Endurance engine build, what to do, what to do?

[Horsewidower]

Well, with the racecar just about at the track, I need to start thinking about getting a spare engine together. I'm starting this thread just to get some initial thoughts going on what to do. This engine will probably eventually be used for the Western Endurance series that NASA puts on here on the west coast. My thinking is colored by Milliken's SAE paper on turbo engines and their superiority in endurance racing. So lets layout some of the assumptions.

• Engine has to be capable of surviving a number of 4 hour roadraces, upto a 25 hour race.
• Needs to make 300-350 rwhp
• Redline at 6,800 rpm
• fuel efficient (c'mon guys I'm talking about relatively speaking, if we got 7 to 8 miles to the gallon it would be awesome!) We'll break this down a little more later, I've got a 22 gallon tank and would like to run for an hour on that.
• As low a boost pressure as possible.
• It would be great if it could run on 91 octane CA swill ($3.35 a gallon) but could go up to 96 ($4.00). Anything over that is $7.00+ per gallon.
• No exotic parts that I don't already own (Yes I have the Bo-ported ARCA head, but is this really the right application)

Some areas to explore:

• 2.3 v. 2.5 stock builds
• Small journal v. large journal architecture
• High Compression/low boost v. low compression/high boost, impact of fuel efficiency
• Will a stock rod last in this low rpm build?

Opinions? Facts? Hard data? Remember, reliability is number one, fuel economy is number 2, horsepower is number 3. And most important, I'm a cheap bastard and want to do this as inexpensively as possible.

I'm not in a hurry, so expect this to last a while. With your help I'll come to some conclusions, build the engine and dyno it in the racecar. Might be fun.

Bob

[vrinner]

Hey...whatever you build, make two of them...I need one too!

I'll give a very basic opinion/observation/experience. With my race car, it has a stock bottom end and has seemed to be very reliable. It has no fancy oiling system, nothing special for cooling, no special oil or coating on any internal parts. The bottom end has never been torn down.

The bottom end on this motor has lasted me through 7 seasons of racing as well as some serious SCCA racing from it's previous owner. The last couple of seasons there were issues with blown head gaskets but that was only after I had replaced the head myself so some installation errors may be the cause.

I typically ran between 18-20 lbs of boost and with the mods I had on the motor (Big valve ported head, cam, ported upper and lower intake, ported E6 and straight through 3" exhaust, 35lb injectors and a chipped PE computer) I'm guessing it was putting out a conservative 250 HP but I never dinoed the car so couldn't tell you for sure.

Most of my sessions were 40 minutes or less and only after installing a water mister for the FMIC would it run just as good at the end of the session as it did at the beginning, so I would think that it would run just as well after 2 hours or more.

So I guess what I'm saying is that the bottom end on these motors appears to me to be pretty good right out of the box and should get you through a few enduros but I'm sure there are things you can do to make them better.

[Jcamper]

Biggest intercooler you can possibly fit would be a great place to start. Behind that, a massive radiator. I would go with a larger turbo than most and run lower boost pressures, this will have an impact on your EGTs and drive pressures. Those are the main things that people don't think about that have a huge effect on longevity on a turbo app. Also, stay away from the short exhaust duration cams (2277) for this kind of application.

Anything that flows more air will be more reliable at the same horsepower, allowing lower drive pressures, more efficient turbocharging, etc. So I would say the ARCA head is perfect.

I know you may question the intercooler a little, but look at most towing applications, huge intercooler first thing, then ac/oil coolers, then radiator.

I would tune it using the EGT gauge as your guide. I think you will find that something much larger than a T3 will be best.

Some pretty serious oil cooling will be in order also. Here again, think massive.

Jcamper

[Pat_in_L.A.]

What are the rules regarding pit stops? Do you have to shut the engine off during stops (you may consider a small accumulator for the oiling system)? Is there a restrictor required to be installed in the fueling system to regulate flow/stop time? Only an hour between stops (that will hurt you later)?

[Horsewidower]

Here are the rules:

http://www.nasaproracing.com/rules/enduro.pdf

Thanks for the replies, we need to have a SVOCA race team for the 25 hour!!

