stock gm lt1 connecting rods..how much power can they handle?

Was wondering what sort of hp...can stock lt1 connecting rods handle..Ive heard various things about them..that they can easily handle in excess of 500 hp at the motor..some say they cant....Im building up a 355 lt1 with a ati 8psi p600b supercharger..Im hoping to have 500 to 550 at the motor...if...they wont handle the power or just to be safe..id appreciate input on what rods to get and from where thanks for the help




Steve

I been running a p600b for many years now on my ride and no issues with the rods. I just freshened up my motor with a forged pistons and was going to the 355 route but as it turned out even with 114,000 miles on the clock the block was still within factory new specs(got to hand it to the guy's at Mobil), so just got the block honed. But back to the subject, and when I looked at the stock rods they were fine. I just slapped on the new forged pistons got the heads also freshened up and now back on the road. I run from 7-10psi. I do know that the stock rods are stronger than the legendary "pink" rods of old. Just my two cents. But I would also tell if you don't have to go .30 over don't, it saves for another rebuild a couple of years down the road. To many people just go right to .30 over when it is not always needed. I just checked all the bores on mine as was pleasently suprised. In any case I hope this helps.

ATMINF it does help..unfortunately..im already in the motor...went .30 over... scat 9000 series crank,srp pistons and rings, hotcam kit.without the cam... comp cams 7-305 cam. comp cams pushrods...runnin 8 lbs ati boost,3 angle valve job on heads..asm 1 3/4 headers flowmaster catback random tech stainless y pipe msd6al ,3.73 gears.. and a 6 speed...that about sums it up heh...just wondering if the rods be ok with the setup ..thanks for the input....


Steve

There was a long thread a month or so ago about the hp limits of various drivetrain parts. If you could find it, that might be helpful.

The relevance is a point that I and a number of others made. Basically, it's that you can't specify a certain hp level as the limit for a given part. The closer you get to the the absolute yield strength of a part, the sooner it will break. Eventually, after a number of stress cycles, the part will weaken and eventually fail. IOW, it's stress over time which causes fatigue, weakening of the part, and eventual failure. The stresses on a connecting rod with a 500hp setup will not exceed the yield strength of a set of new set of stock rods the first time you drive it. Eventually, they will fail.

So, in your hypothetical 500hp motor a set of stock rods might last essentially forever if you never ran near the redline at WOT. The faster and harder you run it, the sooner they will break. How long a service life constitutes "easily handle"? There's no easy answer to this, because we don't know your definition of acceptable longevity or how you will drive it.

All that aside, given typical use, I would not put a set of stock rods in a 500hp motor. When a rod goes, it usually takes a lot of other stuff with it. OTOH, I am using a set of rods that many would consider inadequate for my setup. They're Lunati Pro-Mod rods in a 700+rwhp motor. They have been in for two years, 9,000 miles, and have been used pretty hard though I don't rev very high. I put them back in this year, albeit with new rod bolts. I have my fingers crossed, but it wouldn't be a disaster if they failed, just a chance to upgrade.

Don't mean to babble on, just trying to help and get across that there is no simple yes/no answer. Also keep in mind you can get a better set of rods without spending a fortune. The Pro-Mods are in the $700 range. Many people like the Eagle H-beams at ~$500. Scat makes some nice moderate price rods as well.

Rich Krause

rich thanks for the input and advice.i guiess if i supply some more info it help.the car had 40k miles of which 15k or so were on the blower.the car was..a daily driver.i didnt make a habit of beating on it hard alot because it was a daily driver.im just trying to figure out..if new rods..are necessary...ive looked at the eagle h beams and have found them for a cheapest price of 450.00 bucks at racenet.being that im not a mechanic and this is my first rebuild, i just wanted to get as much understanding as i could about where i could cut a corner and were i cant.a yr or 2 ago i would of just bought new rods.but my funds are a bit limited these days and i want to get the car on the road with as little cash as possible without jepordizing the strength of the motor right off the bat..thanks for your time



Steve

If you want to run the stock rods, take the time to polish the beams, add some good ARP bolts, and get them resized. I am running a set done like this in a 383 with a 250 shot that has been together for about 3 years. He tries to stay under 6500 rpm but has been past a couple times...:rolleyes:
Or, you can pickup a set of 4340 h-beams for $319 from Powerhouse products.
Your money, your choice.

