Hey guys i need some ideas on building a new short block for my Iroc. I am seeking the 10sec zone. This is what i have on top Tpis mini-ram, 50lbs injectors, brobix track 1 heads, vortech r-trim blower, hooker super comps headers and a accel dfi setup. I was either thinking of building a 383 out of the current 100k mile block or moving up to a 406. I need some thoughts and ideas about that and comp ratios, and cams to use.

Thanks
Andy

 

we get shortblock idea questions all the time, so I must pipe in my $0.02, I do from time to time. It starts with the obscenely low priced really strong TRW blower nitrous pistons, Eagle H beam or summit/trickflow I beam rods, and a cola (super strong for the price) crank or stock steel forged crank, in a stock block that has been converted to splayed caps or a bowtie/world products/dart block. this would go 10's and maybe 9's or 8's if carefully cammed.

 

ok thanks, yeah i hope to have something going soon. But i do not want to get stuck with the wrong parts.

 

my recommendation best fits the 350 or 355 setup but there is now a TRW forged blower/turbo piston for 400/406 with the 5.7 rod. so you could use a bowtie/world/dart block (for 400) or a late 350 roller block (for 383).

 

dont bother with a new block....just use the one you have. It'll save you money.

No need for splayed caps honestly....even if you have a 2 bolt main. Just stud it.

Honestly, i bet stock rods would suffice if they were prepped well and used good ARP bolts. But its not worth the hassle anymore....just buy some CAT H-beam rods (same as eagle and you can get them super cheap). For pistons.....just use some TRW or Probe pistons. Probe's are kinda like the TRW of the ford world and they started making them for chevies too. For a crank....i'd get a semi-decent forging. Reason why i wouldn't use a cheap one is because the blower is going to stress the snout and you want something with a good warranty and that'll hold up well. This will probably be your main money grubber. Look into the callies line of cranks....good stuff for not too much.



oh and a dart/world block is not needed for your setup. ONLY get a new block if your machinist feels the one you have isn't gonna cut the mustard...be honest with him and tell him how much boost you wanna run and how much power you plan to put through it and he'll be honest with you. you shouldn't need too much boost with your current combo to get it to fly. You have a good intake and good heads. I'd tell you to leave it as a 355 but you need new crank so you might as well do a 383

jim

 

I only suggested the aftermarket block because there are a few people (not me ) that have had bad luck with stock 400 blocks. I knew they would chime in if you mentioned stock 400 block and boost. I have two now and have had a few others in the past (no failures) he is right go 355 or 383 with the block you have is a great way to save $$$.

 

My suggestion!

1. Keep the stock block punch it 30 over.
2. Get a set of 4 bolt(not splayed) billet caps.
3. Grab a GMPP forged steel crank(3.80 in.), have the journals polished.
4. Set of forged eagle rods 5.7.
5. Good set of blower pistons and have them ceramic coated(along with the combustion chambers of the heads if you can).
6. Have the rods,crank and pistons balanced.

The above combo is for use on a post 86 block with a 1 piece real main seal..............


Pistons vary by manufacturer. Make sure they are balanced they can be off as much as 10 grams(might not seem by much, but it is)

 

ok thanks for the suggestions guys, yeah i think now with the majority saying stick with the stock block thats what i will do, and make it into a 383. Hope to have the motor pulled by the start of summer, and off to the shop. I want to try to get the r-trim to push at least 15-20psi, i think that is what i would need to compete in the class i am looking at.

Thanks
Andy

 

You have quite a few choices in terms of the block:

Studed 2 bolt
4 bolt conversion
4 bolt splayed conversion
Aftermarket block
400 production block

Most of the time it is better to use a stock block that has been well seasoned (50k+ miles) for a stroker motor. But the aftermarket blocks have the strength without having to search for a good core (and you will pay $ for an aftermarket one).

The strongest bottom end is gonna have billet 4 bolt splayed main caps and billet end caps, regardless of what block it is.

Pistons - with the power levels you are looking at, its gonna cost you good money, even with cheaper parts, so why not spend a little extra to get the best stuff (durability wise). I won't knock TRW stuff - its strong, easy to use, and inexpensive; but they are heavy and are not the latest in piston design. I would go for a Ross/JE/Venola/Manley custom piston for a supercharged application, which run about $600-$700 a set at most. Do have the pistons coated.

Rods - typically, if anything breaks in a boosted/nitrous motor its these guys. You can spend $5k for a set of titanium rods that will lighten up rotating mass, but detonate the motor and kiss them goodbye. But in 99.95% of SBC motors, a good 4340 H-beam or I-beam rod is the right choice. There are a million choices of 4340 rods, what you want is a realtively light strong rod with a top-quality fastener. Typically $500-$700 a set. Go for a 6" rod.

Crank - you will need a 4340 crank too - they are the strongest to get. However, not every one is created equal. There are billet 4340, non-twist 4340, hammer-forged 4340... They run from $500 to $1500, depending on what type of metal/forging process it was manufactured with. Callies, Crower, Manley, Lunati, & Cola are a few of the big names.

