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What are the NSX's weak points when it comes to forced induction?
- Thread starter TNH
- Start date
contrar to what some say it can......
yes pistons are a weak point but they have problems because of excessive heat and detonation....control these with tuning and cooling and you should be able to run conciderable boost.
also, airflow is an issue, most FI system seem to work out the airflow issues all the way to the TB. after that they are stock. with work on an intake mani, and some better exhust mani's with even flow you should be able to run alot of boost ( i am obviously speaking turbo)
this is just my .02 and i am sure i will get flamed pretty bad so im stnding here with a flame suit on waiting to see what kind crap i get for this.
yes pistons are a weak point but they have problems because of excessive heat and detonation....control these with tuning and cooling and you should be able to run conciderable boost.
also, airflow is an issue, most FI system seem to work out the airflow issues all the way to the TB. after that they are stock. with work on an intake mani, and some better exhust mani's with even flow you should be able to run alot of boost ( i am obviously speaking turbo)
this is just my .02 and i am sure i will get flamed pretty bad so im stnding here with a flame suit on waiting to see what kind crap i get for this.
I only have moderate knowledge, but from what I understand even if you could keep the stock pistons, the stock cylinder walls are about as thick as 2 paper matches put together, and they warp and walk any much over 425 or so horsepower. GJ said they get expanded in certain areas, so its like at the bottom of the stroke it could be a perfect seal , but 30% up it could be complete blow-by, then another 15% up a perfect fit, then loose, etc. to the top.
This has been hashed over many times if you’d like to do some searching, but I’ll offer a little insight as I see it.
For the most part I agree with Black&Tan, and although I won’t flame 01balcks4 I will suggest that his answer is too generic, somewhat careless, and probably does not reflect personal experience with forced induction NSX engines.
First off, we need to be more specific about what constitutes medium or high boost. Thus far, few if any NSXs are running the levels seen in some engines. But they are often generating more power per CC than others running higher boost, so perhaps we should speak in terms of power per unit displacement. In any case, for our purposes I would consider 1-6 psi as low, 7-12 as medium, and 13 up as high.
As noted, some of the “pioneers” of medium to high boost NSX systems leaned the hard way that both the stock cast pistons and the open-deck block design are potential weak points. That should certainly not be a surprise since cast pistons were recognized as vulnerable decades before the NSX, and other open-deck engines have had problems with cylinder “walk” and warping when turbos were added. (most notably 300ZX non-turbo and Porsche 944 engines).
The stock open-deck/cylinder liner issue is probably related more to power generated per stroke (torque) than peak HP. In other words, a centrifugal SC making 500HP typically creates far less average torque throughout the power band than does a turbo with the same peak HP, and therefore may be less prone to this problem.
Under ideal conditions the stock pistons will cope with medium output levels and may even survive into the higher range. However, “ideal conditions” means very accurate and consistent control of fuel, timing, intake temps, exhaust temps, spotless combustion chambers, good plugs, coils, etc. Unfortunately it is unrealistic to expect that all those things will be or remain “ideal” at all times, and that’s why you need to build in a certain margin for error, or “headroom”. The most important thing to remember about forced induction is that it magnifies the bad with the good, making headroom all the more important. Your stock NSX could be lugged up a hill on a hot day running cheap fuel and a faulty knock sensor, pinging all the way, and suffer no apparent damage. (sounds like every Pinto ever made) A low boost CTSC or turbo that leans out a bit as revs climb might rattle a bit from time to time or cause unhealthy combustion chamber temps, but they don’t generally crush ringlands. A few may have suffered valve issues, but overall they are pretty tolerant. However, the same engine running 12 psi can kill piston in seconds, and at 18psi it can happen in the blink of an eye. Forget knock sensors, at high boost levels they probably aren’t fast enough to stop the train once it starts at those levels. With forged pistons you buy time, and time is headroom. So just because someone manages to generate 500 RWHP on stock internals doesn’t mean it’s “safe”. Impressive, yes, but probably not the best gamble IMO.
For the most part I agree with Black&Tan, and although I won’t flame 01balcks4 I will suggest that his answer is too generic, somewhat careless, and probably does not reflect personal experience with forced induction NSX engines.
First off, we need to be more specific about what constitutes medium or high boost. Thus far, few if any NSXs are running the levels seen in some engines. But they are often generating more power per CC than others running higher boost, so perhaps we should speak in terms of power per unit displacement. In any case, for our purposes I would consider 1-6 psi as low, 7-12 as medium, and 13 up as high.
