Max Boost Sohc vs. Dohc KA

[Iamjohnhayes]

i was just wondering which engine can hold more boost the e or the de. yes i know its a stupid question but i just wanted to know (my friends who don't drive nissans are telling me the dual and im kinda agreeing with them but kinda not). also i would like to know if any one actually knows how much boost the blocks (regardless of fuel setups) can hold with out blowing up.

And i'm allready calling myself an idiot for using the search button and not finding this info so can you please refrain from calling me one it would be appreciated.

[fiznat]

Are you talking about stock internals? If youre talking about built engines, there would be no difference whatsoever in "max boost."

Stock internals, though, I'd guess the DOHC could hold a little bit more simply cause the stock compression ratio is lower in the DOHC than it is in the SOHC.

[klattr1]

im pretty sure that the SOHC has a lower compression ratio than the DOHC.

[95_240sx]

Maximum boost? Ive seen upwards of 38-40psi in mine on a couple of occassions and no problems.

Cast iron block...boost isnt going to blow it up. Titan motorsports, which runs 2JZ's started cementing their blocks, and have split a couple of them. However, they are running 60-70psi and Methanol, and going 6.50 in the 1/4. The only reason I mention this, is because the 2jz is a cast iron block.

Rick

[fabio420]

my friends always said that their 2jz engine was aluminim block and head, with a metal hg. hmm.....

[shockload]

the e pistons will yield higher compression when used in the de so i would assume the pistons in a ka24e are stronger. or they just have a different wrist pin location.

[Iamjohnhayes]

hey guys thanks for the info.

from the start i intended on doing a full rebuild of a motor geared entirely towards a turbo with all new internals ect.

so far the basic plan is to build up a single cam (because a kid in town has a couple of them for cheap and parts seem more readily available for me at least) and use a garrett gt40 turbo

[Ineed2speed]

my friends always said that their 2jz engine was aluminim block and head, with a metal hg. hmm.....

Aluminum head, cast iron block.

[veilside180sx]

DOHC Compression is 9.5:1

SOHC Compression is 8.6:1 with the exception of late '88 which are 9:1 compressoin

[HolyShiznit]

DOHC Compression is 9.5:1

SOHC Compression is 8.6:1 with the exception of late '88 which are 9:1 compressoin

Wurd.

[Titan]

the e pistons will yield higher compression when used in the de so i would assume the pistons in a ka24e are stronger. or they just have a different wrist pin location.

How do you figure they are stronger?

First off, the higher compression that results from using SOHC pistons in a DOHC motor, is a also consequence of the difference in combustion chambers between heads.

Secondly, because the SOHC piston can operate in higher combustion temperatures and pressures, does not warrent it being stronger.

When engineering a component, you always incorporate what is called a 'safety factor'. Basically, during stress calculations you assume the yield stress of the given material to be lower then it actually is by a certain factor. This insures the component isn't operating on the brink of yeilding, and also compensates for any stresses that were unforseen.

In any case, I'm sure the relative strength of either piston is very similar. However, by placing either one into a situation of higher combustion temperatures and pressures (i.e. SOHC piston into a DOHC motor), you are increasing the stresses and likewise decreasing the safety factor.

[fiznat]

DOHC Compression is 9.5:1

SOHC Compression is 8.6:1 with the exception of late '88 which are 9:1 compressoin

Huh for some reason I thought it was the SOHC that had the higher compression. Sorry bout that!

[nissanfanatic]

I would put money on the SOHC piston breaking at very close to the same amount of torque as the DOHC piston assuming they are introduced to the same variables.

[Iamjohnhayes]

my 89 240 has the higher 9.1 to 1 compression but that really dosen't matter because i am replacing the pistons and rods but will prob stick to the 9 to 1 compression anyways because i would rather have power out of boost and have a more powerful engine running slightly less boost.

[PapaSmurf2k3]

I would think the DE pistons are stronger, from an engineering standpoint (I dont know about changes in designs), due to the fact that if the same factor of safety was used (for example, 2) then the piston would have to be over-engineered for the higher compression of 9.5:1. This is all assuming that nissan went with the same factor of safety, which they might not have. Either way, I bet the 2 pistons are relatively close in strength.

[Chezedik]

Doesn't matter, he is rebuilding something, so it might as well be a DE for it's lower BSFC. Means more power, plus if you keep the boost low, it won't matter too much, just need a big turbo.

