A 7.0 liter 928? That would be pretty nice. We would need more stroke, and maybe like a 108 or so bore?

 

7.0 should be possible with a 106mm bore and a longer stroker crank.......Its getting the block happy and keeping it happy at 106mm I am focused on figuring out right now. Ive been told the 85-6 blocks have thicker walls and could take the 106mm bore if sleeved. But then i have heard of failures at 104mm. I don't like breaking things, especially engines so I am trying to figure out how to over engineer the block to deal with being turned into a 7.0. The Corvette uses 104.8mm bore, and a 101.6mm stroke. I wasn't sure we could fit that much stroke in these blocks so I figured I had to get as much bore as possible, and the most anyone would even talk to me about was 106mm.

The Corvette engine still has pushrods and not over head cams which gives the Porsche a potential advantage, and then there is the 32v vs 16v setup which should further tip the balance our way. I havent really started to work on how to squeeze roller cam lifters into our heads but Im thinking about it.....


LS7 at a Glance

Engine type cam-in-block 90-degree V-8

Block configuration cast aluminum with pressed-in cylinder sleeves and 6-bolt, forged steel main bearing caps

Bore x Stroke (mm / in) 104.8 x 101.6 /4.125 x 4.00

Displacement (L / cu in) 7.0 / 427

Crankshaft forged steel

Connecting rods forged titanium

Pistons cast aluminum

Compression ratio 11.0:1

Cylinder heads CNC-ported aluminum; 70-cc chamber volume

Valve size, intake (mm / in) 56 / 2.20 (titanium)

Valve size, exhaust (mm / in) 41 / 1.61 (sodium-filled)

Camshaft hydraulic roller; 15 mm (.591 in) lift (intake and exhaust)

Rocker arms 1.8:1; offset (intake only)

Air intake composite manifold with 90 mm single-bore throttle body

Fuel Premium required. 91 octane minimum

Horsepower 500 (373 kW) @ 6200 rpm

Torque (lb-ft) 475 (644 Nm) @ 4800 rpm

Engine redline (rpm) 7000

 

EB338 it is a question of who copied whom..... the 1963 Pontiac Lemans was a GM production car with a 5.43 V-8 engine with independent rear suspension and REAR transaxle . The sleeveless aluminum Alusil block was featured on the Chevy Vega long before the 928 . The idea of using 1/2 of a V-8 engine ala 928-944 was early 1960s Pontiac Tempest. Four valves per cylinder double overhead cams 1920s. Although the Cosworth Vega was pretty hot in it's time! Aluminum body panels have been used off and on since cars no longer used fabric bodies. In short ,there is almost no single thing about the 928 design that can be considered "new", creative, technologically advanced or superior to what came before it . ( 911 excluded ) . Yet the integration of all this old technology and design, results in a car which works quite well and makes me smile. I am quite content driving the old very brown 1980 with a certifiable dyno run of 194.5 HP ! Even "racing" timetrialing is quite fun because getting the most out of what you have is a challenge at any level and no matter what you do there will ALWAYS be someone with more power more money more talent (you have to at least consider that) who is going to be faster anyway !

 

All very true, but do we really consider the 63 LeMans a GT car?

To put the specific collection of technologies together to build a truly superior GT car was certainly the 928's long before the Corvette caught up. Im not saying the 928 was first, but it was well ahead of the Corvette taking on its 928like arrangement. And in today's market the corvette is really the closest thing to a new 928 so it tends to be where the comparison comes in. Then there is a little bit of the small block chevy powered 928 thing leading me to a bit of a "beat the vette with the Porsche, not with another vette in Porsches clothing" mentality.

I wasn't trying to pick a fight or start a debate with that post or this one, just trying to explain my motives for building a 7.0 street 928 and keeping the Porsche powerplant.

 

I hear ya, it's why I kept my block too but a 7L 928 sounds like a hoot!! IIRC, somebody did that a number of years ago w/custom sleeves - but I'm not too sure how long it lasted/what it really took or if it was worth doing again.... I suspect it wasn't...

it's fairly easy to get 6.4L w/out going too gonzo, but beyond the 104.5mm and 3.75" "standards" seems like a whole nuther ballgame... if we use a longer stroke, the bores really get in the way, juggling rod angles, compression and piston spec's gets ugly, and it's not going to help our windage issues either... and if we go bigger around it looks like some serious sleeve engineering will be in order...