As noted, some of the “pioneers” of medium to high boost NSX systems leaned the hard way that both the stock cast pistons and the open-deck block design are potential weak points. That should certainly not be a surprise since cast pistons were recognized as vulnerable decades before the NSX, and other open-deck engines have had problems with cylinder “walk” and warping when turbos were added. (most notably 300ZX non-turbo and Porsche 944 engines).
The stock open-deck/cylinder liner issue is probably related more to power generated per stroke (torque) than peak HP. In other words, a centrifugal SC making 500HP typically creates far less average torque throughout the power band than does a turbo with the same peak HP, and therefore may be less prone to this problem.
Under ideal conditions the stock pistons will cope with medium output levels and may even survive into the higher range. However, “ideal conditions” means very accurate and consistent control of fuel, timing, intake temps, exhaust temps, spotless combustion chambers, good plugs, coils, etc. Unfortunately it is unrealistic to expect that all those things will be or remain “ideal” at all times, and that’s why you need to build in a certain margin for error, or “headroom”. The most important thing to remember about forced induction is that it magnifies the bad with the good, making headroom all the more important. Your stock NSX could be lugged up a hill on a hot day running cheap fuel and a faulty knock sensor, pinging all the way, and suffer no apparent damage. (sounds like every Pinto ever made) A low boost CTSC or turbo that leans out a bit as revs climb might rattle a bit from time to time or cause unhealthy combustion chamber temps, but they don’t generally crush ringlands. A few may have suffered valve issues, but overall they are pretty tolerant. However, the same engine running 12 psi can kill piston in seconds, and at 18psi it can happen in the blink of an eye. Forget knock sensors, at high boost levels they probably aren’t fast enough to stop the train once it starts at those levels. With forged pistons you buy time, and time is headroom. So just because someone manages to generate 500 RWHP on stock internals doesn’t mean it’s “safe”. Impressive, yes, but probably not the best gamble IMO.
I would like to respond with another answer that is too generic, somewhat careless.... :redface:
I agree with all that sjs has stated but the point I was trying to make as i look back to the original post unfourchanatly does not anwser that question. the point i was trying to make is that more power would and could be acheaved with realitivly low boost when air flow has been increased. i know this sounds like a too generic, somewhat careless point to make but lets face it...Airflow = power, this is why people use FI.
increased airflow with lower psi, without the stress of high psi and you will see better results. it takes more time, money and planning to do it properly then just adding a compressor of some sort which is why it is not always done "correctly".
but hey what do i know I havent even blown up my first nsx motor yet...
I do however have 4 cars in the garage with a total of 6 turbos....
for whats its worth this forum is a good one, great banter..
marc
I agree with all that sjs has stated but the point I was trying to make as i look back to the original post unfourchanatly does not anwser that question. the point i was trying to make is that more power would and could be acheaved with realitivly low boost when air flow has been increased. i know this sounds like a too generic, somewhat careless point to make but lets face it...Airflow = power, this is why people use FI.
increased airflow with lower psi, without the stress of high psi and you will see better results. it takes more time, money and planning to do it properly then just adding a compressor of some sort which is why it is not always done "correctly".
but hey what do i know I havent even blown up my first nsx motor yet...
I do however have 4 cars in the garage with a total of 6 turbos....
for whats its worth this forum is a good one, great banter..
marc
Well I’m not sure how I could have been any more polite, and I don’t think anything I said warranted sarcasm, but no big deal.
That was the apparent core message of your post, not airflow. As I stated, the definition of low, mid, high boost is important but I think it was reasonable to interpret “considerable” as meaning much more than the “relatively low” that you are now talking about. So I still say that your initial post understates the risks of “considerable” boost on stock internals.
As for airflow, you did make some points about that and I didn’t challenge them, but some of your latest comments aren’t quite on point. Yes, more flow is the key to more power, but more flow also means more risk. If your intake and exhaust are more efficient, allowing the engine to produce more power at an indicated boost level, you are still developing power levels that are potentially harmful to the open-deck design. At the same time, more air into the cylinder is more boost even if you don’t see it on the boost gauge, which is reading the manifold pressure not actual charge pressure or volume in the cylinder. A little like measuring a logjam to make assumptions about what’s making it downstream, but adequate for most purposes. So yes you can make more power at the same apparent boost, and the NSX is already better than many in that respect which is what I meant above regarding power per unit of displacement. When you significantly increase CFM being processed there’s naturally room for significant improvement. But again it comes back to my basic point which is that forced induction, even if very efficient, increases the risks and severity of the consequences along with the power. The stock pistons and cylinders can take most anything an NA engine can throw at them, but under “considerable” boost even a small error in AFR, octane, etc. can be catastrophic in seconds. There’s just no getting around that, so a prudent person allows for a greater safety margin.
