Cat Cams

Alex170984
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Cat Cams

Postby Alex170984 » Wed Apr 02, 2014 2:30 am

I have recently fully rebuilt my engine with new oversize pistons, lightened flywheel, lightened crank pulley, 1.0mm cometic head gasket, raised compression from 9.4 to 10.2 and fitted some cat cams 7105137

Has anyone else used these cams before?

I'm yet to give the car a proper run out due to suspension issues and now needing a full alignment.

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oldeskewltoy
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Re: Cat Cams

Postby oldeskewltoy » Wed Apr 02, 2014 1:39 pm

Alex170984 wrote:I have recently fully rebuilt my engine with new oversize pistons, lightened flywheel, lightened crank pulley, 1.0mm cometic head gasket, raised compression from 9.4 to 10.2 and fitted some cat cams 7105137

Has anyone else used these cams before?

I'm yet to give the car a proper run out due to suspension issues and now needing a full alignment.


Here is the timing sheet for those cams... http://www.catcams.com/products/camshaf ... TUP_id=828


Your 10.2 compression is ok, although another 3/4 of a point would be better.
OST Cyl head porting, - viewtopic.php?f=22&t=300

Building a great engine takes knowing the end... before you begin :ugeek:

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Alex170984
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Re: Cat Cams

Postby Alex170984 » Thu Apr 03, 2014 3:11 am

My CR could be around 10.2 to 10.3 as I don't know what my chamber CC is

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oldeskewltoy
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Re: Cat Cams

Postby oldeskewltoy » Thu Apr 03, 2014 9:15 am

Alex170984 wrote: I don't know what my chamber CC is


Was the head 's surfaced machined? Did you have any porting work done?
OST Cyl head porting, - viewtopic.php?f=22&t=300

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Alex170984
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Re: Cat Cams

Postby Alex170984 » Fri Apr 04, 2014 12:54 am

Yeah it was machined very minimally, but don't know of exact amount.

No porting done.

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oldeskewltoy
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Re: Cat Cams

Postby oldeskewltoy » Fri Apr 04, 2014 4:04 pm

Alex170984 wrote:Yeah it was machined very minimally, but don't know of exact amount.

No porting done.


standard oem chamber is 36cc a minimal machining and you may be @ 35.5, or even 35cc
OST Cyl head porting, - viewtopic.php?f=22&t=300

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Re: Cat Cams

Postby Alex170984 » Mon Apr 07, 2014 2:57 am

My CR may even be as high as 10.6:1 after realising I had been using the wrong piston dish volumes for the calculation..

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Re: Cat Cams

Postby yoshimitsuspeed » Mon Apr 07, 2014 11:06 am

Are you running the 9.4 pistons or did you swap them out for smallport or other pistons?
It would be crazy hard to get the 9.4 pistons much over 10:1 so I am very interested to hear what pistons you are running and what you have done to raise compression.

Also how did you decide on your dome/dish?
I stopped using any numbers I could find online when I realized that none of them added up to what they were supposed to.

I will enter all the fixed values I know such as bore, stroke, etc and then adjust the dome/dish till I get the exact CR the piston is rated at. Then any change you make from there like HG thickness should be accurate at least assuming the original factory specs were accurate.
The other option and even better would be to measure the actual dome/dish of your pistons but that's not always possible.

Alex170984
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Re: Cat Cams

Postby Alex170984 » Tue Apr 08, 2014 3:09 am

Hi,

First of all, I may have confused matters, as I did not state that the 10.6 is the potential static compression, not dynamic.

I purchased and fitted these http://www.imoc.co.uk/forums/viewtopic.php?t=167900 - which are 81.5mm 9.4:1 pistons.

Bore: 81.8mm
HG bore: 82mm
HG Thickness: 1.00mm (don't know what compressed thickness is)
Stroke: 77
Rod Length: 122

I believe the piston dish volume is -0.9- i got this info from a thread on the ae86org and one that is identical on here as well.

My deck height was measured at 0.2mm - I didn't have the block decked as it was in excellent condition as it was. I had a machined flat bar put across it and it came out to be okay.

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Re: Cat Cams

Postby oldeskewltoy » Tue Apr 08, 2014 8:32 am

Alex170984 wrote:Hi,

First of all, I may have confused matters, as I did not state that the 10.6 is the potential static compression, not dynamic.

I purchased and fitted these http://www.imoc.co.uk/forums/viewtopic.php?t=167900 - which are 81.5mm 9.4:1 pistons.

Bore: 81.8mm
HG bore: 82mm
HG Thickness: 1.00mm (don't know what compressed thickness is)
Stroke: 77
Rod Length: 122

I believe the piston dish volume is -0.9- i got this info from a thread on the ae86org and one that is identical on here as well.

