Chev70elle is right, that cam isn't even going to be in the zip code of 8000rpm in your combo. For a time attack car, which has to turn and accelerate, you are in the beginnings of a seriously mismatched combo. Don't look at the JDM guys and see the crazy rpm and think you have to copy. Gearing and overall acceleration will make your combo magic. Hard question, do you NEED to run the Low Ram because of hood height issue or something? For a road race style car, it's a negative. You need more power band , not more rpm. Theoretically a HiRam should do everything you need, and I might even suggest a Performance Design carbon intake since it's lighter and has adjustable runner length(suit the track/event) to make the car work better. I just sold the exact cam you mentioned, it's not near enough for what you want rpm wise. For reference, I am building a 392 4.155x3.622 for my street 71 AMX and top end is going to be Brodix BR1 cathedrals w/ Performance Design carbon intake and a Summit Big Gun 2 cam for initial testing. It's a total street car I'm building to embarrass GT3's and Lambo's since I'm in So Flo. It's going 8000rpm ish, but super wide power band.

 

Not only that, but giving up huge average and peak power by cutting the displacement. The bottom end has never been a limitation for rpm.

I dream of building a 4.8 crank engine too, but as a fun thing to do not because it is needed. It would just be for the experience.


In real racing, if there are no displacement limits, they will be built as big and rev'ed as high as possible lol.

 

100% Spanks. I was hoping the OP here…R35Q8 would come back with a why. He’s severely cutting his legs off here. This thing will be a weak running engine with a very short powerband, that’s non-competitive in the application he’s attempting to run. You see it here on Tech all the time, folks trying to mimic a combination that they have read about or been told about, without any consultation from a reputable builder.

 

Totally understand, but as I said earlier the puzzle will be completed in stages. The initial startup will be with this camshaft since I already have it in my garage, and then I’ll check what needs upgrades or changes.

The engine will be moving a 370Z shell, which is not that heavy and has close ratios.

Also, the idea behind using a shorter stroke setup isn’t about whether the stock bottom end can handle it — it’s more about longevity. With the shorter stroke and long rod/short piston combo, piston speed and side load are reduced, which helps extend ring and engine life when spending long periods at high rpm.

 

I get what both you and chev70elle are saying, and I really appreciate the feedback. The project is still in swap stage — the Z still has its factory engine right now — so nothing is finalized yet. I went with the Low Ram mainly because of possible hood clearance issues, and if it turns out I have the room I’ll definitely consider switching to something like a HiRam and even a carbon cover setup later to keep things cooler.



The car itself is going to be a weekend and track-day build, also for local time attack events. I’m not building it to be a garage queen, I actually want to use and enjoy it.



For the cam, as I mentioned earlier it’s for the initial startup since I already have it. Later I’ll see how it feels and either keep it if I like the overall performance, or move to something else if I feel I need more on the top end.

 

The idea isn’t just for the experience ، it’s more about the way the car will behave on track. A shorter stroke helps reduce piston speed and side load, and it also softens the torque hit a little bit. In a lighter chassis like the Z with close ratios, that can actually help the car put power down better when exiting corners instead of just spinning the tires.

It’s not the usual path, but that’s the reason I’ve been considering it ، and I don’t mind giving up a bit of peak power or torque if it means the car stays more controlled and consistent in track conditions.

 

I think your idea to manipulate the torque curve is good, but destroking it isn't the best way.. Trust us, leave the stock stroke in this thing and just play with the cam timing. With that low ram, it's going to be soggy all the way till 6000rpm when the cam turns on some(existing cam). Do this instead, go get a FAST LSXR for this a d sell the low ram. The FAST will fit the hood and has adj runner length, and is plastic to cut the heat soak. It's the single best thing you can do with your existing combo if you want to change one thing and make the whole thing better.