01blacks4 said:
That was the apparent core message of your post, not airflow. As I stated, the definition of low, mid, high boost is important but I think it was reasonable to interpret “considerable” as meaning much more than the “relatively low” that you are now talking about. So I still say that your initial post understates the risks of “considerable” boost on stock internals.
As for airflow, you did make some points about that and I didn’t challenge them, but some of your latest comments aren’t quite on point. Yes, more flow is the key to more power, but more flow also means more risk. If your intake and exhaust are more efficient, allowing the engine to produce more power at an indicated boost level, you are still developing power levels that are potentially harmful to the open-deck design. At the same time, more air into the cylinder is more boost even if you don’t see it on the boost gauge, which is reading the manifold pressure not actual charge pressure or volume in the cylinder. A little like measuring a logjam to make assumptions about what’s making it downstream, but adequate for most purposes. So yes you can make more power at the same apparent boost, and the NSX is already better than many in that respect which is what I meant above regarding power per unit of displacement. When you significantly increase CFM being processed there’s naturally room for significant improvement. But again it comes back to my basic point which is that forced induction, even if very efficient, increases the risks and severity of the consequences along with the power. The stock pistons and cylinders can take most anything an NA engine can throw at them, but under “considerable” boost even a small error in AFR, octane, etc. can be catastrophic in seconds. There’s just no getting around that, so a prudent person allows for a greater safety margin.
To sjs's point about margins of saftey, the stock 11:1 compression ratio has a tendency to amplify any timing and/or a/f errors that are made. To the original question, an ~8 psi or less boosted NSX engine with good (precise and reliable) fuel and timing control, will likely yield a fast and reliable car. Perhaps the best example of this is the number of Nitrous NSX engines that have been VERY reliable under similar, modest-FI-like, internal engine loads.
More FI boost and/or less precision on engine management control would likely demonstrate that the more vulnerable aspect of the NSX engine is the cast piston and ring design.
Keep in mind that Honda has traditionally prided iteself in efficiency in all of their engineering. They designed an engine at 3.0L with a (at the time) unheard of 90HP/Liter. Everything was around this design goal - in contrast to a (perhaps more modern) philosophy of "platform engine design" with different varients at various HP/Tq specs. To this point, even Honda had to do a lot of creative engineering and exotic manufacturing to get a mere .2L displacement increase in 1997. In other engine designs - with less focus on efficiency and packaging, a .2L increase is a boring machine away.
More FI boost and/or less precision on engine management control would likely demonstrate that the more vulnerable aspect of the NSX engine is the cast piston and ring design.
Keep in mind that Honda has traditionally prided iteself in efficiency in all of their engineering. They designed an engine at 3.0L with a (at the time) unheard of 90HP/Liter. Everything was around this design goal - in contrast to a (perhaps more modern) philosophy of "platform engine design" with different varients at various HP/Tq specs. To this point, even Honda had to do a lot of creative engineering and exotic manufacturing to get a mere .2L displacement increase in 1997. In other engine designs - with less focus on efficiency and packaging, a .2L increase is a boring machine away.
Stock compression ratio is 10.2:1 :wink:kpond said:
Good catch Gerard. I was dreaming about 11:1, but then again, maybe I wouldn't have needed the blower if that's what we had! :smile:
The biggest weakpoint to me is my wallet :wink:
NetViper said:
and my wallet :biggrin:
And speaking of compression ratio stock being 10.2:1, what is it at 12PSI? I know that my supercharger came with some numbers. My Mercury Capri that has 8.5:1 stock is about 15:1 at 9PSI. Something to think about... When you already have relatively high compression stock, boost dramatically adds to that...
In high boost applications sleeving the block and lowering the compression is necessary. The stock compression ratio is high and the open deck block can't take the much higher pressures. So I guess you could say the weakness of the NSX engine is it was not designed to be used with forced induction.
I wouldn't be too concerned about the open deck block. I have a B16A with standard block putting out around 550 FWHP at 27psi boost.
