The only experience I have with 3.1 is a car that was in my friends shop about 4 years ago. It was a 76 with fuel injection. I don't know the details of the engine build but the injectors and AFM/throtle body etc. were not stock Z items because they had Bosch markings on them, probably from a BMW. That car pulled so hard through the gears that you'd have sworn he had a V8 in it.

The advantage that a 3.1L has over a 2.8L is simple... 10%.

If the two are built to the same specs, you do the same port work, same induction, all that, you'll see a 10% gain. So the question is how much is that extra say 25 or 30 whp on a pretty aggressively built barely streetable engine worth? If your answer is $2500 or $3000, then the stroker is for you. $100/hp is a little steep for me.

Above and beyond the displacement the stroker has no advantages compared to the 2.8L, and has some disadvantages in rod/stroke ratio. Potential redline is NOT really compromised, as Dan Baldwin has shown in some previous threads. Piston speed goes up something like 50 fps between the 2.8 and the 3.1 at 7000 rpm, but the r/s ratio should mean that the 3.1 would be more detonation prone than the 2.8. Quantitatively how much of a difference does that make, I really don't know. Might be the difference between 93 and 94 octane, couldn't really say, but it is a disadvantage.

The above reply was kind of bugging me, because although im not the master mechanic i would like to be, i do know in the right hands, a 3.1L will gain more than 10%. So...I forwarded this thread to Dave Rebello, who i knew would have a thing or 2 to say on the matter. here is his reply:

Hey Dave,

I was reading thru a Z forum today and came across a bit of a debate I thought you should chime in on....here is a quote from the last post... what are your thought on this???

Lance (me)

From Dave:

If you don't know how to correct the R/S ratio and don't think the bigger bore and proper cam selection will inhance air flow and therefore greatly improve torque and HP then yes there is only a minimal improvement. But the fact is when built properly the longer stroke and bigger bore allows for cylinder head improvements that can't be accomplished on the smaller engine. We see more rear wheel HP with our big engines than a street 2.8 can accomplish at the flywheel. With our long rod 3.2L we are approaching 330 HP & over 300 ft lbs torque (flywheel) with a 7600 RPM redline, (on pump gas). I will let you know when we finish the new package. I remember when the circle track guy's said the same thing about the 327cid vs the 350cid and so on. Further more it should only cost slightly more to build a full blown (3.1 or whatever) than a 2.8 as the engines in question still need all the same parts, pistons, cam, bore, bearings, porting, valve trane, etc. Sounds like you read a one sided article. Why should it cost $3000 more for the bigger engine. The way we build them about the only difference is the cost of the crank. Maybe they put all used parts in their 2.8's? Thanks DReb

Well, OK. Let's break it down as best we can, which admittedly probably isn't going to be very good. In order to accurately break it down you'd need two identical engines with the only variable being displacement to be dynoed on the same dyno on the same day back to back. Not going to happen. But I'll do my best... ;-)

Brian the guy with the ~310 bhp 3.2L Rebello motor figured out his hp by trap speed and figured it at 278whp. When I do the same calculation on my 2.8 that I built in my garage I come up with 239whp. His 3.2 is 12.5% larger than my 2.8. 239 x 1.125 = 268. So if you calculate up then I'm 10 hp off of Rebello's motor size for size. I'm going to say that the extra 10hp comes from Dave Rebello being a better engine builder than me, I'm sure he knows tricks that I don't to free up hp. But, to my credit, I have tuned the carbs quite a bit since then, and I'm now running a higher compression shortblock, so who knows where it is now...

BTW--I'm not sure that I buy the ET hp calculator, and I'm not sure that dynos are much good either since Brian dynoed his car on one dyno and got 225whp after Rebello had dynoed it at 300+ on their engine dyno (http://forums.hybridz.org/showthread.php?t=99611), so this all may be peeing into a headwind. It is really impossible to compare unless you have the same dyno on the same day. But here's how we're attempting to make a comparison:

My car's weight was 2650 with me and a friend in it, trap speed according to an old Gtech was 108. I've been told that the old Gtech doesn't average the last xxx feet, so you need to knock it down 3 mph. So assume a weight of 2650 and a trap speed of 105. Here's the calculator: http://www.4lo.com/calc/dynocalc.htm If you use the trap speed of 108 it comes out to 261 hp, but "corrected" its 239.

