long stroke 8v with 288 cam in a 40/35 shed head. hopefully with more to come. im surprised on open induction it doesnt rev better, im not going to comment on why is doesnt rev, but i hope to see something like 145 - 150bhp ish without sacrificing any torque with more work on the mapping and when i find the sweet spot for the cam.
diesel cranked AGG, everything lightened, the CR is just short of 10.9:1 (so a good opportunity for development later on) mr shed 40/35 PB head, with 288 schrick, 4 branch and 2 inch system, with ported TB and inlet manifold on megasquirt. from what i hearing expect the xflow to make more on a similar spec...
Seems like a good build. I'm surprised at the low power figure EDIT: Sorry PB Head? i thought this was the crossflow thread!
^^I think that engine will probably make more power as it loosens up.^^ It was only about a 20k miler to start with, wasn't it? As for 8v engines and power figures, I wouldn't worry too much about peak power. A driveable 160-170bhp would be very rapid in a Mk1 golf, Scirocco, or a lightweight Mk2, subject to the right transmission, suspension and tyres. The more you push towards 200bhp, the more you spend for every additional bhp, so in fact you're better spending the money elsewhere. Down in the mid 100s, you might get 10bhp for 200 from a new cam, or 500, from a new engine management setup, but as you get higher up, you'll be spending a few grand on throttle bodies, lairy cams, lighteweight valves, titanium valvegear, forged pistons, stronger rods, all so you can rev it harder and blow it up all the quicker. Based on years of watching, organising and competing in club level motorsport, I'd say that most of the guys who go out and spend a fortune on an engine, aren't good enough drivers to get the most out of it, and waste a lot of time fishing for the right gear, or 'off cam' labouring in the wrong gear. Far better to have something driveable, reliable, and spend some money on a decent gearbox/diff combo. Incidentally, that Ferrari 308 head looks a lot like the old Alfa twin cam head, btw, which Alfa first started making in the 1920s, and which evolved through generations of Spiders, GTVs and Giuliettas up until the Twin Spark 2.0 8v cars of the early 1990s (148 bhp from a 2.0 8v out of the factory, with 100k++ longevity, and potential for a lot more power).
There is another point in gong crossflow too. Weight reduction. 10kg lighter cylinder head assembly when compared to the 16v head, and that is not counting the plenum either.
The std crossflow is a backward step on size... dropping from the std GTi size of 40mm to 39.5. The std GTi seat will take a 40.5mm valve, so the crossflow should take a .5mm increase too to make it 40mm, though if we're lucky, it maybe the same insert and take the full 40.5, which would be a bonus!... I'll measure up soon.
I think you may find that the std exhaust valve seat will not take a bigger valve than std without big mods.
No chance getting a 42mm valve on a std seat... I've seen 41mm valves bodged on to std seats by cutting deep, but it's not the way to do it. I've toyed with the idea if fitting a 43mm valve in an 8v head, I'll mock one up at some point. You would'nt need a 36mm exhaust, a 35 would do, and should just fit. I use 41.91 & 35.56 valves together (1.65 & 1.4, hence the odd metric size), and they fit ok.
42's work ok Sam, I know it's been said it's pointless due to the chamber wall, but most flow happens on the long side, which has plenty of room to flow out into the chamber. They are normally fitted to bigger bore engines in fairness, so the chamber wall can be cut back a little.
Is that with new bigger valve seats mr H? I've been to see the machinist I use and he doesn't seem to think that the std exhaust valve seat will fit a bigger valve than the 33mm valve that is in there std. Mind you that's just from looking with the valve still in place, maybe a diffrerent case if the valve wasn't still in the head. It may be more obvious that a bigger valve will fit once the head is dismantled.
Hi Interesting.... Massive material removal in a head and std valves dont normally go hand in hand... these heads (crossflow) dont appear to need a lot of work to get good flow, just basic porting work on the std valve is (so far) producing good results... tho it wont make 200hp on them, so I'd imagine the owners request was misunderstood. All the big power 8v's I've done to date or been involved with rev way past 6k without any trouble. The 1800's make peak power at 7.5k and hold on to 8k well, and can rev past that freely... the 2ltr's tend to hit peak power around high 6's, and rev on to 8 without probs. If a std bottom end is being used, I'm guessing std pistons too? If that's the case, the sensible max on c.r would be 11:1, maybe a touch more (I've run 11.25 on std pistons without probs), anyone who's built a lot of 8v's would know that and should have specced the cam to suit... around a 280 duration... so peak power on a 2ltr with that spec is going to be around 6k, but it should run to 6-1/2 without trouble, but power will be dropping a good bit then. Madasafish summed it up... More cam needs more c.r... over the above c.r and forged pistons will be needed for sustained high rpm use... tell me where your man wants peak power, or what he would like to rev too as a max (peak power would be a little below to max used rpm) and I'll throw a few ideas at you. More cam and rpm then needs a valve train to cope... big cams with rapid valve acceleration need decent springs, which in turn need the right caps to fit and work, which, can lead to collet issues, which, can depend on the valve/stem size/type used... a reason some stick to std valves (or available oversize's) because of the grief involved.... change one thing and a lot of other bits need changing too, subject to what your trying to use with what bits. Did you say it made 150 at the flywheel?.... thought the article said 160? What power at the wheels is it showing? And, where is peak torque happening?
Thanks, remain interested in whether other oe valves may make suitable 42 in - 35 ex substitutions, likewise valve train components
What has the cam been timed up to? If your unsure, get the engine to a true tdc, set up a dial gauge on the inlet cam bucket, turn the engine back until the cam stops lifting and note the reading. Go back to true tdc again, swap the dial gauge over and turn the engine forward and measure the exhaust lift. You need to see the same lift at tdc as a minimum, then increase the inlet lift to 10 thou more.... peak power and the best power spread wont be a million miles off that setting.
Every chance Sam... in all honesty I hav'nt look at the exhaust side much, it's largely just there for the ride. I did start investigating a slightly bigger exhaust valve to fit the std seat, but only got to the enquiry stage. One off's or small batches can be had, but at a price.