In my opinion, the problems with turbocharging an NSX engine would be:
1) Incorrect tuning.
2) Inadequate engine management (ECU, Injectors, Fuel pump, etc)
3) Pistons
I have built a number of turbo B16A setups for customers running up to 18 psi with a completely standard engine except for a thicker head gasket. None of them have ever had any problems and two of them have been on the road for about 5 years now.
You are extremely unlikely to break a bore unless the engine is knocking.
Also, I tend to play it safe with the air fuel ratio. Around 11.0:1 under medium to high boost. This will help keep stock pistons from breaking.
In my opinion, the problems with turbocharging an NSX engine would be:
1) Incorrect tuning.
2) Inadequate engine management (ECU, Injectors, Fuel pump, etc)
3) Pistons
I have built a number of turbo B16A setups for customers running up to 18 psi with a completely standard engine except for a thicker head gasket. None of them have ever had any problems and two of them have been on the road for about 5 years now.
You are extremely unlikely to break a bore unless the engine is knocking.
Also, I tend to play it safe with the air fuel ratio. Around 11.0:1 under medium to high boost. This will help keep stock pistons from breaking.
HYPERTUNE said:
But we aren't talking about a B16A. Keep in mind that most commuter car engines are built with durability as a higher priority than performance or weight savings, and that sometimes translates into things like thicker (stronger but heavier) parts such as cylinder sleeves. With a car like the NSX, parts are designed to be as light as possible without sacrificing too much reliability and durability in stock configuration. As I noted above, there are plenty of cases where other open-deck engines could not cope with more than a few PSI of boost. There are only a couple documented cases of a turbo NSX engine running over about 8psi for an extended period, and those also had problems and we rebuilt.
In other words, we have no specific evidence that an NSX engine can support mid to high boost (turbo), and some evidence that it cannot. So you may or may not be correct, but I don't think your assumptions are supported by relevant facts and I wouldn’t advise the average person to rely on them. It will be interesting to see how well some of the 10+ PSI SC projects hold up. In my opinion they are less likely to suffer sleeve problems than a turbo at similar boost, but they are starting to make some pretty impressive torque so it will be an interesting test.
BTW, we’re not talking about breaking bores, just causing them to “walk” a bit and possibly warp out of round.
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sjs:
I agree with what you are saying to a certain extent, but when people first started turbocharging the B series engines, plenty of blocks got broken, and everyone had the opinion that the blocks are weak and require reinforcement. Over time, this has been proven to be unnecessary if the engine is tuned properly. To me, the NSX block looks stronger in the deck than a B engine. I asked Junichi Tanaka of his opinion of block guards a few years ago and his reply was "we have built two high power B16A turbo engines one with a block guard and one without...... the one with the block guard broke"
It is best to err on the side of caution of course, but if it is possible to make a reliable 550 hp on a 1.6 litre B16A with a stock block, I cant see any reason why it would not be possible with the 3.0 litre C30.
On another note, I was involved in another turbo S2000 recently (I didn't do the whole job, just installed the Motec) and it is making over 500 FWHP with a stock block. This uses the same style fibre reinforced block as the C32.
I agree with what you are saying to a certain extent, but when people first started turbocharging the B series engines, plenty of blocks got broken, and everyone had the opinion that the blocks are weak and require reinforcement. Over time, this has been proven to be unnecessary if the engine is tuned properly. To me, the NSX block looks stronger in the deck than a B engine. I asked Junichi Tanaka of his opinion of block guards a few years ago and his reply was "we have built two high power B16A turbo engines one with a block guard and one without...... the one with the block guard broke"
It is best to err on the side of caution of course, but if it is possible to make a reliable 550 hp on a 1.6 litre B16A with a stock block, I cant see any reason why it would not be possible with the 3.0 litre C30.
On another note, I was involved in another turbo S2000 recently (I didn't do the whole job, just installed the Motec) and it is making over 500 FWHP with a stock block. This uses the same style fibre reinforced block as the C32.
Encouraging information about the S2000 and what it may mean for the C32 (especially since I have one of the latter in my garage with just over 2k miles on it)
I guess my point is that I'm speaking to the "masses" looking for general advice based on what's known, and not known, about our exact engines. Like I said, you may be correct, but the "pioneers" of high boost C30s did have problems and indications were that they were load related, not "tuning" issues. Although it is an entirely different engine and therefore even less relevant that a B16, I don't think you can find a single open deck Nissan V6 running serious boost, and probably not a 944 although the long stroke on that engine may be part of the problem.
