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Mon Apr 19, 2021 4:26 pm

since some of yall seem to be getting sidetracked and trying to make this about answering something that wasnt asked, i highlighted my original post to try and make the question clearer.
" what is the max c.r. a vw engine can run" was never the question.
we all know there's to many variables we can get hung up on, so i tried to word it so we wouldnt and could just b.s. and see what some ppl can do.

Mon Apr 19, 2021 4:29 pm

vwracerdave wrote: It won't do any good to explain my opinion. People are gonna disagree no matter what. We might as well argue about which oil to use.

Build whatever you want. Listen to whomever you want. I guarantee you get to keep all the broken pieces.

You can't read a Chevy book and build a VW engine.

I hate chevy's, but I have built and driven few different VW engine's. I would still like to know why you chose 9.5:1 as the end all compression for ALL VW pump gas engine's. I promise not to disagree with you publicly. I am hear to learn....good or bad. Maybe you know something the rest of us don't?

Brian

Mon Apr 19, 2021 4:37 pm

If I was the OP I would read up on dynamic compression ratio and squish. Try to form your own opinion. There’s no hard set rules. Try to not go crazy with DCR and keep squish within .040”-.060”, make sure you keep the combustion inside the chamber and the better the fuel control the higher static compression you can run.

It is all debatable. I run 9.6:1 with a web 252 and dellortos and have ran 87 just fine with full advance set at 32 degrees. I did make sure to keep a tight deck and I have a .060” “head gasket” with the piston poking up .020” above the top of the cylinders to try to keep the combustion inside the heads. 90 is the highest you can get here and that’s what I normally run. However I’m at a place where a hot summer day doesn’t exceed 90 degrees Fahrenheit.

Lots of old school guys going with the gene berg advice still.. nice thing about a VW is it’s easy to adjust deck.

Mon Apr 19, 2021 5:20 pm

richardcraineum wrote: since some of yall seem to be getting sidetracked and trying to make this about answering something that wasnt asked, i highlighted my original post to try and make the question clearer.
" what is the max c.r. a vw engine can run" was never the question.
we all know there's to many variables we can get hung up on, so i tried to word it so we wouldnt and could just b.s. and see what some ppl can do.

It's not really that people are getting sidetracked, it's that you asked a totally vague question with no real answer. There are 98+ different variables. Even if you duplicated one guys engine combo, even setting the cam up with slightly different valve events will effect your outcome based on the engine you copied. It is impossible to say what compression will work universally. One engine at sea level is WAY different from the exact same engine in Denver.

Might as well ask what the color blue smells like on a Tuesday in the dark.

Brian

Mon Apr 19, 2021 5:58 pm

vwracerdave wrote: Don't let anybody fool you. 9.5:1 is the limit for 91 Octane pump gas here in the USA.
Do you think a race engine with a FK98 would even run properly at 9.5 CR? [-(

That is the hottest VW cam engle has to offer and they reccomend a CR of 13:1 minimum :-k

John from Aircooled.net also recommends 10.5 + for a few different cams they offer, I feel like he's been around the block...

:roll: :roll: :roll:

I think the truth is pretty clear... :twisted:

Mon Apr 19, 2021 6:26 pm

evanfrucht wrote: vwracerdave wrote: Don't let anybody fool you. 9.5:1 is the limit for 91 Octane pump gas here in the USA.
Do you think a race engine with a FK98 would even run properly at 9.5 CR? [-(

That is the hottest VW cam engle has to offer and they reccomend a CR of 13:1 minimum :-k

John from Aircooled.net also recommends 10.5 + for a few different cams they offer, I feel like he's been around the block...

:roll: :roll: :roll:

I think the truth is pretty clear... :twisted:
Is a race engine with an FK98 running 91?

You might not agree with vwracerdave, but he's been racing and has built a lot more engines than you . . .

Well, what is the truth then?

Mon Apr 19, 2021 6:39 pm

Fair enough, but one can have a lot of experience and still be wrong sometimes.

And yes many race cars also use pump gas around town :wink:

Mon Apr 19, 2021 7:25 pm

evanfrucht wrote: Fair enough, but one can have a lot of experience and still be wrong sometimes.

And yes many race cars also use pump gas around town :wink:

Truth right there.

Lots of guys still believe the gene berg thought of low CR required for long engine life.

The 9.5:1 statement is a hint here.. nothing against racerdave just some pick something to believe/preach and it is what it is.

Mon Apr 19, 2021 8:02 pm

Brian_e wrote: Might as well ask what the color blue smells like on a Tuesday in the dark.

Brian

Without any other perimeters, CR means nothing.

Someone’s race engine they run with race gas at 13.5:1 will most likely run on 93 octane pump gas if you retard the timing.

A small engine with a tiny cam like a 2280 could ping past 9.0:1.

An n/a engine with a FK89 could run on 93 pump gas at 11.5:1.

A turbo engine may ping at 8.0:1.

