Stay with FI, or go to Carbs?

Road-race engines and ancillaries - general discussion
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vandor
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Re: Stay with FI, or go to Carbs?

Post by vandor »

Guy,

I took the car to the muffler shop on Monday and they redid the header downpipe and removed the resonator. The resonator was of similar construction to the tips above, ie. a lot of intrusion into the airflow. I had them fabricate a new pipe from where the resonator was all the way to the muffler.
The muffler has only one outlet, the tips were a separate item welded on the end of of the muffler. The tips are totally open.
We are planning on taking the car to the dyno on Saturday.
bye,

Csaba
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Guy Croft
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Re: Stay with FI, or go to Carbs?

Post by Guy Croft »

OK, good. At least - if nothing else - you can then rule out those things as probable cause. Sometimes you just have to do that to fault-find.

Now - your IAP cams. Have you got a lift-degree map or even the cam area data?

G
robert kenney
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Re: Stay with FI, or go to Carbs?

Post by robert kenney »

Hi Guy and Csaba.

I have had the opportunity to eyeball both the IAP 42/82 and IIIa cams side by side when I built my sisters stroker Fiat. There is no comparison. Lobe volume and nose dwell are much larger on the IIIa's hence the reason I installed the IIIa's.

Sorry I didn't see any reason to map the 42/82's after comparing the two.

If this post is found wanting, please delete

Robert
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vandor
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Re: Stay with FI, or go to Carbs?

Post by vandor »

Guy,

I have not measured the cams. If the dyno numbers are unsatisfactory, then I will get out the degree wheel and dial indicator. I have the feeling they may be short of what they are advertised as.
Today we switched to standard plugs (used Iridium previously) and moved the oxygen sensor to the new location, but there is no change in the idle behavior.
Thanks,

Csaba
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Guy Croft
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Re: Stay with FI, or go to Carbs?

Post by Guy Croft »

When you run at idle - take the top off the airbox and see if there is fuel standoff - mist and vapour/fuel droplets coming out of the rampipes. There should not be - though it is normal to get a bit when you first open the throttle (ie: accelerate).

G
vandor
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Re: Stay with FI, or go to Carbs?

Post by vandor »

Guy,

I have not seen fuel standoff, but I have not specifically looked for it. Will do in the next couple of days.

We spent several hours at the dyno this afternoon with strange results. When we started the car only made around 120 hp at the wheels. Ouch. Way off from our best. After several hours we were at 137hp at 6200 rpm. It is still making hp way too low in the rpm range.
There were several things that baffled us. First, we got most of our power increase from advancing the exhaust cam. Retarding the intake made little difference, but every time we advanced the exhaust 2-3 degrees the car made more power.
This reversed from how it commonly works - usually moving the intake cam timing has more of an effect.
Second, we got max power with 29 degrees of ignition advance. More timing actually made less power, which is unusual, as it is my understanding that (up to a point) more timing will not increase power, but will not reduce it either.

We still think there is a bottleneck in the system. Next week I will take the car to the exhaust shop and install a different header, and we will dyno the car with only that change. I will also make a degree/lift chart for the cams to see what we really have.
Thanks,

Csaba
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kpsig
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Re: Stay with FI, or go to Carbs?

Post by kpsig »

Out of my experience, there is a threshold of ignition advance from where onwards you only loose power.
For example, in my car (tu 1600 8V highly modified engine, 12,7/1 CR, 4 ITBs, maximum torque @5800, Megasquirt, double injectors/cylinder, race cam, totally different ignition circuit and components etc) I have maximum power @ 33 degrees ignition advance with a cam of 280degrees and 11,25mm lift. From 35 until 38 degrees (just for a test) I had power loss with no preignition or detonation problems yet. OF course, when I change my somehow restricting exhaust I will have to do a remap.
Air to fuel ratio at WOT, all over rpm range, is around 12,5/1, all other areas around 13/1.
Similar things (more or less) I observed to Toyota Yaris 1.3 Gr. A, Cinquecento kit car, Peugeot rallye 1,3 and 1,6 16V Gr. A.
Kostas, Greece
vandor
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Re: Stay with FI, or go to Carbs?

Post by vandor »

Hi kpsig,

As usual, thank you for your comments. We noticed no power improvements by varying AFR from 12:1 all the way to 13.5:1.
So even at part throttle you run 13:1 AFR? Does it not cause an over rich mixture? Black smoke from the exhaust and the cylinder bores being washed down by gasoline?
Thanks,

Csaba
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Guy Croft
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Re: Stay with FI, or go to Carbs?

