Sean,are you sure the dish volume is only 6cc? That seems kind of small,just the valve reliefs on other pistons are around 6cc. You might want to check those to make sure,usually a small dish is around 10-12cc, I think 16cc would sound more like it? And if they are that would give you a friendly 10.13:1 compression ratio,instead of 11.43:1.
The Scat rods I used were the 7" H-beam FHF rods, using SBB bearing inserts. I don't recall if we had to narrow the big end any or not, it's been awhile. They use a .750" pin which is a bit on the dainty side, but it makes it easy to fit the ring package above the wrist pin. Pistons were very light weight custom Venolia. Wrist pins were very light also, and for their length the rods were light as well with most of the weight at the big end. Here's my take on it though. Good rods can be had pretty cheap. Custom rods, not so much. Given the difference between the cost of high quality take outs and really good new rods, that will pay for the extra cost of custom forged pistons, and then you get to set the pin height and everything else. It makes a lot of sense to put the money into the pistons. That way you do not have to settle for any DCR other than the one you want, the squish height you want, etc, though granted the 350 piston crown may be a bit more of a challenge. On the cam lobe clearance, not all rods will be close and it will vary with the cam used. Seems to me like #6 and 8 were the ones that were close but the 340 and 350 have the lobes spaced differently and the 350 could have a slightly larger base circle. Better check them all. Wet sleeving one of these engines is going to be a whole new ball game. It's been done with the Rover but I do not know how successful it was. Seems like the guy who did it hasn't had a whole lot to say about it lately. That makes me suspect that he had issues that he really doesn't want to talk about. Like maybe something that can't be fixed. The big advantage of the cast monolithic block is that you can thin the webs and make the whole thing lighter because every section adds to the overall rigidity. When you separate the sleeves from the deck and the main web you lose an awful lot of that. It could work but I can't see it being anywhere near as rigid and therefore less reliable. Considering the cost/benefit I wouldn't attempt it. I think head retention would be a big problem. If you look at very many engines designed as wet sleeve, long head studs going down into the main web are a fairly common feature. This may not be possible with the SBB due to the light weight casting, and even if it is, it would be difficult to do. I expect to have my engine running this spring. It's taken longer than I planned but I've made additional improvements along the way. Because of the application and expected usage I expect the engine to be noticeably understressed despite high output potential and built it with a long service life in mind. My only real concern is the small size of the wrist pins. Hopefully the light piston weight will offset that but time will tell. It's all a compromise in the end, and on the plus side it should be able to rev quickly I would think. This engine would not be my first choice for a N/A application but that is not to say they cannot be made to breathe reasonably well. Early on I had pretty good success with a Buick 215 that loved winding to 7 grand using mostly stock internals and no head porting. But that was with a much shorter stroke. I do feel they are very well suited to boosted applications however, especially in street use and particularly with fixed displacement blowers. I have had considerable success with high boost levels combined with the use of natural restrictions to limit top end output in the interest of durability and the SBB lends itself well to such a configuration. The objective is increased boost lower in the speed range to flatten and raise the lower end of the torque curve and increase average power output. From what I've seen the problem you run into in boosting the bottom end is too much boost at redline. So using the natural restrictions of the SBB small cylinder bore and valves to limit top end boost means more boost pressure can be used to achieve the same power levels. Once you do that it also means more boost at lower speeds and the boost begins to build from lower engine speeds. At lower speeds the valves are open longer and there is more time for pressurized air to flow into the cylinders and with higher initial pressure more air gets in. Besides which, the blower pumps better as it's speed goes up so spinning it faster off idle means boost starts to build at a lower engine rpm. All of which jacks the entire bottom end of the torque curve up quite a bit, making the car quick off the mark and extremely responsive in traffic, turning a perceived negative quality into a definite positive. It goes back to working