I have a full tube frame '72 Mav, mild 351w with stock rods (ARP bolts, TRW pistons), I have plans to run a 10.50 index street class with this car, it has run a best of 10.52 on 150hp N2O (weak run at that). Is it unreasonable to expect the stock rods to survive a season of racing at this level? The car is under 3000lbs with driver, 4 link, MII, 10 point, etc.
I think the stock rods would be more concerned with the RPMs more than how much power( torque) you are trying to get from the motor.Unless a rod just breaks (which is rare) its usually the bolts that give up from too much RPM. I have a Buddy that has ran a stock everything 351 with a 150 shot of juice for the last 8 years and has never as so much as burnt a plug. But he has always kept the timing correct and the RPMs below 6000. His car also weighs below 3000 #. He usually runs 1/8 mile with 6.90 ETs.
The stock small block rods are pretty strong.I seen a 302 send a rod out the side of the block(missed shift,5spd,200 NOS shot)tearing the starter in half.Yeah,the bolts broke,and the rod was BENT,but not broken.
If you are not running high compression ratio and keeping the RPM's reasonable, they should work fine. As time goes on, you may want to do some mod's to the engine and then I would look at using some "I" beam rods with floating pins. Also Eagle "H" beam's are very reliable too, especially with floating pins. One thing I recommend is to get the lightest internal parts you can, then use Mahle pistons( light as a feather) TRW's are very stout but weigh a bunch of grams too. Build a spare with the better parts and then run the crap out of what you have. May last forever but with your chassis setup, I would bet you will want to go faster someday.
Thanks for the input guys, here's a few more details: I'm told compression is in the 11.7:1 range, trans is a TH400 with brake and 3800 stall, 4.30 gear with 30x13.5 ET Streets, shift points will be in the 6500 rpm area. I did have intention to change the rods via stroker kit before next season, but I like the idea of getting some use out of the current engine since it will run the needed index number. I figure I'd invest in an engine diaper and give her hell. Might be better to scrounge up another block to build the stroker from. As far as wanting more ET later, the car is grossly overbuilt for any stock block Windsor, I actually have an 800HP 545 BBF that could be used, but I really thought I'd keep the fun factor high by running this 10.50 index class, just becomes expensive and stressful at a certain point.
The stock bolts are the weak link. From what I understand, you should use the best bolts possible and polish the beams. Light pins and piston are always a plus. How much do titanium pins cost nowadays?
I do have ARP bolts on the stock rods, not sure about beam polish/shot peen, but probably not. Light pistons would help, but unfortunately, the engine has rather heavy forged TRW slugs. I'm not sure Titanium would be the hot ticket for pins, it's light and reasonably strong, but very brittle too. Most of the high end pins I've had were tool steel.
Yeah, I don't know about the metallurgy. I know that they are out there. Brodix makes a large selection of them. I never knew titanium was brittle. They make valves, locks, retainers, rods, pins, roller lifters, and rockers out of titanium to name a few things.