After having a daily with a 2276, and an FK10, it’s great being able to zing past 7k. The only issue is it’s driven 99.9% of the time below 3500. The next engine that gets built for another daily is going to have a cam that plays better where the car gets driven from 1500-4500. I’m guessing that’s not going to support much past a 9.5:1 SCR. CR means nothing bragging about your build if your junk isn’t breaking records at the track.

Mon Apr 19, 2021 8:35 pm

evanfrucht wrote: John from Aircooled.net also recommends 10.5 + for a few different cams they offer, I feel like he's been around the block...

Yes, John does recommend 10.5 & up CR on some cams but nowhere does he say you can run them on 91 octane pump gas.

Street car or race car is doesn't matter. You can mix race gas with pump gas in any ratio you want. On my 10.5 CR race engine I mix 1 gallon of 110 race gas with 4 gallons of 91 pump gas.

Nowhere on Engle's website or ACN does it say you can run the FK-98 at 13:1 on 91 pump gas. 13:1 needs race fuel.

When your running a 11:1 engine down the highway at 3400 RPM, your only using 20% of it's power, so the engine might be able to survive on 91 pump gas. Run it down the drag strip at WOT on 91 pump gas and you'll soon start seeing the damage.

Everybody is welcome to disagree with me and have their own opinion, or their own set of facts.

I agree with gkeeton above. The next street engine I build won't be bigger than an FK-8.

Mon Apr 19, 2021 8:41 pm

Fair enough, pump gas is for the street and that's probably one of the reasons very high performance street engines might be able to get way with more than 9.5 CR. A lot of times the peak power is reserved for more spirited driving, but it's not a race track even then. Much of time you will be forced to keep things in the lower RPM's when putting around town due to common sense and safety reasons.

Mon Apr 19, 2021 9:35 pm

evanfrucht wrote: Fair enough, pump gas is for the street and that's probably one of the reasons very high performance street engines might be able to get way with more than 9.5 CR. A lot of times the peak power is reserved for more spirited driving, but it's not a race track even then. Much of time you will be forced to keep things in the lower RPM's when putting around town due to common sense and safety reasons.

Most the time pinging happens at high load low RPMs.

It's all in the combo and the tune. A guy cant say 9.5:1 is the limit for street on pump gas.. something as simple as a cam change or a change in rod length will affect what you can/can't run off pump gas.

I shoot for between 7.5:1 to 8:1 dynamic compression ratio (I think you'll find many do). So with my 9.6:1 static CR and the web 252 IVC of 63 degrees I get 7.8:1 DCR. Plenty safe for the poor quality pump gas I have avail here.

If I was to use a FK89 I can run lots more static compression. Plugging in my numbers for my motor I get 7.35:1 DCR with this cam. I dont get close to where I'm at with the 252 until 10.2:1 static..

I'm just focusing on dynamic compression ratio because it's the easiest change to measure and compare. Where the burn is happening (how far in the cylinder), deck height, chamber efficiency, bore size, state of tune, ambient air temps, heck even the weight of the car and gears will all have an effect.

I'm not trying to pick on dave either.. He gives good advice. Everyone does something different and has their own experiences and opinions. My car/motor setup is a good example.. I have a bigger cam than lots of guys would run in a baja but for my with my use it works perfect.

Mon Apr 19, 2021 10:44 pm

how much "CAN YOU" run?
Sounds like a personal question, and a challenge.

How much DO YOU run would be a more concrete question.

I can think of a few engine designs that would NEED over 10-1 to run pump gas.
CAN I build those? probably yes. Especially if you talk me into it and pay for the parts. :P

Tue Apr 20, 2021 5:10 am

I think the closest measurable comparison of would be cranking psi?

Tue Apr 20, 2021 8:02 am

11.2:1

Tue Apr 20, 2021 8:16 am

I would think a 16:1 would start on pump gas...and probably 18 or higher too.if thats the question your asking.especaily if your running E85 pump gas...

Tue Apr 20, 2021 8:27 am

mark tucker wrote: I would think a 16:1 would start on pump gas...and probably 18 or higher too.if thats the question your asking.especaily if your running E85 pump gas...

e85 is widely available and comes from a pump...

:lol:

:twisted: :lol:

Tue Apr 20, 2021 8:31 am

no issue running an FK-10 and 11:1 :wink:

I used to listen to berg when I was a kid..

but when they preached "nothing over 90.5's" while gary was running nearly 2500cc his story went out the window...

pluto used to be a planet too...

Tue Apr 20, 2021 8:37 am

also it's very important to not build a hp vw engine like a vw engine. perhaps thats why somany vw junk piles are at the swap meats from the clueless ones building vw's

Tue Apr 20, 2021 10:01 am

ac509 wrote: e85 is widely available and comes from a pump...

:lol:

:twisted: :lol:

Yes but we’re talking about pump gas, not pump fuel. 85% C16 mixed with pump gas could run a little higher compression as well.