to compliment the engine's natural advantages. It is known to be good at producing torque. As is the positive displacement blower. In tandem the two can be quite exceptional if coupled to maximize the advantages of each. But bear in mind this is specifically targeted at street usage where the vast majority of operation is going to be below 3500 rpm. It runs counter to what would be expected to produce the best results on the race track and is intended to minimize the chances of high rpm damage to the engine. Where all out high rpm horsepower is desired it is probably not the best approach since the more restrictive intake and higher pressure will also produce some heat. In those cases, once again this may not be the best engine choice. When you start out over 3500 rpm and go up from there the game changes considerably. Jim
Hey Jim,yeah,I wouldn't worry about the .750" diameter wrist pins in your build,the FHF guys run forced induction all the time without hurting the wrist pins. Probably not even close to the level of power you'll be running,but why would they(I think they were eagle rods) claim to handle 700 HP if the wrist pins wouldn't be able to handle that? Nascar runs smaller dia. pins all the time without fail,running 8,000+ RPM. I can't wait to hear how that beast runs! :TU: Derek
Everyone take this post with a grain of salt as it not directed at anyone But my take is that, i believe it would be a waste of time to try and sleeve one of these blocks,or reengineer it too much sort to speak If a stock eliminator type build ,which is limited in overbore,NO porting,STOCK LIFT cam,STOCK intake ,etc ,can run mid 11s with the factory sleeve,rod length,stroke ,etc then a good max effort build up involing porting,oversize valves,unlimited inake and carb,etc ,should yield results beyond what the average street/strip 350 would ever do anyways The vehicle itself along with the trans.coverter etc should be the main focus when working with a limited power combo such as this ,instead of trying to throw money at a already limited engine Carry on
Derek, it's the longevity that concerns me the most. I have no reason to think that will be a problem but the bearing area is so much smaller than just about anything except motorcycle pistons. I guess if at some point they start to knock I'll just have to ream them out and upsize a little. Jim
I highly doubt that the .750" pin dia. will cause pre-mature failure. But I asked about them on a FHF forum for you,and as soon as I hear a reply I will let you know what those guys say about it.(it may take a day or so,because I just signed up today) And if the piston holes wear out,then a bronze bushing might be a better way to go,and run the .750" pins again? And as for the bearing surface,isn't smaller supposed to be better for suface speed,and less friction? Do you have pictures of your pistons? If they are designed like a nascar piston with forged side releif design(FSR),then the pins will be shorter,making them even stronger,and less likely to flex.(the shorter they are the harder they will be to bend,because there will be less leverage to bend them) Not to mention that a smaller hole will usually be stronger than a bigger one in the same space,because there willl be more material around the hole making it much more difficult to distort it. Besides,the thrust is on the top of the pin going both ways. The ingnition of the mixture pushes the piston down pushing on the top of the piston's hole where there is the most material to the top of the pin,the pin pushes on the bottom of the rod hole. On a up stroke,the crank pushes the rod up putting pressure again at the bottom of the rod hole to the bottom of the pin and the top of the piston hole from the top of the pin. And with a 1.82:1 rod to stroke ratio the rod doesn't hardly acuate on the pin to cause much friction,or side thrust on the pin or piston.And a 3/8 radius should be enough suface contact for the load to not hammer the holes out of shape,unless they were setup with excessive clearance new.(more than .002") Dam Jim,the more I think about this beast,the more I want to know how good it runs! Derek
I agree 100% on this idea and that is why I brought up the eliminator engines earlier in the thread. Yes there are ways to make these engines better and there is nothing wrong with exploring those options. Some people like to re-engineer things and modify everything and that is interesting for them. Myself I just stuck with stock stroke, stock length but forged rods, and 30 thou Diamond pistons. I only have 355 cubes but I am using boost so my cubes are not as important. You hit the nail on the head with the chassis setup and car setup advice. I know of a guy who was running mid 13s with a bone stock Buick 350 but the trick was in the tuning and chassis setup. Meanwhile we have other 350s that make more power and still run 13s due to less chassis setup.
