2110 Compression Ratio Suggestions

Joe Boone · Post by **Joe Boone** » Thu Nov 01, 2001 11:39 pm

I hope I haven’t done the wrong thing. I have a 1776, Duel Weber 40IDF’s, Stock heads (SH cut), Engle 120 cam and Empi quiet pack exhaust. When I first set up the motor I was convinced that 7:1 compression was the target, and this is what I did. It seems to run fair but I had to set the timing at about 38 degs to get it to run and it ran a little hot. This past weekend I decided to change my compression ratio to 7.7:1 (Since I had a bad oil leak that needed fixing anyway). When I disassembled the motor the piston tops were thick with carbon after only 5,000 miles.
With the 7.7:1 compression ratio the motor seems to run better and I’m running 32 degs max. advance. Am I looking for trouble? Will this help my carbon buildup problem?

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73Super and 73Vert in Indiana
The Story of KatieBug

James2 · Post by **James2** » Fri Nov 02, 2001 12:10 am

Your missing the whole point John.

If it's not written in the Blue Bible of Tech Articles, it's not going to work. it's that simple

. Gee, come on, how dare you second guess the blue book. I can't believe you and Steve would even think that you could try something on your own.

yeahmag · Post by **yeahmag** » Fri Nov 02, 2001 3:18 pm

OK, I've been reading over this a lot. Lets see if at least we all can agree on some items...

1. Static CR becomes less and less and issue with bigger and bigger cams.

2. Dynamic CR becomes more of an issue with big cams.

3. Timing requirements of an engine denotes the efficiency (speed) of the burn of the mixture. Less timing = quicker burn = more efficient chamber.

4. SH heads are a way of reducing the need for shims to lower compression.

If all of the above statements are true. I would like to then take a leap and say SH heads are inefficient. In addition, CR requirements for an engine are predominantly controlled by the breathing ability of the engine.

I'm sure I speak for us all when I say that I can't wait to see the results from the up coming tests from Jake. Thanks to everyone for this discussion.

-Aaron

JohnConnolly · Post by **JohnConnolly** » Fri Nov 02, 2001 3:34 pm

1. Static CR becomes less and less and issue with bigger and bigger cams.

NO. Static CR is fixed, and depends on displacement, head volume, and deck.

2. Dynamic CR becomes more of an issue with big cams.

Dynamic CR is dependent upon throttle position, how much carburetion, cam duration, overlap, exhaust efficiency, intake temp, boost (if any), N2O, engine temperature, and last but not least, RPM. I may have forgotten one or two.

3. Timing requirements of an engine denotes the efficiency (speed) of the burn of the mixture. Less timing = quicker burn = more efficient chamber.

And the advance curve of the distributor. Part throttle advance is 10 degrees more than full throttle advance (which is why vac advance is so nice). Also hot engines require less advance, since combustion is so much faster. But, you understand this one.

4. SH heads are a way of reducing the need for shims to lower compression.

YES. They also unshroud the valves a little bit. but I believe you lose more than you gain.

John
Aircooled.Net Inc

Bent · Post by **Bent** » Fri Nov 16, 2001 6:00 am

Hi,
I just need to say that Dan makes sense and my own testing shows good results only.
Example .the very first 1770 built by our business in 93 still sounds and runs as if it were new, after much thrashing including regular club hillclimb racing.
Ben
although for high RPM I would say no semi-hemi. Our testing shows no-good above 6000.

Tom Perso · Post by **Tom Perso** » Mon Nov 19, 2001 6:40 pm

Couldn't help to stay out of this one. Is this the bi-yearly discussion on this forum??

I digress... In my "Handbook of Automotive powertrain and chassis design" (ISBN: 1 86058 075 0 - For those who don't believe me) there is a discussion concerning compression ratio.

Pg. 6, 2nd paragraph: "Heating of the inital air/fuel charge by the residual products of combustion can also be noted. The higher the compression ratio the smaller the volume of such exhaust products thus remain and any other means of scavenging these exhaust products improves engine performance"

Now, by reading that - Can one assume that by running a nice set of heads that flow more than stock augmented by a tuned exhaust system should help scavange some of those exhaust gasses?

If so, then running a higher C/R should be OK, right?

Again, if this is true, why do you think VW ran such low C/R? Well, I don't think any of us know the engineers who designed them, but I think it makes sense. A stock VW motor has a fairly mild cam with no a whole lot of lift and short duration. Couple that with a peashooter exhaust and one could assume there would be some residual exhaust in the chamber during the intake stroke.

