which d15 block for high rpm??

[EvoTec1]

Hey, I am looking to put something together piecemeal, and I have some questions. I am looking for a d15 bottom end, then the best nonvtec head I can find (+ a mild cam), and an old si tranny. The goal is to carb it, and make newer kitted b series swaps look bad.

First, hmotorsonline.com has a 130 hp d15b jdm motor.... why does this motor make so much power? Is this the motor that has the good rods and the stock 7200 rpm redline everyone keeps telling me about? The tech chart also doesnt say what obd it is, but since i'm just looking to use the block, it doesnt matter right?

are there any american (read: cheaper) blocks with beefed up internals?

The 91 si head is 12 valve right? Is there a better non vtec head choice for this motor? the stock one has 16, but vtec and webbers would probably run rich in the midrange with vtec

Am i out of my mind? will a d15 like this ever keep up with a b-swap in a newer heavier car if i keep the weight down? (this will go in a 90-91 non si hatch)

 

[99sidude]

the d15b (obd1) is the reving and most powerful of the d series due to its vtec head and high compression ratio. It is my guess that this is also the strongest in terms of its bottom end. If you plan on keeping up with a b series swap N/A you will need to upgrade most of the bottom end anyways in order to run some crazy high comression ratio, so it probably doesn't matter which block you get. The best non-vtec head is prolly the one from the 88-91 civic/crx si's, and no, they are 16 valve. I don't think you are out of your mind, and infact I think that this is a pretty cool project. I think that after the build and a good tune you should be able to suprise the hell out of some b series cars

 

[dtob]

I'd get a used Z6 for cheap, thow some A6 pistons in it, good cam like crower stg3 and then go to town with the rest. Eg. ITB, good header, LSD, port and polish the crap out of it, ARP rod bolts, etc. Its possible to make 160whp with the Z6 NA with a stock honda bottom end and those A6 pistons. Plus the A6 pistions are cheap as hell.

 

[EvoTec1]

I was told the vtec motors had significantly better rods and such than their non vtec counterparts. Dont the base motors redline at 6500? The vtec motors tach out to liek 7200 stock. If building a motor (sigh) is the only way to have a competitive d series then i guess i'll go the cheapest route i can find blockwise.

I want to stay 1.5 liter if possible, the only reason i'm not going with a f series swap is my friend just got a 1.3 litre single cammed 79 ford fiesta ghia from germany, and i wanna be able to run with him on an even playing field. Everyone trying to make d series power goes for that extra .1 liter, i think the carbs will make up for that TINY difference up top.

I figured if I took a motor with vtec and then put that si head and cam on it, i'd be hella understressing it rev and power wise.

112-125 hp or so to the wheels would be the target, with a 1900lb weight and the short si tranny....

 

[EvoTec1]

oh and you got a link to that build blanco? i wanna take a peak

 

[EvoTec1]

well, I dont really think I want a newer bigger vtec motor...

https://hondaswap.com/civic-crx-ef/dual-webber-carbed-d15-vtec-head-swap-89491/

this is kinda what started this line of thinking

 

[jlicrx]

essentially there are only 2 different D15 blocks after 1988 - the ones with the small main bearing journals which are the Civic STD D15B1 and the CRX HF D15B6 - all of the other D15 blocks have larger main bearing journals, but not as large as the D16 blocks - the JDM D15B VTEC has the same block as the USDM D15Z1 - the difference in the JDM D15B VTEC is the crankshaft which has larger rod bearing journals (not larger mains like a D16) and uses the same rods as the D16s which results in a rod/stroke ratio of 1.62 which, for high rpm, is slightly better than the other D15s of 1.59 and a lot better the 1.52 of the D16s - the problem with this set-up is finding pistons other than the stock JDM D15B that work with the long rods - with the non-vtec head you would need at least a flat top piston or one with a slight dome in order to get the compression up with the larger combustion chamber of the non-vtec head

 

[EvoTec1]

thats what i was looking for! ... ive done some searching, but there seems to be no comprehensive head chamber volume chart or info around HS.com.....imma bout to google it.

so you are saying that this motor would have low compression....sounds cheap gas friendly, (if its within reason) ... plus dont low compression motors respond well to nitrous?

From my experience with smog era muscle cars... i know that torque is affected more by compression than horsepower... My 72 smog 350 cutlass eventually hit 13's on 8.2:1 compression..... The lesson was that compression matters less and less as you rev.... You can forget about low end performance with low compression, but revs x torque still equals hp right? You just have to build the motor to take advantage of rpm, contrary to the traditional build it for torque musclecar mentality.

We actually ended up with a powerband similar to a ferrarri, with peak torque from 4500-5600 and a 7000 rpm shift point.


Back on subject, wouldn't this motor be similar? Say cam it to live between 4500-7500? Anyone tried a budget beater 87 octane build?

