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Greetings everyone. I am new to this forum and have searched and read a bunch of threads, but I am sure I have missed a bunch as well. I have a 1988 Spider with the L Jetronic FI, bone stock, 35000 original miles. I have owned the car for a bit over a month and love it. I would like to increase torque and hp between 2500 and 5000 for street driving, better acceleration out of corners. I drive the car nearly every day on 2 lane country roads. I already have a plan to improve the suspension, wheels and tires and am doing that first. I just recently had the fluids, filters, plugs changed and the fuel system and injectors cleaned with one of those machines you hook up to circulate the fuel with a powerful additive while the engine is running for 45 minutes.

The car is rated at 111hp with the L Jetronic and the US cat converter and quite a restrictive stock exhaust header. I think I would be happy with a 20-30 hp improvement in the mid range.

My question is this: what do you recommend I do to improve the performance, and in what order to get the most bang for my buck, so to speak. Again, I may have missed a thread or two, but I have not seen any recommendations on how to modify the L Jetronic system or whether a ported head and/or cams or performance headers make any difference with the L Jetronic system. I have also been frustrated that every vendor of tubular performance headers that I have found on the internet is unable or unwilling to send me a dyno graph of hp and torque, only beautiful photos of the headers. I am afraid these after market headers either do not make much difference or only make a difference north of 5000 RPM, and I do not have the money to do my own experiments!

Any advice or suggestions very much appreciated.
 

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The L-Jetronic's inability to provide sufficient, additional fuel limits the extent of performance modifications you can safely make. With that preamble, you can definitely make the car more enjoyable to drive by raising the compression ratio and adding a better set of cams. I installed a set of Motronic 10:1 pistons and cams from Richard Jemison in the '88 Quad last February and am very pleased with the results. I have confirmed the air-fuel ratio remains around 13:1 at wot through 6500 rpm. So, no excessively lean mixture problems with this setup.

Bang for the dollar, in order, cams, higher compression ratio, better exhaust. Suggest using the two piece exhaust manifold from an earlier car or perhaps an S4 Spider rather than aftermarket headers.
 

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In the Vandenberg dyno sessions at Hasselgren in the 1980s, tube headers were better only at high rpm. For stock or mild engines that don't see much over 5000 or 5500 rpm, cast 4-2-1 1974-style headers gave the best torque and response. We're talking 3-5 HP, not major differences. But what you gain at the high end with tube headers you probably lose at the bottom end on a basically stock engine.

Andrew
 

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"headers" is a pretty broad category. their optimum performance range is dependent on many physical factors, principally diameter and length. if put on headers tuned for high rpm they will offer less performance at low rpm. if get headers tuned for mid range or low rpm, will be better there. comes down to the tune, not whether is cast iron or tubular steel.
 

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Discussion Starter #6
I posted the graphs from a dyno run in the Engine Management forum, titled "1988 Stock Spider Dyno Run Graphs"
 

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Agreed. Way back in the day, John Shankle said the stock 1972-1974 2-piece cast manifold was as good as tube headers for the engine I was building for autocross. Of course, the tube headers available then were 4 into 2 into 1 rather than the newer equal tube length designs sold by Spruell and Vintage Custom for $$$.

In the Vandenberg dyno sessions at Hasselgren in the 1980s, tube headers were better only at high rpm. For stock or mild engines that don't see much over 5000 or 5500 rpm, cast 4-2-1 1974-style headers gave the best torque and response. We're talking 3-5 HP, not major differences. But what you gain at the high end with tube headers you probably lose at the bottom end on a basically stock engine.

Andrew
 

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The L-Jetronic's inability to provide sufficient, additional fuel limits the extent of performance modifications you can safely make. With that preamble, you can definitely make the car more enjoyable to drive by raising the compression ratio and adding a better set of cams. I installed a set of Motronic 10:1 pistons and cams from Richard Jemison in the '88 Quad last February and am very pleased with the results. I have confirmed the air-fuel ratio remains around 13:1 at wot through 6500 rpm. So, no excessively lean mixture problems with this setup.

Bang for the dollar, in order, cams, higher compression ratio, better exhaust. Suggest using the two piece exhaust manifold from an earlier car or perhaps an S4 Spider rather than aftermarket headers.
Hey, I just had my engine rebuilt with 10:1 pistons- with those cams, did Jemison give you an estimate on what HP and Torque figures might be?
 

