ok so i have a sbc vortec crate motor i bought rated at 330hp 380tq, i ran it like that for a while, ran great but wanted some more power. i put 4.11s and posi, built 700r4 with 2500 stall, 750 demon carb, had the heads milled a little, put different valve springs and full roller rockers with screw in studs. Then i changed the cam.DUN DUN DUN. its a lunati hydraulic roller, specs are:
.525/.540 lift 300/310 duration 110/106 lsa
Then it ran like shitttt....it would idle in park at about 1500 rpms and in gear it would try and die unless u kept ur foot on the gas. Also driving it had hardly any power low and mid range and would just bog down if full throttle. and then be ok after that but not fast. i messed with timing and the carb so much and finally gave it up. The only thing i can think that dont match up correctly are the intake and heads which are only 170cc. i almost have the money for new heads and intake. i would just like to know if that sounds like it will for sure fix the problem.

thanks for any input
-andy

 

personally i think your cam may be too big. duration is 300/310.............is that @ .050?
Also LSA ( lobe seperation angle) is it 110 or 106?

 

no at 50 its 242/252 and lsa is 110 icl is 106. sry bout the confusion

 

This looks like a case of severely mismatched components. That cam is way too big for that engine. First, an idle around 900-1000 RPM sounds about right. 1500 is high, but that much duration with that LSA isn't going to idle so good with only 350 inches. I'm going to venture to say that you've got your idle screw screwed in so much that you've exposed the transition slots and are trying to idle off the main circuit, which would be why you've got to keep your foot on the gas (or see below). The fix for that is to drill the throttle blades and close up the idle screw to cover up the slots again. You say you milled the heads "a little". How much is a little? That engine starts out at 9:1 even if you're at 9.5:1 now, you're compression is too low for your cam choice. You don't have enough stall for that cam either.

What bothers me the most about that combo is the fact that the Vortec heads CAN NOT take more than .480" lift without either a spring change to the conical LSx style spring or a standard spring with machining of the valve guides for retainer to guide clearance. You never stated weather or not you swapped the springs. If you didn't change the springs I'm going to bet that you bent all of the pushrods which could very well cause the problems your describing. Very well could be (and probably is) your idle problem as well.

 

Well i have drilled holes in the throttle blades and have valve springs to handle the lift, i was told the CR is 9.5 to 1 or a little more, thats y i didnt know what else to do, so i figured id get new heads like 195cc or 200cc and an air gap intake that are both rated up to 6500 rpm i think(which ill proly rarely get up to). Then id have a cam, heads and intake that are all in the same rmp range. Does that sound right??...also the gears match up, and i do agree a bigger stall would be good. Also on ryans engine combo page there are alot of really similar setups to mine, with damn near same cam but with the bigger heads and intake, and they all make over 400hp....and they all have around the same compression ratio

 

195's would work well, but I don't think that's your problem. Which springs did you use? In some cases just a spring change is not enough and the guides will still have to be machined. Even using the LSx style spring will only get you to around .550" lift safely. You're real close on the exhaust. Did you swap in the standard 1.5:1 ratio roller rockers or did you go to 1.6's? 1.6's will put you way over the limit in the lift department. Also, if you used Comp Cams rockers they are a 1.52:1 ratio not 1.5:1, adding about .007" lift bringing you even closer to the edge on the exhaust if not over it. I would not be comfortable running that close to the limit. In fact, the .550" number from what I've read, is an approximation. You may get more, but you may get less. These are just a few things to think about, but reading your post again and thinking about it some more it sounds like it could be an internal vaccumn leak or external for that matter. Which intake is on the engine? Did you buy it turnkey with the proper GM intake? If you didn't, did you use the proper Vortec intake? I'm not implying that you don't know what you're doing and certainly don't mean to insult you, but sometimes we get caught up in the excitement of doing these things and can overlook some of the details. At least I do! Anyway, without the proper intake and it's raised runners, you'll end up with an internal vaccumn leak and how much meat is left under the runner after milling? If there's not enough, the gasket may have a hard time sealing and cause the same problem. I did something similar many moons ago with the 355 in my '87 Monte SS. I was using the L98 aluminum heads that were fully ported, polished and milled for more compression. The milling was my downfall. The car acted very much like you described. The bottom line was that there was not enough metal left under the intake port after milling causing the intake not to seal. Something else to think about. Oh and I stand corrected on your cam choice. I ran a big solid flat tappet in my Monte with the L98's and a Victor Jr. intake, so who am I to talk! I just wouldn't use a cam like that on the street anymore, too snotty. I did it then, but it would drive me nuts now. Good luck tracking the problem down!