What I would do
3.875" crank for 396ci in a 0.03" over 350 factory roller block
AFR 195cc heads, fully ported 9:1 compression
Miniram ported to match heads
Dual pattern roller cam (something like 225/240 @ 115degrees)
Hooker supercomps
4" mufflex exhaust
7qt oil pan with big external oil cooler

A motor like this is an easy 500hp alone, 8psi would put you in the 725hp range, enough to run low 10's.

 

i never heard of ceramic coating the piston and combustion chamber on the head, what is the advantage to it?

 

Check out Hotrod Magazine's article on ceramic coatings at http://www.hotrod.com/techarticles/51120/

 

I like ceramic coatings but my problem with them, is that even when professionally applied (you sent the stuff to have it coated. when you teardown your motor in a year or so most of it is gone. they promise you ahead of time that it wont wearoff then they wont apply it the second time for free when it doesnt.

 

Why would Ti rods break under dotonation before steel? Maybe you're saying all rods break under detonation which I would agree with. Most rods break on the up stroke which is why it's so important to have good rod bolts. Having said that there is no way I would put an engine like that back together with stock 100k mile rods. Other things that fail on the rotating assembly that don't get enough attention are piston pins. Probably not a big deal if you keep the miles down though. A 4340 forged steel crank is overkill. There is not enough stress on the snout to fail it there. I have never seen or heard of a crank snout breaking off. You can use a 1018 carbon steel crank that has filetted rod journals and it will run all day every day. The filetts on the journals reduce the stress concentrations by going from a clean 90 degree angle to a smoothe radius. You can hand modify stock rod bearings to fit. This costs a little extra because the crank has to be cut down first. You'd probably do that anyway to insure a straight cut crank. A crank with smaller journals also has less friction. I also agree with a splayed block. Be careful with the late model blocks because you can start to get into too much cylinder wall flex. A ten second car probably won't make enough power to worry about that. I would use 6 inch rods and pistons no matter what size engine because it really lightens up those slugs, and reduces your rod stresses. Hypereutetic pistons are really good any more, and are a lot lighter than forged, so I wouldn't rule them out either. Go with low tension positive seal rings on the pistons too. Try and get the torque down as low as you can on the short block. A good number to shoot for is 30 in-lbs.

 

I agree. I have only seen one snout break and that was on an 871'd sbc that the owner drove on the street with his overdriven pulleies on. He was an Alky motor and run deep 9's with a traction problem. I am in the 10's with a juice 400 crank 383. With a huffer on top I would suggest the extra insurance of the spayed caps on a two bolt block also. It may live without it, but if it don't the $$$ will add up quick.

 

Titanium is lighter and stronger than steel in most measurements, but it is fragile like porcelain/ceramic when it changes direction suddenly (like when a motor gets detonation. Kinda like you can rest a lot of weight on a toilet and it won't break, but whack it with a hammer (a lot less weight, but moving in the wrong direction) and it shatters. Although titanium is a metal, its grain structure is almost like cast aluminum, just stronger and lighter. It has to be cast, it can't easily be machined without fracturing. I know the NSX uses titanium rods and it has an untra sophisticated engine management system to control everything, otherwise it would eventually self destruct. Steel is a lot more resilient than titanium or aluminum when it comes to connecting rods (and its heavier), but its hard to break a 4340 rod without something catastophic happening, though they do bend if they are overworked (like hydraulic compression).

Cranks typically do not break snouts, although an LT1 with a crank supercharger will (if it was not keyed). A good crank is definitely worth the few extra $. Its not like a standard forged crank is $75 and a 4340 is $1,500. Its more like $400 and $700 for both. Besides, if you have a 650hp motor than runs in the 10's, why would you get a crank that is only good for 700hp when you know it will eventually be asked to put out more hp? Nothing like buying the same part 2 or 3 times when you could have done it once.

 

I'm going to have to disagree about the Ti rods here. Titanium has a lower modulus of elacticity(stress over strain) than steel(Ti 16.5 MPsi and 4340 30MPsi) which makes it much more resiliant. In fact, that is one of the things that makes Ti hard to machine. When you chuck it in a lathe you have to support the opposite side of the cutter, or it will bend out of the way. Ti does have a lower yield strength and fracture toughness than 4340, which makes 4340 ideal for big power and small geometry and tight tolerances. However Titanium alloy is 1.77 times lighter than 4340. That way you can use more material to reduce stress and still come in lighter than 4340. On a stress-strain diagram with similar stresses, the Titanium will have a larger area under the elastic portion of the curve which results in more resilience. You only want to use the elastic portion in most engineering situations because once you go into plastic deformation you've permanently changed your geometry which results in failures. Therefore, toughness isn't really even a factor. Someone said I needed to give more reasons for my opinions, so there they are.