 

I get it, I really do. I get excited when someone thinks outside the box…it’s how we learn to excel in life in general. I’ve been involved in record setting Cup builds. Leo Jackson put our engine in his car for Harry Gant in September 91’ and he won four in a row with it, only changing valvesprings and oil. We were a R&D shop used by many Cup teams back when teams farmed out engines AND chassis development..been at this stuff a while. The stroke you’re after here won’t soften torque a little bit…it will soften it a lot. You’re looking for RPM where you don’t necessarily need it in what you’re doing with it. Cylinder side loading narratives come into discussion with endurance builds…engines that are turning 8500+ for hours on end. Believe me when I say that I like the way you think, I really do. I just feel like you’re going to be unhappy with the design. Endurance builds are gutless. They have no power below 4500 typically, because they are designed to spin. With RPM comes horsepower by nature, but the design has to be able to breathe up there. A short stroke brings reliability to the package, not by want, but by design. Again I’m talking about 8500+ for hours.
If I were building this for you, I’d spec a forged bottom end 3.75 stroke crank, 6.125 rods, Wiseco custom coated pistons with an extremely thin ring package. I’d go with a 4.155 bore sleeved block and a set of MMS 26X heads up top with a custom camshaft. I just built this exact package for a guy who occasionally road races and/or autocrosses his MIATA up in Washington state, as well as street drives reliably. If you want to be competitive on track, build for as much power as the class rules allow for and then TUNE YOUR CHASSIS to work with the power. I ran NASCAR Pro Late Models for 6 years as an owner/driver so I understand chassis very well also. You can make virtually any chassis work with modest power levels…such as we are discussing here…with enough tuning. It’s a process. You won’t be fast on day one. To me personally, the process was the fun part, learning to understand what the cars wanted on both ends of the track. I miss those days.

 

‏I decided to make up for the displacement loss by going with a 4.125” bore on the setup. That brings it back up to 5.7L, which isn’t bad at all for a destroked engine, and it should help with breathing and overall balance .

‏I really like the idea of the FAST LSXr, especially with the plastic construction to cut down on heat soak. I agree it should pair better with this combo than the low ram. Appreciate the input!

 

thoughts on this camshaft

Intake Duration @ 0.050 in Lift 251°

Exhaust Duration @ 0.050 in Lift 267°

Intake Valve Lift 0.624″

Exhaust Valve Lift 0.624″

Lobe Lift Intake 0.367″

Lobe Lift Exhaust 0.367″

Lobe Separation 115°

Intake Centerline 112°

Advertised Intake Duration 301°

Advertised Exhaust Duration 317°

Valve Timing Intake Open BTDC 37°

Exhaust Open BBDC 95°

Intake Close ABDC 83°

Exhaust Close ATDC 41°

 

What is the power band you are targeting? Those specs even with some runner length are going to be soft below 5000rpm.

 

3.267 stroke 4.125 bore

Road course racing , trying to push near to 9000rpm as possible

 

I think you need to let that 9000rom idea go some. I don't think it's a reasonable range to operate in given it's short road course use That cam isn't near enough for 9000rpm and it'll be slow on the bottom coming off the turns. Gearing is key, but it's not a crutch. You need like a 3000-7500rpm range to make that thing effective. I would start on the lowebd and add more cam if you need it. I would do something like a 240/248 110 and see what happens.

 

trust me when you rev past 8k you can’t quit

beside that I got the supporting mods already shaft rockers springs valves ets the remaining is drysump and camshaft
if i couldn’t decide will stuck to my old camshaft 235/242 111+3

 

The pistons in your pic…post up the data sheet on them please. Curious about the CH….

 

part number 311969 from JE
2618 pistons 1.304 comp hight
-5cc flat top bore 4.125

this made to go with 6.125 rods and 3.622 stroke
but if you compare it with 3.267 stroke and 6.3 rods + half the stroke you will get 9.2375 which is 0.0025 below deck surface

 

Agree totally on the cam. WAY too mild for 9,000 rpm. It might rev reliably to 9 grand, but the power curve will be done at 7,000-7,500 max. Also on the short stroke. 3.27 stroke isnt helping or hurting ability to make power at 8,000-up rpm. May be good for longevity on the street. But low rpm power will be missing some torque with that stroke....

 

R35, I gotta say I LOVE the wording on that piston!! Similar to the biker jacket "if you can read this the b...h fell off!!

 

You’ve got a very mis-matched setup here. You need a piston with a 1.2655 CH, to be at zero deck height. Do you have a builder, or are you doing this yourself?

 

What connecting rods are you running?