Dyno results, tuning help needed

[boogiedude]

Dotto what Mark said. Block and head expand at diff rates, gasket has to allow some slide. Is not supposed to stick. And use no sealer.
Lean does not cause detonation, although rich can calm it a bit, just due to the cooling effect of too much fuel.
Really no need to clean the piston surfaces, they are gonna look like that right away again anyway.

And cranking compression is not going to tell you much of anything. If you have wild enough cams, the cranking compression is going to be a bit low regardless of the compression ratio.
Keith

What could be be the possible causes of the detonation? Too hot of a spark plug? Timing too advanced? Retarded? Also, do the burn marks indicate detonation? I said that purely on a hunch. This is my first time seeing markings like that

[131]

modern gaskets are graphite coated to allow for expansion and contraction between the block and head.

You're never too old to learn, so I thought I'd do some homework.
http://www.enginebuildermag.com/Article ... aling.aspx
(And that was written last century)
So is retorqueing the newer type gaskets going to do anything detrimental to the sealing properties?

[majicwrench]

THe damage to the fire ring in that gasket could certainly be caused by detonation. Lots of things cause detonation, timing too far advanced, too high compression ratio, hot spots in cylinders, engine running way too hot to name a few. Pulling a hiill would be a classic time for it to ping. Without reading back thru the thread, sure looks like pretty high domed pistons.
Keith

[boogiedude]

Got the car back together this weekend after a fight with one of the vendors regarding wrong parts, adding several days to my down time.

To try and combat the detonation issues, I got a set of cooler plugs(NGK BPR7ES gapped to .027), pulled back the timing a bit, and for added measure, poured in a little octane booster and the car is running great. But only time will tell. On a side note, what exactly does detonation in these motors sound like? I've heard it described so many different ways by different people and haven't had any first hand experience(that I'm aware of) to base what I'm hearing on. I do have a small amount of tickingish noises coming from the motor at idle/low load cruising. It's hard to hear much over the carb growl/exhaust when under load/heavy acceleration.

I also have an oil leak that seems to be RPM related? It seems like it's coming from the rear main. The oil drips out from the bottom of the bell housing right onto the exhaust which creates a smoke screen, which would be great if I was in a James Bond movie It isnt very apparent when sitting and idling the motor, but when driving around, I'll pull up to a stop light and smoke will slowly billow from the grill and at the back of the hood near the cowl. The longer I drive the worse it seems to get, and its especially bad after heavy acceleration i.e. taking it above 5k

[So Cal Mark]

there are two different size rear main seals, and some detonation is inaudible

[boogiedude]

Update

I ordered and installed a AEM wideband 02 sensor+A/F ratio gauge. Put the 02 sensor right where the the pipes go from 2-1 near the tranny(PITA to get the sensor to fit in there without knocking on the trans or floor!). And I've got some preliminary numbers.

I'm basically all over the place. At idle, my gauge flat lines(it maxes out at 17:1). And under basically call other conditions I've put it through, it fluctuates from 10.8-13ish:1. The flat lining/very lean condition also seems to happen when coasting while in gear, i.e. engine braking while going downhill. I can't tell if its a false reading or if I'm really going full lean at idle?

I'm running the 45 DCOE, 32 chokes, 60f8 idle 135main 160air corrector f16 emulsion tube. I find the lean idle pretty confusing, since my mixture screw is already 2.5-3 turns out if i remember correctly. My idle jet is also 2 sizes above what was recommended to me.

As for the richness throughout the rpm range, I'm going to take the air corrector up and see how that helps, as opposed to reducing the main jet size

[majicwrench]

Engine braking going down hill is not going to give you good information, just ignore it.
Got any exhaust leaks?? The sensor measure Oxygen, and any way for it to get in will cause issues with the reading. Same if the idle is rough, any cylinder that doesn't burn completely--miss- will pump unburned Oxygen into the exhaust, which will show up as a lean condition.
IMHO that wideban O2 is gonna give you more mis-information than good information unless you really know what you are doing with it.
Keith

[baltobernie]

You're not running all that rich; 12's is where you want to be under moderate load levels, 11's under WOT and full load. 2½ to 3 turns out usually indicates idle jet is too small. Try one bigger idle size, 1½ - 2 turns out.

If you hold a steady light throttle while ascending a grade, what is the leanest number you eventually see?

With the throttle closed, as you describe at idle and trailing throttle, you should occasionally see 13's - no leaner.