[Iamjohnhayes]

yeah i am going to use wiseco pisrtons with pauter rods so the bottom end should not be a problem as for a turbo right now im looking at a garrett gt40. i just need to find a manifold to put it on i believe iap said the will make a manifold with any flange you need but im not sure.

[Chezedik]

GT40 is just T3 flange, right? I know most (if not all, certainly no expert on GTs, or anything really) of the new line just uses T25, T3, or T4 flanges.

[Chezedik]

But oh, yeah, I still would go DE, you will get more power.

[Dragon_284]

Yeah the DE will produce more power than the E provided the engines are stock in terms of compression and head flow (even with a rebuild). One thing I was wondering about is max power output at the highest levels of performance modification. I have heard that at high levels of hp a sohc would operate better than a dohc due to sohc being able to maintain smoother intake and exhaust valve control. Now I know certain issues like these can be overcome in many different ways and im not tryin to downplay the DE at all. Im just wondering if there is any truth what I have heard about this.

[95_240sx]

The Garrett GT40 is a T4 flange. There are also a couple of variations of the GT40. Unless you are wanting 600+hp, I wouldnt use the GT40 as you wont be using it potential. Might look more into the GT35R or GT3071R. You should also checkout the groundzero motorsports manifold.

Rick

[Iamjohnhayes]

well part of the reason for the gt40 was b/c im getting a sweet deal on a brand new one for $399 so either im gonna use it or sell it but i am aiming for a rather large hp number in the end so i'm prob gonna end up keeping it.

[shockload]

Yeah the DE will produce more power than the E provided the engines are stock in terms of compression and head flow (even with a rebuild). One thing I was wondering about is max power output at the highest levels of performance modification. I have heard that at high levels of hp a sohc would operate better than a dohc due to sohc being able to maintain smoother intake and exhaust valve control. Now I know certain issues like these can be overcome in many different ways and im not tryin to downplay the DE at all. Im just wondering if there is any truth what I have heard about this.

the de only makes more power due to its compression. the sohc would most likely make more peak hp due to the head design being more friendly to cumbustion and exhaust flow. the stock pistons should be at least as strong in a de , i have tested mine on 18psi and everything was cosher. i am not sure which engine i have, im pretty sure its a 9to1 engine but the engine was replaced at some point before i got the car.

[Iamjohnhayes]

the pistons should be exactly the same, allthough i am not entirely sure. i believe the reason the compression ratio in the de is lower is because the combustion chamber of the de is larger to fit in the space for the extra exhaust valve.

[SimpleEnigma]

You also have to look at the piston head design.The E pistons are a 2cc (i think) dished piston.

Also, depending on what suits your fancy more, the E will provide more torque than the DE will, but the DE will provide better horsepower.

There really isnt a max boost for the KA block, it can handle as much pressure as you can push into it, but the amount of pressure you should run depends on your setup.

[Iamjohnhayes]

the de only makes more power due to its compression. the sohc would most likely make more peak hp due to the head design being more friendly to cumbustion and exhaust flow. the stock pistons should be at least as strong in a de , i have tested mine on 18psi and everything was cosher. i am not sure which engine i have, im pretty sure its a 9to1 engine but the engine was replaced at some point before i got the car.

well i plan on boosting a 9:1 ratio in my single cam so i'll have to see how kosher things are. watch kinda turbo were you boosting 18psi at?

[TrunkMonkey]

the de only makes more power due to its compression.

the DE makes more power because of it's dohc setup.

there's no way a (barely) 1 point difference in compression ratio is going to create a 15hp difference in power.

-demetrius

[TrunkMonkey]

and just a note.

the DE and late E pistons are EXACTLY the same with the exception of the dish volume. one isn't any stronger than the other.

-demetrius

[Iamjohnhayes]

dude sompression ratio does make a difference. on a muscle car you could have two exactly the same motors one at 11:1 and one at 13.5:1 and the difference in hp is well above 75hp

[TrunkMonkey]

dude sompression ratio does make a difference. on a muscle car you could have two exactly the same motors one at 11:1 and one at 13.5:1 and the difference in hp is well above 75hp

no.

you'll see a 4-5% power increase at the crank for every point that you raise your compression ratio, and that's being a little generous.

trust me. you've never seen a muscle car (or any car for that matter) make that much power just from raising the compression ratio. if that was the case, forced induction would be a complete waste of time and money.

-demetrius