Thread: 9.5:1 to 8.5:1 What to expect?

There is a reason that we generally swap to DET's. Coincidence all the high power guys have DET's and VE/T's? I think not.

Brings the oil squirters, 370cc injectors, oil lines, water lines, sodium valves, some have a small oil cooler in the back, proper oil and water plumbing. There are benefits to just using the factory engineered components. Nissan put $$$ into designing and producing things so why not take advantage of it.

The Avenirs are kind of cheap compared to Honda N/A engines and RWD Sr20det's.

Wow I didnt know about the oil squirters, sodium valves, proper oil and water pump. I'm going for the DET, and maybe in latter swap my actual low port DE head and pistons.

Being able to run more boost is the one of the biggest reasons actually. After a certain PSI the power lost due to lower compression will be made back up by being able to run more timing at that same PSI.

I personally care more about low end torque, so a 9.5 would be better for my daily needs.

Don't do that. Put a VE head on it instead. People are getting gains of around 60 hp with just that head swap.

Since he already has the Lowport head putting that on wouldn't be that bad. The lowport is a better flowing head than the DET highport (Snickers brought it up a while back). A VE head is $$$ plus you need to do some mods to get VVL to work on the DET block. A lowport head and turning up the boost would be cheaper and he can still make great power. If your going to put some 9.5 pistons into the DET your going to have to get them notched otherwise they will shear the oil squirters.


With the USDM lowport you lose the sodium exhaust valves. They can be installed into a USDM head, you just have to decide if that is worth it to you. If you were able to get your hands on a UK lowport they bring the sodium valves.

ANother thing to think about since this is going into a fwd platform. Maybe some lag is not so bad. Instant low rpm torque means no traction on fwd. From what I've read even the 8.5 motors still spool really quick. If it was me I'd probably just go with a proper DET and learn to accept the minor power loss at lower RPM.

Excellant point.
When I increase both wheels in my turbo size, the spool would come on 300rpm later but seemed to help with traction.

I still prefer 9:5.1 for low boost but if you plan on running more then 15psi and are going to drag race it alot, then go 8:5.1. With a 9:5.1 your engine run hotter with high boost, but yes a tune will help.

Ive driven both. I prefer the higher compression.

I went from a 9.3:1 to a 8.5:1. I like the boost friendliness of the lower compression. And boost seems to come on a bit harder and faster, even with the bottom suffering just a tad. The higher compression is great with a large turbo and cams though. But you can't really go wrong with either one. I can safely push about 4psi more boost on the 8.5:1 motor on pump gas, which is more power than the higher compression would do. On low boost the high compression worked great, but I didn't notice much loss in response or power when dropping compression. But I did notice the bottom end was lacking a little bit more, but the dyno still showed about 200rpm quicker spoolup on the lower compression. Perhaps the extra timing I was able to toss into the bottom end helped with the spool while keeping things safer.

Right now I only run about 14psi at the most on my setup now on pump gas 91. Any more than that and I tend to get a bit of light detonation. By light, I mean extremely light. And this is just from reading plugs.

I could push 14psi on the higher compression, but I had to back the timing off 2* and that lost a lot of power.

The higher compression looks like a good route to go for future builds though. I don't really like pushing the boost too much. I'd like to make around 500whp on 20psi one day with just my JWT tune. Perhaps she can do it, but at least I know that 20psi isn't really pushing the setup too hard.