More power!

I have Performance Trends Engine Analyzer software and discovered according to it the stock valve springs are really weak and do not control valve motion above 5500 rpm. The hp curve really drops off after 5500 rpm with the stock valve springs. Even if I change the cam, the power still falls off at that point. If I change to a stiffer (race) spring, the power carries out to 6500 rpm with the stock cam and bigger cams really start to come alive past 5000 rpm.

Has anyone seen this valve float on a chassis or engine dyno? Has anyone only added a valve spring upgrade to their LS1 and notice the car pulls much better above 5500 rpm?

Thanks,

Fred
98 Z28 -- stock.

Another_User

Uhm...anything other than a stock cam and you will need to change your valve springs. It isn't really an option.

calongo_SS

iTrader: (7)

Won't make a difference above 5500 rpm. Maybe above 6300 or so, but the stock cam isn't making good power up there anyway. And if you change to a more aggressive cam you pretty much HAVE to change the springs.

Diolar Magnum

what are you talking about, with a different cam you have to change the springs anyway!

Pro Stock John

iTrader: (34)

Fred, I have on occasion suggested that SI folks go to LS6 springs since they pull clean on Z06's up to 6500. Stock LS1 springs give up around 6200-6300. I'm sure that they are losing power before then too. So while I have seen dyno evidence, I would not hesitate to swap to LS6 valvesprings so that the HP peak would be carried out a bit more.

More power!

I agree that with a cam change valve springs are needed. I never stated anything to the contrary. My question was if anyone had changed only their valve springs, not the cam, and if their dyno or track mph showed an improvement since my software package showed quite a gain when upgrading just the springs. Springs are a lot cheaper and easier to do than a cam, and if the stock cam picks up a bunch at higher rpms with better springs, then why hassle with the PCM tuning et al with a cam change?

Colongo_SS and Pro Stock John understood -- thanks for the input!

What is SI?

ss rally red

iTrader: (8)

SI=stock internal

soundengineer

iTrader: (16)

I had a buddy who changed the springs..while waiting for his custom grind to show up...went to the track reved to 6800.... went faster.....
I dont know if it was the springs..or the fact that he pulled it to higher RPMs.....
but I'm sure the combo of the 2 made the difference....

ssheets

iTrader: (1)

I've heard of this, I'll try and find the email it was in.

777

iTrader: (21)

springs alone should not change hp numbers...stock cam stops making power before 6000 so i don't see how valve springs will net you any gains...you have to change springs when going with a cam..if you want it to last that is

GuitsBoy

iTrader: (4)

Is that software you speak of an analyzer that you hooked to your car while the car was on the rollers? Or is it engine prediction software that estimates your power based on parts you select, sort of like desktop dyno. If its the latter, I dont think its accurate. I think the software is telling you that youre experienceing valve float @ 5500. Thats really not the case in real life.

technical

Any gains from a spring swap are only an indication that the springs on the car weren't up to the task. On a completely stock engine that's a possibility, but I wouldn't expect to see 40hp. That would mean that GM put a real shitty spring on the engine.

cyphur

iTrader: (10)

you may move a little faster by stayin in the powerband a little longer, but the stock cams powerband doesn't go too far, certainly not much farther past where a new set of springs could take you beyond stock. so you gain a few hundred rpm's and you drop a tenth maybe....or swap cams and drop .5-.7 tenths. you'll be buying new springs either way, it doesn't seem like a tough choice to me.

Redlinez

iTrader: (5)

I would say do it and see. Don't forget to get chromoly pushrods. They're easy to swap if you have a dual spring compressor tool. I did it myself.

vettenuts

iTrader: (4)

I think it was Car Craft that had a series of LS1 articles. Valve springs, pushrods and rockers (stock ratio) made a difference on the dyno as there was a dip in the curve around 5,500 RPM that they attributed to valve train instability. The new parts got rid of it and made a few extra ponies up top, but no where near 40 HP. The article did show the inherent weakness of the stock valve train though.

nuzee

iTrader: (2)

At about 6000 mi, I upgraded my stock springs to 918s. After the spring swap I track tested the new springs on the stock cam. I lost ~1 mph trap speed using the same 6150-6200 shift points that I found was optimum for the stock springs. I figured the mph lost was due to the added friction of the stiffer springs. I then bumped the shift points up ~75 rpm for the 1-2 shift & ~150 for the 2-3 and regained the lost 1 mph. Take this info as a grain of salt since this was just a one time only test using only a few runs between adjustments.

Anyway the point of this is that the relatively new stock springs seemed to have problems reving past 6200. And for you guys wondering why I was reving so high with stock cam, I am still using the stock torque converter so I need the higher revs to help the shift extension between gears.

TheBlurLS1

iTrader: (8)

i replaced my stock springs w/ PRC duals and Ti retainers when i had my heads off replacing my lifters (cam swap this summer). it still has the STOCK cam and everything else (mods in my sig). it seems to still be pulling at 6k like it is at 5k, i can FEEL that the rev limiter needs to be bumped up. i know most say "the stock cam runs out of grunt at 6k" but stiffer springs definatly have not cost me anything. this is all going by the SOTP feel of things.

it used to just feel like it needed a shift at (or before) 6k, now it feels like i'm borderlining the rev limiter before i even know it.

More power!

I have attached a PDF of the graph showing the difference between stock valve springs and putting "race" valve springs in an LS1 engine. As all of you have stated, any larger cam change requires better springs before improvements are fully realized. This software predicts some valve float at 5500 rpm and severe valve float beyond that. I would guess the springs from GM are very marginal.

Thanks for all the replies!

RedHardSupra

iTrader: (1)

so what kinds of numbers do you put in for your valvetrain in general? i could never find a full set of data to put it in EAP, and no matter what cam i'd try to simulate, they'd all 'die' past 5500rpm. care to send me your setup file for ls1 valvetrain? marcinpohl at gmail dot com

cyphur

iTrader: (10)

most of the more popular 23x cams would quickly SNAP the stock springs. its not about realizing results, its about the material and load integrity of the stock springs. stock springs can't support the .58x-.600 lift numbers or the ramp rates of the more aggressive lobes these cams are designed around.

actually....they're great for what they were designed to do. control the cam in the car, last for a great deal of time, and do so in a cost efficient manner(in GM's eyes). doesn't make a whole lot of sense to throw stock springs in the arena with patriot gold duals or Comp 921's and make a comparison...as their design specs and expectations are entirely different.