So I'm piecing together a 1.8L engine for my 91 Miata. I've aquired two engines, one with a bad head & a 2004 block, and one with a good 1996 head and bad block. I WAS planning on just using the 96 head, 2004 block and having a bit more compression than normal, with the eventual goal of a turbo & megasquirt.
I just noticed on the local C-List that there's a complete 2004/5 VVT head for not a lot of money. He's building the same hybrid engine that i have with the bad head (2004 block with 99 head).
I know one of the big down-sides of the VVT engine is that you have to control the VVT, but if I'm going to MS it anyway, is that a problem and would the benefits be worth having it on a turbo build?
If you have a way to control it, and you can with MS, it's worth it to get the later VVT head.
Also of note - the 1996 and 1999 heads are not identical. The NB heads flow significantly better, so even if you don't want VVT, you should try and get a 99-00 head.
From what I've been told, the later head is worth it if you're gonna be naturally aspirated. The solid lifters are better for sustained high RPM use and it can handle 8,000 redline. Apparently though the VVT is more fragile and fails more often than the older head. If you're using a turbo it might be better to stay with the older head.
This is all heresay, I'm sure Keith or someone with first hand knowledge will chime in directly.
cmcgregor wrote:
If you have a way to control it, and you can with MS, it's worth it to get the later VVT head.
Also of note - the 1996 and 1999 heads are not identical. The NB heads flow significantly better, so even if you don't want VVT, you should try and get a 99-00 head.
Yeah, I know that the 99/00 heads are "the" heads to have from a flow standpoint, but I don't have a free 99/00 engine with a good head :) The 99/00 heads sell for around 400-500 last time I've seen them, whereas this should be ~100 for the VVT head.
So the question really comes down to whether it's worth the VVT improvements, which you definitely make sound appealing until....
Interesting bit about the fragility of the VVT system, Ky. I'll have to do more research into that.
Thanks so far, Gents!
If you decide not to get that VVT head - let me know. I have one that's missing the cams and actuator so I'll definitely buy it if you don't haha.
I'm not aware of fragility with the VVT system. It's definitely the best option for naturally aspirated power IF you have a way to control it. For boost, the VVT doesn't help but all NB heads are superior to NA heads.
If you're planning to boost the car, remember that a high compression engine will have better response but will ultimately not make as much power. I personally prefer a high compression, low boost engine but you won't win internet bragging rights with one.
WonkoTheSane wrote:
I know one of the big down-sides of the VVT engine is that you have to control the VVT, but if I'm going to MS it anyway, is that a problem and would the benefits be worth having it on a turbo build?
You can control VVT with megasquirt, just need a cam sensor and a PWM output that can handle an 1-2 amps.
You don't have to go to all the trouble of closed loop control if you don't want to. The phaser should be locked at retard (late intake closing) with no power to the control valve. If you're running megasquirt you can just send the valve 12V at an engine speed somewhere above cruising rpm for basic open loop control. This would also let you test and see for yourself if the benefits are worth it for you.
Keith Tanner wrote:
I'm not aware of fragility with the VVT system. It's definitely the best option for naturally aspirated power IF you have a way to control it. For boost, the VVT doesn't help but all NB heads are superior to NA heads.
If you're planning to boost the car, remember that a high compression engine will have better response but will ultimately not make as much power. I personally prefer a high compression, low boost engine but you won't win internet bragging rights with one.
Thanks Keith, that's exactly the engine I'd like to build.. I'm looking for a internet-laughable 180-200HP with lots of usable power.
cmcgregor - I'm going to reach out to the guy.. If I don't pick it up for some reason I'll send you a PM on here with his contact.
RXBeetle - Thanks for the specifics on controlling it!
Thank you everyone, it sounds like this would be good to have regardless of whether I go FI or not.
Cheers,
In reply to WonkoTheSane:
Thanks!
Alternately, if that bad head/good block 2004 engine you have has some good bits, I'm interested. As far as I know mine is good but was partially disassembled before I got it.
Okay, I'll take an inventory next chance I get and shoot you a message.
I can't speak intelligently about the "answer's" VVT, but if you can control it, VVT is a big bonus. If you think about it, a cam is only good for one RPM and everything around it is a compromise. VVT stretches that RPM range a bit. It won't make a ton more power, but it will make it across a broader range. Win/win.
Yeah, from what I understand, the BP6D head (the 01-05 VVT one) won't make more peak power than the BP4W (99-00 non-VVT), but when properly tuned it offers more "area under the curve" and faster turbo spool.