The 351w bolts are 3/8" already...plenty strong for most of us. 99% of the time with 351w rods, the bolts don't break. It's usually the rod itself. They break right where the beam starts to transition to the big end. On the truck rods, there is a "bump"...that bump is a stress riser. I can't count how many rods I've seen broken right at that exact same spot...and yes I've broken one down there too. Mine let go at the finish line at about 120 mph, kicked the rod out the side, coated track with oil....yeah...fun ride. Shiny side stayed up though. Needless to say, that was the LAST time I used stock rods in a 351w.... Just an FYI, the 302 rods are PLENTY strong for 99% of us. Never broke or even seen a 302 rod break. The block will let go before the rods or crank, or at least that's been our experience. That said, I know guys who have abused stock rods for years and never had a problem in higher compression/boost/nitrous engines but then there's guys like me who break them in mild engines at lower RPM with no nitrous, etc. So I guess you could say that it might break (very good chance that it will) or it may last a while. Best bet, though, is to do as old guy said, build a better "spare" motor and go pound on the one you have until it busts, then drop the spare in. As for reducing weight, if pro stock 500" engines are using sub 400 gram pistons and sub 400 gram rods, then surely we can find something light. And they ain't using Titanium.... Mahle is about the lightest piston I've seen that is "shelf stock". You can get light pins from them as well (taper wall). Aluminum is the choice for rods....and al rods do several things. They absorb shock much better than steel or cast, they are lighter, and they aren't as likely to break. That adds up to a much quicker revving engine (more HP) as well as making it a little easier on the already weak block. The only issue with Al rods is stretch....and honestly I think that stretch is something that people worry about too much. GRP Al rods have been successfully used on street cars, and so have others. I think one manufacturer has logged 100,000 miles on a set in a big block chevy, so it appears to me that stretch is something that is over-exagerated. Besides, we're working with under 8000 RPM small block Fords. Our SBF engines have generally small combustion chambers and normally a 4.000"-.060" bore, so we can use small flat top pistons or even a short dome....which makes for a pretty light package, which is easier on the rods. Friend of ours had over 1000 passes at the strip on a 302" SBF, shifting at 9200. When they were pulled out, they had zero stretch. They were GRP rods. He went to a 347" engine, same brand rods but obviously different length, differnet small end, and different big ends. So far he went 5.90/112...in a Mustang 2 4 link car at 2700 race weight. Trust me, he ain't easy on it! 9000+ every shift (5 speed lenco)
Aluminum has some stretch to it, but worse is that it work hardends. It is elastic and has stretch at first, but after cycling and stretching over and over, it becomes brittle. Like I said, I don't know much about metallurgy, but I do know this about aluminum.
Run a .30 over 351w with Ross lightweights in our circle track car,stock rods ARP rod bolts,balanced,turned it 6200-6500 rpm for two seasons never had a problem,driver missed a shift on a restart the first season turned it 7500 and it stayed together...and we raced it the next whole season without any problems....them "funky orange colored" motors were lucky to stay together 10 races before they :%$* the bed,and that was with good rods and cranks in them.
I was looking into piston weight recently and YES!!! mahle are pretty light. I did see the KB hyper are within a couple grams of mahles. Mahles being forged certainly are better.....
You couldn't pay me enough to run KB's. They're quite heavy...well..at least the stuff we've looked at. They're just cast pistons afterall, but with maybe a little more silicon added into the alloy, which supposedly makes them stronger. I call BS because they are notoriously brittle. The rings are too high on the piston. The top ring gets exposed to a lot more heat than, say, "regular" forged pistons, which makes it expand more, which means you have to run a REALLY wide gap to keep it from butting and taking out the top ring land. Even if it's just wide enough, a clogged filter or timing a little too far advanced will pop the ring land right off...and destroy the head, piston, valves....and maybe if you're lucky, that's all. I've been down this road twice with 'em...and yeah they're still in there but the top ring gap is about .040" to keep 'em from butting. I like the mahles because of their light weight, but more because of their low drag rings. And if that wasn't enough, they make a set of ULTRA low drag rings (which I have used successfully). Talk about freeing up some power. I could turn that short block over (minus camshaft) by spinning the end of the crank with my bare hand. I didn't have an inch pound torque wrench to check rotational torque, but I'd guess somewhere around 5-8 lb-ft. Never used a drop of oil either. That was the only change I made to that particular engine, and it was worth about .08 give or take a little. almost a tenth. I'm actually waiting on the machine shop to get done with my crank, and I am going back with a set of ultra low drag rings on this one as well. Hoping it will pick up a little. Combine the AFR225s, super victor, 140 lbs weight loss, HOPEFULLY it will be in the 5.80's...all motor.
I know mine are not as strong as 351 rods but Im sure my stockers are on barowed time especially with one rod having stock bolts..... Dont ask... LOL
i havent read all the responses, but here is my response can you afford to have a rod break under high speed and engine running all out at 100 mph on the track? can you afford a brand new engine if and when a rod breaks? i think that will answer your question.. personally.. if you are running that much N2O and at those speeds and you are expecting a stock rod to last you are playing roulette. its true that no matter the quality or price, something will always fail on the track, but, a stock rod is that. STOCK, and it sounds to me like your setup is far from stock.. good luck
