drknow90rs_ss@y

iTrader: (3)

Ok, I did a search for this and didnt come up with anything that answered my questions.
Next week I am buying a wrecked 97 Tahoe with the 350 vortec engine and as the motor only has 21,000 miles on it, I am considering swapping the vortec motor into my 86 IROC. (The IROC currently has a 305 TPI motor) What I am wondering is: What kind of problems am I going to run into? I know I will need a new TPI base, and would like some suggestions on that. The car also needs to be kept emissions-legal and I have heard that I will have problems with the egr system. What sort of problems? I would also like to put a new (Hotter/better but still streetable) cam in it. This is my wife's "Semi-daily driver" (She drives it every few weeks or so.)
Thanks for the help!!!

Fast355

iTrader: (2)

The only thing I did not do is hook up the EGR. It would have been simple, but on my 1983 G20 Van it wasn't needed.

https://www.thirdgen.org/forums/tpi/...tec-350-a.html

drknow90rs_ss@y

iTrader: (3)

Sweet! Thats got to be the first G-van swap I have seen!
How hard is it to hook up the egr?
What about recommendations on a streetable cam. (The extreme side of streetable that is)

Nelz

I'm doing the same swap. L31 Vortec heads on an 88 5.0TPI on my Iroc. The following issues have been fixed:

1. TPI base bought from Scoggin Dickey in 2003. The TPI Vortec base is now manufactured through edelbrock. (Don't bother paying the $50 for edelbrock to put their name on it, Scoggin dickey's manifold is manufactured by Edelbrock and doesn't have the edelbrock name on it.)

http://www.currymotors.gmmotors.com/...Baseplate.aspx

2. Valve Spring issues....major inconvienence. I bought the 26981 Comp Beehive springs with the 1.24. O.D but the inside diameter is only 0.825. You don't need to enlarge the valve spring pocket with this spring (and any spring with an O.D of 1.25), you do need to machine down the valve guide boss and buy a new valve guide seal after that....or go the cheapie route and just buy regular non beehive 981 Comp springs. This article helped a lot. Your run into retainer to guide clearance issues and
coil bind issues at just above .525 of lift.....

http://www.chevyhiperformance.com/ho...458/index.html

"One area that can trip you up when selecting a performance valvespring is this large guide- boss diameter of 0.900 inch (arrow). Most performance valvesprings have a smaller inside diameter, which requires this boss to be machined down to about a 0.630-inch diameter...."

"This requires purchasing new valve-guide seals, since the factory uses a 0.560-inch guide to locate the seals."

""Another way to go is to have a machine shop cut the guide boss diameter to around 0.760 inch and reduce the seal height and use either the Crane H-11 tool steel spring (PN 99846) or the Comp spring (PN 981)."

Or you can get the Scoggin Dickey z28 springs or there's a set of Crane springs apparantley that you can just drop in.

http://www.gilbertracingparts.com/Cy...ads/Vortec.cfm

The GILBERT CHEVROLET solution is to use Crane Cam’s 10309-1 drop-in valve spring and retainer kit which is good for .550” lift with no machining


3. Lift limitations. Without spending more machine work on these heads, you're limited to a cam with about .480 lift at 50 and 1.5 rockers because of clearance problems....which is fine because the heads start to level off flow at about .500" anyways. After that, you need bigger springs which require machining the valve pockets to fit those spring.

The comp guy said that a 262HR-12 is probably the lowest maintenance way to go with a 305 without re-PROMing the computer (Comp's dyno on this head and a 305 tpi said you'd hit about 240-270HP on stock manifolds at 4500RPM and 370-400ft# tq at 3000rpm.) A 262HR-12 is about all your really need (if you throw in 1.6 rockers and get machining done for that cam, you've maxed out the lift on the Vortec heads at .512") but then you need to make sure your machinist checks clearances for that amount of lift and you may need bigger springs....just make sure you tell your machinist what you plan to do and ask what machine work needs to be done to make those heads work.

The machine work on the heads added about $300-$500 onto the heads. Plus you may have to mill the heads to get the right compression.

Compression issues:
The problem with figuring out the compression ratio after is that I can't seem to find an answer to 305LB9 stock piston valve relief cc's.

The Vortecs had abot 64cc's.
With a stock bore of 3.736
stock strock of 3.48
a gasket anywhere from 0.018-0.026
a stock deck clearance of 0.025
and either flat top pistons with 0 cc's valve relief to 10cc's....does anyone know the correct answer to this without cc' the pistons after you open up your block?

your compression ratio would be anywhere from 8.5:1-9.7:1 or more depending on 64cc combusion chamber, gasket thickness and 0-10cc's on the piston. And if you mill the heads....because the stock heads were 58cc's (some articles said only to mill to 60cc's) well, you can throw your compression ratio past 10:1 and kiss pump gas goodbye. Here's a compression ratio calculator. When you take your old heads off your car, please cc your pistons in the hole in let me know what value you get. I don't plan to install my heads until later this year. I heard 87 and later pistons had more cc's in the valve relief than pre 87 pistons, but it makes a difference.

http://users.erols.com/srweiss/calccr.htm

Nelz

As for EGR issue, Scoggin Dickey sells an EGR kit for the Vortec TPI swap.

And as for the comp tool for machining down the guides, it cost just the same to get a machine shop to do it for you.

drknow90rs_ss@y

iTrader: (3)

WOW!! Thank you! That helps! As long as the compression is good in all cylinders, I wont be removing the heads from the block. I just dont want the "Stock" truck cam in it. My wife has a habit of blowing motors, so I imagine I will be doing somewhat of a rebuild on it soon, anyways. I will probably use the crane 10309-1 kit that you mentioned. The whole idea of the IROC is for it to be the least radical of my cars (Most streetable). What would be the most radical "Street" (Roller) cam I could use?
I will be using a 350 prom and 24# injectors if that helps.

Nelz

How come you're using a 350 prom and injector set? Your Prom tables on that prom are calibrated for an engine with an extra 45 cubes and better breathing with a 4inch bore. You may want to just consider staying with the stock computer and bumping up the fuel pressure instead.

Let me know how those crane springs work, because I don't konw exactly if they drop in. They have an inside diameter of 0.87 inches. You may still have to machine the valve guide boss down (Unfortunately, there may not be a way around it-again talk to a machinist.)

As for lift, keeping retainer and guide clearance and coil bind in mind, probably .480 lift is it. Anything over that requires more machining on the heads to work and again, these heads start to drop off flow after about .500 lift so there is no point in sticking a cam with more lift than that.

drknow90rs_ss@y

iTrader: (3)

the prom and injectors are just laying around. I have never tried to use them with my 305. I am dropping the entire vortec 350 longblock into the car. I would like to avoid any machine work altogether, but if the compression test dosent turn out well, then I will do a complete rebuild. I would like to stick with the stock machining if I can. Thats my question: How big can I go before I need machine work? And, what cam will work for this?

91 1LE

iTrader: (1)

Pull the heads and have the bigger, better springs put in. If your wife has a propensity for blowing motors you need to get rid of the stock valvesprings if you put in any bigger cam. I would recommend the LT4 Hot Cam for use with these heads. IIRC the ports were basically copies of the the LT1's. You could get the hot cam kit and have those springs installed at a machine shop after the requisite machining and then all you would need would be screw-in studs. My $.02

drknow90rs_ss@y

iTrader: (3)

Yeah, I am beginning to see that my budget "Blowable" motor is not going to be so.... "Budget" . LOL! I was hoping to not have to remove the heads, but oh, well. I really should do something about a rev-limiter....