dished to flat pistons

[Glenn]

I'm rebuilding a 77 FI Type 1 engine. The original pistons were dished and the new ones are flat. Will this be an issue? How much will it raise compression? Should I add shims to increase the deck to compensate?
_________________
Glenn
74 Beetle Specs | 74 Beetle Restoration | 2180cc Engine
"You may not get what you pay for, but you always pay for what you get"

Member #1009

#BlueSquare

[Danwvw]

How many cc's do the dish pistons differ from the flat?
_________________
1960 Beetle And 1679cc DP W-100 & Dual Zeniths!

[75smith]

Dished pistons lowers the CR...roughly half a point, this depends on the size of the dish(3-5cc most of the time)

to get the equivalent with a flat piston, it is roughly .04" deck-height change, assuming same size bore and stroke

I believe the FI cars had a CR of about 6.6
_________________
My 1975 Beetle Build Updated 8-21-12

My engine build

[Jimmy111]

The question is, does it have to pass smog??
Going from the dished to the flat tops will probably top out the NOX.
Other that that, go for it.

[slalombuggy]

Won't be a problem, done it lots of times. Small motors hardly notice a change in compression even with changes in pistons or combustion chamber cc's, they just don't have the cylinder volume to change static compression that much.

I like playing around on CB's engine calculator. Changing the size of motors and head ccs and how much or little it affects compression based on displacement of the motor.

brad

[SRP1]

[Glenn]

[skills@eurocarsplus]

just mock it up like any other build and figure out the c/r. honestly, it will be fine. i just did this for a guy. *ahem* do not use deves rings
_________________

[nextgen]

I had a T-4 engine that hat 2.0 stock 71 mm rods I was told I had to run dished pistons because the 1.7 heads combustion chamber were too small the compression would have been to high. I finally did a cc check and with the dishes it came to 8.4. The machine guy I guess was right. I have no clue what the compression with the 2.0 flat tops would have been, any clues.

GLENN You are right Love NY, just safety test, blinkes, honk the horn step on the brake and away ya go!
_________________
email: [email protected]
The TYPE IV UPRIGHT CONVERSION MANUAL
BEETLE MAGNETIC DEFLECTOR SHIELDS
LETS TALK DUBS https://www.youtube.com/results?search_query=joe+cali+ghia https://letstalkdubs.libsyn.com/ep-200-joe-cali-ty...qI3xJTCzjs

[modok]

If you throw in a mild cam(web 73?), vintage speed muffler, then the extra compression (8.75 or so?), , it should be ok, and a heck of a lot quicker too

[Glenn]

Nah... it's staying stock with FI.

This guy doesn't care about quick.


Another question... looks like the crank needs to be replaced. I'm thinking of upgrading it to a counter weighted crank. The problem is all CW cranks are 8 dowel and all 8 dowel flywheels are lightened. My thinking is a stock Super vert would be better with a stock weight flywheel.

But all the stock weight flywheels are 4 dowel and cast (not forged) and all 4 dowel cranks are not CW and also cast. I spoke to one vendor and he said a cast crank/flywheels is perfectly fine in a stock application.

Thoughts?
_________________
Glenn
74 Beetle Specs | 74 Beetle Restoration | 2180cc Engine
"You may not get what you pay for, but you always pay for what you get"

Member #1009

#BlueSquare

[vwracerdave]

On an 8 dowel crank you can remove 4 pins and only use 4 to bolt a stock flywheel on. There is no need for a C/W crank on a stock engine that will never see above 4500 RPM

Cast cranks and flywheels are fine on engines up to 10 HP. I have hundreds of races at the drags with 2 engines 80 & 95 HP that have cast cranks.
_________________
2017 Street Comp Champion - Thunder Valley Raceway Park - Noble, OK
2010 Sportsman ET Champion - Mid-America Dragway - Arkansas City, KS
1997 Sportsman ET Champion - Thunder Valley Raceway Park - Noble ,OK

[Glenn]

Thanks Dave.

BTW... I assume you mean 100hp.
_________________
Glenn
74 Beetle Specs | 74 Beetle Restoration | 2180cc Engine
"You may not get what you pay for, but you always pay for what you get"

Member #1009

#BlueSquare

[slalombuggy]

My buddy Todd ran low 13s for years on the same cast crank making over 1000 passes without issue. If you want a C/W crank you could also just get a stock flywheel drilled to 8 dowels. PErsonally that's the way I would go.

brad

[gooser]

looking at aircooled i can't see a whole lot of difference in prices between a low cost counterweighted crank and a stock crank. don't know if the el cheapo counterweighted is any good though.

[Bashr52]

I think I CC'd a set of stock dished pistons before, and came up with around 5cc's. I could be off a bit thought, that was years ago

[satterley_sr]

We have broken cast flywheels with 70 hp in Formula First, stick with a forged flywheel. ( Cast cranks seem to be okay)
_________________
DDC racing

[modok]

[johnnypan]

I mated a welded DPR counterbalanced crank to a stock flywheel on a stock build.Flywheels by design store energy and smooth impulses,stands to reason the heavier flywheel adds to the dampening effect of the CW crank.I just four doweled the crank,the other four bores were blinded by the flywheel...crank stability issues by leaving the bores open is moot.

Maybe you don't need a CW crank if you don't plan on exceeding 4500 rpm..but you will notice a pleasant difference if you use one.

[Glenn]

asked Jose @ DPR and he can do a forged cw crank and a stock weight forged 8 dowel flywheel. looks like the way to go.
_________________
Glenn
74 Beetle Specs | 74 Beetle Restoration | 2180cc Engine
"You may not get what you pay for, but you always pay for what you get"

Member #1009

#BlueSquare