difficult cam choice

[Facey]

Hey guys
some of u already know, but for those who don't i have some unknown dimensions on the engine that i got assembled...rookie mistake, w/e live and learn.

but now since i need to drop the engine to change the oil cooler (small leek), and will be swapping engine shrouds at the same time, it feels like a good time to take out the s or mod s cams, and put in something that likes to rev at least a little bit more.

this is what i know:
100mm Mahle P&C's
74.4 mm Crank
extra thick cylinder to case copper ring seals (2,x 1mm)
46mm webers
twin plugged, electromotive
less than 11:1 cr, likely closer to 9.5:1
non-stock heads, were fly cut, big valves, ported...
George's european racing headers, M&K muffler
arp bolts, upgraded studs, 930 oil pump
edit: jerry woods valve springs

last time the car was on the dyno (like what 2 years ago?) i was running B&B headers, with a different muffler (still M&K), minor carb adjustments, on an engine with less km's (though not nearly enough!!!), it made a best pull of 278 rwhp. I don't need to be lectured about doing everythign else as well, has harness bar, triangulated strut towers, aggressive brake pads, 23/29mm t-bars, big contact patches, blisten sport shocks...etc.... it is not one dimensional, and i do not drive like an idiot on the street (k so that is all out of the way)

what i would like:
to make good power up to 7500 or perhaps more...
loosing some mid range is acceptable, car is not daily driven

is there enough here to make an educated safe guess? or is it too much stipulation (actually c/r, deck height, cc.)?

i appreciate your help
N

[camgrinder]

Post up the dyno graph. also, it would help to know which cam you have, S or Mod-s.
In that size engine to make hp past 7500, the dc80 would be the cam. But, your compression ratio is nowhere near enough.

[Steve@Rennsport]

Nick,,

John is right,.......your CR is really too low to use any long-duration cams without taking a BIG hit to your low & mid-range torque.

I'd also tell you that running a 100mm motor to 7500 RPM with stock rods isn't a good idea and especially without all the oiling modifications to the crankshaft, case and main bearings.

Keep it below 7K and you'll be fine.

[Facey]

damn, aight.
thats too bad, but at least this saves me from having to round up the funds to pay for new cams.

what c/r is required for dc80's?
i don't think i'm using stock rods, but they were not new either.

[Facey]

got some good news today. engine builder said that i've got some nice aftermarket rods, pistons and rods were balanced. he also mentioned that we doubled stacked the cyclinder to case seals, two 1mm copper rings were used, because my heads had so much work done to them...

i need to drop the engine to fix the oil cooler anyways, and like i said above am going to switch out the engine shroud (cf or bare fg?, or a colour?...gonna do the fan at the same time...), i am going to pull the cam towers and try removing one of the seal rings, is it possible to just slide the cylinders about an inch off and snip one of the seals? (or are they going to be pressed together? or simply not enough room).

anyways, while i'm in there i can check the deck height, and if someone could provide a method i could measure the cc. this should remove any guessing, and allow me to calculate the c/r and select a proper cam, who knows, it might simply be too tight w/o that other 1mm... but 12:1 is doable for a street engine with twin plugs is it not???? always run 94 anyways... (could probably get away without).

and just because i could make good power up high doesn't mean i would, when i mean sacrifice some mid range i mean loose some of the 2500-5000 pull, STILL set the rev limit at something reasonable like 7200rpm and simply turn the dial to 7800 (or 8000, lol) for the dyno and track.

but who knows... opening an engine is risky, could find something in there that i do not want to. (dare I take the plunge?)... open to thoughts, seems to me like a good x-mas break project).

[Facey]

dug out some old info:
the cam covers have been back dated to the magnesium ones
the case is an 86 turbo case ( verified), and the heads have custom porting
. the casting number is 84K1926R, the port sizing is about 43mm, (1 and 11/16")

wish i had written more of the measurements down those 3 or so years ago..

[911st]

I think you can check the CR before you take it apart.

Set a cylinder at TDC on a firing stroke w the motor on a motor stand and tilted so you can see how much ATF it takes to fill the combustion chamber to the bottom of the spark plug hole. Then use the quantity against the size of your motor to compute the CR.

If there was a lot of head work they may have fly cut more material from the heads than usual. You may want to check the piston to head clearance by putting a pice of soldier on a piston and run in through a cycle before you start taking out base gaskets.

[Facey]

that was exactly the technique i was planning on using.

sorry, what is atf?

[Flieger]

atf = automatic transmission fluid (heavy weight oil)

[Steve@Rennsport]

Hi Nick,

A few things,.....

You cannot run 12:1 CR on 94 octane fuel, twin-plug or not. Attempting to do so will cost you new P/C's (unless you are using Motec M600).

Choosing engine components is not like ordering a dinner in a restaurant (al la carte) if one expects a successful outcome. Each and every part of the whole entity must work in concert with each other and that includes factoring gearing, vehicle weight, and usage.

I employ a holistic view of modifications to the entire car so that the end result meets and exceeds the owner's expectations and requirements and that means considering the upgrade project as one entity.

An engine with a 2K powerband situated in the 5500-7500+ range MUST have close-ratio gears to perform well. Further, engine operation above 7K with these big bore motors really needs better rods as well as a whole host of oiling modifications to live.

Hope this helps,

(BTW, ATF is a SAE 7w oil; light stuff)

[Flieger]

I stand corrected. Thanks, Steve

[kenikh]

Originally Posted by Steve@Rennsport

You cannot run 12:1 CR on 94 octane fuel, twin-plug or not. Attempting to do so will cost you new P/C's (unless you are using Motec M600).

Assuming this is because it integrates knock sensing?

[Wayne 962]

I agree with Steve, you're asking for trouble. It sounds like a really good setup you have there, I would stick with it. Most people would love to have that engine - I think you need to be a bit more realistic in what you're trying to achieve. If you want something a bit different, then it sounds like you would have to build a new motor from the ground up...

-Wayne

[Wayne 962]

Originally Posted by kenikh

Assuming this is because it integrates knock sensing?

Yes, that's the assumption, although on these air cooled pre-1990 cars, it's sometimes difficult to get accurate reading out of knock sensors, since the engines have a lot of vibration to begin with. Steve, have you successfully been able to run a 1990 or earlier engine with engine management and been able to reliably get a good signal from the knock sensor under track conditions?

-Wayne

[Steve@Rennsport]

Originally Posted by kenikh

Assuming this is because it integrates knock sensing?

Nossir. M600's capabilities in the right hands permits VERY precise control of fuel & timing events at all RPM and load points. One can integrate knock-sensing, if desired.

An excellent programmer can set it up to run high CR's on pump gas using custom cams quite safely. This is NOT for the DIY'er nor the faint of heart,....

We have run M600 together with closed-loop aftermarket knock-sensing using the factory sensors on the 3.6.

[Facey]

aight

i will take the advice, save my money, get some news wheels and save for some brake bling

thanks for being honest and straight foward.
N