Hopefully the current super SCs will prove reliable and be followed by more attempts with turbos on stock liners, but if were tearing down an engine to install forged pistons today I think I'd go ahead and do the sleeves at the same time. Beats doing it twice until someone else paves the way. There are several options including the F-X approach with a stronger liner and no guard, or a T-sleeve with integral deck ala Darton Pro.
I guess my point is that I'm speaking to the "masses" looking for general advice based on what's known, and not known, about our exact engines. Like I said, you may be correct, but the "pioneers" of high boost C30s did have problems and indications were that they were load related, not "tuning" issues. Although it is an entirely different engine and therefore even less relevant that a B16, I don't think you can find a single open deck Nissan V6 running serious boost, and probably not a 944 although the long stroke on that engine may be part of the problem.
Hopefully the current super SCs will prove reliable and be followed by more attempts with turbos on stock liners, but if were tearing down an engine to install forged pistons today I think I'd go ahead and do the sleeves at the same time. Beats doing it twice until someone else paves the way. There are several options including the F-X approach with a stronger liner and no guard, or a T-sleeve with integral deck ala Darton Pro.
sjs said:
I like what you are saying about the long stroke. The main reason I decided to stick with the B16A is the shorter stroke and shorter bore. I figured that the bores would be stronger compared to a B18C with a taller block (my theory being longer sleeves, more prone to flexing).
That is one of the reasons I am suggesting the C30/32 should be OK. It has a similar stroke to the B16A. I also rev my B16 to 10500 rpm. I am searcing for a decent black manual NA1 to replace my Civic, and I wont be happy unless the thing will rev to 10000. My engine runs all TODA parts in the head and TODA have parts for the C30 engine so I think my goal should be attainable. I know the guys as TODA in Japan quite well and will get their advice on the limitations of the C30.
TODA work closely with Mugen and I might even be able to get some info on the new turbo JGTC C30 engines (M-Tec (Mugen) prepare the GT500 NSX engines) it would be very interesting to find out what they do regarding block preparation. If I can find out anything I will let you know.
Do you have a torque curve for the monster B16? What is the bore & stroke on that engine? Peak HP isn’t enough info when comparing various types of load and stress between engines. Since HP = rpm x torque / 5252, and you are turning fully 30% higher RPM than the “typical” turbo NSX, the torque required to reach a given peak HP is that much lower. But I think torque is more relevant than peak HP to this discussion so it would be interesting to compare the torque/liter though the meat of the power curve where most of the action takes place. Then we can try to factor in any difference in thrust loads from a shorter stroke (if it is shorter) and greater cylinder rigidity due to a smaller diameter bore. We may find some hints as to how a B16 making 500 whp at 10,000 rpm could be less prone to certain types of failures than a C30 making the same peak power at 7,500, or we may prove just the opposite.
The only graph I have with me has power and boost graphed. Also, the bottom line is kph, not rpm. From memory, it made peak torque around 8K.
It doesn't start going hard untill 6K but as you would imagine (from a peak torque at 8K), it would be making max power around 10+K. The bore of the B16 is 81mm and the stroke is 77. something I think. A touch shorter than the C30.
It doesn't start going hard untill 6K but as you would imagine (from a peak torque at 8K), it would be making max power around 10+K. The bore of the B16 is 81mm and the stroke is 77. something I think. A touch shorter than the C30.
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It looks clean! It reminds me of when I had boosted my 1.6l D16z motor! This was back in 95. It was completely built with everything, including Arias pistons, Crower rods, and a Dan Paramore [DPR] Stage 6 head. When dynoed, it pulled 295 to the wheels, but after blowing 2 head gaskets due to walking sleeves, I sold it....what a beast it was!
Well, I've made some progress since I last participated in this post.
Next week I will take delivery of a 91 Black NSX. Finally I will have the ultimate car (well, a new R would be better, but hey I'm getting there!) from (in my opinion) the ultimate car manufacturer!
The intention is to turbocharge it and find out for sure what is or is not possible. If all goes well, I hope to produce a kit in the not too distant future.
I can't wait!!!!!!!!!
Edit: found an old pic of the S2000 i did a few years ago. It is now back in the shop undergoing a re-construction and will definately be up there with the best of them.
Next week I will take delivery of a 91 Black NSX. Finally I will have the ultimate car (well, a new R would be better, but hey I'm getting there!) from (in my opinion) the ultimate car manufacturer!
