2L HC experiences

[scampbel98]

I've got a Franken-Fiat with the following block/head combination out of a 1980 Fiat 124 2000 (supposedly a 49-State Federal car)
BLOCK
132A1.040.6
08501264

HEAD (does not have EGR port thru the front head)
132AC.AC
4439644

Was running OK, but started to blowby way too much so I tore it down. I've had the block bored .8mm over, crank polished, head reworked (mild), etc. and have new VAS 84.8mm high-compression pistons being fitted. Anybody else running a setup like this?

Thanks in advance!

[narfire]

Is it carb'd or FI? I have a fi with 84.4 and a 1800 head on the fi and love it

[scampbel98]

Carbed - 32/36 DFEV (makes a great noise)
You're running the VAS HC pistons?

[sptcoupe]

Do you know what the dome height on the pistons is? The oversize bore is not a problem, but getting the head shaved (even mildy) AND running the 8mm domed pistons commonly sold as HC pistons could cause you problems with detonation. Here in Texas we are lucky enough to be able to but 93 octane fuel at the pump, but as you get near the 10:1 CR range, you may have to retard the timing and do other things to the combustion chambers to avoid detonation running the more common 91 octane. What cams are you running?

Measure the CR before you put it together - don't leave it to guess work.

I normally shave the domes down to 5mm or 2.5mm, depending on the CR, which I like to keep around 9.8 or so, depending on what else I have done in the way of engine mods. Any decent machine shop can shave the domes for you. Another alternative is a thicker head gasket to get the CR where you want it. I prefer to do it by re-sizing the domes.

[scampbel98]

thx sptcoupe...
when you have them shaved, is it just a straight shave or are the "edges" of the crown worked smooth?

[scampbel98]

BTW: with 1756 block and crank and 2L head along with VAS HC pistons.. is this now an interferrence engine? sure looks like it

[sptcoupe]

I just shave them straight across and have never had any problems.

Just a note or two on HC mods from the experience gained in building many HiPo engines over the past 38 years or so.

If you shave the pistons, don't take off more than about 2.5 - 3mm. Most of the aftermarket pistons sold have around 8mm of metal in the crown, so going more than 3mm could lead to other problems. If you calculate that you need less than that, then have them made to your specs.

The pistons that are advertised to by 9.8:1 CR, with 8mm domes, will yield a lot more than that in a re-build. When I did use them "out of the box", I would typically get around 11.5:1 CR, after taking the typical .0020 - .0030" off the head to clean/straighten it. That was great back when you could buy 96, 98 and 100 octane (leaded) gas at the pump, but with the typical 91 octane sol today, you will have detonation. The last motor I built that had 8mm domed pistons in it was in 2004. It was a 2.0L, with a 2.0l head, and .0020" taken off. It was impossible to drive unless I mixed 104 octane racing gas with 91 pump gas, to get about 98 octane. And even then, It would detonate under extremely heavy loads.

Granted, you can reduce compression/detonation by the more common methods (gaskets, re-shaping combustion chambers, cams, etc), but when you do those things (especially re-shaping the combustion chambers - how many of us have done before and after dyno runs to see what the HP results were after messing with the combustion chambers keeping all els the same?) you introduce a whole lot of variables into the build that can effect the total performance/output of the engine. So if you want to control the variables and you need/want to increase the CR, measure it up and put the right pistons in.

Finally, I have learned the hard way that "a silly millimeter" is not the same to all manufacturers. I have had supposedly 8mm domed pistons arrive with domes that were actually 9mms, and 4mm domed pistons that were only 2mm. So when you take those puppies out of the box, stop drooling long enough to carefully measure the domes (and diameters).

[manoa matt]

sptcoupe, a couple of questions.

I'm building up a 2L and using a 2L FI head. The cylinder bores are only slightly worn and are still within spec for "standard" pistons. I'm looking at two sets of pistons. One set is 4.5mm dome, "standard" and should drop right in with a light hone of the cylinder bores, these are reportedly 10:1 CR. The other set is reportedly 9.8:1 with an unspecified dome measurement, however they only come in 84.6mm which means I would need to overbore the cylinders to the largest size, something I'm not fond of, since if there were a problem later, the cylinders are bored out to the largest size and the block is then scrap.

I have several head gaskets of varying thickness. I can use a thick one (0.5mm thicker than standard) and get the CR down if I go with the 10:1 4.5mm dome set. The highest grade of pump gas available here is 92 octane, others are 87 and 89.

The owners manual for a new car I just bought says to use 87 octane for the 4cylinder version that has 9.7:1CR and use 89 octane for the 6 cylinder version with 10:1 CR.