just for a reference point - using a 5.85" rod, my rod angle was pretty aggressive (not as bad as the 5.7" stuff though), but it was a bugger to get the compression just to 11.3:1, even w/custom slugs using a .043" head gasket....the "dish" ended up taking out material in the "quench" area... runs fine, but I was also pretty much at the limits for ring land spacing to the piston top and pin placement if I wanted it to last for a while, according to JE.... greg grey has been around the block on this one a time or two, IIRC....

a 6" rod would probably be needed w/the even longer stroke?, and there's just no room for it all w/out mongo head gaskets or making a bigger chamber somehow, unless you plan on burning methonal...

re-engineering bores, heads or crank placement just makes my head hurt, although I suppose a dry sump could solve the windage issue/maybe scrapers too?? sterlings custom block thing w/nice fat 108mm slugs sounds like the magic cookie to me.... keep the external dimensions and yeehaa...

been lots of cool threads on this one, but I suspect our block limits play a major role w/the motivation for a low comp design w/FI on the 928, as FI does open up major HP potential w/a minimum of re-engineering (murphy/ brendan are well down that track, IIRC)....

should be interesting to see what happens w/the drive train at over 600rwhp though... IIRC, mark A's beast is pushing clutches pretty hard at only 517rwhp or so w/decent slicks - but it is a total hoot to watch on the track eating up those 911 guys... in fact, it's always a kick watching a 928 munching on 6 figure exotics - so you gearhead meisters better plan on in car cameras!!!

 

Alas, Murphy is the one driving the 928s and building killer CS kits for many people, and I'm the idiot TALKING about it and constantly changing the end game and never scoring.

But thats soon to change.

 

If we can get to 106mm bore we should only need about 3.89in or 99mm of stroke to get to 7.0L so we are only talking about an additional 3.55mm or .14in of stroke (beyond the 3.75). I would fully expect to have some clearancing work to do but it should be possible, shouldn't it? How difficult was it to fit the 3.75 in there?

Sterling, I assume you are using a 3.75 with a 104mm bore? What rod length did you end up using? What piston size? Also I am curious why you only put 1 in of block filler in if we have almost 3 extra in of water jacket? Do you think it could be filled further? About how much water jacket do you think you have now after the filler and the deck plate? How thick was the deck plate material you installed? How much material did you end up removing from the original deck height by the time you got everything leveled up? I am not in any way nit-picking or criticizing, I genuinely want to know. I think I will have to do at least what you have done to get 106mm bores to work. I think the engine work you did is very impressive. Why did you opt to sleeve it? Isn't it possible to do 104mm without sleeves? Did you use torque plates when boring? I would imagine they would have a larger impact on your engine with the solid deck plate in there. Is that balancer a Fluidampr? TCI? How much work had to go into making it fit?

 

For me there are two important reasons. Local legistlation do not allow engine change very easily. For '92 model year cars it's virtually impossible. Also starting from '92 SC, turbo etc. is not allowed at all. For '88 to '91 models installation reguires $1500 rolling road emission test. And then there is mailing costs, customs fee and VAT on top of $5k+ SC kit price. End result is $7k minimun for basic SC kit. In stroker option most of these limitations are much smaller. It's not visible to the outside and some parts are easier to get from inside EU. This meaning smaller mailing costs, no customs and usually smaller VAT (between 15-25% in different countries, 22% in Finland) in most other EU countries. More important reason though is that stroker is what I want.

 

Sterling, have you had any problems with block filler or deck plates other than pain of having to do them? I'm little worried about using them but would like to add them just for some extra strenght.

 

Sterling:

Do you regret having done it, or just don't feel it was necessary since you didn't boost the engine? Have you seen any adverse wear or cooling characteristics from the work performed? Have you had it apart at all since it has had some miles on it to see how the deck plates and particularly its welds are holding up? Did you end up using torque plates when boring it? What if anything did you do to prevent cylinder bore distortion from the heat of the welding process when installing the deck plate? I am trying to over build the engine to prevent failure or premature wear in addition to attempting to bore to 106mm so I am very interested in the work you performed. I am still concerned about the remaining bore area between the deck plate and the grout when going to 106. I have not settled for sure on whether to boost or not to boost so I also want to build the engine to leave that option open. I don't see any real way to go to 106 without sleeving unless I can somehow reinforce the bores from the outside with some sort of sleeve or the addition of material. But then the sleeve becomes the wear point rather than the block itself which might make the engine rebuildable later rather than a throw away because I wouldn't have any material left.

How much clearancing did you have to do to fit the crank in the bottom end? Who's crank did you use and how limited were your connecting rod choices? There has been some talk about stroker cranks made with small block chevy size rod journals which would open up a huge world of rod choices which might ease clearance issues, length and design choices and certainly rod cost. I have had a lot of very good experience with Fluitdampr units on all types of engines and was hopeful to fit one to the Porsche on its merits alone. I would much rather keep the balance internal.