 

yes i do have 1.5 rockers and i did buy it turn key with the proper intake, but yes i know what u mean lol...however i think ive just decided to go ahead and get new heads and intake like i decided, but also get a diff cam...i wana go with the comp cams xe 288 hyraulic roller...what do u think about that setup?..it saids needs only 9.1 CR and i deff have that, and also alota lt1's on youtube have that cam with stock heads and intakes and it works fine......btw i appreciate your help thanks

 

I like that cam better! It's still close to the edge on the exhaust side but, I think it'll make better power in your combo than the Lunati cam you're running now. I bet it'll get you in the 400 range. If you have the money, go for the new heads. They'll only help you in the power department, but I don't think it's necessary. Save your money and swap the cam. This will also give you the opportunity to make sure everything is sealed properly and that the pushrods are straight.

 

awesome and yes i do have the money for new heads, and intake, for sure want to help the power dept. out lol....so with a good set of heads and say the air gap intake with that cam wuta u say 430-450ish?.....and yes ive already disassembled and the push rods are straight

 

Depending on the heads, I think that's reasonable, leaning towards the lower end of the range. If you're going with an aluminum head, I'd go with a smaller chamber to raise the compression while you're at it. Given the heat dissipation properties of aluminum, you can raise the compression by 1 full point safely (9:1 to 10:1). I think that'll put you right in the 450-460 range.

 

How much did you have the heads milled? That's alot of cam for 9.5:1 and a 2500 stall

 

ya i was planing on aluminum but wow i didnt realize it would raise the CR a entire point....thats sweettt....i really cant wait to get it running with all the new stuff!

 

i dont know exactly on the mill, just know it had "9.5 or a little more"

 

Just to be clear, you will need, depending on the volume of your valve reliefs, a 59cc combustion chamber as opposed to the 64cc's of the Vortecs, to achieve the 1 point bump in compression. This will require the new heads to be milled. I can't think of any that have that size chamber out of the box. Fortunately, most manufacturers will perform this operation for a fee at the time you place the order. Just tell them what you want. FWIW, I based the 59cc number on a 4.00" bore, .039" thick gasket (Fel Pro 1010), pistons .025" in the hole and 7cc valve reliefs. This is not an optimum combination because the quench is too loose, but you get the idea.

 

cool i didnt realize they could do that for you from the manufacture, i was looking into the jegs heads 197/64cc but i now came across the trick flow 195s i believe and 62cc, so it wouldnt take much to get the heads to 59cc if i got the trick flows, which itd proly be better to spend the extra $200 on them i suppose.....but ya, around 450hp is exactly where i wanted to be so thats great, thanks for all ur help again

 

Any time, glad I could help!
Just one more thing to consider. I'm assuming you're planning on the Trick Flow Street/Strip 23* head. The max lift on the springs on those heads is
.540" (you're at the absolute limit) and if they are anything like the AFR's I have on my 388, they won't have enough pressure to control the valve with your hydraulic roller cam. You should really consider their Super 23* Street/Strip head package. They use a .600" spring and I would imagine, should have enough seat and open pressure to control the valvetrain. Isn't this stuff fun!

 

ya just after my last reply i noticed that lol....and ya sureeee alotaaa funn...money money money

 

im running this cam and love it. revs really fast. my heads still have stock valves and just bigger springs. and i use a 1.6 rocker

http://www.trickflow.com/partdetail....1&autoview=sku


heres a little video i took before i put exhaust on it.

http://s195.photobucket.com/albums/z...utlassidle.flv

 

what Fast01 said.
sorry but your combo is way..... jacked up.
i have a 327 "331" vortec headed with 20 milled,valve guides cleared for the 282 cam turbo 400 and 4.56s and run 7.60s in the 1/8th all day "bracket racing"
just a combo to take a look at.
vortec heads are real good, but easy bro you can over kill them too.
good luck

 

sweet man...does it sound good at idle?