Just a thought. Maybe I'm talking out of my butt. But, thats what I am getting from this book. Of course, I've never built a motor before (I am right now), so maybe I'm dead wrong.

BTW, I am building a 2270cc T4 with (gasp!) 9.1:1 compression. I guess under danimals assumption, I should be dropping a valve seat here soon.

Regards,
Tom Perso http://www.qtm.net/~persoj

69bajakid · Post by **69bajakid** » Tue Nov 20, 2001 1:27 am

thank you guys for thinking so much.
Im 19, own 2 VWs both of wich are not even close to stock..one baja one street.
my entire life i have been the kid who would stay home and make things go faster..i love to know and learn how things work..and how to improve desings..about 4 months agao i got a job at a blasting company and have been stressing over what im going to do with my life..seeing as i need to get these bugs on the road and get the hell out of my parents house..for almost a year now i have been fighting with the idea of taking mechanicle engineering..altho i have never taken a course..i have the brain of a engineer...and reading your posts and seeing the diffrent oppinions and what can and cant work and just how diffrent ppl look to diffrent ways to make more power..
i have decided to follow my gut and take the course..im working on some of my own little designs at the moment to get more power my way..but i assure you..im going to be backing up and learing from what jake and john and Dan and all you guys are doing at this moment..i will be in your shoes one day..i want to have ppl ask me questions like they ask you..and i want to have real hands on answers..times are changing..methods of educating ppl are changing methonds of performance tuning are changing..technology is allowing us to milk more power then ever out of our trusty flat 4.
and i guess this is my promise to all you ppl who come to this list to learn and look for answers just as i do..i will do my best to take our motors to the next level..there is always a way to improve a design..and i will find a few of them.
i have told many i cant allow myself to die untill i beat a Viper in a bug..sounds tough..but i need to do it

and when i find out how im going to do it..i will let you all know..
but straight up im gonna say that when i get my show on the road..im a fan of the small but deadly..i want to make smaller displacement motors that make serious power though head flow and all the goodies.

i know this is just some rant..but thank you for making me certain this is what i have to do with my life

you guys watch out..so far im working on a 2 car canadian race team built owned and operated by me

got the off road and the drag race in mind

see you all around
Cale Fraser
1975 mini motor giant killer
1969 class 5 unlimited baja

"its not how big you build it, its how you build it big"

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"Its not how big you build it, Its how you build it big"

Ron Bullard · Post by **Ron Bullard** » Tue Nov 20, 2001 10:38 am

Wow, I just spent 25 minutes reading this whole thing, it's hee-larious. Steve, got a 1/4 time for that 2276?

Ron Bullard
[email protected]

yeahmag · Post by **yeahmag** » Tue Nov 20, 2001 10:55 am

Well... I just thought I'd give you guys an update on where I'm at seeing as I started this monster

The 2276 is built and the final CR came out to be around 8.2. I'm a little upset with Dave at Proformance because he forgot that we had discussed setting it around 9:1. He reassured me that 3/4 of a point would only make 5HP or so and my engine will run cooler and longer with the slightly lower CR. Only time will tell I guess... As for the rest of the specs:

AJ Simms 42x37.5 heads - they are gorgeous.
WebCam 121/125 Cam and fancy lifters with the hole in them - Thanks John C.
A gorgeous 1-5/8 header and A1 Muffler - Don't know where Dave at Proformance got the header, but it is good looking!
My tiny but faithful Dual 36 Dells with 30mm vents.

It's been run for a few minutes at a time to harden the cam (by Dave) and to check oil pressure and all that jazz - Damn, did it sound wild! It will be in the car Thursday or Friday this week. I suspect I will have about 2 days before my worn out tranny gives up the ghost.

Seeing as it's winter I'm going to try and get away without an external oil cooler (keeping a close eye on Oil Temps). Sooner or later I will have to shell out the $ for one though.

Thanks to everyone for all the help. I'll post smokey burnout pics when I can.

-Aaron

[This message has been edited by yeahmag (edited 11-20-2001).]

danimal · Post by **danimal** » Tue Nov 20, 2001 12:59 pm

>>>He reassured me that 3/4 of a point would only make 5HP or so and my engine will run cooler and longer with the slightly lower CR.<<<

lol, imagine that...

>>>356; again, we have a chamber with canted valves (around 30 degrees out of index from one another), so how that applies to a VW chamber, I have no idea.<<<

perhaps the schoolboy can back up his criticism with an explanation of what canted valve placement has in common with deck height/squish...

hint: when are both valves closed

and how does valve placement affect things then?

next he might ask himself where it's written that semi-hemi chambers are perfectly round in all directions; indeed, he could look at some of the 4-valve chambers in use today for further clarification.