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Richard Jemison
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Torque & HP

Many factors affect Tq/Hp even with similar engines.
With the cams for these Bosch L-Jet motors you should get 20 to 30 HP depending on the Pairing. Rich has a tad bigger exhaust cam than I typically use, but with Ed`s technical expertise I anticipated they could take advantage of it, and they did by opening the LSA by retarding the exhaust cam 3 degrees. I don`t think he`s been to the dyno with it, but others with my cams in their L-Jet cars might be able to speak up.
Your engine stock "rated" at 111 HP is crankshaft Hp. at the rear wheels will be under 95 hp. info from most dynos will be in RWHp.
The big gain is torque & drivability from idle to the fuel cutoff`s redline on the computer. Hp is only a math conversion from Torque. "HP sells cars, Torque wins races" (Know who said that?)
 

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John533i, there isn't much to add to Richard's post. I have not put the car on a dyno although it pulls harder, longer than it did with stock cams and pistons. I have put about 8000 miles on it in this configuration with no issues wrt cams and pistons.
 

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My experience with Richard's cams and Webers is that they need smaller main jets than you might expect. When I switched from Colombo CB47 cams to RJ136/785 I had to go down in main jet size from 145 to 140. The engine made much more power and torque and also got better mpg. So it does not surprise me that you can get better performance out of an L-Jet motor when you install the cams that Richard suggests.
 

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John533i, there isn't much to add to Richard's post. I have not put the car on a dyno although it pulls harder, longer than it did with stock cams and pistons. I have put about 8000 miles on it in this configuration with no issues wrt cams and pistons.
I'm still breaking in the engine, but with just the motronics I'm really impressed, over the stock, worn pistons. I had pretty good compression before I lost cyl #3, but I can really tell that it's got more power. I've only taken it to about 5K rpm for short pulls about 2x. I'm thinking what cams would do for me now.

BTW, even though I'm running premium, I can hear pinging under light throttle. At cruzing. It's done this since I picked it up from the engine builder, but he didn't hear it when I brought it in for it's head torque. Additives for octane don't help at all, just turn my plugs orange. Should I take it back to him, change plugs, or look for vacuum leaks?
 

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BTW, even though I'm running premium, I can hear pinging under light throttle. At cruzing. It's done this since I picked it up from the engine builder, but he didn't hear it when I brought it in for it's head torque. Additives for octane don't help at all, just turn my plugs orange. Should I take it back to him, change plugs, or look for vacuum leaks?
Leaks at the exhaust manifold can sound like pinging.
 

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A set of Richard's cams will take the engine to the next step. In the case of my '88, the cams not only increased torque and horsepower, they improved the character of the engine.

The detonation issue is odd unless the head has been cut a significant amount. I am thinking 0.040" to 0.050" or more would be needed to raise the CR high enough for it to ping on premium gas with Motronic pistons. This is just my best guess. Maybe Richard will weigh in and confirm. Are you certain what you hear is detonation? Ed's suggestion regarding exhaust manifold leaks is a good one.
 

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Richard Jemison
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Pinging

Pinging is generally an ignition timing problem. Particularly at lower RPMs (off idle to 3000)

But I suggest first confirm there are copper gaskets between the head and the exh manifold. If so get the engine hot and re-tighten the exhaust nuts . That is a common issue with re-assembled engines.


With the L-jet controlling the ignition I don`t know how you can resolve that but there is another fix that will, and that`s to convert the ignition (and fuel timing) to distributor control. On the L-Jet I suggest using an RML distributor (as it will trigger the coil directly and I don`t know if a 123 will. ED?)

On the coil there is a fat white wire on the negative side, take it off and bend it back and tape it well covered. The distributor lead will go in its place.
If you use an RML, call Ric (Lovecchio) at 386 212 0450 and tell him you want a advance curve a bit slower through 3000 RPM with the advance not starting until 1000 RPM. Max advance of 15 degrees should result in idle setting of 4 degrees BTDC. That should result in a 34 degree Max advance.
 

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L-Jet gets it strobe pulse from the ignition so you need to know to make this work if you start to modify it. The fuel pump relay also uses an ignition pulse.
 

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No, I'm not going to do anything like a different distributor. After re-reading threads on vacuum leaks, I found out that this could be a cause of pinging also. I'm going to pull the whole intake track off, check the injectors for tightness to make sure there's not a leak there, then carefully put everything back. I have some propane that I can flow to check, also.

I just fixed an exhaust leak on the down pipe flange; the threads had come out of one of the new brass nuts. I'll look at tightening the exhaust again, also. Do you guys use that Centerline thick one piece exhaust gasket? I gave mine to the 'old school' engine builder, and he didn't like it so didn't put it on. Or give it back :frown2: $30...

If I can't find any air leaks, my next guess would be that the head was milled too much. Compression isn't that high though- 200-195 195 200; seems like it would be more, since another guy that just put in Motronic pistons has better compression than I do...
 

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I strongly suspect that if you have vacuum leaks large enough to cause detonation, there would be other drivability symptoms. You are certain the sounds you are hearing are detonation?
 
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