cams vs. compression

danimal · Post by **danimal** » Wed Jun 06, 2001 10:27 pm

>>>Dan your running both a smaller cam and a turbo, which both increase the static compression Ratio! Your just proving John's point.<<<

not hardly! depending on how they are configured and driven, turbo engines will spend a very small amount of time on any significant boost... maybe 5-6% of the operating time?

when i'm on 12-15 psi of boost, my dynamic c.r. could easily be well over 11:1... don't tell me that's gonna make the motor run cooler

>>>Look at all the people running 8-1 plus on the street and not having problems.<<<

we just quoted 4 motors that run low c.r. with no overheating complaints.

part of this problem of "overheating" is personal definition of the word.

without a common, reliable denominator like the berg dipstick, your idea of overheating could be completely different from mine.

then there are the people who claim to be overheating, but aren't smart enuf to be running all the sheet metal, including the thermostat vanes, the sealing frame, those little pieces of sheet metal pressed into the heads, maybe they run aftermarket heads, the jetting is wrong, the timing is wrong, etc.

other "overheaters" usually fail to vent the engine compartment correctly, or they aren't using the latest factory vw technology, like the fuel injected fan shroud, or even the type 4 oil cooler conversion.

the list of possible screwups is nearly endless... how many vw people have you seen who didn't have the fan belt at the right tension? or maybe they had leaves and crap in the cooling fan??

btw, are you running the berg dipstick?

dan
oceanstreetvideo.com

danimal · Post by **danimal** » Wed Jun 06, 2001 10:40 pm

>>>you fly in. Calibrating gauges has been a routine of mine for over 20 years. but maybe I'm l#$^g to you again, dan,

.<<<

lol

i believe you, tom.

the kind of gauges you refer to usually cost lots more than the stuff we get for our vw's.

for jake, the guy who found the gauge was off by around 20 degrees was diddler, a kg person who has been around for a long time.

if he said it was off by that amount, it was... you'd have to look at the q/c milspec quantity percentages to see how significant that was, i.e., how many gauges you tested vs. one that was really off... tom would know what i'm talking about.

on top of that, it's very difficult to test the linearity of the gauge/sender, so even if it's only 8-10 degrees off at the boiling point of water, you don't have a clue how accurate the rest of the scale is... what if it's off by 20 degrees at 220?

i guess now i'm gonna have to go out and dig up an old gauge to test myself

dan
oceanstreetvideo.com

Matt Harris · Post by **Matt Harris** » Wed Jun 06, 2001 11:19 pm

Dan,

The dipstick was calibrated with boiling water and a chemist's pyrometer (expensive thermometer) that I took on loan from a very respected VW company. The dipstick was too hot to handle, and the Berg oil dipstick was pegged and then some. The gauge was off by about 10 degrees, I was at 231 and it read 240, not too far off. Either way it was too hot, and I was very upset and hurt by the fact that I spent all this money and went conservative on c/r, sacrificed power and then it still ran hot. I don't buy low c/r, so when the heads are off I'm going to raise it and see what happens. If I don't like it then I'll go back to lower c/r, but I'm going to see for myself, cause I've seen that low c/r with loose deck and a big chamber made my engine run hot so I'll see what the higher c/r will do. I'll bet it'll make it run cooler becauause it will be more efficient and not have to run 40 degrees of timing to get the pig to run right. My numbers are real, taken from an expensive gauge/pyrometer that read to 1 "one" degree. I'll be at DQ tomorrow. I drive a yellow super beetle with Nardi wheel, polished 8 spokes, 42 DCNF's and autometer gauges. You can check out my engine for yourself if you you think one of the laundry list of problems is what is making my engine run hot, but it's unlikely you'll find anything.

Tate,

The engine ran just as hot after the the jetting was "right". See the O2 sensor said it was correct in both jetting configurations, but it was just the slightest difference that cleaned it all up.

I find it hard to believe that only one person has calibrated their dipstick against boiling water. I have my BS in biochemistry and understand the importance of such things. So no only did I calibrate it against boiling water and a chemist's pyrometer, but measured the distance between the ground and the swivle arm to be 1/8" or so. So it was correct. And I took the 231 temperature with the pyrometer itself, right after I got done putting the berg dipstick in the hole and watching it light up my oil light. And just becuase you quote 4 low c/r engines that don't overheat, doesn't mean that a low c/r never will. And just because other people a low c/r engine is here telling you that they overheat doesn't mean that they don't exist. And the list of things that could be making my engine run hot are all taken care of. I didn't drop $6500 into the engine and take the time to build it myself just to let little things like an engine seal kill it prematurely.

My readings were real actual degree numbers and I wouldn't even want to guess what head temp was. So there everyone goes.

------------------
Matt Harris
78 x 90.5
2007cc
1971 Super

[This message has been edited by Matt Harris (edited 06-07-2001).]

type11969 · Post by **type11969** » Wed Jun 06, 2001 11:57 pm

John-
Thanks for the in depth reply to my post, it has definitly cleared some things up for me. Of course I know have a few more questions and clarifications to add.