There are supposedly some 7500 RPM resonance issues with the BP6D head that showed up in heavy autocross use. I don't know any details though.
MS3 has native VVT support, otherwise budget for their a la cart VVT box. Also, plan on relocating the oil pressure sender. The feed for the VVT solenoid taps into the same spot as the OEM pressure sending unit, so your oil pressure will read low, if you care about such things.
We've not seen any real improvement in spool with the VVT. I want it to happen, but it just doesn't. Big difference naturally aspirated though.
Definitely some resonance problems with the stock cam. We had a National level autoxer that was breaking stuff over and over again.
Keith Tanner wrote:
We've not seen any real improvement in spool with the VVT. I want it to happen, but it just doesn't. Big difference naturally aspirated though.
I wonder if that's an altitude thing? I have a BP4W head, so no personal experience, but I know a couple other folks down here at sea level who've tried it and seen useful spool improvements.
Any time our dyno doesn't match what everybody knows, it's blamed on altitude 
I can double-check with Jeremy, but last time I checked the VVT wasn't getting us anything for spool. Cleaner, though.
In theory, if the VVT gives better low end power in an NA setup, it should help spool with a turbo on the same motor. However, that's not necessarily a given. Depending on the turbo being used, how fast it spools, where it spools relative to the engine's NA power curve, etc. the difference may or may not be noticeable.
I'd expect it to help more on a setup with a larger turbo that spools later in the rpm range.
I think you need an MS 3 to PWM the VVT.
MS2 will do it on/off.
Hydra has full control as well.
rslifkin wrote:
In theory, if the VVT gives better low end power in an NA setup, it should help spool with a turbo on the same motor. However, that's not necessarily a given. Depending on the turbo being used, how fast it spools, where it spools relative to the engine's NA power curve, etc. the difference may or may not be noticeable.
I'd expect it to help more on a setup with a larger turbo that spools later in the rpm range.
You know what they say about theory and practice :)
Keith Tanner wrote:
Any time our dyno doesn't match what everybody knows, it's blamed on altitude I can double-check with Jeremy, but last time I checked the VVT wasn't getting us anything for spool. Cleaner, though.
I've seen back-to-back dyno comparisons where it made a very visible difference, so this isn't just a case of "theory says it ought to do that". I can't account for Jeremy's experience except to speculate about altitude, because we know that to be very relevant to questions about turbo performance in general.
I'm thinking for now that I'll just rebuild the engine to stock 1.8 2004-spec, get the car running well with the MS3 and play with/tune the VVT NA, and eventually turbo it.. Or not. It may have enough of a power/driveabilty bump that the reliability becomes worth more than powah. I dunno, we'll burn that bridge later and the guy selling the turbo stuff I wanted to buy stopped responding as soon as I started asking questions about it anyway.
Keith - I've never gotten to play with the Hydra and I'm sure that if it's you guys' preference, it's awesome and bulletproof like everything else I've gotten from you, but it's almost 2/3rd of my yearly car play/race budget, so I'm going to have to go with what I know.
Oh, and embarrassingly, I discovered last night while doing a parts inventory that I already have a full VVT head with intake and injectors. It came with the car that my 04/00 hybrid engine came with, so no need to buy the craigslist one. This is what happens when you do two engine swaps, one rebuild and part two cars between projects. Whoops.
Luckily I discovered it before I contacted the clist dude :)
I've confirmed with Jeremy that, while the theory says it should and while it occasionally proves to be the case, the VVT does not always provide improved spool. Altitude is not really a factor here, the relative pressures do not do a step change at 100 kPa ambient.
The lower redline and potential for valve problems mentioned earlier would make the 99-00 head Jeremy's choice.
Not popular, but then again our dyno charts often are not. We had a very upset ITR owner on our hands one time when we failed to give him the dyno chart he knew he deserved. It was later that he discovered the rebuilt non-ITR engine with low compression pistons.
As for the price of the Hydra, make sure you add up all the bits you need to get an MS to that level. The price difference isn't as much as you think. Also, we have a new option coming that's more megasquirty in terms of price and capability.
cmcgregor wrote:
In reply to WonkoTheSane:
Thanks!
Alternately, if that bad head/good block 2004 engine you have has some good bits, I'm interested. As far as I know mine is good but was partially disassembled before I got it.
Did you get the pm that I sent to you about that vvt head?