If I use the 4.5mm pistons with 10:1CR will I be ok running on 89 or 92 octane?

[sptcoupe]

Matt,

First, the clyinders can be bored out to 84.8mm, so going to 84.6mm leaves you room for another re-build. I have had them bored to 85mm. If you are doing the re-build anyway, you should be sure that it isn't best to go to .6mm over and get a really fresh engine that will go a long way before need to do any work on it. Do a compression check and see what you have. Does it push any oil?

The CRs on new cars can't be used to compare with our cars. The modern ECUs make instantaneous adjustments in ignition and valve timing to protect the engine when they detect pending detonation. They are always running at the maximum parameters that they can with a given octane.

I guess what I am trying to say is you can't go with what is advertised to be the CR. You should measure it to be sure.

A 10:1 CR should be fine with 92 octane in a healthy engine that has no carbon deposits on the piston crowns, etc, and is properly tuned. I wouldn't go any higher.

If the 4.5mm domes in fact yield a 10:1 CR, after you clean up the head mating surface, then you are good to go. If you end up with something like 11:1, then I personally would consider either shaving the domes down some (if there is enough metal in the crown to leave about 5mm), as that is the best and most permanent fix, and since you will be able to measure the CR, you will eliminate a variable.. That said, gaskets can do the job a lot cheaper and be a good fix if you aren't going to run it hard. You can have some HiPo gaskets made, or if I am not mistaken, Auto Ricambi may have some HiPo gaskets in various thicknesses, and you can get exactly what you need to get that 10:1 CR with those 4.5mm domes.

Typically, the pistons advertised to be 9.8 CR have 8mm domes, but the seller should be able to measure them and let you know.

[TulsaSpider]

Just when you think you have your mind made up...... Ok I am getting close to ordering pistons and I was going to go with the Vick's 8mm domes. Now there is all this controversy between the seller and you guys in the know. So Now I have two choices. I have a complete 1800 motor, currently in the car. I just tore down a 2L to re-build (79 carbed). All looked good except for the end of the aux shaft. Still not sure about that, anyways do I order the 8mm pistons and use the 2L head? Will that reduce the CR? to manageable levels? Mark, care to chime in on this thread????

[scampbel98]

TulsaSpider, I'm going to try and run the VAS 8mm pistons with 1800 block bored .8mm+ and 79 Carbed 2L head. Fingers crossed. Waiting on new rod bolts, new oil pump and a couple of gaskets.

Using Guy Crofts excel calculator I come up with around 9.2:1 - 9.5:1. I didn't burrette measure any of the dome, reliefs or head chamber). A 2L/2L looks to be in the 10:6 range (others will surely chime in). Sounds like this is viable for my setup, but a 2L/2L combo might be too high for even hi-test gas.

[BEEK]

ive used "9.8-1" pistons in 2.0 blocks with 1800 heads, static compression numbers over 200, using stock cams i had detonation unless i used 110 octane or kept the timing under 26 deg total adv. when i put a much larger cam in i was able to run 93 octane and 30 deg advance. the dynamic compression was effected by overlap. just some imput.

my curent project zagato has 2.0l with 1800 pistons, small valve relief. an 1800 head and 42/82 cams . compression tests at 180psi. runs on pump gas all day. im looking for a 60cfl throttlebody if anyone knows where on is.

[So Cal Mark]

since I've been accused of unfairly criticizing VAS, I won't comment on their pistons. My experience is that the 8mm dome does create much more than 9.8 compression. If it was me I'd look for 4mm dome pistons at most.

[BEEK]

im a beliver in mores law, more is always better

[TulsaSpider]

TulsaSpider, I'm going to try and run the VAS 8mm pistons with 1800 block bored .8mm+ and 79 Carbed 2L head. Fingers crossed. Waiting on new rod bolts, new oil pump and a couple of gaskets.

Using Guy Crofts excel calculator I come up with around 9.2:1 - 9.5:1. I didn't burrette measure any of the dome, reliefs or head chamber). A 2L/2L looks to be in the 10:6 range (others will surely chime in). Sounds like this is viable for my setup, but a 2L/2L combo might be too high for even hi-test gas.

Ok now I am confused. The 2L head had a larger combustion chamber that the 1.8 so why would the CR be higher?
People put the 1.8 on the 2L block to raise the CR. With the discussed HC pistons the CR with the 1.8L head would be HIGHER than the CR on the 2L 2L combo. Or am I missing something? 9.5 to 1 sounds good or 10to 1 I don't really want higher