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L24 for production class racing application

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Hi all! 


I have been searching the forum and having trouble finding what I am looking for. Maybe I just don't have the right keywords. I am looking for an evaluation on individual engine components and how they effect/affected by racing applications, based on first-hand experience. For example:


1) What components are most likely to fail under high RPM's (7-8k), and in what likely order?

2) What components pose an issue on durability/longevity in a racing application?


A quick update on my SCCA class EP car, specifically on the engine. Would love to get some of your feedback!


The head is at Steves Machine Stop in Azusa, CA. They are working on it this week and should have it back by the end of the month. Here is what they are doing:


1) Ovate Beehive valve spring upgrade. Checked with SCCA to ensure legality.

2) head and SU carb manifold port match up to 1" into ports on either side. Limited by class rules to SU's and depth

3) valve seats being ported and unshrouded. Chamber polished and deburred to limit detonation risk.

4) stock N42 head as a core. exhaust valves being turned down to 33mm to meet class rules.  

5) Cam lift set to .495. Class limited to .500. Duration and offset still being tinkered for a 3000-6000rpm optimal torque range.

6) head deck milled to increase CR. CR yet to be determined. will need to be optimized for cam specs and 91 octane. 

7) Viton valve seals. These should last a bit longer than the stock rubber ones. 


The bottom-end was rebuild about 20k miles ago, but is otherwise stock. Read Frank Honsowetz book (how to mod OHC...) cover-to-cover. My take from his book is the stock bottom end should be OK for an NA racing application if additional measures have been taken to keep heat down (already have oil cooler) and is properly tuned. Going to give it a try and see. As long as I don't have a catastrophic failure like a lost rod, i can always rebuild the bottom end with Franks recommended changes when I rebuild. Distributor already has an AM electronic pick-up, but still using the diff head to distribute spark. 


Back to the topic of RPM's, I have no idea how my head mods will effect my prospective redline. I'm inclined to keep it at 7k, unless I can gather more research on what components may be limiting. 


Thanks again for reading!

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Sounds like you are on the right track.  I would say most successful EP 2.4L engines are built for 8k or better.  They replace rods with Carillo or Pauter. Forged pistons. Nismo bearings. Deep oil pan with windage or throw in a dry sump. All kind of standard stuff, done to lower risk, if not preventing failure. Why are you running 91 octane? EP max is 12:1 compression.  You need all of that.


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41 minutes ago, clarkspeed said:

Sounds like you are on the right track.  I would say most successful EP 2.4L engines are built for 8k or better.  They replace rods with Carillo or Pauter. Forged pistons. Nismo bearings. Deep oil pan with windage or throw in a dry sump. All kind of standard stuff, done to lower risk, if not preventing failure. Why are you running 91 octane? EP max is 12:1 compression.  You need all of that.


Hey someone responded!!! Thanks! 

Great point on the CR! My plan was to max-out the head this time around for pump gas, Then drop in domed pistons when I eventually rebuilt the bottom end. With the valve overlap, it will likely settle around 10:1 with the stock bottom end on this head rebuild.  


This is my first race car, so I still have a very steep learning curve. I don’t have any direct experience with E85 or race fuel, for example. 

it sounds like you have some experience, and at a minimum have read the EP spec line! I am definitely all-ears if you have anymore advice or tips for me! So far, it’s just the technical folks at SCCA I have been in contact with. 




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If your first race car, does that mean new to racing also? Been to school yet? Then having a reliable car and getting as much seat time as possible is very important. EP is a very fast class and most have serious built cars in my region. Not necessarily the best class to start with but not impossible.  I am mostly into vintage racing but have done some engineering for the EP guys. 

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I purchased it as an old race car that seemed to have last been raced in 2002. I discovered quite a bit of rust that had not been clearly disclosed , after purchasing the car. I have been restoring and upgrading it since.


I thought it may have been EP at first since it’s still an L24 and stock brakes, but you are

making me reconsider. It does have SCCA “vintage racing”  stickers in a few places.


I am open to picking a less competitive class if I became familiar with other options.


I don’t have experience racing. I purchased it with the initial plan to use it as a hotrod platform, but switched to restoring it as a race car after appreciating all the work that had already gone into it for a race application. 

I may never race it. I may sell it on BAT after eliminating all rust and making it track worth again. Just hoping to break even if I did. 

would you recommend a different racing series or class? 

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The suspension had cut springs in the back and stiff front springs. I just sectioned my strut assemblies using ground control coil over sleeves, and purchased Koni racing shocks. Also purchased bolt-in camber plates in order to not cut into the body (another EP rule). 

Folks on here were really helpful in selecting parts. My springs are 350 in the front and 300 in the rear. 

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Some of the main differences from EP to other racing classes is 15x7 wheels with slicks, full fiberglass fenders, hood, and hatch to meet min weights, along with engine mods. If really going for it, I would recommend a turn key engine build from a race shop that specializes in this formula. A 240 also fits into ITS class with much less modification.

Vintage cars are typically built to 1972 SCCA production rules. Some organizations are tight on rules, others not so much. Either way, they will still group the car to race. Check out SVRA website for some 240Z rules. 

I you want to give racing a shot, I suggest doing a SCCA school with a rented car or one of the other national schools that provide the car. 

I specialize in restoring and building old race cars for the vintage circuits. If you give up on your project, I might be interested.😀

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Hey thanks again for the Input! I will look into those racing classes/orgs you mentioned! 

I’m committed to restoring the car, but as I mentioned I may not race it. Therefore, I may sell the car but it would be as a “restored” race car. Given the quality of the suspension components I chose and head modifications (with exception of final CR), my hope is the car will be a good “platform” for myself or someone else to start as a base and work towards individual class compliance. I have made extra effort to ensure the permanent mods will not disqualify the car, but it all depends on the class of course. 

I’m also working on structural reinforcing (with weight in mind) using my engineering background. Here is a picture of the internal monocoque work I have done in the rocker, while replacing all the rust. I’m considering removing the roof structural support with a lighter solution as well, since it would lower my CG. 

if you may be interested in the finished product, or interested in general, feel free to shoot me a Message! If I found an interested buyer, I’d be happy to work towards a specific spec for that person. At a minimum, I assume anyone would want the rust replacement work Already underway to be competed. 




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