D15b4 engine Build

I have been looking at several different engines i could put in my 4g4d, and am seriously contemplating keeping the d15b4 dual carb. I was planning a cam uprgrade, proper air box with a cold air setup and ram tube/bell mouths on the carbs inside the box, some good extractors, and possibly a mm or two shaved off the head for compression, getting the carbs bored out and larger jets fitted. I know many of you will say, "fit a sohc zc, they are 130hp" ect, but i already have around 105hp on the d15, so i dont think a whole engine swap, plus wiring in a computer is worth it for a used engine with 25 more hp MAX. I would expect something like this to make around 140hp or more, i dont think this is unreasonable. Also a b series is out of the question, i cant justify spending $4000 + on an engine install on a $6000 car. Any other ideas?

well im a big fan of carbs, i say why not give this a try. you mentioned a cold air set up. i have never noticed a difference in my old datsun with dual 42mm webers(bored out 40mm) with or without a ram type air box while on the strip. maybe have the combustion chambers welded up to bump up the compression.....have a reputable company port and polish the head.....and run a set of say 38mm carbs. IMO carbed engines are so much simpler to extract hp out of in NA form. especially due to the fact carbs can compensate for added air flow and such. i dunno man give it a try and let us know how it turns out.

Also a b series is out of the question, i cant justify spending $4000 + on an engine install on a $6000 car. Any other ideas?

i only spent about $2100 on my ls swap. and my car only cost $1300. but hey let us know how your set up goes. also what kind of torque numbers are you getting?

I have been looking at several different engines i could put in my 4g4d, and am seriously contemplating keeping the d15b4 dual carb. I was planning a cam uprgrade, proper air box with a cold air setup and ram tube/bell mouths on the carbs inside the box, some good extractors, and possibly a mm or two shaved off the head for compression, getting the carbs bored out and larger jets fitted. I know many of you will say, "fit a sohc zc, they are 130hp" ect, but i already have around 105hp on the d15, so i dont think a whole engine swap, plus wiring in a computer is worth it for a used engine with 25 more hp MAX. I would expect something like this to make around 140hp or more, i dont think this is unreasonable. Also a b series is out of the question, i cant justify spending $4000 + on an engine install on a $6000 car. Any other ideas?

Here is some modding info for those carbs I posted on another board, those keihins are very tweakable. I will also post some mods by other dualcarb owners, as well as links...

Conefilter and acceleration spring mod:First, get two motorcycle cone filters, the ones for performance bikes. Then, remove your stock airbox completely, and block off all attached piping. DO NOT block off the breather hose that goes from your valve cover to your stock airbox, get a breather filter for this one. Remove mesh guaze covers and spacers over carb throats. Take the two cone filters and push their rubber ends THROUGH the spacers. Bolt the spacers with filters attached, back onto carb throats, without the mesh covers. File them in the dustbin... you might have to bend two little copper pipes next to throats slightly inward to accommodate the cone filters. Don't worry, they are purely for athmospherics. If you are not sure about the size filter, take a spacer, drive to your bike hop-up shop and compare sizes before buying. If you can, get filters with the rubber ends slightly larger than the hole in your spacer, to ensure a snug fit. You might have to use super-glue to make them stick... do not worry about a CAI. Carbs respond much better when they are sucking in air from 360 degrees, as opposed to from one direction only, such as a CAI. The gains from two cone-filters on the throats is much bigger than what you would gain from a CAI. Cold air is great for FI, but free breathing is GREAT for carbs... link to dual carb setup with performance bike cone filters...

http://www.d-series.org/viewtopic.php?t=1661&postdays=0&postorder=asc&start=40&sid=2bb3f30df013e133233758241b1636a1

Next, you do the Keihin CV Carb mod: You will see two silver lids on your carbs, where it says KEIHIN. Carefully remove these lids by unscrewing the screws that hold them in place. Careful not to drop any screws or dirt into the carbs once you've taken the lids off. Underneath you will see two long springs. Take out the first spring, measure it, and then cut off 3-4 coils of the spring. Now, stretch it to the original length... repeat the process with the second spring. Make sure they are the same length as before they were cut. Next, look at the open carbs again. You will see two little plastic stoppers on top of the two pipes that the springs fit over. Mine were black, so yours might be too. Remove and file them.

Now, take the springs and put them back where they came out of, with the uncut ends facing DOWN. Carefully replace the carb lids.

What you've done: The springs control the rate at which the diaphragm piston valve rises when you push the accelerator. After the mod the valve rises much quicker, due to lessened spring density. This vastly improves throttle response. The plastic stoppers prevent the diaphragm valves from raising above a certain point, to keep fuel consumption low. The higher the diaphragm raises, the bigger the needles open, the more fuel you get into your engine. The increased air from the cone filters and the fuel from the quicker lifting and higher lifting diaphragm means a cool 10-15HP increase (if you have a decently built engine already, otherwise, expect less)...

If you want to go even more, you can machine one (1) millimetre out of the carb throats (you will need bigger butterfly's), and source larger jets from Honda bikes or Harley Davidson bikes. They use the same carbs... But this is going extreme. Harleyheads get an extra 20HP from machining and rejetting their carbs. But then they are not very streetable, and your fuel consumption goes for a dive...

But then again, performance means more air-fuel is needed.

Accelerator pump mod:
This is another "free" mod, but you have to go to this link to see how it is done, it has pics that I cannot post here...

http://www.d-series.org/viewtopic.php?t=1661&postdays=0&postorder=asc&start=60

Carb Balancing:
this link is to a good website that shows you more mods, and carb balancing, which frees up more "free" power:

http://home.netvigator.com/~bricheun/

i only spent about $2100 on my ls swap. and my car only cost $1300. but hey let us know how your set up goes. also what kind of torque numbers are you getting?

Have you heard of Australian Dollars...? Yes, a B16 motor can cost $4000.00 if you have to pay in Australian dollars... therefore, not worth it. Plus, car tuners ask more than is justified for such a motor because it is a "performance" motor...

Stick to the D15B4... feed your kids, make your wife happy...

Yeah i realise the 'free mods' to the carbs, which i have already done, except the twin filters, i have the airbox gutted, ie no diflector piece or filter and a cold air pod. But i want more than these few little mods can achieve, which has only been small.

Yeah i realise the 'free mods' to the carbs, which i have already done, except the twin filters, i have the airbox gutted, ie no diflector piece or filter and a cold air pod. But i want more than these few little mods can achieve, which has only been small.

Well, then your biggest power robber is still your airbox... it was designed to detune the engine... your carbs are still only sucking air from one direction, as opposed to 360 degrees. She's starving, even with a pod filter on there. After removing mine, I had a big gain in power... also, see if you can get your hands on the SOHC ZC camshaft, should kick you in the arse nicely... mine does...