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July 2014 Question IT

Fixing what you broke

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Got a burning question or simply need some advice with problems you've encountered while wrenching on your current/future projects? Ask our automotive guru Eric Hsu anything—literally, he's going to answer every single question, as long as it's automotive related.

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KA24DE Trans Swap

I'm currently working on my project turbo KA24DE with a target goal of 300 to 400 whp. I already have most of my engine setup figured out, but I was wondering which transmission would be my best option. I don't really know how much power the stock 240SX five-speeds can take, and I've seen some conversion kits for the 300ZX tranny. I have an automatic tranny right now so I'm going to swap it out anyway; I'm just wondering which transmission would be better suited for the project.

-Abel Garcia, via

If you keep the power under 350 hp, the 240SX five-speed transmission will probably be fine. If you turn it up to 400 hp, you'll probably destroy transmissions if you consistently drive hard. Keep in mind that a turbo KA24 will probably make as much, if not more, torque than it does horsepower. An SR20DET doesn't have this problem so it'll take a 450hp SR20DET to make as much torque as a lesser power turbo KA. If your budget allows and you plan on 400 hp with your turbo KA, then I'd definitely go with the 300ZX transmission. Mazworx and Xcessive Manufacturing both make 300ZX transmission adapter kits for the KA. Other than synchros going out from abuse, the 300ZX transmission will be able to handle whatever you throw at it with a 400hp turbo KA.

E85 or Race Gas

I am going to take us back in time, but I remember you used to crew for the record-setting Sierra Sierra Evo a few years back. If I remember correctly you mentioned that the Sierra Sierra Evo switched from VP MS109 to E85 at one point in time. With the switch over, the engine generated an extra 42 whp and quicker boost response over the unleaded race gas at the expense of hotter exhausted gas temperatures. At 60 degrees F the latent heat of vaporization in Btu/pound of gas, ethanol and methanol is 150, 396, and 506 according to Since E85 is closer to C16 race gas, why didn't the team make the switch a full-time switch, especially since methanol isn't allowed in Time Attack outside the United States? Also, being close to Bentley fuels you wouldn't be getting seasonal blends. It seems too logical an option to pass up. You always say if it's good enough for Sierra Sierra it's more than good enough for us. So, in this case, why wasn't it good enough for Sierra Sierra?

Furthermore, considering the ferocity of the exhaust gases with E85, couldn't you create a blown diffuser effect? Or would the added heat of E85 be too much for the rearward vehicle components. Thanks.

-Henry via

If I remember correctly, back in 2010 we made the switch from C16 to MS109 first because the Australian sanctioning body at the time for the World Time Attack Challenge did not allow leaded fuels. Then, we did a test on the dyno using MS109 versus E85, we discovered what you wrote in your question. We did make the full-time switch to E85 after World Time Attack 2010, but depending on when and which story you read on, you might have read about the one test at Buttonwillow where we made a team decision to go back to MS109 because we were unsure of Australia's sugarcane-and-wheat-derived E85s versus our American corn-derived E85. After that particular test, I think we decided to go full-time E85. As it turns out, the Australian wheat-derived E85 (a bit more expensive than the sugarcane-derived E85) was actually even better than the American corn-derived E85. Or at least it performed better in the Sierra Sierra Evo engines. It was, in fact, good enough for Sierra Sierra so SSE did make the full-time change.

Flat Valve Advantage?

I've been working on cars for all but 10 years now, and I'm at a crossroad with my current build. I own a '93 Civic coupe that I'm building an all-motor LS/VTEC. I'm going to use 81.5mm Civic Type R pistons with a GSR head. I plan to have the head worked over and this leads me to my dilemma. I've heard flat valves raise compression a little but, other than that, are they of any benefit?

-Josh Zartman, via

For your application, they would have absolutely no other benefit other than raising compression. But if you're running CTR pistons with a GSR head, your compression is going to be nice and healthy already. From memory, your compression ratio should be just under 12.0:1 depending on head gasket thickness. Flat-faced valves would bring your compression up to or just above 12.0:1.

In the past, I've used Supertech B-series valves with success many times and believe the difference in weight between their dished and flat valves of the same diameter was somewhere between 2.8 and 3.5 grams (depending on size and material). This probably isn't enough to require stiffer valvesprings if you're keeping the revs under 9,000 rpm so I wouldn't worry too much. If compression is what you're after, go with the flat-faced valves.

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