Personally I wouldn't go with stock rods if your trying for 500-550 hp, After I tore down my 355 that had about 450- 475 rwhp my stock rods had been twisting tearing up the bearings and the stock crank was cracked. If your gonna do the motor anyway spend a few extra bucks on some better rods and then no worries.

rcf925 thanks for the input i just ordered some eagle 4340 hbeam connecting rods off of ebay for 389.00 shipped.so i took care of that problem i hope lol




Steve

Good price on the eagles... I'm not sure how much it costs to have the stock rods reworked, but by the time you do that and upgrade the bolts i'd imagine you'd be halfway there for the entry level forged ones. So, Unless you're on an extreme budget, that few extra hundred should provide some peace of mind, as well as giving you the option of adding more boost later on down the line when you get bored.

timbrss thanks for the input...i just want to say this site is the bomb...had to get that out heh....ive posted like a madman for the last few days..because my project is finally starting to come together..this has been a huge learning curve for me.....the only rock left unturned and i posted earlier was my cam.... its a 07-305-08 i think comp cams...its a rather mild cam..suggested to me by comp cams...im not sure if i should go with something more radical or not..or just use the cam and hope it works out well with my setup..again thanks to everyone thats posted to help me along.. i couldnt have gotten this rolling without the help......





Steve

Originally posted by RCF925
Personally I wouldn't go with stock rods if your trying for 500-550 hp, After I tore down my 355 that had about 450- 475 rwhp my stock rods had been twisting tearing up the bearings and the stock crank was cracked. If your gonna do the motor anyway spend a few extra bucks on some better rods and then no worries.

Sounds like you had some serious detonation issues if you cracked the crank, and I have no idea how you would twist a connecting rod. I have bent them in the plane that they operate in, but unless the piston hit the head, of something came apart and binded up the rod, I don't see how that is possible.

Of course, this IS the internet, and there are lots of 9 sec Vipers.. so anything is possible!! :D :rolleyes:

you mention finding a place to cut corners, rods would not be one. If a rod fails, it can take your whole motor out. Id say the best place to cut the corners is the crank.

Originally posted by SteveLT1
timbrss thanks for the input...i just want to say this site is the bomb...had to get that out heh....ive posted like a madman for the last few days..because my project is finally starting to come together..this has been a huge learning curve for me.....the only rock left unturned and i posted earlier was my cam.... its a 07-305-08 i think comp cams...its a rather mild cam..suggested to me by comp cams...im not sure if i should go with something more radical or not..or just use the cam and hope it works out well with my setup..again thanks to everyone thats posted to help me along.. i couldnt have gotten this rolling without the help......


Steve

Steve: two proven "blower" HR cams for an LT1.

CC XE #3190/3192 on a 114lsa. 214/224 @ 0.050" .530/.567"
CC XE #3192/3196 on a 116LSA 224/236 @ 0.050" .567/.585"

Both will need a good set of springs, pushrods, and rockers as the lobes are quite steep, actually as steep as a mild SR lobe.

The 503 cam does not have enough exhaust duration relative to intake fo a blower car.