 

I've heard that Ti is stronger and lighter, however once any damage is inflicted(even the smallest pinhole or dimple) it will crack continuously(kinda like a windshield). Forged aluminum is supposed to be very efficient cause it absorbs more shock, but I'd assume it would bend a little easier than 4340 would. Weightvs strengthvs cost I'd go with 430 steel(not the lightest or strongest, but a good compromise betwen the three choices)

 

Basically that's it, as long as TI has no scratches, nicks, dings... it's a great material, as soon as it does it will fall appart. It's much more suceptable to stress risers then any steel

 

bringin back the old thread.

what do you guys think of running a forged aliminum rod on a mild street engine. will they hold up for a number of years or will they stress out too much?

I can get a set of Childs & Albert forged aluminum rods that cost over $1000 for around $400 and they are brand new. I was thnking they would be nice for the weight savings and they look and feel pretty beefy.

what do you think?

 

I'm not sure what the life is on a set of Al rods, but there is a finite lifespan (X number of cycles). Figure out how long you want the rods to last at WOT (i.e. minutes * rpms = # of cycles), and what your max torque or hp is... The only reason to go AL is if you need a light rotating assembly to spin high (over 7500) rpms. Otherwise, I'd probably go with a set of $500 forged H-beam steel rods, so you don't have to worry about the Al rods fatiguing out. Yeah, they're trick, but its something that won't add more than a few hp, and hurts long term reliability. Now, if it's gonna be an engine you tear down every winter & check rod stretch, then go for it

 

I was kinda thinking that, but I cant seem to get over him buying them for less than half price. What about just buying them to resell?

I was thinking they should last a few years and be alright.

I know they are only supposed to go for a certain number of cycles but isnt that if they are being used hard? I was thinkin if they stay within their natural material properties and not be stressed like they would drag racing, that they may last longer. I may be wrong but that was just my way of thinking.

 

titeride, I thought of reselling them but I dont really want to spend money I dont know I can get back.

Askulte, I cant say I want to be in the motor more than once every couple years. I am also thinking they will give more than a few HP. I am working on a 408 small block. with the longer stroke, the less weight I am slinging around should give me a quicker rev and free up more tq. It will also have Lunati pistons that are weighing in at 431 grams. so the rotating assembly will be pretty light. will it still stress the rods as much?

now for anyone, this engine will not be running a power adder. It will be a 400 or so HP 10:1 engine. It will only have an occasional track pass and will only be driven during the nice weather. around here I am lucky to go from april to september maybe october. It will not be a daily driver.

with that being said, my thoughts tend to follow tideride's. What does everyone think?

 

Look at this combo guys, this is what i'm gonna do. Dunno what your discussing Ti rods for unless you have almost 4K you plan on spending on rods. I am gonna use an eagle 4340 non twist crank about $550, Eagle 4340 H beam rods about $339 with 7/16 ARP bolts, probably JE dished pistons 9.0:1 compr, 400 dart little M block and some really, really good rings. Still debating on cam supercharger and intake but either Stealth Ram or TPI, Trick flow heads. Think this set up will hold up to alot, what you guys think.

 

I haven't seen any specs on the rods at all. Whether it be 4340 or Forged aluminum, you have to take into account the size of the rod for longevity purposes. If you are gonna use a 400 block AL. rods may hold up well in 5.65in. This puts more load on the cylinder wall and skirt of the piston compared to a short skirt long rod combo. If you are gonna go 6" or longer I'd go with the 4340 just because of the known history(don't know too many engines running long aluminum rods for thousands of miles).

If you are building a 400 to rev and want it too last go with the 4340 rods. The last thing you want is a shattered rod at 6000 rpm wrecking the wall of a very expensive block and/or custom slugs.

I'm partial to steel anyway. Look at the turbo buick rods(cast steel) they handle at least 600lb/ft and usually the crank snaps first. Just my .02

Good luck with the combo!

 

the rods are Childs & Albert forged aluminum rods. they are 6" (5.990 actual) made of 7075 T6 aluminum. they weigh 580 grams with a double I beam look. they are rated for 1,000 hp and 10,000 rpm.

I was thinking that since I would not be running them hard or often, that they would hold up for quite some time. I am looking at 400-430 hp and 425-450 lb-ft. Engine will be in 1500-6500 range in occasional driving and up to 7500 or so less occasionally. the car may get 5-7,000 miles per year tops.

 

What you say is true. Life of aluminum is a function of stress and cycles. If you have low stress you can run a lot more cycles. However, Aluminum WILL BREAK eventually. May be a very long time depending on how you baby it, but it will catch up to you. Same with all these people running al rocker arms. Aluminum is for race only applications where you can acurately predict load and cycle time. Steel is much more durable, and if stress is low enough and there are no inclusions in the substrate, can achieve infinite life.

Bottom line, it's your engine. If I were you I'd go ahead and put those rods in there and ride her till she bucks ya. I'm not you though...