My deck height was measured at 0.2mm - I didn't have the block decked as it was in excellent condition as it was. I had a machined flat bar put across it and it came out to be okay.


private note to yoshi.... deck of .2mm means the short block specs out there can't be right.... just saying...

Alex... what type of head gasket, metal? Metal doesn't compress, so 1mm = 1mm. 9.4 to 1 pistons will only get to 10.6 with a MASSIVE head cut. Typicially a 9.4 to 1 4AGE engine can get to about 10.1 to 10.3 before piston replacement is highly recommended
OST Cyl head porting, - viewtopic.php?f=22&t=300

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Re: Cat Cams

Postby yoshimitsuspeed » Tue Apr 08, 2014 8:49 am

I hate those threads. They threw me off for way too long as well until I decided to double check all the numbers.

So if we take all those numbers and punch them into a compression calculator we get 10.13:1 on the stock 1.2mm HG. The manufacturer rated HG thickness should be it's compressed thickness.
But we know that piston is supposed to be around 9.4:1 right? So where is the inconsistency? Well we know most the other specs are right. I did discover the compression height is much closer to 0 than many online sources claim but I have only measured it with calipers and haven't gotten around to micing it so I believe it's 0 +- a small margin for error. .2mm is close enough.

So if that piston is actually 9.4:1 like everybody claims then there is no way that is the dish on that piston. It has to be closer to -4.8 in order to hit 9.4:1 using all the other known parameters for the 4A.
Now using that figure if we go from 1.2 to 1mm hg it takes us to 9.5:1.
It would require taking off about 1mm off the head to get down to 10.6:1. That doesn't include the reduction in chamber volume so it would be a bit less but as you can see it would take quite a lot to get that kind of compression out of 9.4:1 pistons.

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Re: Cat Cams

Postby yoshimitsuspeed » Tue Apr 08, 2014 8:51 am

oldeskewltoy wrote:private note to yoshi.... deck of .2mm means the short block specs out there can't be right.... just saying...



What do you mean? Are you talking about deck height?

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Re: Cat Cams

Postby Alex170984 » Tue Apr 08, 2014 8:59 am

What is my static compression ratio then?

It's a metal head gasket.

Are we talking about dynamic or static compression here?

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Re: Cat Cams

Postby yoshimitsuspeed » Tue Apr 08, 2014 9:21 am

Alex170984 wrote:What is my static compression ratio then?

It's a metal head gasket.

Are we talking about dynamic or static compression here?


Static.
Don't even worry about dynamic. DCR is like trying to explain string theory in a short equation using only addition and subtraction. It should also not be called dynamic because the whole equation is based on static calculations which makes it next to useless.

We really need to know how much the block was decked to find your actual compression ratio but let's assume it was decked .25mm. I'll go with OST's guess of 35cc.

So with your thinner HG, the deck, and the reduced compression chamber volume that would put you pretty dead on 10:1.

For a head that was machined very minimally I expect those numbers are on the optimistic side so I would guess that your compression is around or just under 10:1.

If it was decked .1mm and say 35.5 that would put you at 9.77:1.

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Re: Cat Cams

Postby Alex170984 » Tue Apr 08, 2014 12:01 pm

The block wasn't decked.

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Re: Cat Cams

Postby yoshimitsuspeed » Tue Apr 08, 2014 4:17 pm

Alex170984 wrote:The block wasn't decked.

I didn't say or mean to give the impression that I thought it had.

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Re: Cat Cams

Postby Alex170984 » Thu Apr 10, 2014 7:51 am

So ultimately, are my cams going to struggle?

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Re: Cat Cams

Postby yoshimitsuspeed » Thu Apr 10, 2014 9:27 am

It's not that they will struggle, it's more that they will not be optimized.
I will use this Poncam dyno to illustrate.
To oversimplify a theory the more cam you can run the more compression you can run because it moves the VE curve higher in the power band where detonation is less likely.
If you raise the compression and keep it near it's limits you will keep the performance up in the mid to low RPM while gaining even more in the upper RPM.
Here you can see the black line is stock compression and stock cams.
Then when they add just the cams it looses just a little power in the mid RPM. Similar to your cams this is a mild cam so the loss isn't drastic but you might run into the occasional hill that you used to barely be able to pull in forth that now you might have to drop to third.
The blue line is the same cams with a compression bump. Now they make at least stock power up to 3500 RPM and then from there significantly more power from there to redline.

Image

In this same way it is likely you will notice a decent gain in pep above 4000 RPM with the new cams while maintaining similar to stock power under that. If you increased your compression you would notice a good gain above that across the whole power range.

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