I guess we could measure the CC but I think 6 is correct. Compare the pics of my other diamonds (13 cc dish) to these ones. Here are the other diamond pistons I have that are stock spec. They weigh 555 grams so the first set above must be even lower boing much shorter. These pistons save about 200 grams per piston compared to stock!!!! 13 cc spherical dish, .300 down to top of first ring land & thick deck for nitrous, ambidextrous deep valve relief's for any cam 58 cc head 030 deck height = 9.49-1 compression 55 cc head .010 deck height = 10.22-1 53 cc head .005 deck height = 10.58 ---------- Post added at 08:01 AM ---------- Previous post was at 07:33 AM ---------- http://smg.photobucket.com/albums/v732/seanbuick76/Guys Skylark/
Sean Something doesn't calculate correctly. A dish that is .300 deep and about 3" in diameter is around 30cc Paul
Hi Paul, I am tired worked 14 hours night shift and up still past my bedtime... The top ring on the piston is 0.300 down from the top of the piston for nitrous use. I am running a 50-80 shot of nitrous on this turbocharged engine because nitrous is a great intercooler. The dish is confirmed to be 13 cc, and on my engine the deck height is not decked down it is just cleaned up and I have 60 thou gaskets to keep the compression in check. :TU:
These are flow restricted engines. This is one reason why they respond to boost/nitrous so well. This also means they will respond favorably to faster lift and closing rates, for the valves, ie. roller cams. Dumping that cast iron lump, called a "cam" and the little .842" flat tappet, is a step in the right direction. Who among you has checked the ramp rates, on their favorite flat tappet ? Rollers are usually in the .008"-.010", per cam degree, at the lobe. Onward, roverman.:3gears:
Not great photos, but not bad. Note, like Sean's pistons these have a thick crown for a supercharged application, and I think we are both very close on the weights of pistons and rods. However, note the thin wall and small size of the wrist pin which is considerably lighter, and the small mass of the rod beam and head. Some weight is picked up with the teflon buttons, used because of the short pin length. Thinner rings are also used. Valve clearance with .500" lift and .042" squish was nearly 1/4". The SBB piston has about 5/8" to work with on the compression height before you even have to worry about getting into the ring package. A shorter compression height also makes for a lighter piston. Jim
Hey Jim,nice parts,yeah thems some LONG rods! Sorry,a couple of pics didn't work,not on my computer anyway,just the top 2,so if there is a pic of the pins,I can't see them. No biggie though I can take your word for it. Thats a lot of valve clearance,whats the deck clearance,and the compression distance you had the pistons made? Here's a link of an example of a FSR(forged side relief) style piston; http://www.ebay.com/itm/4-182-DODGE...pt=Race_Car_Parts&hash=item1e6ab221d7&vxp=mtr I got a couple of replies from some FHF guys,it was interesting to find out that the antique FHF pistons used wrist pin inserts in the pistons. I'll copy and post what was shared,heres the question I left; "Hello Flathead faithful,I have a friend that is using after market Flathead rods and custom pistons in his 340 Buick,and is worrisome about the diameter of the piston pins. The engine has a 671(I think) on it,and is worried about the longevity of the pistons with the small pins in it. My question for you Flathead guys is,has anyone ever experienced any problems with the pin hole in their pistons from excessive wear? Or pin bending on boosted applications? I would think there wouldn't be any problems with them,but I have never used them,so if anyone can let me know for sure,it would be appreciated.Thanks in advance." Heres the response; "I always check the wrist pin bushings for wear and usually replace all of them. A Merc crank, .60 over Flathead is around 273 ci, you are talking about 3 times that displacement....I get lost there, that is engineer work. Experience tells me that compression ratio would be one very important factor, though Flatties have run a long time with 11:1, though those heads are no longer available. Some people have worried about connecting rod strength when supercharging Flatheads, but those rods are plenty tough stock to handle just about anything. Even with the 3/8 X 3/8 engines, nothing special was done to the rods, wrist pins or pistons. Be scientific. Build it and see if it runs." Heres a follow up question; "Thank you for your reply,one question for you,are the wrist pin bushings in the pistons,or are they in the connecting rods that you are referring too?(never seen bushings in the pistons,but I'm not to familiar with antique FHF engines. Thanks in advance." Heres a answer; "The wrist pin bushings are pressed into the piston. New piston almost always come with new bushings. They set in a bit so there is room for the wrist pin retainer and some folks do not even know they are there. Like cleaning the crank holes. It may be with newer materials in the pistons that only the rod bushing is used. Most of what I rebuilt, though not all, was stock for over the road 'races' where only stock can be used. There have been many occasions, such as carb linkage, where a shaft is worn and a bushing is fabricated or prefabricated and inserted. Hope that helps." A Derek
WHY exactly would one want to run a lightweight piston pin on a forced induction,hi cylinder pressure application? Bad things happen when a pin flexes!!!!!!!!!!!