>>>Also, where is this "30-32 total" advance that VW has recommended? I haven't seen this bulletin or spec in any shop manuals (St. Muir doesn't count).<<<

neither have i... but last weekend i did see the allen weiss renn kafer cup sedan run a 12.46 on 91 octane pump gas, with 34 degrees total advance... he runs that timing because that's what makes the most power.

so much for the connelly/arndt masturbatory fantasy of "negative work", as they call it.

dan
oceanstreetvideo.com

Steve Arndt · Post by **Steve Arndt** » Tue Nov 20, 2001 2:03 pm

<BLOCKQUOTE>quote:<HR>Originally posted by Ron Bullard:
Wow, I just spent 25 minutes reading this whole thing, it's hee-larious. Steve, got a 1/4 time for that 2276?

Ron Bullard
[email protected]<HR></BLOCKQUOTE>

Not yet. It was stupid fast with over 150 pounds of tools and spare parts in the trunk, and a gas heater!! I took all this BS out of the trunk and couldn't keep the wheels down

I'm installing Haltech, quad 48mm throttle bodies, bigger exhaust, high performance coatings on friction parts, more compression, higher RPM valvetrain parts, then it will be ready for a quarter mile test run. I don't want to make the half hour drive through the desert out to our NHRA 1/4 mile strip if I'm not going to run at over 100 mph.
Steve

[This message has been edited by Steve Arndt (edited 11-20-2001).]

James2 · Post by **James2** » Tue Nov 20, 2001 3:51 pm

<BLOCKQUOTE>quote:<HR>Originally posted by danimal:
[neither have i... but last weekend i did see the allen weiss renn kafer cup sedan run a 12.46 on 91 octane pump gas, with 34 degrees total advance... he runs that timing because that's what makes the most power.

so much for the connelly/arndt masturbatory fantasy of "negative work", as they call it.

dan
oceanstreetvideo.com[/B]<HR></BLOCKQUOTE>

Specs?

JohnConnolly · Post by **JohnConnolly** » Tue Nov 20, 2001 4:18 pm

OK smart ass.

Does the intake charge have mass? (YES).

Does the intake charge have velocity? (YES)

Does this mean the intake charge has momentum and kinetic energy? (YES)

Dan, when you open your mind and realize that every engine is different, and requires different timing requirements, the World will be a better place for all. I see you are still designing all engines around a 30-34 degree full advance timing requirement.

John

<BLOCKQUOTE>quote:<HR>Originally posted by danimal:
[B
>>>356; again, we have a chamber with canted valves (around 30 degrees out of index from one another), so how that applies to a VW chamber, I have no idea.<<<

perhaps the schoolboy can back up his criticism with an explanation of what canted valve placement has in common with deck height/squish...

hint: when are both valves closed

and how does valve placement affect things then?

What DIRECTION is it going with canted valves? Is this the same direction into the chamber as VW valves? (NO)

Does this mean the swirl in the chamber is the same in the two engines? (DUH, NO).

Next he might ask himself where it's written that semi-hemi chambers are perfectly round in all directions; indeed, he could look at some of the 4-valve chambers in use today for further clarification.

>>>Also, where is this "30-32 total" advance that VW has recommended? I haven't seen this bulletin or spec in any shop manuals (St. Muir doesn't count).<<<

neither have i... but last weekend i did see the allen weiss renn kafer cup sedan run a 12.46 on 91 octane pump gas, with 34 degrees total advance... he runs that timing because that's what makes the most power.

so much for the connelly/arndt masturbatory fantasy of "negative work", as they call it.

dan
oceanstreetvideo.com[/B]<HR></BLOCKQUOTE>

danimal · Post by **danimal** » Tue Nov 20, 2001 4:36 pm

>>>OK smart ass.<<<

from the clf today:

"Steve, the most I have ever seen was a 2275, with 8.5 compression, 215hp on the dyno, with no belt and muffler.
DRD
Darren"

"You mean that was the most semi-hemi power you've seen?"

"Yes, semi hemi power.
Darren"

>>>Dan, when you open your mind and realize that every engine is different, and requires different timing requirements<<<

FINALLY the schoolboy is paying attention

maybe next time you guys will build a motor that is capable of running advanced timing on pump gas...

dan
oceanstreetvideo.com

yeahmag · Post by **yeahmag** » Tue Nov 20, 2001 4:58 pm

actually... I think if you read further up he states that it is not semi-hemi. I might be confused though - look for subject "Subject
Since Steve A is asking............"

-Aaron