Bullet Ride's 2.8L Stroker Project (Updated: Dyno Plot pg. 6)

[blasphemy101]

A 24v swap would obviously yield better performance/$ but there's not really anything for me to learn from doing a 24v swap because it's already a well documented process. My goal with this project was just to learn about building a motor because it's something I had never done before. I happened to already have an M20 sitting around collecting dust so that's what I decided to use for the base of my build, but at the same time I didn't want to spend the money to rebuild a motor and end up with stock B25 performance so I opted for the 2.8L stroker route.

That makes perfect sense. I was just curious about your motivation.

At some point, I would like to do something similar. Did you end up spending much more than you expected on this build?

[Cinnabar325is]

This seems like a really nice build for an M20. Does this make more power (peak or under the curve) versus an M52B28? It just seems like a lot of work for +45-50whp - not that I don't appreciate the build, because it's great!

Just wanted to throw in a few reasons that I also built a 2.8 M20 as opposed to going 24v.

-originality
-a dressed up M20 is a whole bunch cooler looking than an M52
-M20s sound better than 24v motors (not that 24v's sound bad)

Those reasons may not be a big deal and for most people, not enough to justify the cost vs. hp increase, but it was enough for me.

[Bullet Ride]

It ended up costing more or less what I thought it would. However as you can see I did the majority of the work myself. If you were to pay a shop to build this motor for you, you'd probably be better off just buying a metric mechanic crate engine.

[nando]

This seems like a really nice build for an M20. Does this make more power (peak or under the curve) versus an M52B28? It just seems like a lot of work for +45-50whp - not that I don't appreciate the build, because it's great!

yes. but an M52B28 is probably going to have 100,000+ miles on it, and if you just did a proper stock rebuild, would cost a significant sum. if you wanted to do an apples to apples comparison, then you'd have to rebuild the M52 to "brand new" as well, and the cost difference would be minimized significantly.

also, the M52 would still be stock and not have a standalone ECU that you can dyno tune.

[Bullet Ride]

I went to a dyno day today held by a group of local BMW enthusiasts. I decided to put my stroker on the rollers again just to see what it'd put down on a different dyno. It's worth mentioning that earlier this year I had the timing belt off to do some work on the front of the motor and when I put it back on I retarded the cam timing by 4 degrees because based on my dyno results last year I felt as though it was a bit too advanced.

In order to get a scale of the numbers, there were a couple E46 M3s on the dyno today running in the 285whp range and a couple E39 M5s running in the 315whp range...

First run I ran the timing map I've been running all along, second run I tried adding some timing, third run I tried pulling some timing. Seems as though the timing map I had from the get go was pretty good.



For reference here is last years dyno plot again...



To get a sense of comparison between the shape of the power and torque curves with the advanced and retarded timing I plotted values from both graphs...



The magnitude of the numbers isn't really relevant since they are from two different dynos, but the shape is telling. The horsepower climbs better on the top end and doesn't drop off as drastically, the torque peak is shifted forward, the overall shape of the torque curve is a bit better and it also doesn't drop off as drastically on the top end.

I'm speculating that if I was on the same dyno that I ran on last year, the numbers would look more like this....



But that's just me doing some wishful speculating

[redlightpete]

Does the result of the cam timing change feel like your 'wishful speculating'? You'd think that you'd have noticed if the torque had dropped off as much between 3k and 5.5k as the dyno comparison shows. I'm interested because I'm putting together the same cam and motor setup and was just going to use a stock cam gear.

[Bullet Ride]

Does the result of the cam timing change feel like your 'wishful speculating'? You'd think that you'd have noticed if the torque had dropped off as much between 3k and 5.5k as the dyno comparison shows. I'm interested because I'm putting together the same cam and motor setup and was just going to use a stock cam gear.

Confusion is definitely coming from the fact that two different machines were used. The guys at the shop do call it "the heartbrake dyno" because cars usually see lower numbers on it than they'll see on other dynos. I can say that the car definitely doesn't feel like it's noticeably missing any torque compared to when the cam was advanced, and last year above 5500rpm the car really felt like it was falling flat, which it shouldn't be with a 284 cam. I've got nice square HP & TQ numbers now which is what I was expecting out of this set-up.

You definitely should install an adjustable cam gear if you're going to put in an aftermarket cam and/or having your head and block machined. As you can see from my results it's important be able to dial things in.