 

Why? You will then be building an engine that isn't the best it could be.
Decide on SC or NA and then move forward.

 

I fully intend to decide before I build the complete motor and make compression and cam choices among other things, but I want to build a bottom end that could comfortably handle the engine being built either way. Like I said earlier, I want to over build the bottom end of this engine as much as possible, I hate breaking things especially if there was anything I could have done to prevent it, short of never starting the engine at all of course

 

hey b - I'm sure you'll "git'er done".... you've gone way too far not to....

gotta admit, it does the ego good comparing a new vette to an "old" shark and not being that far off, almost makes up for the repair bills, ha!

EB338 - cool vette specs!! what was the rod length?? my chamber vol measured at 38.1cc for 11.3:1CR vs the 70cc the vett needed to get a 7L down to 11.1:1CR... might want to ck those compression calcs for your 928 stroked FI motor if you're expecting a low comp stroker... here's a calculator that I used - http://kb-silvolite.com/index2.php to explore the implications of stroke/bore/etc vs compression.... to get you started:

gt heads cc at about 38.1cc w/the 968 valves installed,
custom pistons maxed out at 28.5cc,
0 deck ht, head gasket about 8.5cc/.043" same size as bore (4.094"/104mm),
5.85" rod

watch out for cc vs cu and deck clearance - they mix them around in there a bit....

(OEM is 5.905" rod and 3.106" stroke, piston vol/head depends on MY, CH is about 1.217"), IIRC... should give you a starting point for a "typical" 6.4L stroker NA motor w/comparisons to OEM 5.0L specs... the calculator also does dynamic compression (I used 50deg closing), but IIRC, even dynamic compression has to be under about 9.6:1 or so to use street gas....

IIRC, the bottom end influences the ultimate comp quite a bit, so you might want to mess around w/some models 1st to get a feel for what we're dealing with on our U boats...

forgot about the pan thing, might want to ck the crossmember clearance too if you do a custom pan, it's all pretty snug in there... I had to clearance my block for rod bolts also, but I used 2.1" ends and 7/16" bolts too... IIRC, olivers and pauters don't need clearancing, but my builder likes carillo and that's one guy I didn't want to **** off/about same price anyway... if you use an 85 block w/later MY intake stuff, you'll need to grind off the throttle body mounts... depending on ECU choices, you might have to mess w/the flywheel pickups, bell housing and starter mounts too... fun, fun, fun

not sure if I'd contemplate a smaller rod end w/massive power, but I'm not a pro so there's lots of stuff I'm superstitious/totally ignorant about.... hope this helps.... bout time for that drinking thread or girls w/great butts, isn't it??? sorry EB - you need to sign up as a member for the good stuff...hehehe...

 

Sterling:


I have been through your website several times, very nice site by the way, which has led me to my questions for you. Sorry if I overlooked my answers there and am asking redundant questions. I was very impressed by the work you have done and you are the only one I have found who has seriously addressed block reinforcement so you are the only person I know to ask. I really like your exhaust setup, I don't think I have seen another true dual exhaust system on a 928 and everyone I talk to about doing on tells me its a waste and will make less horsepower than a big single. What mufflers did you use? I assume you had the entire thing custom fabricated? Why didn't you go with headers? (or did you and I misread the site?)


928SS:


The vette specs were all I found on the site I got them from. I havent gone looking much farther since I knew trying to mimic it too closely and squeeze it into the 928 block would be a nightmare enough to stop any fearless builder. I havent gotten too far into pistons, rrods and compression yet, still trying to decide if I can really get 7.0L and keep it reliable then fill in the blanks rather than go all out and get the whole thing worked out and find out I cant get the block to do it. I actually initially intended to do all this with EuroS 16v heads and I am just getting into whether or not I can make those heads breathe enough to feed this 427 (oops i mean 7.0L... cant let anyone know Im and American car builder too

I will definately look into the calculator you sent. I still haven't figured out for certain what all the differences in the blocks are, but I keep coming back to the 85-6 supposedly having thicker cylinder walls, and that is something I do want!

So what all am I missing not being a "member" now???

 

well, right now I'm looking at a hottie wearing nothing but duct tape, and we are discussing other uses for the duct tape... it's in the OT forums - for rennlist members only.... it's just one of those things you need to belly up the bar and pay your rennlist dues -if you want to fully appreciate all the innovative automotive engineering accomplishments that rennlist has to offer...

love to help out more, but this duct tape thing really has generated a lot of ideas for "maintaining" our sharks