Rich Krause

I lost a rod this past weekend.. Bolt on's only.. Seems like the rod bolt failed.. But the motor had 150K on it.. SO it served its purpose for a good while.. :)

so rich whats the difference between the 2 cams..which is more streetable. the car ..will...er i think be a daily driver from april..to september etc. i dont need that few extra hp in sacrafice for streetability..etc... thanks for your time








Steve

Originally posted by SteveLT1
so rich whats the difference between the 2 cams..which is more streetable. the car ..will...er i think be a daily driver from april..to september etc. i dont need that few extra hp in sacrafice for streetability..etc... thanks for your time

Steve

The 214/224 cam is extremely mild. Will idle at 750rpm at ~18in of vacuum on a 383. The 224/236 is also very streetable, but not quite as torquey down low. ~13in of vacuum at idle. The 214/224 will peak at ~5,700rpm the 224/236 at 6,200 or a bit more.

Rich Krause

ok rich thanks.....i guess basically here is the plan for the motor then.... pontiac formula 1995 355ci 6 speed 3.73 gears, 1.6 roller rockers,comp cams pushrods,keyed crankshaft hub,3angle valve job on stock lt1 heads,52mm tb,random technologies dual cat y pipe,flowmaster cat back,24lb bosch injectors,eagle connecting rods,srp pistons and rings..aprox 10.4 to 1 compression ratio, ati p600b 8 psi with front mount intercooler,msd 6al,msd power coil,ls1 driveshaft, and one of the comp cams you suggested...just wondering with my mods....if it be wise to goto 6200 rpms or not..if not.....the compression ratio is around 10.4 to 1..basically what it was before the rebuild...thanks a ton for the help





Steve

Originally posted by SteveLT1
ok rich thanks.....i guess basically here is the plan for the motor then.... pontiac formula 1995 355ci 6 speed 3.73 gears, 1.6 roller rockers,comp cams pushrods,keyed crankshaft hub,3angle valve job on stock lt1 heads,52mm tb,random technologies dual cat y pipe,flowmaster cat back,24lb bosch injectors,eagle connecting rods,srp pistons and rings..aprox 10.4 to 1 compression ratio, ati p600b 8 psi with front mount intercooler,msd 6al,msd power coil,ls1 driveshaft, and one of the comp cams you suggested...just wondering with my mods....if it be wise to goto 6200 rpms or not..if not.....the compression ratio is around 10.4 to 1..basically what it was before the rebuild...thanks a ton for the help


Steve

FYI, you will gain ~.15 points in CR with the ovebore. With the 1.6 rockers the larger cam is going to be pretty high lift for a street HR cam (over 0.600"). You might be better off with the lower lift versions of the same lobes. #3314/3316 gives the same duration but .544/.555" lift vs. .605/.624".

With your CR, as opposed to the 116LSA/112ICL I usually recommend with this cam, you may want to use a 116ICL to bleed off a little dynamic compression and help avoid detonation.

As far as which cam, the smaller cam is great and may be all you need/want. But with 3.73's I think you will like the bigger of the two.

Rich Krause

Rich forgive me..but i got a bit lost lol im not a mechanic nor do i claim to know much about cams..and their profiles etc.. are you basically saying either cam will do...and basically where can i find the cams your describing....just call comp cams again? is it a custom grind your saying i should get....im sorry if im not fully understanding this...tryin my best.. take care and thanks for your time






Steve

Originally posted by SteveLT1
Rich forgive me..but i got a bit lost lol im not a mechanic nor do i claim to know much about cams..and their profiles etc.. are you basically saying either cam will do...and basically where can i find the cams your describing....just call comp cams again? is it a custom grind your saying i should get....im sorry if im not fully understanding this...tryin my best.. take care and thanks for your time
Steve

They are "custom" cams, but anyone can get them for the same price as an "off the shelf" cam. Usually takes Comp 3 days from order to shipping. You need to specify the core (just the year and model will do), the lobes to be used, the lobe separation angle and the intake center line.

Yes, either will work. The smaller cam may not actually give up much hp with a blower, but the rev range will be lower. You will thus loose torque multiplication from staying longer in the lower gears and it will not be as fast. The smaller cam will accelerate harder in the mid-range (typical street use). OTOH, with a stock bottom end, you may prefer to keep the revs below 6K, in which case the smaller cam is a better choice.

