1982 3.0L rebuild - Page 2

carslutt · carslutt's Garage

nice build, looking forward to reading more of your progress.

TibetanT · TibetanT's Garage

I also don't see any reason to split the case with a low mileage engine such as this, but I am no expert.

Now that I have your attention, any chance you might want to part with one head from the old 3.0L parts? I am looking for one head only.

thanks

1topcat · 03-16-2009, 04:56 AM

Well, progress on the 3.0 is slow but as a great motivation, a fellow Pelican came over this weekend and gave me a hand in removing the 2.7L from the '73 911. Wow, he made it easy, major thanks and Kudos to Mede8er. Here are the obligatory shots.

mede8er · mede8er's Garage

Tony's got the makings of a super sano ST backdate here....excellent tub and wait till you see his suspension upgrades!!!

I'm drooling here....

1topcat · 05-23-2009, 09:37 AM

Well, the new Goetz rings are on and the p&c's are on. I am about to do a dry-fit and check the valve to piston clearance, but I see something that concerns me.

The headwork was done on a set of '84 3.2L heads. New valves and springs/ret. The pistons have the deep valve pockets and I suspect I will ok in the depth direction. But the width of the pockets is very close to the width of the valves. Looks like maybe 2 to 3 mm wider pocket than valve. I measured with calipers and will have to go back out and check again to get specific measurements. Assuming the alignment places the valves dead center in the pocket, is this too small a pocket????

1topcat · 03:56 AM

The Intake valve is 49.19mm in dia and the exhaust is 41.65mm.

Compared that to measurement of the valve pocket; intake is 51.88mm and exhaust is 42.96mm.

Anyone? What is typical for clearance in this direction?

Thanks

1topcat · 05-24-2009, 03:56 AM

Perhaps the answer is that since all 3.0 and 3.2L engines had 49mm intake valves and 41.5mm exhaust valves, then any piston valve pocket designed for a 3.0L should work. Just because I am using a 3.2 head, it shouldn't matter as it is still the same size valves.

Does that make sense or can somone confirm???

Is there a way I can or should check the valve to piston clearance between the valve and the SIDES of the valve pocket?

tom1394racing · 05-24-2009, 01:39 PM

The standard piston-to-valve interference check will detect the point of interference between the valve and the piston.

The pockets on the RSR pistons are designed for the valve sizes you are using.

The key checks will be deck ht and compression ratio.

1topcat · 05-29-2009, 05:04 AM

Hey, Thanks Tom,

The deck height was just around 1.2 to 1.25mm after many reverifying vernier checks. But why is the cc'ing to verify c/r so important. At this point, isn't it the proverbial "It is what it is". If I find it is say 10.2:1 instead of 10.5:1, What could I do about it?

tom1394racing · 05-29-2009, 10:58 AM

Tony

The RSR type pistons you are using are designed to run at around 10.5 CR. If your combustion chambers are the correct volume, you'll achieve that.

Your stock combustion chambers may be too big. If so, the CR will be lower and you will not realize the performance benefit of the increased CR due to the RSR style pistons.

After you do the cc volume checks and the CR math, you can make adjustments by changing base gasket thickness and/or by machining the heads. You'll want to get as close as possible to the 10.5 CR. Too high and you'll need race gas. Too low and you will not enjoy the performance benefit.

I have a very similar motor running with early SC heads that have been cut to produce the 10.5 CR. It is a great running street/track motor making around 285 HP and runs great on pump gas.

Others more experienced than me can jump in to help, but if you do a search on CR checks, you'll find that many of us have found surprises when doing them.

jpnovak · 10:45 AM

Hey cool, you bought Dave's old 73. That was such a fun little car with the 2.7. the PO is a good friend and used to live in Austin.

What are you doing with the 2.7?

What your final compression ratio measures is really up to you and how much time it takes to build the motor or do machine work. You may get to a point where you are high enough to be acceptable. If too low that is a problem. If too high that is worse of a problem. I was targeting 10.3:1 and ended up at 9.98:1. I don't think I would feel the difference except with dyno numbers.

You mention a deckheight of 1.2-1.5mm. Was this with or without base gaskets? Using some base numbers for a 3.0 build (stock head volume, and a piston crown volume of 48cc you get 10.1:1. If you drop the deckheight down to .9 or so (removal of 0.25mm base gasket) you get 10.5:1.

