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Honda City
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Discussion Starter #1
I'm getting a stock bore Z6 block for cheap. And I have a D15 (3-stage vtec) block also with me.

I want to boost it with the ITBs that are currently on. Both blocks are still on the stock bore of 75mm. I want to run Vitaras with forged rods. I already have a set for my D15 block but I can sell them and buy a set of D16 Eagle/FJT rods if needed.

Which block would be recommended for boosting? The other block will be built for high-comp NA, so I can switch blocks whenever I want and have both motors at my disposal. The head will be my mildly ported Y8 that I'm using currently.

Between the 2, the Z6 is known to be a lot stronger, with the crank having bigger rod and main journals, better oiling. However, with my D15, I can have a better rod:stroke ratio of 1.61:1 with my forged rods, than with my D16 which would have a ratio of 1.52 or 1.54 depending on the H/I beams I buy from FJT.

I want to make atleast 300 whp, preferably 350+. I cannot afford sleeving either one, so that's out of the question. Boosting on stock bore unless the clearances are too much.

Your opinions?
 

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Classic Man
Civic
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since u want high HP im gonna say try the D15 out and rev it up nice and high. i dont like taking D16s to 9000+rpm but its gotta be done to have a decent power band.

but i think that the D15 wouldnt mind the high RPM so much.

only one way to find out!!


and when in doubt the best thing to do is KISS, which to me means build the D16 since its been proven so many times.



its really up to you! id say go d15 since u got the rods and block!
 

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The D16 has been proven so many times to be a great motor...handles boost well, cheaper, and multudes of aftermarket parts available for it. Would your D15 make that whp goal? Yes. So the question is...what motor to use? It's really up to your personal preference.

Thumps up for using the ITBs under boost!!!
 

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Honda City
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Discussion Starter #6
Between revving a D15 to ~7500 rpm and 9000 rpm, what prep work has to be done to the block and head? I'd be upgrading the valvesprings so that's already accounted for.

I'd guess maybe different pistons with a shorter comp. height, thinner rings, a crank scraper, a 22teeth water pump? What can be skipped and added to that list?

Making that list so I know what extra cash I'd have to pony up to keep the motor safe from becoming a bomb at 9000+ rpm for a good amount of miles.
 

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boost with ITB's!! i wanna see some pics when this is done!:yes:

IMO id go with the z6, but in a way the obd1 d15b 3 stage vtec is basically a smaller clone of the z6.

Thats all up to you, seems like your gonna be throwing alotta money at it
 

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i read somewhere that a jdm d15b uses the same rods as a z6?is it true that we can use d16 forged rods with vitaras on a d15b?
 

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Honda City
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Discussion Starter #9
The OBD1 D15B, yes. The one which I have is the OBD2 D15B which originally came with the 3 stage vtec head, 137mm rods and 42mm rod journals.

If you have the OBD1 D15B JDM motor, it uses D16 rods with 45mm rod journals and 55mm main journals.
 

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98 EK Hatch,97 Supra
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Personally, I would go with the z6 for boosting because of the better oiling over other single cams. Vitaras and fjts should enable u to put down ur Power goals no problem. Gluck
 

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Honda City
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Discussion Starter #14
Yeah. I've spent way too much time and money to throw away my ITB setup which has been working nicely. So boosting with ITBs. The fabrication part is going to be loads of fun. Hope to buy some welding stuff so I can learn tig/mig welding at the same time.
 

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Love the Civic
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Yeah. I've spent way too much time and money to throw away my ITB setup which has been working nicely. So boosting with ITBs. The fabrication part is going to be loads of fun. Hope to buy some welding stuff so I can learn tig/mig welding at the same time.
Damn fine, damn fine, I cannot wait to see this set up, ITBs are the realness. Good luck mang.
 

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1991 Honda CRX
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You will enjoy the ITB's with boost. I had a friend a while ago that had a civic hatch with a turbo GSR with ITB's, it was very responsive at any rpm. One word of advice though, try a few sizes of plenums, there can be good power gains with the right size plenum.
 

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Honda City
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Discussion Starter #17
You will enjoy the ITB's with boost. I had a friend a while ago that had a civic hatch with a turbo GSR with ITB's, it was very responsive at any rpm. One word of advice though, try a few sizes of plenums, there can be good power gains with the right size plenum.
Yea, it's funny though how atleast Hondas running ITBs with boost are so rare. I remember a 'Teg which was running a boosted B with ITBs by a guy called TonyTheTiger but barely any info available about his setup. I remember a cool setup on a D14 by a guy in Europe, linking it here:
My ITB's + Turbo setup - Honda-Tech

With the ITBs, I even have the option of changing runner sizes and lengths independently apart from the plenum dimensions, so it'll be fun playing around with them too. My wish is to create a setup with variable length runners but that's probably out of my league and budget right now :TD:
 

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Classic Man
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to spin the D15 to 9k, i wouldnt do anything but use forged rods with beefy ARP rod bolts.

if u really feel like it get the rotating assembly balanced.


then let her rip!


ive taken two different d16's that werent balanced past 9000rpm and the only reason the first one blew up was from too much timing and cracked a sleeve.
 

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'93 DX Hatch; FZ1
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I definitely vote for the D16.

Yes, the D15 can rev higher, but the D16 pulls in more air with lover revs.

If you observe a max mean piston speed of, say, 23m/s...

You get 8165RPM as the limit for the D15B, and 7666RPM for the D16. At their respective max RPMs, they pull in identical amounts of air. But, at every other RPM lower, the D16 pulls in more. And it works its valvetrain less.
 

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to spin the D15 to 9k, i wouldnt do anything but use forged rods with beefy ARP rod bolts.
But 9k on Vitaras? Probably slightly safer with a D15, but still seems kind of risky with Vitaras. Yes, only a few sets have cracked/broken around the wrist pin and/or shattered, which might or might not have been from high RPM, but still seems kind of risky... You know, just sayin'.

I'd do a D15 over a D16. Lighter crank, less displacement (so it should make the more power on the same boost, right?), different.
 
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