Cams illustrate TINSTAAFL (There Is No Such Thing As A Free Lunch) as well as anything in life ;)

Rich Krause

ok so rich if i go with the smaller cam, what are the cam specs you recommend...ie.... im gonna be like a parrot and just regurgitate the specs to comp cams for them to make the cam.....if your in rochester sometime let me know....i at least owe ya a lunch or somethin heh take care and thanks for tolerating all my questions






Steve

Your compression ratio of 10.4:1 is too high. Try to get it down to around 9:1.
Ed

eds thanks but how can i lower compression? im tryin to keep this ...as cheap a upgrade as possible.....are you saying i cant run that motor at 8 psi... at 10.4 to 1 compression? this stuff..i wish i knew more about motors heh.....thanks for the help..

SteveLT1, If you want to lower compression which would be smart, you can get dished pistons or if porting the heads you can open up the combustion chambers. FWIW lowering compression on a blown motor won't lower your HP much at all but will keep your motor from going Kaboom and easier to tune.

rcf925 i hear ya but already bought the pistions..i couldnt find pistions at 9.5 to 1 compression for my size chamber heads etc...could i reduce the compression with a thicker headgasket..or...something...this the whole engine rebuild went father than my dollar can stretch already...so im sorta in a pickle...im really concerned about gettin the right cam at the moment...go figure i call comp cams..tell them what i have in mind..and suggested a lame ass cam...i should of done better research not blaming them but...such is life..ive learned alot for better or worse lol




Steve

8psi may not be too much at 10.4:1, but it certainly will be without hella strong pistons!

But back to cams, tell them that you are ordering an hydraulic roller cam and what year/motor the cam is for to get the right core. Then, specify the lobes (#3190/3192), the LSA and the intake center line. Until you decide on CR, I can't recommend a specific LSA and ICL.

Rich Krause

You don't really want a thicker head gasket with a blown motor. Since you are allready doing some headwork check into some porting , specifically opening up the combustion chamber.

ok rich... well id like the compression ratio to be around 9.5 to 1...the srp pistions..with the stock 58cc combustion chamber is 10.4 to 1...i'll have to look into some porting i guess...i was tryin to find pistons...that would be around 9.5 to 1 compression..but couldnt with the stock heads. i found 9.0 to 1 .or 10.4 to 1...i opted 10.4 to 1 perhaps i shouldnt have...i was running 10.3 to 1 compression before i did the rebuild...with stock internals..would running 10.4 to 1 on 8psi really be that much of a problem? if so i guess i'll do more headwork then








Steve

The srp pistons i got...are 10.4 to 1 compression with a 58cc head 9.8 to 1 with a 64cc head and 9.2 to 1 with a72cc head i just had a 3 angle valve job done on the heads...will that have to be redone now if i had the combustion chamber opened up? i should of planned this better...








Steve

I havent read all the posts to this, but... isnt it a bit mis-leading to rate con.rods by horsepower? Dosent engine RPM have a huge factor in this? Piston weight? Usually rods break in tension...correct?

-Rich: How come no mention of CC-218-230? This is the cam I run and works excellent for me. Nice sound but more imporantantly...great driveability....I drive this car everywhere.

-take care all.

Originally posted by boosted-lt1
I havent read all the posts to this, but... isnt it a bit mis-leading to rate con.rods by horsepower? Dosent engine RPM have a huge factor in this? Piston weight? Usually rods break in tension...correct?

-Rich: How come no mention of CC-218-230? This is the cam I run and works excellent for me. Nice sound but more imporantantly...great driveability....I drive this car everywhere.

-take care all.

I don't know the cam specs except for the 0.050" duration, which at 218/223 is right in the ball park for a hp street blower cam. What's the LSA and the lift for this cam?

You can't make huge gains in chamber size by hogging them out, but it may still be worthwhile. But you need to call JE or Ross and them them what you need. You can often get a "custom" version of an off the shelf piston for essentially the same cost as a stock configuration. If they can make you a set of -31cc dome pistons in the correct compression height, I think that would work well.

