I have been reading a lot on this forum to learn about the VQ engine series. I road race with the SCCA in a class where there are two rules. The engine must be smaller than 2.5 liters and no form of supercharging (ie no turbo, or NOX).

My car is a RHD Porsche 914-6. The aircooled engine really cannot make enough HP for this class. I would like to reach 300 HP. Plus the engine parts are getting hard to find and expensive. So I am looking at water cooled V6's as a replacement.

From what I read, the VQ35 has the breathing capability so I would start with a VQ35, change the crankshaft to a 73.3mm stroke from a 3.0 and have the block sleeved for 85mm pistons to get me the 2.5 liter displacement.

What is a reasonable compression ratio and what cams have people used to increase the HP? And finally what is the opinion of this community that a VQ25 can produce close to 300 HP?

 

If you absolutely can't use an existing Porsche flat 6 from some sort of Carrera I would suggest starting with this.
https://en.wikipedia.org/wiki/Nissan_VQ_engine#VQ25HR
It fit most of your criteria and it probably has the lung capacity to get close to 300 crank hp. Check with the G forums and ask the G25 owners what they're doing, if anything.

 

I would stick with a flat-6 platform if possible. The VQ might be a cheaper engine but factor cost of getting the 914 transmission to work with a VQ block. Also the VQ is water cooled and will have a higher center of gravity, so you would sacrifice some handling and take on some weight.

 

Kennedy engineering makes an adapter plate and flywheel to couple the VQ to a Porsche 901 gearbox. Cost $550. The CG I do not believe is significant.

I have worked with the flat sixes for 5 years now and they are not up to the task. Need the water cooled engine to make HP.

 

What about a built rb25 and rev her to the moon?

 

OP said no turbo or supercharging, otherwise i was going to say RB25DET NEO or 1JZGTE

otherwise maybe go 4A-GE. slap on some cams, ITB, etc and you can have a peppy engine. not many sub-3.0 6 cylinder engines out there

 

I didn't say anything about boost

high CR build and 9k rpm ought to make some power on e85

 

I do not have the room for a straight six. The V6 will occupy about the same room as the flat six.

Question: why are you suggesting other engines than the VQ? I thought this was a good choice for an engine

 

most sub-3.0 straight 6 are ***** without boost. thats why theres next to no NA RB20DE Skylines around anymore. 3.0 and higher youre at least making enough displacement to get a couple hundred horsepower, 110hp NA stuff like my Supra is fine for cruising but if you want to romp youre in for disappointment

 

The VQ is a great engine platform and is commonly used as a powerful V6 swap. We're merely suggesting that it might not package correctly in a 914 (It might just be too tall). And I don't know what people are thinking with these I6 suggestions as they would be the least likely to fit.
Anything that is built to house a flat engine will most likely have to stay with that almost proprietary platform. That being said, in this case I would say a V6 would be a third and final option. First I would make every attempt to stay with a flat 6, and I doubt you'd really have to convert to a water cooled setup. Are there no 993 air cooled engine options available?
If not, my second choice might be to use something from Subaru. They've made 2.5 liter flat engines for a couple of decades now. I am not sure of the aftermarket for 2.5 NA boxer engines because Subaru is more known for turbo applications but it could be worth a look.
I hope this clears things up a little. I think it would be a neat thing to do, and you would get the power you need. We're just saying there might be easier options available.


edit: This might be a better answer.
https://en.wikipedia.org/wiki/Porsche_Boxster

The 2.5 liter Boxster engines are all over car-part.com. And you could probably use the entire drivetrain.

 

Just thinking out loud here. How about import a vq25, possibly with variable intake (00vi or mevi) and 6 speed maxima transaxle? Would there be enough room to set it up mid-engined? Might have to do body work to move the wheels back a bit.

Sent from my XT1060 using Maxima

 

Why import one? If he wants to he could use ones that are available here. Link provided in the second post.