Pat: no restrictor, I'll check on the engine on or off rule. We'll run a 3 quart accusump. I'd love a longer period between stops, would probably require bigger than the 22 gallon tank I currently have. We'll have to calculate it.

Vrinner: Thanks for the information on your engine reliability. Esslinger contributed a chapter in the Steve Smith "how to build a ministock" book. If I recall (can't seem to find the book right now) they state that the stock rods are good to 7,200 rpm with a change in rod bolts. Speedway Motors has them for a very low price with upgraded rods. http://www.speedwaymotors.com/p/1795...tock-Rods.html. Given our stated redline of 6,800, I wondered if they might work. I'd probably only do it if I stuck with the ironhead. I wouldn't want to risk an aluminum head for $350 price of a set of Crower sportsman rods that are good to 8,200.

Do you have any info on fuel consumption.

J: Good points, can you elaborate on the comment about the 2277. My current setup is with a 2277. I've also got a SLA roller 2233.5 and a ranger roller. I've wondered about going to a cam with a gentler opening and closing ramp in order to gain reliability.

I run a C&R NASCAR radiator with an integral oil cooler/warmer. Right now we have to tape off the duct opening to get any heat into the engine.

I agree on a larger turbo in order to gain the cfm needed without excessive boost pressure. As an aside, Jay Chen has a great column in this month's Sports Compact Car on boost v airflow thats right on this point. I currently run a t3/t4 hybrid that gets me 305 at the flywheel with less than stock boost pressure. That's with 91 octane California swill, no intercooler and only 19* of advance. AFRs are 11.8 to 12. That Haltech is finally paying off.

OK, now low cr/high boost or high cr/low boost. It would seem that the opinions are starting to lead me to high cr/low boost. I'm currently running 9:1 with about 16 lbs of boost on a bo-ported and polished big valve head. Reports are that Roush ran 9:1. I wonder if running 10:1 has any real benefit. While it might make the car a little snappier in transition, I wonder if it will help with any fuel economy, especially if you have to crutch the 91 or 96 octane with a fatter AFR? You might be able to cure that with a massive intercooler but on a warm summer day (what's warm, 105? I've been to Willow Springs where the air temperature on the track surface was 120) wouldn't you have a heat soak problem? Vrinner you've had that problem. I've got a water/alky set up that I havn't installed, but then you add yet another system that has to be reliable and something else that you have to fill on pit stops.

??

Bob

[Pat_in_L.A.]

but then you add yet another system that has to be reliable and something else that you have to fill on pit stops.
Bob

More nececcary in the heat of the day than at night.

I'd focus on lower boost and a cam whose valve train would survive.Lower boost would add track time between stops.

The SSGT Saleens (In the good old days) had over 300HP. My SSB car had a measly 174 HP (supposed to be 120 hp). Different class but a decent comparison. They lapped me in 1hr 15 minutes. They stopped for gas at 1 hr 30 minutes. I unlapped myself when they pitted and I stopped at 2 hr 15 minutes. My car had less wear and tear on brakes/suspension/driver than theirs as well.

Math question: How many hours did it take for my piss ant car to lap a Saleen?

[Horsewidower]

Pat: Saw the same thing happen at the 25 hour this year. Third and fourth were an S2000 and a Miata, 5th and 6th were the 300+ hp Miller Motorsport spec mustangs. We are talking overall, not class.

[Jcamper]

If you have really good cooling right now, that will be perfect for installing the biggest intercooler you can up front. That will mean the lowest combustion and exhaust temps you can get. Meaning more timing, leaner AFR, better mileage. I think the cam will be a big question, and someone other than me will know better what kind of profile will withstand endurance racing. Generally the 2277 is a good compromise for streetability and getting a turbo spooled, but that won't really be an issue for you as much.

With your stated redline, I don't really see an Essy cam that fits the bill, a grind that takes into account your head's max lift potential(which we don't know) in a reasonable ramp time, with a relatively wide lobe centerline, with a duration that allows it to peak at a bit less than your stated redline would be perfect. Maybe custom grind? I know that isn't necessarily cheap, of the 3 you have currently, maybe the 2277 will have to do.