 

[EvoTec1]

also, cant you weld material into the combustion chamber to decrease its size, and optimize its shape? I mean I would never think of doing such a thing... but i know people who port that would be comfortable doing the job.

 

[EvoTec1]

so back to the point,

If i took the d15b block, sold the head and put SOHC head on it, then ran cams that peaked near the stock vtec cams, the motor would be durable like stock, but have lower compression, right?

If i was under stressing a vtec motor rev and compression wise, it should be golden to beat on, especially with that r/s ratio...

 

[EvoTec1]

well, honestly I dont have enough money to rebuild a motor. I mean, your build seemed really close to what I would want to do, but I just cant afford it.

What I can afford is 500$ motor and cheap JDM 4.250FD tranny from Hmotors.

I figure putting a 75$ USDM civic SI head on a block that is meant to rev past 7000 from the factory would be adding a significant margin of safety, while retaining use of all factory parts. Its not like i'm going for crazy power, or i wouldnt be looking at d15's.

But still, no matter how you build a motor, a motor built similarly, but with a better r/s ratio will always put less strain on the internals and will last longer if operated for extended periods at high rpm under heavy load. Since I am building a car to daily drive as well as to have fun with at the track with a friend, that durability is important.

 

[EvoTec1]

what does that have to do with what i said?

If you take a motor and run it in its high rpm range all the time it will wear faster than if you aren't beating on it so hard. If you take that same motor and cam it so theres less rpm involved, you are effectively not beating on it as hard.

that reasoning is ridiculous?

I'm saying I want to put a non vtec head on a vtec motor, not a mini me

i dont care about how flexy and crappy old v8's are, it has nothing to do with any of this. I work on all cars, i'm into european shit, and i originally got into foreign cars through rotaries, so quit acting like i'm a knuckle dragging redneck. (or a dumb kid)

Now, with the jdm d15b, i assume the combustion chambers not the pistons are what are giving it the high compression, and i understand using other d series heads will lower compression

So with that said, what is the best flowing d series non vtec head, or, what head has the most meat for porting?

 

[EvoTec1]

well a nice fellow at d-series.org pointed out that it would be possible to just put the older non vtec cam in the d15b head

anyone disagree?

"Are you even remotely aware of how big a role the valve springs play in how high these engines can rev? Of course you aren't or you wouldn't be so fixated on the block."

what??

I'm not ignorant. i simply plan on running the engine hard. at a lower than factory redline. valvesprings dont come into the equation.

if you had a vtec motor, but never hit vtec rpms, the motor would probably last as long or longer than the car right?

so you built the motor most people built, in the car most people build. I'm sure its fun to drive. i'm looking for a 1.5 liter motor that can be beat on regularly, and will be a good race for my friends car. a specific goal.

I'm not looking to be the fastest. I'm simply looking to do something that isnt routinely done in a make and model of car known for everything already being done to death.

 

[dtob]

This is helarious because the title of this thread is which d15 for high rpm and now he's saying that the doesn't want to rev it because he wants it to last. Sounds like he doesn't know what he wants.

 

[EvoTec1]

dude, i just said that valve springs wont be a factor in this build,
as for the title, i was asking which block was best, and someone that was into something other than talking shit already gave me the information i am looking for. the d15b has the best rod/stroke ratio.

For the record, i am here asking these questions to learn, and i do hours of research. Why do you think i have been posting things like this? i didnt know, now i know, and for the record, most people that build d series motors go a6. and yes. thats a good dyno pull. 135 hp at the wheels rocks.

I dont have the funds to properly build a motor, or do ANYTHING really cool for that matter....

 

[EvoTec1]

jeez, i was just asking which block would last the longest when you were constantly revving it. I wouldnt say you were talking shit as much as you were acting like i was a complete idiot for assuming a few things about hondas. I mean i know quite a few basic things about engines in general. One of the universal things, is that an engine with a favorable rod/stroke ratio will show less bearing wear than a less optimal design.

Understressing the motor might not seem like a necessity, but I will feel better about driving past the cams power range in a motor that has been detuned slightly. In fact, being able to rev safely, well past your power peak is a benefit in most forms of racing, from rally to simply driving twisty roads.

Again this isnt honda, but remember when scc magazine made that ultra cool datsun 510 rally project? They built a stout little motor for that thing, but instead of camming it to hit 7k and make hella power, they cammed it conservative for torque, usable powerband and durability.

Back on subject, you said that a d15 couldnt make it up hills, but at the top of 2nd gear.... could this be because of the transmission? I had a friend with an 91 si hatch that took hills great, but his d15 crx sucked balls, i know its a different motor but wouldnt the si have a more aggressive transmission, in addition to .1 liter and a better efi system and induction?