3.1L build / peanut shaped chambers

[PalmettoZ]

Hello-

New to the website but have been reading info for about 6 months.

 

I am in the process of building a stroker motor with the V07 crank, 133mm rods and 89mm pistons into a N42 block. I have had the crank weights turned down (knife edged) to reduce weight. Lightweight flywheel and throttle body injection with stand alone megasquirt.

I will be using a N47 head that has stainless undercut valves in them with bronze guides. Also the combustion area has been relieved by the valves, along with the standard bowl cleanup. Only port matching to the manifold at this point. Camshaft is still up in the air at the moment, but probably around 280 duration and .460" to .480" lift. I would like to go higher on the duration but not sure of the outcome.

I am considering having the combustion chamber welded to create the peanut shape chambers in the head, and wanted to know how much of an advantage this would give me in terms of horsepower. Is it worth it for this mod ? Car will be street driven, but not a daily driver. I am looking for smiles per gallon not miles per gallon. Any input would be appreciated. Thanks-

[JMortensen]

I'd go bigger on the cam, it will require aftermarket springs and retainers, and different valve stem seals, but I think what you're considering is pretty small. I'd also pick a different head. I haven't priced it out, but I'm guessing you can buy a P90 or P79 and shave it and do the headwork again and still come out a hell of a lot cheaper than you can welding an N47, milling, shaping the chambers and doing the port work.

 

The main advantage to welding the chambers is that it increases the compression ratio. If you have the N47 on a stroker block with flat top pistons your compression is going to be really high to start with. Weld the chambers and you're talking race gas only.

 

There are a lot of overlapping factors here: compression ratio, camshaft, quench, octane necessary to keep the thing from pinging, timing, etc. I suggest you read some more about all of these things before you decide.

[PalmettoZ]

Thanks Jon-

I know its not too agressive a cam, there just doesn't seem to be much that I have found between 280 duration and 300. I am tempted to go the route of the higher duration cam but know the port sizes won't justify it. I also have an N42 head that I could use as well, but I prefer to use the current one since I already have some of the machine shop work done already on it. The main reason I thought about the peanut shape is that I thought this increased power due to the reduction in the quench area. Since I have not purchased the pistons yet I could opt for the dished ones to lower compression with the peanut shape.

What lift and duration cam would you suggest ? Compression ratio will be high ( I assume around 10 or 11:1 ) using flat top pistons and a 1 mm gasket. I think with the .6 mm positive deck height I will need to turn down the pistons about half a mm or so.

At what lift cam will I need to check the valve seals ? I thought I would be safe up to about .510 or so. Of course I will be doing a check with the cam installed and rotated thru with the head off of the block. Thanks-

Scott

[JMortensen]

Cam lift for valve stem seal interference depends on the valves and how they're cut, but somewhere around .480 lift you better start taking a look at it. .510/300 or around there would be a really hot engine that would still be streetable. I have a .490/280 and wish I went larger. I'd go 300 duration without a second thought at this point.

 

Do some research on quench. What you said there doesn't make any sense. The smaller the chamber the more quench you have, so running an N head with very little quench and then bumping the compression up is asking for detonation on pump gas in my opinion. My opinion is as a guy with an ~11:1 compression E31/L28 combo that pings with less than 95 octane.