First, I meant when I said that the term "dynamic compression ratio sucks" that tacking "compression ratio" onto "dynamic" throws me off because compression ratio was defined to me as max vol. over min vol which wouldn't change except in the case of bleed off. In my mind, whether more or less vapor is being compressed, the compression ratio stays the same because the volume stays the same. I guess I gotta change how I define compression ratio.

>>Why? torque is the same, you are only firing the cylinders faster! You are creating more heat, because you are making more power at high RPMs, but you are also spinning the fan faster. Additionally, if you take Thermodynamics, you'll find that efficiency increases as you increase compression.<<

You stated this in my response to my question if a high compression engine equipped with a long duration cam running at high rpms would melt due to that added heat. I do understand that engines run more efficiently at higher compression ratios, but I did learn in thermo that there are limits to what cr's can be run, like material composition, coolings systems, etc. If we had better materials, for instance, we could be running tremendous cr's on diesel engines and not worry about the heat and pressure those cr's generate, and also have a really efficient and powerful engine, better than any gas engine possible. Unfortunatly we don't have those materials. Regardless, I know that when you increase the cr, the efficiency goes up, more enegry is used for power instead of rejected as heat, but more heat is also generated because more vapor is being compressed (unfortunate by-product of compression). I thought that this added heat might cause detonation or melt the engine because we all know that one of VW engine's worst enemies is heat. I didn't think an a-c cooling system could keep up, guess I was wrong.

Anyway, I guess my real question here is now what suggestion do you, or anyone for that fact have for a cam/compression ratio for an essentially stock 1.7L type 4 engine? I posted this on the t4 forum, but didn't get any replies. I also e-mailed Jake because I know he probably has the most t4 experince out of anyone, hopefully he will reply. Actually, if you are concerned with starting a flame war, which I can totally understand in this forum, please e-mail me directly with your thoughts. Anyway, the engine will be stock with dual singles like 34 icts or 40 solexs, home-brewed exhaust, and a mild porting job done by myself, nothing else. I want to be able to run on pump gas and still have decent power. Any opinons will be greatly appreciated because even if I totally understood the theory behind using enough cam with a certain cr, I don't have the experience to make a good choice.

Once again, thanks for the in depth response.

-Chris

danimal · Post by **danimal** » Thu Jun 07, 2001 12:59 am

>>>And just becuase you quote 4 low c/r engines that don't overheat, doesn't mean that a low c/r never will.<<<

i don't know about that, but i sure do hope that you find a definite solution to the overheating problem.

thanks for taking the time to spell out the details.

dan
oceanstreetvideo.com

Darryl · Post by **Darryl** » Thu Jun 07, 2001 1:46 am

[QUOTE]Originally posted by danimal:

with regards to the webcam 119, it's rated at .422 lift, and 240 degrees duration at .050.

what kind rpms do you turn with that cam dan
thanks darryl

danimal · Post by **danimal** » Thu Jun 07, 2001 7:28 am

>>>what kind rpms do you turn with that cam dan<<<

i haven't turned it much over 6,500 rpm so far... making big power while keeping the revs down is one reason i wanted a turbo.

i have noticed that the engine starts dropping off radically around that point, tho... but that could be the dinky c.b. exhaust, among other things... i'm still working it out.

dan
oceanstreetvideo.com

MASSIVE TYPE IV · Post by **MASSIVE TYPE IV** » Thu Jun 07, 2001 8:27 am

My favorite Web cam for TURBO is the 218, with a wider lobe center, and a set of 1.25 rockers. We have Johnson lifters and one hell of a valve train.

I have one of these in our TURBO car, as a mere 1776 she has pulled an 11.77, in a full bodied 57 oval, with a really nice gearbox..

The engine is apart right now, going to an 86 x 94 combo..I'm undecided about the cam, I may leave it in there, or try and design a better one..We have a local mustang guy that is running a 200 shot of NOS, and is .3 second faster than the oval, he is in our sights, and it has caused alot of wagers..

Steve Arndt · Post by **Steve Arndt** » Thu Jun 07, 2001 9:05 am

Dan
The Webcam 119 has 240 degrees of duration, that is why your 7:1 works perfect and cool. Sure, boost changes things. .but you aren't on boost 90% of the time.

I tried the blanked idea of 7:1 also, but on an engine with a "296" cam that actually had more real duration than a K10. 268 degrees @ .050. The best MPG I have ever earned from a tank of fuel was 13.5 miles/gallon with the engine jetted perfectly on dual 40 IDFs w/ 32 vents. 1835, 40x35 heads port matched, 1 5/8 exhaust w/ 2.25" turbo muff, etc. With this cam and this compression it could not pull the skin off a custard below 3000 RPMs. Terrible miles/gallon, no power, and runs warm. Low compression kicks.
Building it up now as a Haltech injected 2276 with 9:1.
Steve

Steve Arndt · Post by **Steve Arndt** » Tue Jul 10, 2001 2:47 pm

cam and compression

http://victorylibrary.com/mopar/cam-tech-c.htm

Updates since the last time I posted the link. Read the bottom. Also try the excel doc linked to from the page. It gives you cranking PSI depending on rod ratio, intake closing event, altitude compensation, etc. It shows in simple English why I was stupid to try a [email protected]" cam with static CR of 7.3:1 a year ago. It isn't rocket science anymore, there is a light

It also dispels somewhat OceanstreetDan's claim that with a big cam and bigger compression you absolutely require higher octane fuel vs. the same CR and a mild cam in the same application. I am learning a lot!

