Cam choice??

[TWIN86GNS]

A "friend" of mine recently purchased an almost complete engine, some assembly required.
 
The short block is plenty stout for what his ultimate goals are and it came with a set of GN 1 aluminum heads as well.  The only part that this engine needs is to have a cam purchased and installed.  He is looking for cam suggestions and he is leaning towards a roller cam.
 
So does anyone have any suggestions for a roller cam for a mostly weekend bruiser that will never be a daily driver but will see the odd road trip here and there along with a few trips to the track.  Currently he has a 2800 stall lockup torque converter and will be using a stock turbo until funds allow a larger turbo, a season probably.  He already has a good intercooler for when the larger turbo comes along and the car is currently running a good fuel system along with Julio's alcohol kit.
 
My friend would appreciate any and all thoughts on cam choice, thanks.

[Steve Wood]

If a roller, I would pick something close to 210 degs at .050 lift.  Very little lost on the bottom end and good to about 6000 rpm....more if he has the no preload lifters....act ually almost no preload..

Hopefully it has more than stock compression to offset the poorer thermal efficiency of the heads.

[earlbrown]

Any idea what the static compression is?

[TWIN86GNS]

If a roller, I would pick something close to 210 degs at .050 lift.  Very little lost on the bottom end and good to about 6000 rpm....more if he has the no preload lifters....act ually almost no preload..

Hopefully it has more than stock compression to offset the poorer thermal efficiency of the heads.

Steve,
 
Thanks for the thoughts, so a 206-210 roller like Mike at Full Throttle sells should be a good choice?  Here is the kit on Mike's site:  http://www.fullthrottlespeed.com/customkititems.asp+kc+001BUROLLMOREL+eq+
 
Mike also offers this kit with both Morrel lifters and Comp lifters, any idea which would be the better choice?  I was thinking the Morrell's would be superior, but then I noticed they were cheaper, and am concerned since cheaper quite often isn't better.
 
 
Steve / Earl,
 
The engine is probably going to be assembled with RJC Racing's steel head gaskets which Jason claims bumps the compression about 0.4:1 because the gaskets are 0.015 thinner.  Also both the block and the heads were each decked 0.003" (so combined 0.006") so that should bump the compression another ~0.1:1.  In other words the stock 8.5:1 compression ratio should be increased to about 9:1.  I am thinking that 9:1 should be a good choice for an aluminum headed street car, your thoughts?
 
Thanks for all of your thoughts and comments, keep em coming. 

[earlbrown]

Stock is 8.1:1, I'd be running 10:1 with alum heads if it were me and make sure that the quench distance was between .040" and .060". Closest to .040" if possible.


I've NEVER heard of anyone correctly guessing static compression. The guesstimation is always higher than actual.  The only way to know is to measure and it's a bitch to get static up to 9:1 in real life.
  As a comparison. My engine ended up 8.99:1. That was with the block decked .010", bored .195" over, .027" gaskets, .006" off the heads, and oversized Ferrea valves sticking as far into the chamber as I could get them.
 
Any idea what the CC's are on the heads?

The reason I asked about compression is for two reasons. One is that alum heads need about 1 full point to be on par with iron. And second is that the wider cam lobe you use the less dynamic compression you end up with. When you're in overlap and/or delaying the intake closing event you're bleed off cylinder pressure and that has to be made up with static compression.

Here's a java calculator to play with...
http://www.wallaceracing.com/dynamic-cr.php


Oh, and Morel's all the way. The comp cams lifters aren't worth the box they come in.

[motorhead]

The reason I asked about compression is for two reasons. One is that alum heads need about 1 full point to be on par with iron. And second is that the wider cam lobe you use the less dynamic compression you end up with. When you're in overlap and/or delaying the intake closing event you're bleed off cylinder pressure and that has to be made up with static compression.

Oh, and Morel's all the way. The comp cams lifters aren't worth the box they come in.

Both very key points.

[$1987 GN$]

Oh, and Morel's all the way. The comp cams lifters aren't worth the box they come in.

Morels are as good as it gets!

Not sure if Mike gives you the setup with them or not but this is what I had have.

AJ___

[Steve Wood]

Earl elaborated on my thoughts

This will not help much with the aftermarket heads but it might give you some idea in general  http://www.vortexbuicks-etc.com/compression_ratio_calculations.htm

[larrym]

I went with a webber set up and I'm quite happy.


its set the opposite of the full throttle 212 on the intake and 206 on the exhaust.


