The new big valves are here. What’s so special about these valves? Who benefits? Allow me to elaborate a bit.
To begin, let’s look at the stock valves. Stock L24 valves: IN: 42mm x 116.5, EX: 33mm x 116.5mm (*the overall Exhaust length is actually 117.5mm, 1mm longer than I just said, but this is irrelevant because the bottom part (below the cut) is 1mm thicker. The length above the guide is exactly the same as Intake, so for the sake of this simplicity, let’s say the length is 116.5mm.)
N42/N47 Valves: IN: 44mm x 116.5mm, EX: 35mm x 116.5mm*
P79/P90 Valves: IN: 44mm x 114.5mm, EX: 35mmx114.5mm*
No matter your parts combo or the spec, or which cylinder head to use, one of the “must-dos” in a Natural Aspirated engine setup is to raise compression and to run a bigger/better profiled camshaft, and the stock valves are usually the limitations.
Bigger diameter, Longer length
Everyone agrees that the bigger the valves, the better for performance. But why are DSI valves longer? When running a very big cam with stock valves, at the full lift, the valve spring retainer and the stem seal in some cases collide. This is a bad news for the engine. So to prevent that, one would not be able to run a high lift cam, and in doing so, you are making compromise, foregoing performance, or leaving money on the table.
This is why longer valves are beneficial. And some big valves usually require you to replace the valve seats too, but we thought it through an came up with the biggest valve diameters that still fit with the stock valve seats.
Use in P79/P90/P90a
P79, P90, and P90a all have the same very large combustion chambers–not suitable for high compression, N/A engines. But they do indeed have interesting and a bit more efficient combustion chamber shape than the other heads, so using P79/P90/P90a in Natural Aspiration setup is not a bad idea at all. You just need to mill the head quite a bit to raise compression. The issue is, the P79/P90 valves are even shorter thanN42/N47 valves, so a long story sort, you will need longer valves, if you want to use P79/P90 in a high-compression N/A setup. Some people do it this by using N42 valves. Stock N42 valves from Nissan cost about $220, but this is just stock, 40year old design valves with no added benefits. Well, it is bloody 2013, and with a few more pennies, the DSI big valves, harnessed with the latest technology and material science, will let you go a whole a lot further.
E31 and E88 heads are off of L24 engines. They have the same length valves as in N42, but much smaller diameter. Also, E31/E88 heads were designed to go with Leaded Gasoline, and as such, they have brass valve seats. Nowadays, we have Unleaded gas (and in some cases corn gas (ethanol), so the brass seats must be replaced with hardened steel ones (or other rare metal seats for race applications). Well, if you will have to replace the valve seats, why not have them throated, and go with bigger valves.
N42/N47 are mostly identical, except the EX ports. They have longer (116.5mm) and bigger (44mm, 35mm) valves, and it is rather easy to find N47 (1977-1981 280Z, 280ZX). N42 is much harder to find. Both N42/N47 are very good heads for Natural Aspirated setup, as in our STR setup, but if you want to go one step above, the DSI big valves will take you there.
Aside from all of the benefits I just mentioned above, our big valves are lighter and stronger than any other valves in the market. Think about what light weight means at 8000RPM–even 1g difference makes a huge difference. I will let the picture speaks 1000 words.
N42 Nissan OEM valves: IN: 83.2g, EX: 77.5g. No nitrated. $220. Short, heavy valves.
Kameari Valves: IN: 84.9g EX: 69.2g Nitrated, but not so good quality. equivalent of $500 plus International shipping
DSI Valves: IN: 82.9g EX: 68.7g. Latest and Best nitrated technology applied. $408
What a bargain.
Product Link: http://datsunspirit.com/?wpsc-product=dsi-big-valves