 

There are fwd versions oversees that would be perfect for mid-engined applications. I believe they may come in cefiros even.

Sent from my XT1060 using Maxima

 

At first i was gonna come in here and blast this thread thank god its a legit question lol.

All depends on your budget. If i were you i would first look into the VQ25HR that is found in the G25s. They make 230hp on 10.3:1 compression. Im pretty sure bumping that up to high 11s:1 or 12s:1 plus a aggressive set of cams would get you very close to the power level you are looking for but it wont be "cheap". I think that would be better than starting with the VQ30/35 just due to that HR head which has a ridiculous flow rate, you'll easily make up the difference in price just because of the head. I dont know if it will make 300hp but it will be close.

 

This.

This too most likely.

Weight.

VQ=low 300lbs
RB=mid 400s

Weight again.

4A-GE would lack torque and why? If that were the case just stick with the stock 914 motor.

The VQ is a fantastic choice for what you want to do. Very low weight, good parts availability, and very tunable. There are other great options but the other options being mentioned are just fanboying because JDM y0.

Guys remember if he is talking about racing he will need low weight(all iron block motors RBs and 1/2JZs out), easily available parts because **** is going to break and a solid power output WITH GOOD TORQUE(good bye most 4 cyls). Stop the fanboying.

 

When the VQ DEBUTED IN 1995 there were 3(?) iterations: VQ20DE, VQ25DE, and VQ30DE. USA only saw the VQ30DE. Jim wolf technology in USA made cams for the VQ30DE. As you all know, these cams gave the VQ30DE a crazy top end. I wonder, would it be possible to import a (JDM YO!) VQ25DE motor and drop the JWT cams on top? I get the sense that the cams on these motors were the same, so the JWT built for the 3.0 should also work on the 2.5? Conjecture? perhaps.

 

Importing and camming an old VQ would cost as much as yanking a new VQ25HR our of a G25...... And net less power.... And be weaker.

Back on topic.... I like the Scooby swap option, seems to work best with what the OP has.

if not... VQ25HR dat beesh.

 

Crusher,
You mention the G25 heads, Do they flow as much or better than the VQ35 heads and intake?

 

Im pretty sure they are the same VQ35HR heads. And well just look a this flow bench result to know how good the HR heads are:





If the VQ25HR has the same heads than that's the headflow you are looking at. And there is still more to be got out of the HR head so its quite the upgrade from the older DE head.

There is also the added benefit of all the parts you would need to make a normal DE engine rev is already in the VQ25HR because its built to rev, so valve springs, oil pump, the HR headgasket with its added cooling benefits. You'll be pistons and cams away from your goal, i dont think you will have to address rods with an HR motor but it would not hurt to get a stronger set just for piece of mind. You'll pay more upfront but almost everything little nagging issue is already taken care of the motor should be good up until 9000rpm. The majority of your effort will go towards tuning. You will need either uprev or megasquirt for your goals.

What are your plans for a transmission if you go VQ route?

 

Very good. I did a little more research on the HR and found that made it what we used to call a long rod motor, very good for HP. I think this is the right answer. Plus you can get one off ebay for about $2500. This price point is considered free in the Porsche world. I think I can get a pretty good engine put together for about $10K, if I do not go dry sump.

I will be using my Porsche 901 gearbox. They are good to 400 hp. I hope to need a LSD for this engine.

Thanks Crusher,

neil

PS. Any thoughts on camshafts?

 

Ok so your just going to adapt the Porsche gearbox, i had something else in mind but adapting a that is MUCH easier as im sure its PnP and has information everywhere on it lmao. Yea you'll need the LSD

But **** 10K around here you are building one BEAST of an engine. Cams for your goals. JWT, Kelford, Tomei. Pick your poison. Kelford makes the most aggressive cams, so going with a set of 272* with atleast 11mm of lift would be best, That model VQ has VTC on both the intake and exhaust cam so even with hyper nutter cams you can tune it to be very flexible which is an obvious plus. You will be a bit of a trailblazer because not much tuning has been done on the VQ25HR but VQs are like legos, they are almost totally backwards compatible.

