the distributor timing to advance in the mid range. I may need to make some adjustments to the Bosch L Jetronic fuel injection system after those mods and plan to do at least one more dyno run to check.

The car is running lean at WOT, but I believe this is typical for the Bosch L Jet FI system. I will try and figure out a way to measure the AFR just driving around town. I suspect the AFR is closer to 13.5 when street driving, even when doing spirited street driving, but I don't know.
 

Attachments

·
Registered
Joined
·
276 Posts
AFR not lean actually - from Ljet's perspective. its job it to keep stoichiometric AFR which it is doing pretty admirably. certainly not a performance fuel map, but it is doing what is supposed to do.
am used to most dyno runs in 4th - is 1:1 ratio to the final drive (pretty close anyway) so keeps final hp & torque calcs simple. as long as the overall gear ratio is in the dyno, will do the math for you. in any case, those numbers look roughly correct. keep in mind that if you take to another dyno shop, will get different numbers - possibly close to these, maybe not. staying w one will give you a good reference point to see what tuning changes are yielding in output changes.
Ljet ignition curve is all in the ecu - the distributor is empty save for a rotor arm. only way to recurve "distributor" is to change map in the ecu - which can not be done in Ljet (or motronic) - they are not programmable.
you are right, the dash tach is usually wildly inaccurate.
 

·
Premium Member
Joined
·
1,032 Posts
John802,

Just came upon your post and wondering how goes your performance updates?

Also, as you probably know, we have Variable Valve Timing (VVT) on our engines that advances the intake cam 20* at WOT via contacts on the throttle position switch. If you turn on your ignition (no start) then go around to the passenger side and slowly open the throttle, you should hear a click at the VVT solenoid, very close to WOT.

There have always been questions about how much of a performance improvement results from VVT activation, and frankly, no matter how carefully I have tried to engage VVT, my calibrated seat-of-the-pants evaluation has never been able to sense any difference.

Perhaps the next time you do a dyno run, you could do all L Jet owners a favor and include a "not quite WOT" run in your testing. Or you could run WOT up to a certain RPM, then back off enough (see above) to drop out of VVT.

Thanks in advance!
 

·
Registered
Joined
·
276 Posts
i don;t think the vvt is meant to be an actual performance "enhancer". it is meant to give you clean idle. cold starts etc, then once past ~ 1600 rpm, it advances the cam to a position that any normal cam would have had for a start point.
 

·
Premium Member
Joined
·
13,082 Posts
i don;t think the vvt is meant to be an actual performance "enhancer". it is meant to give you clean idle. cold starts etc, then once past ~ 1600 rpm, it advances the cam to a position that any normal cam would have had for a start point.
Agree. VVT is to improve low end torque.
I have seen data from a race car that had the engine on Jim Steck's engine dyno and a couple of weeks later on a Mustang chassis dyno. The transmission loss was 19%. Applying that to the best of these charts gives 100 HP at the flywheel. Alfa claimed about 112 HP so you are 10% down.
My understanding is that the lambda sensor AFR control is over-ridden at WOT to drive it towards 13.2 for max power. I assume that is achieved using the TPS. Maybe this one requires adjustment?

I had my Spider on Al Mitchell's Dynomite dyno a few years ago. We did all of the tuning runs in 3rd gear and the final run in 4th. The numbers were just a little higher in 4th, maybe 3 or 4 HP, from about 136 to 139.
 

·
Registered
Joined
·
1,025 Posts
pretty senseless to compare a dyno plot to what the manufacture has claimed. ESPECIALLY AN ITALIAN oem... :)

Most newer cars are actually pretty close these days accounting for reasonable drivetrain loss. BMW is notorious for underrating motors- they often make to the wheels what is claimed to the crank.

Plus, I wouldn't expect an untouched 30 year old motor to still have all the ponies it came with.
 

·
Premium Member
Joined
·
13,082 Posts
It is unusual to have the torque peak at 2700 rpm. I would expect it to be around 4500 rpm. The torque value at 2700 is pretty good but it does not build from there. I would check the valve and ignition timing and look for restrictions in the intake and exhaust. For instance Is the butterfly opening fully, is the cat clogged?
 

·
Premium Member
Joined
·
1,032 Posts
So jon802, you have yet to weigh in!

How goes it?
 

·
But Mad North-Northwest
Joined
·
9,859 Posts
There have always been questions about how much of a performance improvement results from VVT activation, and frankly, no matter how carefully I have tried to engage VVT, my calibrated seat-of-the-pants evaluation has never been able to sense any difference.
On my '91 when the VVT solenoid failed it was quite noticeable. Seemed like the car lost quite a bit of pep, which is why I investigated and found that the solenoid wasn't working. New solenoid brought it back to normal.

VVT on the S4 is triggered differently (engine load instead of throttle position) so maybe it's more noticeable when it goes out on the later cars? Mongo dunno, but it definitely made the car feel slow.
 

·
Premium Member
Joined
·
1,032 Posts
"Mongo pawn in great game of life." :)

While I concur VVT tip-in on S3 2.0's may only put cam timing where it would otherwise be, and helps address the performance compromises mentioned by barboncino, there must still be a dyno difference in Torque/HP and I for one would very much like to see curves, with and without VVT.

Interesting, but not surprising that an S4, with the more sophisticated Motronic System would seem to exhibit a noticeable performance difference.

Why do I care about this stuff? I dunno. Too much time on my hands? :)

And jon802, wazzup?
 

·
Registered
Joined
·
1,306 Posts
I spent a long time figuring out how to get my VVT working reliably again, but when I had the engine rebuilt late last year it was once again, inop. However, with 10:1 pistons in a fresh rebuild, I'm really happy with the seat of the pants that I have now. It's still irritating that I have to chase that stupid VVT issue AGAIN though.
 

·
Premium Member
Joined
·
13,082 Posts
There are a few posts with dyno curves for 105 motors in various states of tune. A little searching should find them.

I agree with Andy that if the cam was stuck in the retarded position it would enhance the low end at the expense of mid/top end which could be part of the problem.
 
1 - 17 of 17 Posts
Top