Post by Guy Croft »

Csaba - struggling to make 137BHP - your cams are the problem - I am now sure of it.

No other thing would make this engine so unresponsive (ie: difficult!).

G
kpsig
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Re: Stay with FI, or go to Carbs?

Post by kpsig »

vandor wrote:Hi kpsig,

As usual, thank you for your comments. We noticed no power improvements by varying AFR from 12:1 all the way to 13.5:1.
So even at part throttle you run 13:1 AFR? Does it not cause an over rich mixture? Black smoke from the exhaust and the cylinder bores being washed down by gasoline?
Thanks,

Csaba
Hi Csaba.
Well, in part throttle (20 to 70% approx. of TPS range) regimes I have tried leaner mixtures (like 14,5:1) but it did not work well, I had some stumbles and hesitation in throttle response. This is somehow expected with aggressive cams (at least more than the OEM). I do use leaner mixtures for 5 to 20% of throttle position sensor.
For everyday driving (which I do with my "road legal" 205) I use leaner mixtures like 13:5 to 14+:1 and increased acceleration fueling but for track use ~13:1 part throttle AFR is good enough. For WOT, a little richer AFR could be needed.
I have absolutely no black smoke with 13:1, my spark plugs are OK and my exhaust ports seem not to have carbon deposits (a boroscope is a very helpful thing!!!).
On the other hand it makes me wonder why from 12:1 to 13,5:1 AFR you see no difference. Maybe you should revisit your ignition maps.
From my experience, acceleration is improved especially when you exit corners (especially if you drive "slow in fast out") or going uphills.
I agree with other people that you should identify your cam profiles.
Let me say another thing. Before putting all bits and bytes to my engine, I run some engine simulation software.
Very interesting, very time consuming for someone who has no help, but really rewarding.
Before I decided to buy my camshaft, I tried to see the power and torque output with different profiles and duration.
It was clear that for some types, provided that I kept all other factors constant (header tube diameter, port flow etc) I could identify flat spots, variation in power and change in usable power range. The output of the simulation software was assuming that I was able to use ideal AFR and ignition tables, so the numbers of power and torque were ideal.
The result comparing software simulation output to real life was interesting: With the software I saw an output of 150hp@ crank, in reality I see 140hp@ crank but with very similar graphs, which is well within the error accepted due to software assumptions in its algorithms and my less than ideal programming and other modifications I have done.
So, check your camshaft and its timing!
Kostas, Greece
vandor
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Re: Stay with FI, or go to Carbs?

Post by vandor »

OK, I will check the cams tomorrow!
thanks,

Csaba
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engineerted
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Re: Stay with FI, or go to Carbs?

Post by engineerted »

Csaba,
I am very interested in your results as I too use the IAP 42/82 cams in my race car, but do not have any of the issues you are having. This is not apples to apples as I run twin 40 idfs with 32mm chokes, 4 into 1 header, 11.2 CR. The motor can pull WOT from 3500rpm up to redline (7600), below 3500 not much going on but does idle nicely at 1200. I would like to see what an other header (extractor) does to the HP/rpm as I have some reservations about the Snake type header you are using with the abrupt angle turn at the exit of the cylinder head.


Ted
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Guy Croft
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Re: Stay with FI, or go to Carbs?

Post by Guy Croft »

Can we all just be clear about one thing, most of the cam manufacturers who do TC cams - do sell regrinds and billets (I won't touch regrinds FWIW).

I have no doubt that a billet 42/82 (similar to or mastered from an Alquati type) will work fine but a regrind would do what Csaba is experiencing and in this case I still have no idea which are being used.

I point this out because I have no wish that IAP be done a disservice on this site (it's against Protocols anyway), and the reality is to a great extent that the buyer is responsible for that regrind/billet choice.

A mfr of regrinds is hardly going to say 'they are no good' and good luck to them! There is no good argument at all in my book for chosing the former, even cost (which is always much less).

GC
vandor
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Re: Stay with FI, or go to Carbs?

Post by vandor »

Hello,

The cams are billets, ie. new cams, not regrinds.
Thanks,

Csaba
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Guy Croft
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Re: Stay with FI, or go to Carbs?

Post by Guy Croft »

OK, cool. Any sign of that cam map or degree x inch data? They would show me the area under the curve.

G
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