cams vs. compression

danimal · Post by **danimal** » Wed Jul 11, 2001 2:41 am

>>>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!!<<<

matt, this may be where you start running into the limitations of the type 1 fan shroud... i think john c. was on the right track about that, but it's not just an h.p. limitation.

i had a conversation with clyde the other day, wherein he related some of the testing they did for that bentley book someone is writing.

they used manometers and temp sensing devices going up the cajon pass, with different combos of things... my understanding was that they reached an rpm cooling limitation of the stock type 1 fan/shroud/oil cooler, i believe it was somewhere around 3200-3300 engine rpm's.

our conversation revolved around the usual methods of changing the fan vs. engine speed ratio... but we never mentioned using a 356 pulley.

in the testing that i have done, i put a large scoop on the deck lid of my ghia, and it was good for another 10 mph on the freeway before the berg dipstick lite flickered... so there are things that can be done.

and btw, clyde said that the semi-hemi heads ran very slightly cooler than stock heads in that testing, but i don't know any of the engine details... most especially, which cam/c.r. was used.

dan
oceanstreetvideo.com

MASSIVE TYPE IV · Post by **MASSIVE TYPE IV** » Wed Jul 11, 2001 7:09 am

I won't touch this one......Not again.

Steve Arndt · Post by **Steve Arndt** » Wed Jul 11, 2001 8:45 am

I agree on both points.
It is also absurd to claim that you can't ever run more compression, the inverse of your last statement. Too many variables.
I am going to report back how 9.4:1 CR works out in a daily driver situation with a radical cam, 91 octane Chevron, 2800 elevation, and 105 degree temps in the summer (high desert Boise).
Steve

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by danimal:
<B>>>>

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</B><HR></BLOCKQUOTE>

[This message has been edited by Steve Arndt (edited 07-11-2001).]

Dave Cormack · Post by **Dave Cormack** » Wed Jul 11, 2001 9:04 am

< sticking head up out of foxhole>

Is it safe to come up yet?

JohnConnolly · Post by **JohnConnolly** » Wed Jul 11, 2001 9:42 am

well it's TRUE. How true depends on how different the cams are. But, even if you disagree with this you will see it's less absurd than saying one compression ratio is required for one octane fuel for ANY cam.

John

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

JohnConnolly · Post by **JohnConnolly** » Wed Jul 11, 2001 9:46 am

Dan,

part of the problem is it's easy to find ONE example of something that agrees with any point of view. The key is seeing the pattern developing in the big picture.

But, I don't feel there is an exception to the rule of more cam = more compression can be tolerated on the same fuel.

Matt Harris · Post by **Matt Harris** » Wed Jul 11, 2001 9:53 am

Dave, you crack me up!!

Hi Dan,

Hey thanks for the information from Clyde. I also know of the engines you were talking about, I was just done building my engine when they were doing that. The first engine they tested a 1600 semi hemi with kadrons 6.6:1 I believe and oil temp got to 260 degrees F. Then they built a 1776 with kadrons, engle 100, semi hemi and 6.6:1 and the oil temps got to 260 as well.

I know that 4000 rpms is on the verge of the limit of the type 1 shroud but I have an external cooler, which I know some say can't cool the heads, but I don't buy that. And I have went for 4000 rpms with my setrab and fan for 6 hours straight with my oil temp between 200-205 the whole way on a hot 85 degree day (this was on the way back down from the Sac BOR). We'll see how it does when I go on the Berg cruise in less than a month.

Thanks for the tips though Dan.

John, how about a c/r recommendation still

[This message has been edited by Matt Harris (edited 07-11-2001).]

MASSIVE TYPE IV · Post by **MASSIVE TYPE IV** » Wed Jul 11, 2001 12:45 pm

A 1776 with oil temps of 260??? whats up with that? Maybe it made all that heat hjust trying to sustain life, and make 30HP..

The oil temps on my 2613 did not get to 260, before I added an external cooler, and I had over 8:1 and 103mm pistons!

One octane for any cam and head combo simply does not make any sense to me at all. It is almost implying that the cam will not change the engines power at all.

I will keep on running 8:1+ and leave that hemi cutter hanging on the wall, behind the mill. The last time I looked at it, it was starting to rust!

Dave Cormack · Post by **Dave Cormack** » Wed Jul 11, 2001 1:27 pm

leave that hemi cutter hanging on the wall, behind the mill. The last time I looked at it, it was starting to rust!

Uh-oh, the semi hemi deal again, back into the foxhole. You guys wouldn't BELIEVE the s**t that started with the "semi hemi pros & cons" article in the magazine....
Can I at least get some chow before I go back in? I've been getting a little hungry the last few days..

JohnConnolly · Post by **JohnConnolly** » Wed Jul 11, 2001 1:47 pm

Matt,

run an Engle 120 or Web equivalent with 1.25 rockers, and 9:1.

Cool and reliable, and easy to drive!

Dave: Like I said in the opening paragraph,

"If you had to choose one topic at a meeting of VW engine builders that would result in an argument, you would be hard pressed to come up with a better topic than whether or not to put a semi-hemi chamber into the aircooled VW engine".

Even with this disclaimer I get hate-mail!

John (o\ /o)

[This message has been edited by JohnConnolly (edited 07-11-2001).]

Steve Arndt · Post by **Steve Arndt** » Wed Jul 11, 2001 2:06 pm

We have beat this topic to death, and I can say I have picked up some great information. It is a shame we had such conflict back in May, but things are better now. At least we have Dave's jokes to lighten things up a tad.
Steve

Matt Harris · Post by **Matt Harris** » Wed Jul 11, 2001 4:44 pm

Cormack you are hilarious!!!! The semi hemi thing is a passionate subject and I do know of some of the drama that the article incited, but it's good to question things because that's how progress is made.

Hey John, thanks for your recommendation. That sure seems like allot of c/r for a 255 @ .050" cam, but you know your stuff so....

As for the 1776 with 260 oil temp etc, the details are going to be in a book that Bentley is coming out with soon, so more the details will be inside that as well.

If you want exact details about the engines in question please call Gene Berg Enterprises and ask, as I am know way an expert and may have the oil temp wrong by a few degrees so get it from the horses mouth (I am covering my butt if you didn't notice).

But Jake, I don't believe that 260 is too out of reason if you are pushing 80 mph up the cajon pass with 2 people in the car on a 90 degree day like when the testing was performed. Bentley just wanted to see how hot the engines would get.

[This message has been edited by Matt Harris (edited 07-11-2001).]

Dave Cormack · Post by **Dave Cormack** » Wed Jul 11, 2001 6:26 pm

Even with this disclaimer I get hate-mail!

Nah, not as much as we got, John

I understand what the word "opinion" means, but it seems that some other readers don't, nor did they read the last part of your article that asks them to form their own O-P-I-N-I-O-N

Guess it's not safe yet, huh?

<ducking back into foxhole>

JohnConnolly · Post by **JohnConnolly** » Wed Jul 11, 2001 6:46 pm

You can run 8.2:1 with a 110, so another 10 degrees is around 1 point of headroom.

Matt Harris · Post by **Matt Harris** » Wed Jul 11, 2001 9:28 pm

Good deal John, thank you very much. How did you determine the 8.2 for a 110 and 9.0 for a 120? Just curious, experience or ?

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Matt Harris
78 x 90.5
2007cc
1971 Super