Well that's the bad thing about being stuck in a box, you don't think outside of it. Not saying that is something I like, but both sides; lots of rules and no rules have their advantages.

Bret

 

Well I do agree that lots of rules brings out the differences in the real engine builders and also those with the most experience. It's hard to beat someone right off the bat that's already been through years and years of that kind of class racing but then again sometimes you see something that they never did. I've helped people like this out from time to time and I can sometimes pick them up but I didn't do all the work that got them up to there either and vice versa. Also, I've been helped by some people that saw something that I didn't because of the experience in their arena of racing! So it can go both ways when you share knowledge.

 

You touched on a good point: Rod/stroke ratio and reciprocating mass.

As 358 Cup engines strokes dropped from about 3.50 to about 3.25 over the years, and the revs climbed into the mid 9000 range, lower mass parts became even more critical. With stock deck heght, a 6.25 rod and a 3.50 stroke (1.79 R/S) gives a 1.025 compression height. If you reduce the stroke .25 and reduce the rod .50, you are still at 1.77 R/S, but now CH is 1.65. You can now drop the deck .625 and keep the 1.025 CH to keep piston mass down. If you further shorten the rod to about 5.56 or so, you still have a 1.72 R/S and a deck height that approaches 8.2 inches. Even with short rods, you don't get anywhere near the 1.64 R/S of a stock 350.

As you shorten the rod you increase maximum piston g's but not significantly. Probably the reduction in mass from the shorter rod pretty much offsets the efect of the higher g's, even at 9500+. With a mandated minimum rod weight, you can more effectively use the material in the rod to offset the inherent weakness of the relatively small rod bearing diameter, about 45 mm (1.77 in) I believe.

2003 BMW F1 engine, with a 19,200 max rpm had a R/S about 2.0, if you calculate from the piston speeds and max piston g's BMW published (10000 g's!). Of course with a stroke about 1.54 inches, that's a rod about 3-1/8 inches long! I guess packaging is a real concern here.

My guess is that shorter rods, shorter strokes, shorter decks and smaller bearings evolved as a combination in the search for more rpm in engines. If NASCAR hadn't put a limit on bore size, we might be seeing 4.25 bores and 3.155 strokes and maybe rods under 5.5 inches today.

My $.02.

 

Yes the weight is always worth it. Actually the rods with the smaller big ends tend to be stronger and retain roundness better than the larger sizes but the crank becomes weaker.

 

Not to turn this too far from present course but Joe made a good point way back there....

We do get overly fixated on dyno numbers, I agree to that. Some of these threads can get a bit hilarious too....

Example,

"I want 400rwhp"

why?

"To run low 12's in the 1/4"

guys have done that with bolt on cars and a great setup.

The dyno is a great tuning tool plus it gives you an idea on potential but that's about as far as it goes. Then again, if your goal is to run low 10's, you really need to have a plan and some idea of the power it takes to run those times.

-Mindgame

 

Lets put it this way:

Weekend drive 3rdgen, 3200-3300 pounds with driver, 10 point cage, no more than a 4000 stall, I want it to run well into the 10's on the motor.

My stipulations are that I dont want to run shaft mount rockers or offset lifters or any of that kind of stuff. Streetability/gas mileage is of no concern.

 

I do agree with the point you are coming across with. Not to offend anyone but since the LS1/LS6 motors came out people have been obsessed with rear wheel numbers.

 

Shaft rockers are only a little more than good rockers but regular rocker and guideplates can still work of course on normal street rollers and hydro rollers.

 

Interesting thought Eric......

The best Stud mounted rocker setup is a Comp Hi Tech at 52,000lbs per inch of deflection.... The best shaft mount numbers I have ever seen are the Crower Stainless Shaft mounts at 180,000lbs per inch of deflection.

I don't know about you but 3.4 times as much stiffness is pretty impressive, I would consider that better than "a little more than good"

12Second3rdgen

"3200-3300 pounds with driver, 10 point cage, no more than a 4000 stall, I want it to run well into the 10's on the motor."

How about a 9.77 @ 139 with a 355 and 3250lbs, non ported heads or intake, .485 lift flat tappet cam and a 150-200hp N2O shot. All with a automatic tranny w/ a converter.

Here are the rules.....
http://www.fasteststreetcar.com/2004...eapstreet.html

Great class to run in.

If you don't have rules then a 400 block would be the best bet and do a 377 or 406 with at the most some Raised Runner 23 deg heads or some 18X Brodix heads and a Super Vic. Since you want a 4000stall at the most you can do that easy with 360-400 cubes easy.

Bret

 

We're still going on this one eh?

Guess it comes back to that age old question of $. How much ya got and how much are you looking to spend?

To me, this seems to be the logical way to build an engine..... Figure the budget, decide the goal, then allocate funds to the right areas of the build. If you want to avoid RR heads, offset valves and the like then your best bet is to build as big an engine as you can afford.

-Mindgame

 

Mindgame brings up probably the most valid point. Figure out your budget and allocate the money accordingly as to where the power is made (ie. heads and cam/valvetrain for a NA motor). However, no engine build ever retains the original "budget". Plan on spending at least 30-40% more than allowed.....thats just the way it always ends up.

In all honesty, people make it way more complicated to build powerful NA motors than it really is. But thats just my opinion.

 

Bret,

When I said:

""Shaft rockers are only a little more than good rockers but regular rocker and guideplates can still work of course on normal street rollers and hydro rollers.""

I was talking about price! I ALWAYS think it's good to use shaft rockers if you can afford them and like I said they're not always that much more when you add up all the costs of good rocker/guideplate systems. Maybe 75 per cent of what we do is shaft rockers. We even make our own stands for Jesel and T&D rockers since they didn't make what we want all the time! We just turned 9000 rpm tonight on T&D stands that we made our selves and some existing T&D rockers.

 

If you want to hook me up with some used shaft mount rockers for 23* heads, I would be forever grateful

 

Don't have any but you can always check Ebay and you might get lucky. Just be careful and remember you usually get what you pay for ..... or less!

 

Most appealing combination in a moderate cost bracket I've seen:

- 383 with Wiesco pistons cut to accept 23* AND 18* valves.
- Brodix 18x heads which will utilize 23* valvetrain & 18* valve placement.

Obviously a 388 (a 383 with a 3.8" crank now available under a few names like Scat and Eagle) would be a nice touch if you didn't want to get into 396 territory (I'm passing on the block prep hassels myself) and still wanted a few more cubes.

From discussions here it's pretty clear that most coatings probably arn't worth the cost if hp is your sole goal, but for durability some (like bearings) may pan out; especially in a street-strip motor that has to do double-duty (high rpms, and long life).