[go3go]

Just read through the thread. Amazing build and the car sounds mean! I'm hoping to do something along the same lines next year when I graduate, and will definitely be referring back to this. Thanks for the documentation!

[digger]

Confusion is definitely coming from the fact that two different machines were used. The guys at the shop do call it "the heartbrake dyno" because cars usually see lower numbers on it than they'll see on other dynos. I can say that the car definitely doesn't feel like it's noticeably missing any torque compared to when the cam was advanced, and last year above 5500rpm the car really felt like it was falling flat, which it shouldn't be with a 284 cam. I've got nice square HP & TQ numbers now which is what I was expecting out of this set-up.

You definitely should install an adjustable cam gear if you're going to put in an aftermarket cam and/or having your head and block machined. As you can see from my results it's important be able to dial things in.

guys who run these sort places always say that....dont even worry about comparing the two graphs and reading too much into it.

i have done shitloads of dyno tests, air filters/boxes, x-pipes, exhaust back pressure, port matched intake manifold, camshaft and timing, exhausts. seat of the pants doesnt work in 90% of cases....... lots of times i though something was better but it wasnt and vice versa.

one thing for sure is small cam + big engine does not peak at high rpm unless something is mismatched terribly

[Bullet Ride]

one thing for sure is small cam + big engine does not peak at high rpm unless something is mismatched terribly

No, but if the cam is timed correctly shouldn't I expect the overall shape of the curves to be similar to a stock M20?

Here's a comparison between my latest dyno and a bunch of SpecE30 cars, the shape is very similar...



There will be some proper dyno play coming this summer. I'm looking at converting my car over to a wasted spark set-up so I can keep the cap and rotor off the motor, that'll make it much easier to play with the cam gear when on the dyno.

[tinkwithanr]

Nice graphs.

Any reason your planning for wasted spark as opposed to individual coil packs?

[Bullet Ride]

Unfortunately the DIYPNP only has 4 ignition outputs, so even with individual coil packs I'd have to run wasted spark. I'm probably going to use a coil pack off of a GM 3800 because they are a dime a dozen at the scrappers and upgraded coils are easy to come by.

[digger]

No, but if the cam is timed correctly shouldn't I expect the overall shape of the curves to be similar to a stock M20?

Here's a comparison between my latest dyno and a bunch of SpecE30 cars, the shape is very similar...



There will be some proper dyno play coming this summer. I'm looking at converting my car over to a wasted spark set-up so I can keep the cap and rotor off the motor, that'll make it much easier to play with the cam gear when on the dyno.

IMO the car comes on cam much more steeply which suggest non idea timing events (later inlet valve closing point), i would not necessarily expect it to be like stock, the exhaust lobe is only a 272 and you are 12% more engine size with no headwork? the exhaust side cant evacuate the exhaust gas and you end up with residual exhaust gas in the cyl preventing some inlet charge coming in as rpm rise and then the small duration creates higher pumping losses and hp starts to fall.

if you ran a 284/284 then it would be peak higher. that much split on the cam doesn't make much sense on the M20 the exhaust flow is not very good as it is so it is bandaiding something. on mine it bandaids having lack of P to V on the exhaust side with MM pistons....

alternatively more CR with retarded cam helps

play around on the dyno and try, look to improve the average power of the curve don't look at peak so much

[Bullet Ride]

IMO the car comes on cam much more steeply which suggest non idea timing events (later inlet valve closing point), i would not necessarily expect it to be like stock, the exhaust lobe is only a 272 and you are 12% more engine size with no headwork?

But you can see that the slope of the torque curve as it ramps up is essentially the same between when it was advanced and now when it's been retarded. My torque does come on a bit steeper, but the scale of the y-axis makes it look a bit steeper than it actually is when compared to the plot below with a y-axis that starts at 0.

The exhaust ports have been gasket matched and smoothed out a bit, that's the only head work I did...

[digger]

But you can see that the slope of the torque curve as it ramps up is essentially the same between when it was advanced and now when it's been retarded. My torque does come on a bit steeper, but the scale of the y-axis makes it look a bit steeper than it actually is when compared to the plot below with a y-axis that starts at 0.

The exhaust ports have been gasket matched and smoothed out a bit, that's the only head work I did...

easy way to tell is wait for the next dyno day that will end speculation.