Pulls well for me with mildly ported heads.

[larrym]

Here is the card.


http://photoshare.shaw.ca/image/a/4/f/119991/camcard-0.jpg?rev=0

[TWIN86GNS]

Any idea what the CC's are on the heads?

The reason I asked about compression is for two reasons. One is that alum heads need about 1 full point to be on par with iron. And second is that the wider cam lobe you use the less dynamic compression you end up with. When you're in overlap and/or delaying the intake closing event you're bleed off cylinder pressure and that has to be made up with static compression.

Oh, and Morel's all the way. The comp cams lifters aren't worth the box they come in.

Earl,
 
I don't know what the 14 bolt Champion heads have for volume and I don't have the proper instruments to measure that.  I've got some paper work from the machine shop but these heads were only vacuum checked and milled the 0.003".   
 
The shortblock already has pistons, pins, rods, crank, etc installed / assembled, so how should I go about raising the compression ratio?  Mill the heads some more (after getting the volume checked ?) and then get custom length pushrods if needed?  Also how much extra performance will I gain with a bit of extra compression?  I think I have read that on N/A engines 1 full point of CR is worth 10 - 15 horsepower on a V-8, what would it be worth on our boosted V-6?
 
My other car, was originally built using stock (ported) heads with TRW pistons and after reviewing the notes from the machine shop and when my Dad switched to Aluminum, M&A heads nothing was changed but the heads and the car didn't seem to suffer any performance issues at that time (early 1990's).  In other words, I am wondering again how much performance I will gain for what amount of money spent to increase the compression ratio more than it already is?  What about a little extra boost to make up for the loss of static compression ratio?
 
I am trying to get this engine running and installed without a huge outlay of cash over and above what I have already spent on it.  But if I need to spend some more money, than I will budget accordingly and readjust time lines for when this engine will be installed in GN #2.
 
Thanks for the props to the Morel lifters, I thought they were more desireable but I wasn't so sure after I saw they were cheaper than the Comps.  Also it appears that Mike at Full Throttle has this cam kit on sale right now so that is good news.

[TWIN86GNS]

Sorry I just realized that I have to update my signature on this board to show both GN #1 & GN #2 and their respective performance.  I will get to that shortly.
 

[motorhead]

Paul, get a copy of "desktop dyno" (I think Comp Cams still has it, or a variation) and build the engine based on what you know, or know to be reasonable, then run different cam profiles and boost levels to see the approximate impact.

I don't imagine that you are going to leave a lot on the table, at least anything that would be noticeable.

[earlbrown]

Paul, if you have any device that can measure CC's and a small piece of glass or flat clear plastic you can measure whatever you want.  When I did my heads years ago in my kitchen I used a plastic syringe that came with a rebuilt powermaster I think WalMart sells a turkey baster with a CC scale on it in the kitchen section.
How To LS1 DIY Head Combustion Chamber Measure CC + Valve Seat Seal Test

Do it like this but with a piece of plexiglass over the hole. Don't worry about drilling a hole in it, just slide it over and leave yourself a 'half-moon' to put the water in.

 If you put your pistons at TDC, fill the area and see how much it took. Do the same with the heads (don't forget to install a spark plug) and write those two numbers down....

Go here and plug in the numbers...
http://users.erols.com/srweiss/calccr.htm

Since you measured the short block assembled it's going to be screwy inputting the numbers..

bore size is 3.800 +what ever the overbore says on the piston (IE 3.830 for 30overs)
 stroke is 3.4
 combustion chamber volume CC's is what you measured for the heads PLUS whatever it took to fill up the cylinder too...
 piston cc's=0
deck =0

the head gasket is what you play with to see what range you can get the static compression with no machining. (Cometic's go as thin as .027" up to something stupid like .140")


If you have a set of calipers, measure how far in the hole the piston is from the deck surface at TDC. It's nice to have that dimension plus head gasket thickness add up to .040"~.060".  Having some quench will give you more detonation resistance. We like detonation resistance.

[84 BuickGNYorkPA]

TWIN86GNS,

210/215 roller over hear from Mike at Full Throttle mated to 1:65 roller rockers in champion iron heads, 98% street car, lights up the tires at 55 mph in 3rd gear when you go WOT. Not scary, but you can hear them spinning.

Earl,

Thanks for this information above, good stuff!

Chuck