LS1 Powered S14 by SicBastard

9 minute(s) of a 390 minute read

Builds been on a slight hold while I'm preparing for a liscensing exam. But yesterday I went with my girl to this really nice seafood restaurant here in Long Island. It's finally crested 69 degrees here in the NE, and we took the miata with it's supercharger and Link fuel management computer. The valets were standing there but I just parked my self anyway. And as we were walking into the restaurant they were kinda pushy about getting my keys. So I finally just handed the Dick my keys not wanting to make a scene, for my girls sake. The aftermarket ECU surges a bit, doesn't like light throttle, and requires ~30 seconds of waiting in the accesory position to turn on, prime the fuel pump, and sync the cam and crank angle sensors, before it will let you ignite the engine. 

We had a great dinner and when we came out instead of getting bent out of shape, I just handed the Dick my valet stub, then whispered to my girl, "Watch this, this is going to be funny." Of course the Dick couldn't get it started, my little miata is parked between some $100k Mercedes and Jaguar turning over and over. We both laughed as the Dick came back with his head held low and handed me back my keys without looking me in the eyes. Then we hopped in the car, and because I waited the requisit time before turning it over, it started instantly. All the valets were watching as it started right up, and with a little creative clutching pulled out as though it was dead stock. As I drove past the Dick I said, "There was a reason I didn't want to give you my keys." My girl thought that was a good show.

4/24/09

Well I'm mad cash strapped until I get a job after I graduate in June, so I put some parts up for sale on e bay. The Ohlins are up for sale if you think you're crafty and can get them back together with a reserve of $100. I'm probably also going to list my black billet hi mount alternator bracket, and c5 throttle peddle with TAC.

eBay Motors: Ohlins Nissan 240sx coilovers S14 JDM silvia springs (item 130302376520 end time May-01-09 13:54:26 PDT)

I also rolled out to the weekly car gathering in the parking lot of Best Buy in Woodbury last night. I couldn't believe how many guys rolled out there. Good time, smelled like gas and burn outs.

5/19/09

So I'm starting at the back.

So I left my stock s14 fuel tank back in CA when I moved to the East Coast. It's actually a pretty good design and if it was still here I'd probably use it. Most of the stock tanks volume sits above the diff between the rear shock towers, then has two legs that go forward and below the rear seats on either side of the drive shaft. 

My idea is to try and get the weight of the tank a bit lower and further back. I also want to build my own rear diffuser. So originally I was thinking of cutting out the bottom of the trunk, and making a custom aluminum tank whose bottom doubled as the majority of the diffuser. 

My dad was pointing out that aluminum tanks should probably be rubber mounted to reduce the likelyhood of fatigue cracks which Aluminum is susceptible to. Anyone have any experience with aluminum gas tanks? 

So what does a fuel tank have to do with the exhaust? Well with the sides of the drive shaft space open there is extra room for my expansion chamber and cats.

From Random Technologies Website: "...a 3" diameter 7000 series SuperStainless catalytic converter flows 617 cfm. Most 3" diameter high performance mufflers flow less than 475 cfm at the same test pressure."

I also found these test results where 2.5" aftermarket cats were tested and compared to stock LS1 f-body cats.

Table 1

CFM @ 20.4â€Â H2O

CFM @ 28â€Â H2O

Passenger Side Catalytic Converter

299.5

350.9

Driver's Side Catalytic Converter

268.3 

314.4

TTS Bullet Catalytic Converter

277.1

324.6

Carsound Catalytic Converter 

372.7

436.7

FLP Catalytic Converter

376.0

440.5

First a word on CFM flow rates. Heads are usually flowed at 28â€Â H2O, while carburetors are usually rated at 20.4â€Â H2O, and my hero David Vizard rates exhaust flow CFM at 20.4â€Â H2O. By the looks of things Random Technologies rates their cats at 28â€Â H2O.

But why care about cats on a 700hp v8? Redline time attack street class rules, that's why. Oh and they are way more restrictive than you might think.

David Vizard’s research shows that 2.2 cfm of flow at 20.4â€Â of H2O will support 1 horsepower. 2.2 cfm is the optimum flow through the exhaust keeps horsepower losses under one percent.1 Removing the stock catalytic converters on the LS1 usually results in a gain of 8 rear wheel horsepower. 