I'm assuming you've checked your float levels, and set them to specs. Even a mm or two can dramatically change how the car runs; specifically the transition from low to main.

Get the low circuit working before moving to main and air jet experimentation. Bigger or smaller low jets affect the overall mixture ratio under all RPM conditions.

[boogiedude]

You're not running all that rich; 12's is where you want to be under moderate load levels, 11's under WOT and full load. 2½ to 3 turns out usually indicates idle jet is too small. Try one bigger idle size, 1½ - 2 turns out.

Just to make sure I'm on the same page as you, we're referring to mixture and not idle speed, right?

If you hold a steady light throttle while ascending a grade, what is the leanest number you eventually see?

while on an incline, in the range of 11's. while on flat ground, it can fluctuate from from 11's to 14's. Thats over a few hundred yards at 30-40mph. There's too much congestion in this state to find anywhere to drive for anything near a mile without needing to lift/accelerate to follow traffic.

With the throttle closed, as you describe at idle and trailing throttle, you should occasionally see 13's - no leaner.

I'm assuming you've checked your float levels, and set them to specs. Even a mm or two can dramatically change how the car runs; specifically the transition from low to main.

Get the low circuit working before moving to main and air jet experimentation. Bigger or smaller low jets affect the overall mixture ratio under all RPM conditions.

I haven't found any float spec for our cars and this set up, so i've been running the float level described for a BMW 1800TI running dual 45 dcoe's(as listed in Weber Carburettors Tuning Tips and Techniques by John Passini) which is 7.5mm and 14mm.

Engine braking going down hill is not going to give you good information, just ignore it.
Got any exhaust leaks?? The sensor measure Oxygen, and any way for it to get in will cause issues with the reading. Same if the idle is rough, any cylinder that doesn't burn completely--miss- will pump unburned Oxygen into the exhaust, which will show up as a lean condition.
IMHO that wideban O2 is gonna give you more mis-information than good information unless you really know what you are doing with it.
Keith

I know I have a few pinhole leaks in the welds where my resonator was removed, but those are a few feet downstream of the sensor. I don't think it would allow air that far up the system?

[baltobernie]

Just to make sure I'm on the same page as you, we're referring to mixture and not idle speed, right?

Yes.

[boogiedude]

Well, I havent updated this thread in a while, so here's a little update

I managed to get the single 45 running pretty damn well. Never managed to get it to the dyno to get some real numbers, but it was a very large step ahead of the 38ADL I had on the motor before then. I'm guessing It's putting out about 105-110RWHP. Not too shabby.

But I've moved on from that project and picked up a set of IDF's to play with. They're an original set of 13/15 series on a waffle manifold. Freshly rebuilt out of italy. I got them on the car last week and have been slowly dialing them in since then, and while it is running pretty well(it goes like stink when I punch it in the top end!), it feels a bit lack luster compared to the single DCOE. Especially on the bottom and in the transition. I'm chalking that up to the fact the I don't have it running at 100% just yet.

In the IDF's I'm currently running 50 idles, 135 mains, 200 air correctors, 34 chokes(I think, the chokes aren't stamped and I don't have a micrometer to measure them) and f-11 emulsion tubes.

My A/F mixture is pretty good across the board. It ranges from high 12's to high 13's under normal driving conditions(cruising, light throttle), 11-12 under WOT and when I'm going up hill(which is a large chunk of my commute everyday, seeing as I literally drive over a mountain going to and from work)

My biggest Issue with the carbs is the transition period. The car has a ridiculous flat spot right there and I flash way lean until I give it an extra 20% throttle and force the carbs into the main circuit. I've been looking around online and really can't find much of a general consensus on how to minimize/tune out the flat spot. Some sources say to increase the air corrector size to bring in the mains sooner, some say to change to an f-7 or f-9 emulsion tube to richen up the middle range of RPMs, and others say you can't tune it out without decreasing your venturi size. Who has experience setting these up, and who has dealt with the flat spot?

[131]

I had IDFs on my 2 litre, it was great. Standard chokes on the 13/15 carbs were 32mm, they run on the idle circuit for a fair bit of the throttle opening range, so if it's leaning out before getting on to the main circuit I'd try 55 idle jets.

