Well, I don't think it's for that specific reason. Cup applications use a 9.200" deck with a 3.500" stroke, so the piston isn't going to be uber short anyway. Compression heights are high 1.200's to 1.300's. Couple that with the fact that wrist pin diameters get really small (some are down to around 3/4"), the pin is easily kept away from the ring pack.

Actually all of the Roush/Yates engines used in cup cars use a 3.25 stroke crank......

David

David's right. They generally favor the shorter stroke, but I've seen the smaller bore combination on a few engines, especially if we're looking at "Ebay take-off's." :)

In NASCAR the cubic inch limit is 358,back in the day they would start out with a 350 chevy or 351 ford and this would allow for a few rebuilds/borings on stock blocks..........that has long since gone the way of the dinosaur,nothing is "stock" in the cars or engines and has been that way for a long time......

They want fast revving short stroke engines now-a-days hence 3.25 inch stroke,depending on the track, they are turning these engines 9500 +rpms and they have to use a solid lifter, non-roller camshaft....These engines only have to last one race,so saving a few dollars is not in the equation.....
Yates has experimented with stroke combos in the 3.10 inch range........

David

too much rod angle and not enough piston speed with the 5.4/5.155 rods. stock length rods will produce best results by far. Done much testing in this area. 1.69 rod angle much better than 1.8.Actually would prefer more like 1.65.Jim kuntz 870-246-2595

I am going to be using Calles Compstar H beam rods, I have Mahle pistons, a prepped Steel Boss 302 crank, ATI Balancer, McLeod Aluminum Flywheel all of which will be internally balanced. A unique cam drive setup from Roush. Lightend polished lifters, custom ground cam to match the flow of my heads. Everything on the block is already ARP studded, but I am going to step up to 7/16 rocker studs, and change the fulcrums in the Crower Rockers to acomodate the larger studs. I am also considering having the locations of all the lifter bores checked, indexed and relocated as necessary. This is commom practice in Sprint Cup. The teams do this to their blocks to assure the cam timing events are precisely the same in all cylinders. I enjoy discussing the technology of the upper end engine building practices although they are seldom are made available.

If you're planning to turn a lot of revs, I would skip the stud mounted rockers altogether. I would also use a 5/16" .105" wall pushrod at least, if not a 3/8" pushrod if you can fit it in the tubes.

Brent I think 7300 -7500 will be the absolute max. All my rocker gear currently fits under 1st generation valve covers, I want to keep it that way, for the sake of originality.

Edit: I have my fingers crossed on this but today 2 different Camshaft sources of which I inquired, after running the specs through their engine programs are indicating that the engine with the specs submitted should be capable of between 432 HP at 6800 RPM or 452 HP at 7250. I will be tickled to death if these numbers are remotely close. They may be optomistic but if they are even close it will widen my smile :)

Brent: Currently using Comp Cams 1 piece with .080 wall?

Gotta have priorities Rick.....if you're going to be turning 7500 and shifting at possibly 8000, I couldn't care less about how pretty the valve covers are.

Most of the shaft mounted stuff will fit under the valve covers that a roller rocker fits under anyway. Even if you had to stack gaskets or run spacers, I would.

I wouldn't even feel comfortable with a stud girdle at 8000 rpm.

The 1.8 rod ratio is great for high revs......it seems that is the
desired result.......

The usual line of thought is to make the stroke what you want, get the piston light and made how you want, then connect the two.

It's amazing how many times I've heard one guy say he's tested a particular combination with all different rod lengths on the dyno, and someone else has done the same thing and come up with a totally different setup.

I really dont think I'll be turning 8000 RPM, it will not be cammed for that nor will the block accept it. I certainly like the shaft rockers, and have both the Jesel & T&D catalogs. T&D is a couple of hours away from me in Carson City Nevada, may actually go see tham at some time. My heads are ported Iron Windsor Jrs, I got them when they first hit the market. Yesterday I called the fellow who flowed them and he checked his records and confirmed flows were 262/202 @.600. They're are not the best available by far but ARE what I will be using. I respect everything you do Brent you have a good rep and are an asset to the Cobra Website. I research, read, study, talk to and try to make informed decisions with in my budget (we all have one). I would like the shaft rockers, but in interest of originality want it to appear "Old School". What I have has been rock solid reliable for 20 years (289 short block) at estimated 350 HP, currently shift at max 6800. My goal which I think is realistic is 425 or a little more, I will be happy. I just enjoy the build process, exploring options and trying to keep it in a budget that the other half wont scream too loud about since she thinks the car is "Useless as Tits on a Boar". It is after all a street car, drive it in the foothills and terorize the older Corvette Drivers. Please don't take offense, I appreciate any input you have. Next decission is bearings, coated ACL or King seem to be favorable.

Rick, I have never taken offense to anything that you've said to me. You tend to be very thorough in thought, and I can respect that.

I think your hp goal is pretty realistic and now that you have the rods bought, I would look very hard at valvetrain components as they are equally as important in the overall scheme of engine reliability. Lots of deflection in parts at 7500 rpm, and I think that if it's got enough cam to make power up there, you'll find yourself above that mark. No need in building the bottom end to be bulletproof but short-siding yourself on the top end.

Not sure what you're using for a cam or lifters, but it takes a good bit of spring pressure for things to stay in contact with each other at those rpm levels. Pushrod quality is paramount, and rocker arm stability is paramount. I guess what I'm trying to say is that there's no need in hamstringing yourself over a set of valve covers. ;) If you are using a flat tappet cam, I would look long and hard at having the lifters EDM'd, and I would not restrict oil to them or to the rockers/springs. At those kinds of rpms, springs will weaken quickly from heat.

As for bearings, I like both brands and use them pretty much exclusively, using more ACL over anything else. King will size up differently than the ACL, so before you pay the big bucks to have them coated, I would buy one or two of each and do some clearance mock-up.

Just for your information. I used a 3.25 stroke and a 5.565 rod giving me a rod ratio of 1.71 and a compression height of 1.00.
It made 451hp @ 6100rpm and 433ft at 4300rpm

Rossba...Good numbers for 331..unusual rod length. Any oil consumpsion issues??

I'm going to use a 3.00 stroke 5.4 rod, 1.3 compression height, 1.8 rod ratio. Currently using 5.155 rod with 2.87 stroke 1.79 rod ratio. Torque curve should be very similar but with slightly more created than I currently have. Conservatively looking for 50-75 more HP.

Rick,

No oil consumption.

With a higher rod ratio you also get longer dwell time TDC and BDC so allow for that in your camshaft specs.

Ross

Hi Rick,

For the short bursts of high RPM's we see, I have never been let down with ARP 7/16" studs and Crower SS rocker arms. As others mentioned, don't scrimp on the push rods...this combo worked in my roller cammed Boss 302 and multiple other windsors.

Now at the fork in the road for Main Bearings. Questioning whether to user 3/4 groove mains with the Cross Drilled Boss Crank, or 1/2 groove. The cross drilled crank will create more " leakage". Just don't want to be concerned with rod bearing starvation or oil pressure. Leaning toward coated bearings as previously mentioned. Will probably continue with high volume pump.