FLP or Carsound = 373cfm

373/2.2= 170 hp per cat (w/ 2.5â€Â i/o)

Random Technology 3" diameter 7000 = 617 cfm (probably 524 cfm @ 20.5" H20)

524/2.2= 238 hp per cat

Now it should be a little more clear.

If you're rolling a single cat, you have a restriction if you're making over 170-240hp, regardless of which fancy pants stainless "race" cat you're running! Bogus!

This also means that if I'm running FLP aftermarket race cats that I would need 4 (3 if I ran the randoms) of them in parallel to build a truely free flowing exhaust! I've never seen anyone run cats in parallel. The reason for this is either cost, space, or you can't get enough heat into them. I dunno.

To make sure that street class participants aren't running gutted cats, redline states that they will use infraread thermometers to make sure that your cats are lighting off. 

more from random technologies web site: "...Under normal operating conditions, the catalytic process doesn’t begin until temperatures inside a converter reach 500 to 600 degrees (F). If air/fuel ratio is on target, and the exhaust is free of contaminants, internal converter temperature stays at about 1200 degrees. But when unburned fuel enters the picture, temperatures can reach 2200 degrees and either burn the precious metals out of the washcoat, or literally cause a melt down of the bricks."

So now the real question is: will three or four parallel cats get up to temperature if they are sitting five feet from the heads with an expansion chamber between them? By definition anything richer than 14.7 will have "unburned fuel". And considering my car will be running richer than 13:1 most of the time, maybe the extra exhaust temps will actually be useful? Redline doesn't say when them test your cats temps. I'm pretty sure I'd be ok after a hot run.

This is getting too long, but here are some pics of preliminary measurements for the rear diffuser/new fuel tank area, and I'll talk about expansion chamber design another day.

This is a pic of a one inch piece of steel stuck to the bottom of the subframe. The piece of steel creates two rectangular spaces about 3"x5" on either side of the diff. Should be enough for four 2.5" exhaust pipes.

would four 2.5" exhaust pipes flow enough for 700hp?

Check this out:

A section of straight pipe the length of a typical muffler, rated at the same test pressure as a carb (1.5â€Â of mercury= 20.4â€Â H2O), flows about 115 cfm per square inch.

open horsepower

pipe supported w/

size single pipe

2.0â€Â D = 3.1 A X 155/2.2 = 218 HP (x4=872 HP, probably a better idea)

2.5â€Â D = 4.9 A X 155/2.2 = 345 HP (x4=1380 HP, yeah should be ok)

3.0â€Â D = 7.1 A X 155/2.2 = 500 HP

3.5â€Â D = 9.6 A X 155/2.2 = 676 HP

4.0â€Â D = 12.6 A X 155/2.2 = 887 HP

Proof Hondas with 4" mufflers are built by assholes.

It seems that diffusers can sit anywhere from 4-14 degrees. Less than 7 degrees to prevent flow seperation/drag unless of course you have a massive wing within a verticle foot for interaction like F1.

So I just took a look at the revised 2009 Redline time attack rule book and it looks like full undertrays are now allowed in street class. The wording on the fuel cell rules is a little strange:

"1.6.4 Fuel Cells permitted (modification of factory floor pan is allowed for installation of

Fuel Cell)

1.6.4.1 Good quality fuel cells contain a bladder constructed of Nylon or Dacron

woven fabric impregnated and coated with a fuel resistant elastomer and

are FIA FT-3 (or higher) rated.

1.6.4.2 The cell should be in a container made of at least 0.036-inch steel, 0.059-inch

aluminum, or 0.125-inch Marlex, fully surrounding the bladder.

1.6.4.3 Foam internal baffling is required, as per FIA FT3-1999 (or higher)."

So it says that fuel cells are permitted, then it goes on to define a good one as one with a bladder. It doesn't seem to expressly require a bladder within the cell though. The rules also seem to say that there "should" be a container for the bladder. Does should = required? Or am I just seeing what I want?

Bladders are around a $1000. I was hoping to get the car on the road without one, with just a custom aluminum fuel tank, then add a custom bladder to it way down the line.

How do you guys interpret the above?