Make sure to convert all your mm numbers to inch for the doc to work.

bad62bug · Post by **bad62bug** » Tue Jul 10, 2001 3:45 pm

Took the new turbo system for a nice ride, A fellow vw nut needed a part and I needed to take the car for good ride about 65 miles each way. Drove 75 to 80-mph and alot of 100+ mph blast, system still needs some fine tuning only got 22-mpg, ran cool BB 911 fan shroud seem to work well oil cooler fan never came on, although it was cool out nice T-shirt weather. Plus I was only able to get 14-psi of boost, bleeding pressure off at the pressure cover seals sounded cool when I lifted.
PS. it?s not the seal?s fault it?s the covers, I used sand system covers they don?t fit as well as the covers CB provide, making new seals to take care of it

[This message has been edited by bad62bug (edited 07-10-2001).]

Matt Harris · Post by **Matt Harris** » Tue Jul 10, 2001 4:24 pm

In light of all of this. Anyone have a c/r recommendation for a 2165 engle 120 255 @ .050" 42 x 37.5 heads 48 IDA's etc? Thanks.

JohnConnolly · Post by **JohnConnolly** » Tue Jul 10, 2001 4:39 pm

This model only calculates cranking issues, so it's not directly applicable to running engines BUT...

It DOES show you what happens at low RPMs, and the concept still carries over to operating RPMs, though it's not as dramatic as during cranking.

So, it's in agreement with my assertation on cam/compression, but doesn't serve much use for us other than another toy to play with.

Matt: what use? miles/year? expected engine life? valve adj frequency? Operating RPM? Race/pump gas?

[This message has been edited by JohnConnolly (edited 07-10-2001).]

Matt Harris · Post by **Matt Harris** » Wed Jul 11, 2001 1:19 am

Use: Daily driver to take me from medical school and back 40 miles per day. Plus any trips I want to make to Phoenix, Sacramento, SLC, or Colorado. Basically I'm going to drive it all the time, everywhere.

Mileage per year: 12,000-13,000

Expected engine life: Don't know what you mean by this. But I would like to see 35,000+ between valve jobs, and 80,000-100,000 on the bearings and case (already has 20,000 on it). You know me, with the 2007cc 6.6:1 beast

. Same plans to drive it everyday, but want something a little more conventional design wise.

Valve Adjustment Frequency: Every 3,000 miles just like what I do now with my 2007cc, engle 120 engine.

Operating RPM: MUST be able to cruise at 4,000 rpms for long stretches of time, ie 6 hours straight from So Cal to Sacramento or 12 hours from So Cal to SLC!! This is priority. RPM limit is 6500-6800 rpms very rarely, maybe 4 times a week. Must be easy to drive off the line, and easy to drive in traffic as I will be in traffic a bit during my drive to USC med school and back.

Gas: Only pump gas.

I know you remember me John with my semi hemi 2007. My bug is my only car and daily driver. I'm trying to get the most out of my car and have it last the longest. I need stone reliability as I don't want to have to screw with things whilst in med school.

------------------
Matt Harris
78 x 90.5
2007cc
1971 Super

danimal · Post by **danimal** » Wed Jul 11, 2001 1:43 am

>>>It also dispels somewhat OceanstreetDan's claim that with a big cam and bigger compression you absolutely require higher octane fuel vs. the same CR and a mild cam in the same application.<<<

o.k., steve, per your link, how do you explain the following info:

"...Late (radical) intake valve closure causes some mixture to escape even at moderate speeds, reducing cylinder pressure during the operating range (at the lower end of the torque curve). The point in the engine's RPM range where this reversion stops and full-stroke capture (or more!) occurs is frequently the torque peak, and depends on many factors, including cam timing, port efficiency, mixture velocity, manifold runner & port cross-sectional area & volume, resonance, harmonics, exhaust system design, etc. I have no method of applying math to these factors - too complex!
If you have (or plan to install) a long-duration cam, you can (and should) regain some of this lost pressure by raising the compression ratio, but the 2 effects do not always "cancel each other out" - you can't get something for nothing. Even though a higher compression ratio will give you back a higher pressure gauge reading, the power may still be lower, at least at low to moderate speeds."

the bottom line is that you must have enough octane to match the mep of the engine... mep is NOT always determined by cranking pressure, but it is rpm dependent when the cam is radical.

it is absurd to claim that you can always run more c.r. with bigger cams, because cam designs have so much variation.

dan
oceanstreetvideo.com