When ordering a "custom" piston or rod it's smart to buy a set of 10 rather than 8 pieces. The "custom" pieces often have a lead time associated with them and single pieces may be 30-50% more expensive than the unit price for a set due to setup costs, etc.

Rich Krause

rich thanks for the advice...i'll work the phones and see what i can come up with....ideally i was hoping for 9.5 to 1 compression.. or do you think i should go lower...at 9.0 to 1..just to be safe or to be able to ramp up the boost at a later time..? again thanks for the help






Steve

SteveLT1,
I assume you got the srp flat tops. If you are going NA, these would be fine. But you're not, you are bolting on a blower. So I would return those and get the dished ones. :p
It'll run better with the lower compression.

Oh and on the rods, I would go with H-beams. They are very strong and you can get them for around $400/set. You can get the traditional forged I-beam rods for around $250/set, but once you see an H-beam rod in comparison, it is worth the extra $150.
There have been a few rod failures on the stockers. I haven't heard of an h-beam rod failing yet.

eds i got a set of 5.700 eagle h beams off the net for 389.00 the pistons i got were low compression pistons supposedly..its the 58cc head that makes my compression crap..ive been trying hard to find an off the shelf piston as good as the srps that would give me a 9.0 to 1 or 9.5 to 1 compression and have yet to find em....im still lookin...this ****s stressin me out heh





Steve

Speed Pro and Wiseco both have pistons for a 3.48 stroke with 5.7 rods that come out around 9.5-9.6 with 54-58 cc chambers. They are listed as 8.9 with 64 cc. I am pretty sure the JE makes some also.

tex thanks for the info the speedpro ones i found werent forged with that compression they were cast...i'll prob end up sending these pistons back to jegs..see if they carry pistons that will work for me










Steve

tex are speedpro powerforged pistons real good?.reason i ask is i found the pistons you were referring 2 for around 40 bucks a piston ..so 320.00 for a set...the srp's i got were 515.00 bucks a set....the speedpro pistons were 8.35 to 1 compression with a 64cc head.... at least the ones i saw at jegs...srp makes a good piston but..its for a 6.00 rod... they didnt have a piston at 9 to 1..with a 5.700 rod standard stroke at least..not at jegs..






Steve

Speed Pro is the old TRW. They are plenty strong, and a little bit heavier than the JE, pretty close to the SRP.
Wiseco pistons with rings come in around $500 also.. I don't think Summit lists the combo you need, but you can call and ask for them.
The Speed Pro is what I plan to run in my turbo motor.

I run the Speed Pro Forged Dished pistons in my car, and i know of 2 others as well. No probs with bottom ends.

Bill

guys thanks a ton for the help.....i'll call jegs..and tell them i got the wrong pistons for the application..when i orderd them, i asked them if they thought these would be good pistons for my setup...i should of known better......i'll get the speedpro's tomorrow...if jegs carries the speedpros that i need, i'll just get em from jegs..when i call in to have my other pistons returned for refund...again thanks for the help...cant say that enough lol






Steve

Rich i reordered pistons...the setup will be a 355 with stock stroke and rod length, 3angle valve job on the heads..with speedpro pistons here are the specs

SB-Chevy: 350
Supercharger or turbocharger piston with 21cc D-shaped cup and floating pin. Compression ratios:
8.35:1 w/std. stroke & rods, 64cc head
7.55:1 w/std. stroke & rods, 76cc head

844-L2441F30 +.030'', Each $38.99

the dude i talked 2 said...with a 58cc head id be at 8.8 to 1 compression or so........now id like to pick your brain about a cam selection..and call comp cams with the specs you provide..if you have the time..of course....also with that low of a compression should or could....i run 12 lbs of boost...its an ati p600b with a 2 core intercooler that will be front mounted...and...lastly what are the negative issues in reguards to running such low compression? will the car be a slug gas wise? id like to keep it as streetable as possible...ie..if i wanted to take a long trip..without driving from mobil to sunoco to hess every 150 miles etc lol again..guys thanks for all the help theres no way i would of done this without it...





