Theorycrafting my combo before i start buying too many parts, any advise is much appriciated.

Ok i have a 327 9 bolt limited slip rear end to go in my car. I plan on replacing the t5 and 350 with a t56 and a late casting gen1 block (probably vortec roller 4 bolt mains). My question is what cam will work well with this trans and rear end gear on the street? or should i just save myself the headache and put 373s in now? I plan on running nitrous (150-250hp single stage carb plate) so the cam would have to be a grind that optimizes that.

The car will see alot of street time with a bit of track time just to brag about time slips.

Thanks in advance for the help guys.

 

If you run nitrous you may want the 3.27 or so gears if using a 26" tall tire. Depends on alot of things however, like how much power will you make and how high is the motor going to spin?

Need to know what is gonna be in that bottom end, what intake/heads you want to run, and basically how fast you want to go/how much power you want to make.

For instance, My car last year made peak power at 6300 rpm and holding that to 6500 rpm so i shifted around 6600. This car would trap 118-119 in the 1/4 mile so with a 26" tire, optimal gear would be somewhere around 4.11 or even 4.30.
Same car with 150 shot would trap 128 mph, still peak in the mid 6000 rpm range, and optimal gear with same 26" should have been 3.90's or 3.73's

So faster you go the less gear you'll need

 

Thanks for the quick reply

Im lookin at a basically stock roller vortec short block, cast iron vortec heads (with some work on the ports and bowls of course) Probably a dual plane intake for torque on the street. I like edelbrock carbs but only because thats what im familiar with and i already have 3 of em, headers and duals with no cats with flowmaster super 44s. Think a dual plane intake will be a choke point? Im hopin to maintain some streetability.
Id be happy with low 12s high 11s, is this realistic? Its all subject to cam selection i think, i havent figured out what grind im gonna run.

With nitrous i know ill have to run somethin like a 6AL, i havent looked into the ignition much.

Ill prolly keep the 327s and see how they run. Im guessin the 9 bolt is gonna break anyway and ill have to get a 12 bolt.

 

Running low 11's on the engine alone is doable with a Vortec combo, just takes a well exectuted plan. You need to do some minor bowl work to clean up the heads, don't worry too much about the runner entrance, many people make the mistake of going real big here and leaving the choke point relatively untouched. Make sure your intake and intake ports are matched but don't worry about matching the gasket, you can fill that void in with RTV. Enlarge the choke point, this is the area where the pushrod travels next to, this is essentail to get around the 500 hp mark. You DON'T need to go to larger valves but they will help. I presume you'll want to keep a hyd. roller valvetrain. Go with LS7 rollerlifters (about $100 a set) and some good beehive springs that are matched to your cam. Run flat top pistons with 2 shallow VR's, if you want nitrous go forged here, if you want to stay NA just go with hypereutics. You need to get your quench distance between .035-.040", run a RPM intake for street duty or a Super Victor if its mostly track duty. A 750 carb is about the right size, Edelbrock's are okay but Holleys are more tunable. Run 1 3/4" long tube heareds. You should end up around 10.5:1 compression The Comp Cams 280XFI would be a good match for nitrous but get it on a 110 LSA instead of a 113 for best performance.

 

Thanks ap72, some good things to think about there.

Im definetly gonna run N2O, how much would be safe with this combo?

Will the vortech heads have to be modified for the high lift of the Comp Cams 280XFI?

Also why the smaller LSA? I assume because im running a carb rather than FI but is that correct?

There is a ton of good info and good people on these boards. Thanks for the help.

 

i'd be careful grinding on those vortec heads, they are very thin. i'd personally run them as is. i do highly recommend the dart iron eagle heads. even they need a lot of porting to work properly though. very few heads work well "out of the box". comp cams recommends a 112 lobe sep. with more lift on the intake for n2o.

 

150 shot or so wont need a special grind for the nitrous. Just get something that will suit your needs since the car will be on motor majority of the time.

RPM intake and vortec heads with right cam will run hard. Watch the compression ratio with flat tops, dont wanna be too much over 10 to 1 with iron head for pump gas. Most flats are gonna give 10.3 to 1 or so, but depends on the cc's of the valve reliefs.

For low low 12's to high 11's out of a vortec 350-355, your gonna need something thats gonna make 425-450hp on motor. Dont need too high lift since vortecs usually crap out after .500-.525" lift anyway. Keep it under .550 for sure but the duration i'd say something in the higher 220's would work. Custom grind is best bet from someone who has great experience with vortec heads, but most off the shelf cams should be ok. Vortecs seem to have decent intake flow numbers but the exhaust side usually needs improved with mild porting. Good flowing exhaust side usually means you can take some duration split out of the cam, but not always the case. I ran a very large split cam with nitrous use on heads with great intake/exhaust flow ratio and it ran well on and off the bottle. I'm not sure what vortec combos like the most, but cam like comp cams 276hr or advanced inductions 226/234 or crane/gm's 846 cam are good proven cams for hyd. rollers. Lunati has some voodoo grinds that look really nice

Just need to have vortecs machined and fitted with good springs to handle those lobes of some of the more aggressive cams out there.

 

Thanks for the info.

Cam grinds are like voodoo magic to me, i dont pretend to understand all the details involved in picking the right one.

Thanks a ton for the help

 

Vortec heads already have really poor exhaust flow, which is the opposite of what you want for use with nitrous, and even if you modify them to improve that, you'll still be better off with COMP's NX270.

 

I cant find an NX270 on comps website. Am i looking in the wrong place?

 

You want a 110 LSA because it is a NA combo driven on the street with occasional nitrous. A narrower one would give you better NA power and a wider one would work better with NOS and a flatter tq curve- 110 is a good balance for most people, though I personally liek a little lower. Despite what many people preach carb/FI has nothign to do with it as long as you can tune your FI with a weaker vacuum signal.

Also, the Vortec's do not need the excessive exhaust duration many people put on them, nor does a smal shot of nitrous- all of these things are spread by magazine articles and people who know enough to be dangerous but not actaully help. A few degrees more is plenty for occasional nitrous use. If it was a 250 shot for track duty only THEN you would need an extra 10 degrees or so, but not with your combo.

On lift- get as much as you can without sacrificing the durability you want. Stopping where the head flow stalls is just dumb. Also, some bowl work will move the Vortec's stall point up a bit any way... Don't go overboard though, just clean it up- it is possible to do more damage than good if you get carried away.