Anyone have any experience with gas ported pistons on a street/strip car? The motor in question is a 540ci BBC expected to make ~650hp with a 150-200hp nitrous shot to be used at the track. Expect to see 4-5,000mi/y. Is the extra hp worth the added ring wear?

Rich

 

You have to weigh out whether it's worth it or not, but at ~650 hp you're looking at ~10 hp using a 1.2mm top & 3mm oil ring using lateral gas porting. BTW, lateral is the only way to go for a street car.

Take it to the next step by adding a vacuum pump and you could see another 30-40 hp. The setup is going to be a little harder on the cylinder bores but we are talking about an aftermarket block.... the new castings are pretty darned hard. I remember when they first started making the thin rings and they weren't near as durable as they are now. Not to mention, the pistons have gotten a lot better.

Good luck.

-Mindgame

 

MG: why are lateral ports preferable?

Rich

 

One, you don't have to worry about carbon plugging the "ports" (standard port piston).
Two, no path for oil to reach the combustion chamber.
Three, less chance of a crack starting from one of the ports.

Lateral Ports

-Mindgame

 

Yeah the parrallelism and ring land flatness play a big part in this. Thank god for good CNC piston turning machines.

BTW Rich, on a side note from the block thread. The stock 502 block would probably be more than enough for 650-850hp.


Bret

 

Bret: wrt the 502, I thought about it, but a new 502 block is ~$1,500, not too much less than a Dart or WP block. Now, if I found a nice used one that would be another story.

Rich

 

I am betting that this won't be any kind of a problem once that giggle gas starts flowing

Lateral gas ports should be fine in your application Rich.

 

Why add to your maintenance requirements? For the power level you are trying to achieve, you can run a standard tension 1/16" ring package with no gas ports. These racing "tricks" do indeed work, but for your desired results, you can build a motor that will perform for years with only a periodic valve spring swap. Vacuum pumps do require rebuilds on a periodic basis as well.

No need to build an engine that needs taken apart unless you want an 800+hp 8000+rpm motor, then it will need seasonal rebuilds anyway.

The 572, 620 HP motor sounds ideal (not to mention a warranty). It dyno's at around 700hp (620 is a consrevative rating) on pump gas. Have you considered this? It has some good parts & is ready to run. The extra cubes will help the street manners & mileage will suck regardless. Just a thought.

 

Good points Lonnie.

Like I said, throw the data out there and let Rich decide. I'd skip the pump and the lateral ports, but that's just my opinion.
What I did in my engine is reduce the friction by going with a .047/3mm ring set. It's a hardened ni-chrome plasma ringset from Speed Pro. Requires a particular hone but the assembly turns with ~10 lbs less torque in comparison to a .062/3/16 setup... of course the oil ring plays a big part in that too. Either way, it's a nice alternative to a 1.2mm ring and gas ports -maybe vacuum too- to keep them sealed.

On the engine... I hate to sound like a broken record but I'd go as big as I could go. Makes it that much easier to make the power... makes it that much more streetable.

Just throwing stuff at you... take what you like and leave the rest.

-Mindgame

 

I agree with Mindgame...again.

PS: I like your new siggy quote:


When dealing with people, let us remember we are not dealing with creatures of logic. We are dealing with creatures of emotion, creatures bustling with prejudices and motivated by pride and vanity. -Dale Carnegie

 

Mindgame...
As far as bigger is better.... absolutely. Just stay away from custom bore spacings & strange deck heights as all the custom parts can add thousands of $$ for a minimal return. On a BBC, stay under 4.6" bore (subtract to allow room for a few bore jobs as well) & under 4.5" stroke. You can make big HP & keep it under 7000rpm so there is less chance of parts leaving the block. The more HP per cube you make, the more stress it must endure.

I'll agree with you on rotating friction, it is significant. I just prefer to sacrifice a few hp in the sake of reliability. Still looking for the ultimate compromise myself. Keep me posted on your combo.

I read in a car magazine once to use the KISS method.
"Keep It Simple, Stupid...... It definitely has some merit.
No need to spend money on latest tricks. Look at the HP gains vs. dollars spent & you will see the ones to avoid. Do not forget to factor in the additional maintenance costs associated with these as well.

If you have competition in mind & intend to race for profit, then get a sponser & do what ever it takes to make the last HP. If you have something to prove (to yourself or others) & need to be the fastest just bring a budget to match.

Personally, I'd rather have a car that I can drive instead of one I had to work on constantly. I see some locals that race weekends & repair all week to be under a half second faster than cars that guys drive to work all week.

It's all in what you consider enjoyable.

 

To fit it into the car I am going with a short deck, and as Lonnie suggested a 4.500" bore to allow for future overbores. I think that a 4.25" stroke (540ci) is kind of a sweet spot for a short deck block when everything is considered.

Rich

 

Yes the GF type rings are good and are great for power adders and they also outlast normal .043 rings by twice. I always like taking free power when I can as in lower ring tension if you can still keep the oil out of the chambers.