The lower compression will help your ability to maintain timing with the FL heat and humidity. The slightly lower compression will also mitigate the octane requirements. The higher compression will increase torque a few percent.

1topcat · 05-30-2009, 01:23 PM

Hey Jamie,

I was hoping you might chime in on this thread. Yeah, this is his old car. His 2.7 was removed for this 3.0 project. It is for sale in another thread.

The deck heights are around 1.2mm. This was with the .25 base gasket. I am about to cc the heads and cylinders and I am trying to search for the best method possibly without removing the p&c's. Any good threads?

With the 3.2 twin plug heads, no fly cut, 10.5 Mahles, base gasket and no machining of the case I hope to achieve between 10.3 and 10.5:1. I suspect it will be on the lower end and maybe even as low as 10.1:1. I would like it as high as possible, but would be happy in that 10.3 to 10.5 range. Anything else to consider to help with the FL heat and humidity?

cgarr · cgarr's Garage

A quick way to check would be to bolt up one head, roll the engine up on its side, set it up to TDC and CC the chamber thru the spark plug hole, this gives you a very accurate measurement of the combustion chamber then you will know exactly what the CR will be.

1topcat · 05-30-2009, 06:13 PM

Heya Craig,

The heads you did for me are a thing of beauty. How'd the mirrors turn out?

Is there a little more description I can find on the method? Like what to use for fluid (ATF or isoproply?) and what to measure with? I assume I would intall one of the two twin plugs. Do I need to seal up the piston/rings with anything? Any other tips? I've been doing searches but haven't found that idea cc'ing post for this method. Thanks all.

cgarr · cgarr's Garage

I got a 50ml which is (50 cubic centimeters) burette off ebay for about 16 bucks, I did install at least the top ring along with a bit of grease, I used fuel oil in mine but ATF or any light oil would work, install the lower plug and turn the engine so the top plug is level and see how many cc's it take to fill the chamber. Here is the program I used to calculate the CR using mm. You only fill in the Cylinder Bore Size, Stroke Length and the Combustion Chamber Volume In CCs, Zero out every thing else and hit calculate and it will give you the CR.

http://www.csgnetwork.com/compcalc.html

I have the mirrors on the car and they look great but still need to figure out the wiring to work with my 86

tom1394racing · 05-30-2009, 06:47 PM

Here's some data from my trails and tribulations of determining the CR on my 3.0 RSR build.

Everything turned out fine in the end.

What's Your Head Volume?

1topcat · 05-31-2009, 05:38 AM

Craig,

I know what you mean on the wiring.. I tried everything but could not get it right. Then I took apart my old flags enough to see what wire had gone where. Once I did that and realized two wires were actually tied together and coodinated the wiring to what WAS in the flags, wala!

With respect to your method on the cc'ing. How can I be absolutely sure I am at TDC if I do not have a dial indicator? Also, can I wipe a film of assemble lube on the cylinder wall then take the piston up to TDC to get that "seal" at the top ring, then place the head?

1topcat · 05-31-2009, 06:15 AM

Tom,

Yes I had remembered reading that post, but couldn't find it again. Thanks and sounds like we are following similar paths except for my heads are 3.2's. It is my understanding that the 3.0 and 3.2 heads are the same volumns and in the stock range of 89 to 91. My heads were not fly-cut so I have not picked up some c/r in the way that Auto Associates coordinated for you. I am using the .25mm standard base gasket and have a deck height of 1.2 to 1.25mm. I will cc my volumn as soon as I get my burette.

Maybe a potential solution for my situation would be to reduce or eliminate the base gaskets as opposed to fly cutting at this point?

tom1394racing · 05-31-2009, 06:00 PM

Tony

The stock heads are in the range of 90 cc.

Try using some of my numbers for piston dome volume and and the stock head volume in the CR calculator to see what your CR will be and what your options are.

The cylinders can be shortened to raise compression using the thin .25 mm base gasket. This will come at the expense of reduced deck ht.

Keep us posted on your results.

mede8er · mede8er's Garage

The lower compression will help your ability to maintain timing with the FL heat and humidity. The slightly lower compression will also mitigate the octane requirements. The higher compression will increase torque a few percent.

Hey Tony...can't argue with this logic....

Can't wait to fire this badboy up....