My Megasquirt recipe for Alfa Nord 4-cylinder - Page 2 - Alfa Romeo Bulletin Board & Forums
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post #16 of 32 (permalink) Old 04-03-2017, 04:02 PM
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Excellent thread and documentation. Thank you. Can you provide some details regarding your engine modifications? Or, did I miss them?
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post #17 of 32 (permalink) Old 04-03-2017, 08:41 PM Thread Starter
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Excellent thread and documentation. Thank you. Can you provide some details regarding your engine modifications? Or, did I miss them?
The engine has a Richard Jemison ported head with RJR 550 / 785 cams, Motronic pistons modified per Richard's direction, ceramic coated headers, and a Magnaflow exhaust. It should get up and move pretty well once the FI is all dialed in.
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1989 Spider driver
1974 Spider restoration project
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post #18 of 32 (permalink) Old 04-04-2017, 05:07 PM
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Indeed it should go. Breathing certainly won't be a problem.
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post #19 of 32 (permalink) Old 04-14-2017, 11:54 AM
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This is an INCREDIBLY well documented...great work. Hats off.
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post #20 of 32 (permalink) Old 09-11-2017, 05:52 AM
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I am looking to wake up my 1988 Spider engine and found your document very helpful. I am no expert at all, just trying to piece it all together. I am wondering if the larger injectors will get enough air at mid range and WOT with the L Jet throttle body and plumbing to the intake plenum. You might not be able to really tell if this is the case until the engine is under load. What are your thoughts on this point? Thank you.
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post #21 of 32 (permalink) Old 09-11-2017, 05:59 AM
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Megasquirt controls the ON time for the injectors. Larger injectors get less ON time. You may get a little less resolution at low power/rpm but you may not notice it.
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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 #22 of 32 (permalink) Old 09-11-2017, 06:28 AM
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Ed, thank you for your reply. I have read a number of your comments on other threads and have learned a lot. In this case, I am still wondering. If the engine has performance cams with overlap and a lower back pressure exhaust system, those improvements would increase the volume of air the engine can take in and expel out, no? More air would flow through this modified engine that would flow through a stock engine, no? I am just wondering if the stock L Jet air intake system (throttle body, black tube across the engine, etc) would be restrictive. I have read somewhere else that the L Jet air intake system was actually designed to be somewhat restrictive over 4000 RPM for the stock L Jet to meet US emissions requirements. Thus my question, if the air flow isn't there for more fuel, how to larger injectors help and how do you get a power/performance increase? Thank you.
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post #23 of 32 (permalink) Old 09-11-2017, 07:17 AM
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L-Jet limits what you can do. A 3L V6 made an extra 30 HP when L-jet was replaced by Megasquirt due to increased airflow when the AFM was removed and improved fuel supply.
But L-Jet can handle a bit more airflow. 65Sprint has better cams in his L-jet spider.

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 #24 of 32 (permalink) Old 09-11-2017, 08:10 AM
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As Ed points out, at some point air flow to the intake probably becomes a limiting factor in an L-Jet Spider as was the case in the 3L GTV6. But at what state of tune? 160hp? 180hp? Jason's effort may help answer that question.

I am running stock L-Jet with 10:1 (nominal) Motronic pistons and a set of Richard Jemison's cams in the '88 Spider. Recent tests confirm the L-Jet is able to maintain a wot AFR around 13:1 through 6500 rpm ... no lean mixture issues. Compared to Ed's and Jason's engines, my changes are quite mild but the car is much more enjoyable and for the first time in 29 years the engine likes to be revved above 5000 rpm.

Rich Hanning
'65 Sprint GT, '78 Spider, '88 Quad
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post #25 of 32 (permalink) Old 09-12-2017, 06:30 PM
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Ah, my mistake. I just received the book "How to Tune & Modify Bosch Fuel Injection" by Ben Watson. In the L Jet performance tuning section, it states that the primary problem with the stock L Jet is getting enough air into the engine, not fuel. On a stock system, the airflow meter peaks between 3000-3500 rpm. The book goes on to say the second airflow restriction is the stock throttle body and that larger throttle bodies can help with this problem. Only then does the book talk about fuel, and there are a few problems noted there as well. First, under acceleration, the engine is first starved for fuel because it takes time for the pressure to travel through the plumbing to signal the pressure meter to increase the fuel. Second, the stock fuel pressure can not deliver more fuel to the injectors above 3000 rpm. Anyway, that is what Ben Watson wrote in his book.
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post #26 of 32 (permalink) Old 09-12-2017, 07:32 PM Thread Starter
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With my Megasquirt setup there is no AFM, which is the biggest airflow restriction. The stock plenum and throttle body are still a restriction compared to a set of Jenvey throttle bodies or similar but the plus side is that you get a much better vacuum signal from the plenum, which is a must when using a MAP sensor.

Unfortunately the Spider project has been shoved on the back burner due to a cabin build in the mountains, but once I have the roof on in a month or so I should have some time to get the Alfa dialed in.

-Jason

Jason Arrington
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post #27 of 32 (permalink) Old 09-12-2017, 08:13 PM
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My Megasquirt experience is with a V6 motor and there may be some differences. My 3L motor has a plenum and throttle body from a 2.5. The plenum has been modified for better air flow but the butterfly is stock. The original 2.5 motor made a little less than 160 HP and my motor with the same throttle body makes a little over 250 HP, so I don't think the throttle body is a limiting factor. You can always get more fuel by installing bigger injectors but I have yet to hear of anyone successfully controlling bigger injectors with an L-Jet computer. The route to high power with the V6 includes bigger injectors and Megasquirt or other programmable FI.

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 #28 of 32 (permalink) Old 03-12-2018, 09:00 AM
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This looks really great Jason, I am in the process of collecting parts to do the same except with ITBs. Would basically be the same installation except the injectors probably. Thank you for documenting your work.
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post #29 of 32 (permalink) Old 03-12-2018, 09:47 AM
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I am in the process of collecting parts to do the same except with ITBs.
Do you plan to use throttle position or a composite MAP signal for controlling fuelling?

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 #30 of 32 (permalink) Old 03-12-2018, 01:54 PM
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Do you plan to use throttle position or a composite MAP signal for controlling fuelling?
I have a little bit experience tuning but this would be my first time with ITBs, I was reading up on it and the Megasquirt 3 software has a special mode for ITB that uses MAP for partial loads and TPS for WOT and higher loads. This seems like a good compromise for driveability and performance, I think I'm going to try it this way.
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