[baltobernie]

I'm learning to live with a flat spot with my single 38DGS. As I understand it, with performance cams, there is not enough vacuum to pull the mixture from a big carb under conditions as you describe. One suggestion is to use a vacuum advance distributor. This would "light the fire" earlier under low vacuum conditions, providing more burn time. Basically, you're dealing with the same difficulties as early pollution motors; a temporary lean condition under light load, low RPM, and partial throttle. I tried a Plex setup from a late-model Spider, and it did not improve my situation. YMMV. Good luck, and please report back with your results.

[AndyS]

My biggest Issue with the carbs is the transition period. The car has a ridiculous flat spot right there and I flash way lean until I give it an extra 20% throttle and force the carbs into the main circuit.

the transition circuit on the IDF's is a weak spot on tuning those carbs on the Fiat Twin Cam. First of all, your idle jets are too small. put some 55 in there, or if you can find them 57. The transition circuit is very much dependent on how your idle circuit is tuned, and if the jets are too small, you end up with a lean flat spot. . Also, I synchronized the carbs and adjusted the idle mixture screws at about 2500 RPM's instead of at idle. This allows you to tune the transition circuit,

Or you can chuck those pain in the butt IDF's and put a highly tunable single progressive weber 36 DCD-7 on there like I did. Still making about 100HP at the tires, get better mileage, and no constant fussing.

http://www.piercemanifolds.com/product_p/18910.139.htm

[boogiedude]

I had IDFs on my 2 litre, it was great. Standard chokes on the 13/15 carbs were 32mm, they run on the idle circuit for a fair bit of the throttle opening range, so if it's leaning out before getting on to the main circuit I'd try 55 idle jets.

The rebuilder I bought them from jetted them to my application,(even though the jetting was off.. 55idle, 127 main, 210 air) which leads me to believe he changed the chokes to 34's as well. Also, when I had the 55 idles in, i was told by a local porsche/vw mechanic that he felt the idle jet needed to come down. I'll try putting it back in and see what difference it makes

I'm learning to live with a flat spot with my single 38DGS. As I understand it, with performance cams, there is not enough vacuum to pull the mixture from a big carb under conditions as you describe. One suggestion is to use a vacuum advance distributor. This would "light the fire" earlier under low vacuum conditions, providing more burn time. Basically, you're dealing with the same difficulties as early pollution motors; a temporary lean condition under light load, low RPM, and partial throttle. I tried a Plex setup from a late-model Spider, and it did not improve my situation. YMMV. Good luck, and please report back with your results.

If I understand what I've been reading about in the different weber books, and on different forums, the reason for the flat spot is due to the number of progression holes in the carb. IDF's have less progression holes than DCOE's which is one of the reasons why the DCOE's are almost always chosen over IDF's on all kinds of engine builds when the space permits. Although the vacuum could also be a culprit, but I'm turning an eye of denial on that for the time being... the cams are gonna stay in the motor, regardless

My biggest Issue with the carbs is the transition period. The car has a ridiculous flat spot right there and I flash way lean until I give it an extra 20% throttle and force the carbs into the main circuit.

the transition circuit on the IDF's is a weak spot on tuning those carbs on the Fiat Twin Cam. First of all, your idle jets are too small. put some 55 in there, or if you can find them 57. The transition circuit is very much dependent on how your idle circuit is tuned, and if the jets are too small, you end up with a lean flat spot. . Also, I synchronized the carbs and adjusted the idle mixture screws at about 2500 RPM's instead of at idle. This allows you to tune the transition circuit,

Or you can chuck those pain in the butt IDF's and put a highly tunable single progressive weber 36 DCD-7 on there like I did. Still making about 100HP at the tires, get better mileage, and no constant fussing.

http://www.piercemanifolds.com/product_p/18910.139.htm

With such a large idle jet, I'm going to need the mixture screw to be in at like 1/2 turn from seated to get the A/F right at idle, wouldn't I? I'm a 3/4 of a turn out on the 50 and my A/f at idle is in the 11's. Too rich still

I'm curious about syncing the carbs at such high RPM's. I read a couple differnt sources recommending that, but if you're using an STE type syncrometer, you would be flowing in the 20's at least, and at the point of the range the indicator on the syncrometer is much much less sensitive. I can't see how you could really get them dialed precisely in at that range.

Chucking the IDF's sure ain't happening. I've run a single progressive 38ADL, a single synchronous 45DCOE, and now dual 40IDFS on it. The 38 didnt come anywhere near feeding this motor and bring out the power in it the way that the 45 was able to. Let alone a 36. My 38ADL put out 98whp on this build.