Search Car-part.com, i just found 5 VQ25HRs going for $1500 here in NC so im sure you can get one for less than $2500. I would pull the motor down to the bare block and send it too the machine shop and have it fully checked with your purposes in mind. That extra $1000 that you would save can go towards things such as main bearings, ARP headstuds and rod bolts, Nippon piston rings, and better rods. It's not completely necessary but just a piece of mind especially in a racing environment as i have mentioned before. Which i haven't heard of a VQ having oil starvation problems but there is a Drysump system available, GTM has one FS and it cost $6000, just saying that makes my knees weak.

Are there any fuel limitations in this race class? I see more compression in your future if not.....But anything else we can do to help we would be glad too, i know a good shops around here that specializes in the VQ and would be glad to help. I cannot wait to see the results of this if you go with the VQ.

 

I saw the dry sump system on the web and went a little weak myself. That is why I would try to stay wet sump. We can run up to 116 octane fuel but it has been my experience that really high compression (over 12.5:1) gives little benefits and lots of problems. I was going to probably cap compression at 11.5:1. I agree with your approach I would feel better with some H beam rods and new bits through out.

Question - are the lifters/buckets between the cam and the valve hydraulic or do they have to be adjusted manually?

 

The lifters/buckets are one piece and solid (under cam). The only way to adjust the lash is to remove the cams and buckets and install new ones of a different spec. And you should know, getting the cams and buckets out of a VQ engine is a major task which will trace your disassembly all the way down to the lower oil pan. It's a set-and-forget task.

 

^This.

Luckily and fortunately Nissan almost completely engineered out the need for valve adjustment while retaining a completely solid valve train. Unless something goes terrible wrong once you set your clearances once you never have to touch it again.

 

Instead of a full blown dry sump setup, running an Accusump setup is a lot more affordable. They spray extra oil into the motor when the oil pressure goes low during hard cornering and recover it when the oil pressure goes back to normal. Race cars on a budget use them and they are even showing up on some street driven cars at HPDE and time attacks. I've contemplated getting one but I have only seen the oil light flicker on once on a hard right turn when I was down a quart. With the external cooler and extra oil it hasn't been a problem since.

I would get a swirl pot as well for the coolant to prevent any cavitation with the new water cooling setup.

 

When you get new high lift cams do they provide shims or some way to compensate for the different cam?

I have used Accusumps before and I agree this would be a welcome addition. I would also add a box around the oil pickup with swinging doors to help trap oil around the pickup in corners. old racer trick from the 70's.

The swirl pot is a new one on me. If your system is burped and sealed how can cavitation occur? I will also probably have to change the pulleys since this thing will be living between 6000 and 8500 RPM.

 

When you get new cams they do not provide new shims and/or buckets, you have to check the clearances do the math on the lifters that are in the car then order new ones and recheck clearances until its spot on, math formulas and calculators are involved. Its tedious and annoying some of us install cams and and as long as they are close we are fine lmao but street car vs race car different tolerances so just go through it. Those lifters are about $20 a piece and they are 24 of them so my suggestion just let a machine shop take care of that part of the cam install i dunno if you were planning on building this motor yourself.

It would be nice if the still made shims for the VQ30s lifters but they dont as its a 2 piece lifter cam bucket and the shim ontop so you just replace the shim but on the later VQs they made the lifters 1 piece so you just replace the whole thing.

 

I drive the car to track events so I have an overkill setup for oil and cooling. After upgrading to a Griffin radiator I haven't had any cooling or cavitation problems that I am aware of, but I am running a near stock coolant setup on a low power N/A VQ30DEK swap. Higher sustained RPMs and having the radiator up front and engine out back might be a cause for concern.