I think you might need to figure out what turbo will get you where you need to be in terms of power at a low boost/drive pressure, without surging. Then make the call whether you can get away with 10:1 with 96 octane for endurance racing. My guess would be that you will want to stick with 9:1, but the higher the compression ratio, the more efficient the engine, everything else being maximized.

[Horsewidower]

I'm wondering if we are going about this the wrong way. Perhaps we should figure out how much fuel would be used for a 2 hour stint and then design to it. ??

Everything seems to lead to an advantage to a lower hp car.

[Horsewidower]

What are the rules regarding pit stops? Do you have to shut the engine off during stops (you may consider a small accumulator for the oiling system)? Is there a restrictor required to be installed in the fueling system to regulate flow/stop time? Only an hour between stops (that will hurt you later)?

We will run in the EO class. There are some interesting limitations. We have a 22 gallon cell, the race director can make us put no more than the amount of fuel that was in a stock mustang.

A huge limitation is that we can't put in more than 10 gallons per pitstop, that fuel can only be contained in approved 5 gallon containers.

For races of less than 6 hours, you only have to dump one 5 gallon container in the car. Seems pretty irrelevant becuase I don't know how you would make it for 6 hours.

Looks like the cars do not have to turn off during fueling. We have a 3 quart accusump.

No restrictor, we can modify the approved 5 gallon cans, just no "dry breaks" etc.

Bob

[Horsewidower]

I thought maybe the answer would be in the length of the races, but 1 2.5, 2 4 hour, 2 6 hour and a 25 means that you empty your initial fuel cell, then are stuck with 10 gallon refills. Seems to me that you have to find a way to make the most of 10 gallons of gas. Don't need to solve for the initial tank fill because efficiency on the 10 gallons will carry over to the initial fill. 5 gallons per hour, not likely. I'm starting to think a 2 hour goal is unlikely. Time to run some numbers.

An initial thought, you have to use water/alky injection in order to safely lean out your AFR. True? According to Snow Performance, you can safely lean to 12.5 to 1.

Interesting aside, RACER magazine has an article on the LeMans Corvettes. A couple of years ago they had a problem fragging carbon fiber driveshafts. Everyone assumed that the driveshaft manufacturer was at fault. In truth, the ECU folks had introduced a new fuel algorithim that shut off cylinders in order to have better fuel efficiency. Unfortunately this sent a harmonic through the driveline that shattered the driveshafts.

Bob

[vrinner]

I think it was our last years 2 hour enduro at Buttonwillow with the Alfa Club, the overall winner was a Porsche 911 with a 22 gal fuel tank. He didnt run the fastest laps however he also never did a pit stop. 1 driver, 1 tank of gas and he won the race.

My team had some pretty quick lap times however we also had 3 driver changes. We did it more for the fun of it. If we were really serious about winning, we would have only done a two driver race.

[Pat_in_L.A.]

10 gallons per stop. That sucks.

OK.

Time to work the gas stop strategy on every caution and top off upon multiple stops then. Long stop first. Short stop second.

Also, practice brake pad changes per axle to line up with gas stops. My pad changes were fronts every second stop (4+ hrs) and rears every third stop (every 6+ hrs). Brake pad changes were always done before refueling was completed. One guy did both sides, a side at a time just to eliminate the possibility of mistakenly blowing out a caliper piston.

[Horsewidower]

So we ought to design for 11 gallons per hour, which is 64.9 pph. What do you use for a margin of safety.

Bob

[Pat_in_L.A.]

What do you use for a margin of safety.

I had a transfer pump move the fuel from the cell into a 2 quart aluminum reservoir. The pressure pump fed the engine from the reservoir. This eliminated the dip in fuel pressure around turns when gas in the cell got low. You may consider that setup as a secondary feed to switch on once the fuel pickup currently in place warns you of low fuel when the car starts to sputter. You may have two to three gallons left in the cell and it could start seeing air at the in-tank pickup when going through a long turn.