Now for Dave's bit:

"If you don't know how to correct the R/S ratio and don't think the bigger bore and proper cam selection will inhance air flow and therefore greatly improve torque and HP then yes there is only a minimal improvement."

Using a LD28 crank and a 240 rod yields a rod ratio of 1.60. Stock L28 is 1.648. So the r/s ratio IS better with a stock L28. If I were smarter and had used L24 rods, I could have had 1.68 r/s ratio. Maybe he's using some custom rod and piston, but to my knowledge he uses the LD28 crank and L24 rod like everyone else.

Cam selection helps both engines, so this is not an advantage for a stroker. I unshrouded the valves and notched the block on my build, so that might take some of the advantage away from the larger bore being further from the valve, but that's a couple hp you're talking about there.

"But the fact is when built properly the longer stroke and bigger bore allows for cylinder head improvements that can't be accomplished on the smaller engine."

Such as??? And how come it doesn't show up on Brian's motor?

"We see more rear wheel HP with our big engines than a street 2.8 can accomplish at the flywheel. With our long rod 3.2L we are approaching 330 HP & over 300 ft lbs torque (flywheel) with a 7600 RPM redline, (on pump gas)."

My garage built engine put out 85.36 hp/liter. That 3.2 Rebello stroker put out 86.88 hp per liter according to the drag racing calculator. So I'd have to disagree with this statement. Looks to me like it's worth 1.5 hp/liter, IF everything else were exactly the same, which again, it admittedly isn't.

"Further more it should only cost slightly more to build a full blown (3.1 or whatever) than a 2.8 as the engines in question still need all the same parts, pistons, cam, bore, bearings, porting, valve trane, etc. Sounds like you read a one sided article. Why should it cost $3000 more for the bigger engine. The way we build them about the only difference is the cost of the crank."

The only difference is the cost of the crank? I was under the impression that you have to do a lot more machine work, sonic test the block to bore to 3.2, probably a good idea on 3.1 too, get ahold of the crank, rods, pistons, etc. Yeah, I did reuse a lot of parts in my build, because I'm poor. I used an L28 block, had everything balanced, cast pistons, E31 head, 280 valves, did all my own porting and polishing, cc'd the heads, deburred the block, notched the block, unshrouded the valves, etc. etc. etc. I spent about $2500 in machine work, did a lot of it myself and got 239whp (according to the calculator).

If I'm wrong on the cost of building a stroker vs building a 2.8, then so be it. If it only costs $250 more to make it a stroker (seems to be about the going rate for the crank) then it's DEFINITELY worth it. 10% increase for $250 is CHEAP. If you're buying a motor from Rebello, and he's only charging $250 more for the stroker that's one thing. But if you're putting it together yourself, maybe that's another. Here's a writeup on strokers I think is pretty useful: http://zhome.com/rnt/3.1HanveyProject.htm

Here's something else for you to read (just to add to your research): http://geocities.com/zgarage2001/z.html

My stroker project...

This just an overview. A lot of thought, machine work and cash went into the finished product. It still sits on the engine stand waiting for the SC nose support and belt tensioner to be fabbed. It will have to wait until the new garage is completed.

LD28 block

V07 crankshaft

L20B rods

JE Pistons

P90A mechanical head

custom Isky cam grind

custom head bolts

custom intake

water/air aftercooler

M62 supercharger

Punched block out .020 to clean bores.

turned crank .010 & balanced

shot peened & balanced rods

lightly dished forged pistons providing 8.3 c/r

bore is 85mm

stroke is 83mm

b/s is 1.024

rod length is 145.9mm

r/s is 1.75

Edited November 21, 201212 yr by ezzzzzzz

Sounds good Mark.......can't wait to see how she runs!