Steve

Comp Cams XE lobes #3192/3196 on a 116LSA with a 112 intake center line. Set up the blower pullies to max out at the blower at ~6,200rpm.

You will like it.

Rich Krause

rich you are the ****..i cant thank you enough...serious....1000 thanks...if i can order ya a lunch and deliver it to do your door let me know lol















Steve

ok rich....he said..about the cam..... piston to valve clearance may be an isssue..and he stated the cam was quite radical...with 1.6 rockers im lookin at.... .606 intake and .626 exhaust lift..also...suggested for sure i get new lifters at around 230.00 bucks or so....asked me to call him back after i made contact with you in reguards to this cam..thanks for your time







Steve

Steve,
If you run a 12-rib belt setup on the P600B, you can either run a 12 psi pulley or a 15 psi pulley on the blower. I run the 12 psi blower pulley and see around 10-11 pounds on the gauge. I do have the twin intercoolers though-there would probably be a pound or two more of a loss of boost thru the smaller 2 core. You may want to check with ati on this one. The 2 core is supposedly only good to 500 hp. The fan shroud will have to be modified for the 12 rib setup to work, no biggie and well worth it.

ok eds where do i get.. a 12lb pulley and rib belt etc setup. also if i were around 8.8 to 1 compression or 9.0 to 1...what would be a safe lb boost to run...i dont know what sort of hp this engine will put out...in reguards to the 2 core intercooler......i mean could i go 15 lbs boost...on a 8.8 to 1 compression 355 and still be ok? would bosch 24lb injectors support 550 hp or so at the motor? im contacting comp cams now in reguards to a custom cam...hoping to hear from rich rskrause..and then go from there...thanks for the help






Steve

rich i went with the...

CC XE #3190/3192 on a 114lsa. 214/224 @ 0.050" .530/.567 cam..i guess its much milder than the other you suggested..i was tryin to get a hold of ya im sure you were busy...thanks for your help..it and a set of lifters came out to approx $520.00 dollars...this stuff..isnt cheap heh...i just hope the rest of this is smooth sailing ..again thanks for the help..






Steve

Originally posted by SteveLT1
rich i went with the...

CC XE #3190/3192 on a 114lsa. 214/224 @ 0.050" .530/.567 cam..i guess its much milder than the other you suggested..i was tryin to get a hold of ya im sure you were busy...thanks for your help..it and a set of lifters came out to approx $520.00 dollars...this stuff..isnt cheap heh...i just hope the rest of this is smooth sailing ..again thanks for the help..



Steve

That's the cam I used for two years. You will like it. My 4,100lb pig went 10.66 @ 134mph with it!

Rich Krause

rich thanks for the help....i cant wait now....im itching to see progress..my friend got my block and heads...said they look mint...we had it bored it .30 over and did a 3 angle valve job for 550.00 dolars..also milled the head a small amt.just to clean em up......so.... im hoping with the speedpro powerforged pistons...which are approx 8.8 to 1 on a 58cc head..plus he milled it a little..im possibly around 9 to 1 compression.. then run 8 to 12 lbs of boost.....ticks me off though comp cams ..and the fact i got the lifters for 230.00 dollars from them..oh well its a done deal now...there isnt anythin left of the old motor now.... everythin has been replaced internally.. crank rods pistons timing chain roller rockers pushrods new keyed crankshaft hub heads have a 3 angle valve job...i know im babbling im just excited...and hoping the car is very streetable and not a complete pig...at the pump..the way gas prices are goin..it may be regulated to a weekend cruiser lol take care and again thanks for all the help rich...and from everyone...im sure i'll post as i get more progress on the motor





Steve