BDC

Just two days ago, I had the pleasure of attending an all-day long dyno session. A few of us and friends rented a local shop's Dynotech dyno for a day. One of the cars in question was an '88 model with a recently rebuilt series 4 block that I half-bridgeported rather aggressively. We went into the dyno and tuning session knowing that we could blow the car up but didn't care (one of those kinds of deals; not a customer type) so we didn't have any quams about running large amounts of boost and the like.



Tuning around high 10's:1 at 13-14psi, we wound up making well into the 430's and we believe into the 440's/450's but the dyno had a problem from overheating due to constant, long-term use (according to the guys who own it at the shop). We managed to get a 413hp run, then one that was jagged in the 430's, 440's, then the graphs came out looking like a 2-year old with a blue crayon in-hand.



The combination here was a modified T66 that uses a larger than Turbonetics P/Q-trim turbine housing, a series 4 block that was half-bridgeported fairly aggressively as I mentioned before, series 4 gears, replacement stock rotor and main bearings, your typical rebuild parts (new o-rings, oil control ring o-rings and springs, 2mm 2-piece apex seals and springs, and FD corner seal springs underneath solid corner seals). What is interesting to me is that this block is older than dirt itself (16 years thereabouts), yet seems to have no problem making loads of horsepower well into the early 8000rpm range without any rotor clearancing, additional dowel pins, or anything else. I tuned the engine to run fairly conservative leading advance and trail-split timing as well as run conservatively-rich mixtures well within the 10's:1 air-to-fuel ratios.



Here's the kicker: According to many, this engine, much like some of the other noteworthy, high-performing series 4 blocks out there in rotary history, is supposed to jettison itself into space far earlier than this power range. The thing I'd like to know is just where do people stand when it comes to this issue, and more importantly, _why_ they do. From my vantage point, it seems to me that we're barely scratching the surface of the power these engines can make, even the older series 4 blocks, if we can prevent them from knocking hard in the first place. In contrast, the series 5 and especially series 6 13BREW and 13B-RE blocks have considerable strengthening advantages over these older blocks (such as thicker iron casting around the rear iron tubular dowel pin land).



Does anybody have anything to say about this or am I off my rocker in thinking that an older block like this can push 500 to the wheels and still happily drive home and idle well afterwards?



B

IGY

I'm with you on this. The only thing that I have seen fail on S4 block is the cracked rear plate around the dowel pin near the oil filter. I have seen this happen on motors making as little as 330rwhp(2 weeks ago was the most recent), but I have also seen S4 blocks that were reinforced with welding in that area go over 500 and not break. When are extra dowels really necessary, or are they at all? Is this something that came about because the older motors were prone to cracking plates and it just carried over to the newer motors? Oh well, I guess I'll just keep doing what I'm doing until I break something.

93 R1

Was this 87GTR's car by any chance?

BDC

Nope. It was our buddy Hassan. He's an ESP Solo Auto-X guy normally but he also got the itch for rotary so I built him a motor he could blow up.

BDC

I've seen one motor, that was a series 4 block, that had three cracks about 60 degrees apart on the rear iron tubular dowel pin casting near the oil filter stand. I'm not sure why this is the same place that keeps coming up but there's definitely something going on. The front doesn't crack there yet it's cast nearly the same. It might have something to do with an odd combination of heat and other related factors that eventually lead to it.



In any event, that particular setup was knock related. Running an aftermarket EFI system, the trigger leads to the ECU weren't connected well and one of them was intermittently grounding itself to the engine, causing spikes in ECU RPM reading (16000rpm). A few good knocks that rattled the car and boom -> oil leak #1. The same thing kept happening and happened two more (major) times until a third crack surfaced that wound up taking a large chunk of the iron out, causing a fatal oil leak (5qts in less than 45 seconds of running time drained out). This was done at barely 330rwhp levels; nothing to write home about.



The last engine I ran was a series 4 block as well. I never one time knocked the engine, made over 420hp to the drive wheels, ran fairly high RPM's (up to 8200rpm), and mine never cracked. I beat that thing to death and it never once showed any problems even though it was, then, a very old and used block.



All of the so-called "experts" (tongue-in-cheek) all say to pin the engine but I'm beginning to believe it's more of a bandaid to keeping the housings together than anything else. Here's why: does anybody here happen to have comparison figures for standard combustion chamber pressures on a normal working engine, say boosted with twice the atmospheric pressure, vs. combustion pressure spikes due to severe knock (auto-ignition of too low octane fuel, too hot spark plug, too advanced leading or trail-split spark timing, too high charge temperatures, etc.)? I bet they're leaps and bounds different and I think the problem is a result of engines that are severly knocking, undergoing very large "spikes" of pressures exceeding 10,000's of psi that are perhaps pushing the housings apart and exerting tons of force in that general area. This would come from having the setup untuned and not configured right in the first place. If you look, the area that people commonly pin on these older blocks is always from about ~75BTDC to ~10ATDC in that range beginning from mid-way through the compression stroke all the way just past the point of ignition. The 13BREW blocks don't have this problem because they've got nearly twice the 'meat' of iron around that rear dowel pin casting, therefore the likelihood of them cracking is probably considerably less.



Here's the strikes the older S4 turbo blocks have against them:



- Uneven-lengthed secondary intake port runners on stock lower manifold

- Rear secondary fuel injector last in fuel injection/rail sequence prior to FPR

- EGR passage through rear iron housing



I think this is all a tuning issue. If the charge is kept cold enough, if the fuel octane type is slow-burning enough, if the chambers are kept awash in water or fuel enough, and if the tuning is done right, then I think these older blocks are plenty strong and can produce phenomenal power levels without cracking anything.



B

Travis R

I agree with your logic. A good knock will rock the engine's world. I'll email an engineering friend of mine to get some numbers.

BDC

Thanks, Travis. I'd like to see some numbers on this. I've been told that there's a vast difference between normal, "sine-wave" type combustion pressures that rise and fall due to load and varying RPM's vs. those of substantial engine knock. Even though I've seen no numbers or SAE papers or anything on it, I'd like to know what the real differences are. Those numbers may also clue in on the potential of the engine under real, heavy loads and just what they're capable of.



B

j9fd3s

yah there is, i dunno where to get a graph though.



i think the engine breaking the rear dowel has something to do with the location of the engine mounts, notice every time they increase the power they move the mounts further back?



mike

BDC

yah there is, i dunno where to get a graph though.



i think the engine breaking the rear dowel has something to do with the location of the engine mounts, notice every time they increase the power they move the mounts further back?



mike [/quote]

I'm not sure why they do that.



B

j9fd3s

ah ok, so you know how fc's always have 1 borken engine mount? and its always the same one? i think when you drop the clutch it tries to twist the motor, too much twist = broken rear plate.



mike