The intention is to turbocharge it and find out for sure what is or is not possible. If all goes well, I hope to produce a kit in the not too distant future.
I can't wait!!!!!!!!!
Edit: found an old pic of the S2000 i did a few years ago. It is now back in the shop undergoing a re-construction and will definately be up there with the best of them.
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I'm admittedly unfamiliar with the NSX, but no stranger to forced induction. If I were to do a FI system on an NSX, here is where I would start, and mind you, this will be a generalization.
Engine management - Whatever you decide to go with, make sure you have a good tuner. I personally think a stand-alone ECU is a crucial component. I run a Haltech, but there are many options available.
Fuel delivery - Upgraded fuel pump and injectors if necessary. I don't know what the fuel system on the NSX is capable of, but it definitely needs to be researched.
As a big safety measure, I'd lower the compression ratio and go with forged pistons. 8.5:1 is the magic number with MR2s. Stock CR for the MR2 Turbo is 9.0:1 IIRC. With the MR2, I'd stay stock bore size and use Toyota rings. I can offer no insight with the NSX.
I have seen and ridden in a 489 HP NSX running on stock internals, so I know with proper tuning, fuel delivery, and a big enough supercharger, it's definitely possible. His name was Romeo Ortiz, board name ZRO260B4U. Very cool guy who may be able to offer some insight. Also, I'd opt for the supercharger route vice the turbo route. With my limited knowledge of the NSX, (disclaimer) I see the SC system being alot less complicated.
My .02. Your actual mileage may vary. All disclaimers apply.
Engine management - Whatever you decide to go with, make sure you have a good tuner. I personally think a stand-alone ECU is a crucial component. I run a Haltech, but there are many options available.
Fuel delivery - Upgraded fuel pump and injectors if necessary. I don't know what the fuel system on the NSX is capable of, but it definitely needs to be researched.
As a big safety measure, I'd lower the compression ratio and go with forged pistons. 8.5:1 is the magic number with MR2s. Stock CR for the MR2 Turbo is 9.0:1 IIRC. With the MR2, I'd stay stock bore size and use Toyota rings. I can offer no insight with the NSX.
I have seen and ridden in a 489 HP NSX running on stock internals, so I know with proper tuning, fuel delivery, and a big enough supercharger, it's definitely possible. His name was Romeo Ortiz, board name ZRO260B4U. Very cool guy who may be able to offer some insight. Also, I'd opt for the supercharger route vice the turbo route. With my limited knowledge of the NSX, (disclaimer) I see the SC system being alot less complicated.
My .02. Your actual mileage may vary. All disclaimers apply.
Haltech hey? Can't beat the Australian made computers! :tongue: Haltech are about 5 minutes walk from my workshop. Their stuff is very good, But I usually use Motec, mainly due to the fact that I am more familiar with the software. I definately agree that stand alone is the way to go. If I do a kit, I will probably go for around 800cc injectors, even for low boost applications because it makes it easier to upgrade the system in future. Bigger fuel pump - definately.
It doesn't seen too hard to turbocharge the NSX, in any case, I think any extra effort required compared to a supercharger would be well worth it.
I think any compression ratio between 8.5 - 9.0:1 is good. On any NA engines that come with domed pistons, my first exercise is too work out the comp using a flat top piston. If it falls between that range, its all good. Some people get too tied up with the "high comp to reduce lag" deal. It really makes very little difference to lag, but it certainly affects the amount of power you can run with pump gas. Any street car is better off below 9.0:1 IMO.
Engines running race fuel only however, rarely are limited by engine knock. In all applications I have encountered, you can keep going up in the timing to the extent that you no longer make any more torque before you will get knock with a good fuel (C16, ELF MOTO124 for example).
It doesn't seen too hard to turbocharge the NSX, in any case, I think any extra effort required compared to a supercharger would be well worth it.
I think any compression ratio between 8.5 - 9.0:1 is good. On any NA engines that come with domed pistons, my first exercise is too work out the comp using a flat top piston. If it falls between that range, its all good. Some people get too tied up with the "high comp to reduce lag" deal. It really makes very little difference to lag, but it certainly affects the amount of power you can run with pump gas. Any street car is better off below 9.0:1 IMO.
Engines running race fuel only however, rarely are limited by engine knock. In all applications I have encountered, you can keep going up in the timing to the extent that you no longer make any more torque before you will get knock with a good fuel (C16, ELF MOTO124 for example).
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