What sort of bad things exactly? To start with, the wrist pins are made from hardened tool steel so they are much more durable than the standard materials. I'm not concerned about flexing of the pin, and if anyone knows a thing or three about pistons for supercharged engines it is Venolia. They made the recommendation. Weren't you the fella that was wanting folks to go out on a limb with unconventional approaches? Something about not doing things the same old way and getting the same old results IIRC. Don't think you can have it both ways. Why you ask? Because a lighter reciprocating assembly is inherently more likely to survive higher rpm operation, and because a lighter reciprocating assembly has less mass to get moving over and over so the engine will wind up quicker. Because a lighter assembly can potentially run more efficiently, and because I just wanted to do it that way. I don't think you understand the design goals with this engine at all. If you did it doesn't seem to me that you would even have to ask. Max power is not the objective here, anything over 300hp is excessive in this chassis anyway (8lbs/hp) and 500 is easily achievable (<5lb/Hp). It's a daily driver so economy is a significant concern. Static compression is 10.6:1 and boost will be much more limited than in the preceeding engine but even so, a large intercooler is equipped. The function of the blower is primarily to enhance and extend the operating range by overcoming the inherent upper rpm limitations of the engine. Most of the time it won't even be used. When it is, it will be worth watching. Jim
You are correct, i suggested people think out side the box But i dont remember asking anyone to do anything that went against the grain,that would cause other issues by doing so Pushrods and wrist pins arent the two places i would ever sacrifice weight for durability But hey,sounds like you have all the answers already Good Luck
Nick One of the problems is if you want to use a 7.00" rod for use with a short CH light weight piston, the only 2 choices are the off the shelf low cost Flat Head Ford rod or a $1600 billet rod. I have gone through this because I will need a 7.5" long rod for a 263 Buick S8 and will have to pay the billet price because there aren't any forgings available for that long a rod. 7.00" Ford rod comes with the .750" pin and there isn't enough material to make the pin hole larger. Take it or leave it. The 6.440, 6.460 and the 6.560 LS rod will take any boost you want to throw at it that the SBB block will handle. Jim wasn't concerned about pin size because the very occasional boost and power levels are low. I think he covered the thought process behind his engine build very well and answered why he would use a light weight piston for his particular case I mentioned about sleeving the SBB out to 4.00". The 4.24" bore center makes this job very difficult. You would have to use ductile iron sleeves with flat sides and there doesn't appear to be room for more than a .185 thick sleeve before running into the head bolt holes. The deck would be totally violated and the only way to restore enough integrity so you can bolt a head down without pulling up the deck surface would be to make deep "V" grooves between the top of the sleeves and the deck and weld the sleeves to the deck. This would work for a high rpm Naturally aspirated application. Use the 6.560" LS rod, 1.899" rod journal (3.95" stroke) and you have a 397 cu in short block looking for a head to breath enough cfm to match. Paul
Jim wasn't concerned about pin size because the very occasional boost and power levels are low. I think he covered the thought process behind his engine build very well and answered why he would use a light weight piston for his particular case I wasnt questioning his research,just stating that i think no matter what the app.let alone in a hi cylinder psi forced induction app,regardless of boost,(because lets face it,noone will ever turn up the wick ) ,that lightweight wrist pins are never a good idea,esp when one is already working behind the 8 ball with a smaller availabe pin size Use the 6.560" LS rod, 1.899" rod journal (3.95" stroke) and you have a 397 cu in short block looking for a head to breath enough cfm to match. There in lies the problem,its hard enough to feed 400 inches woth a "GOOD HEAD" available,let alone what the Buick Sb community has to work with I think you only exasturbate the problem of limited induction when you add another 50 cubes to the mix Paul[/QUOTE]
