Jason E

1991 LO3 305
1) Converting from TBI to Edelbrock Performer 1406 square bore 600 CFM carb
2) Edelbrock 7116 Performer RPM Vortec-type dual plane intake manifold
3) MSD 8362 HEI Distributor
4) 170cc GMPP Vortec heads
5) LT4 hot cam 218/228 .492/.492

I already have supporting mods such as a full 3" Edelbrock TES headers/y-pipe/Magnaflow cat & catback, and an Edelbrock 14x3" open element air cleaner. Will this get me to 300hp? Close?

Thoughts are appreciated. This is my first ever engine build. The long block has 119k on it and is in excellent health...barely uses 1/2 quart of oil in 3,000 miles. I plan to continue to use the stock T5 and 3.08 rear for now, adding a Detroit Locker posi unit. This will not be a DD, but if this is too crazy a combo that will end up giving me 15 MPG or a bad idle, let me know.

What else do I need to do that I haven't thought of yet? Thankfully, a good friend of mine is an experienced GM tech, and he's indicated he's willing to work on this with me. I've never torn into an engine myself before, but this will be a fun learning experience for me and hopefully I can pick up a lot. Thanks in advance...I have a lot to learn here. Obviously, emissions are not an issue

305sbc

iTrader: (3)

It sounds like you should land somewhere on the high side of 250 HP.
IMO, how close you get to 300 HP depends on how much effort you put into the heads and valve-train.
By that I mean getting flow out of the heads, especially the exhaust side.
Some mild porting and a performance valve-job should pick up the low-lift flow numbers. You'll want some good quality valvesprings and rocker arms as well.
Then you want to make sure the rocker geometry is set up correctly with the proper push-rod length.
Basically I think attention to detail centered around the heads will determine if you make your goal or not.

Jason E

Interesting comments...thanks for the info. I always thought the Vortec heads were pretty damn good right out of the box. I take it that isn't always the case? What RRs would you recommend? I'd like to get to 300hp if I can, while maintaining some semblance of MPG and drivability.

J91

Well, working those heads is a good idea and will be needed, w/ that cam I'd run 1.6 rockers that'll give you approx. .033" more lift on both sides, or just go w/a slightly larger camshaft.... RR- Comp Magnums....

Jason E

Couple questions...again, bear with me

1) If I add 1.6 RRs, which makes sense, will the Vortecs handle the extra lift? I'm not sure what the max lift is Vortecs can safely handle.
2) Is there a better cam choice than the LT4? I wanted to stick with as much GM as I can, for an obvious reason...but does that not make sense?
3) Will my compression be ok putting 170cc Vortecs on an otherwise stock short block? I know stock is 9.3:1...what would by approximate compression be throwing these heads on?
4) I imagine a 600 CFM carb is more than adequate for a streetable 305? Is it potentially too big? I don't know much about carbs, but I believe a 600 is about as small as it gets, right?

J91

Don't know much about those Vortecs?? Look up some threads on them.
Compression should be OK, what's the combustion chamber size? Vs your stock heads? If smaller you'll gain compression. A 600 should be fine...

vetteoz

iTrader: (13)

http://www.2quicknovas.com/vortecheads.html

Solution

http://www.alexsparts.com/products/V...AT-TAPPET.html

https://www.thirdgen.org/forums/post...681-post1.html

Jason E

^^ THANK YOU. Great information...will read through it further later. I have a lot of time to plan this...I'm running the car at the track this Spring...the first time I've been to a track since 2003, and the first time ever running this car. I want to run the car with my current setup, then go back this Summer with my new setup.

By adding 1.6 RRs, milling the heads, and adding better valve springs to the above, would I be close to 300hp? 280hp? Any thoughts are appreciated. With this engine, a stock T5 and 3.42s, I'm hoping I might be able to run close to a 14 flat. Maybe I'm crazy, but if I'm getting close to stock LT1 HP and have an LT1 rear gear, I don't see why I might not be able to run an LT1 time.

Any thoughts are really appreciated. Sometimes I think I might be crazy to do this to a 119k mile motor, but because its completely healthy, I don't think I'm too nuts...

Jason E

So, as I continue to do research this, I've been thinking...is it a bright idea to do this to a 119k mile engine? It uses about 1/2 to 3/4 of a quart of oil in 3k miles, and other than that is in 100% perfect health. The car has never been raced, to my knowledge. I will probably go to the track 1-2 times this year for a couple times each run, and may never go again. I'd like to get a baseline run the way I sit, then after I do the work.

But do I open myself up for headaches by modding a motor at this age? Any other HP estimates or thoughts are really appreciated...thanks.

305sbc

iTrader: (3)

Probably not any more than with any other motor of any age.
During the process of modification you will be inspecting and refreshing several areas that would likely need attention due to age and miles. You may be better off after the modification.

Unless they are modified the Vortec heads will only allow around 0.450" of valve lift. This can be changed by either machining the heads or using different valvetrain parts that increase the retainer-to-guide clearance.

How much power you get will depend heavily on the flow efficiency of the cylinder heads. That is to increase the air flow through the ports without enlarging the ports in the wrong places. The vortec port responds very well to pocket-porting, and especially on the exhaust side. This means opening up the throat area of the port below the valve seats and narrowing the valve-guide bosses. A fresh 3-angle valve job with blending is helpful, and I would also radius the exhaust valves.
These modifications significantly increase low-lift flow, and therefor increase mass flow area under the lift curve.
While a 305 engine doesn't tax the maximum flow capability of the vortec port, you will still see a very usable power increase across the board with these modifications. This assumes a competent porter and machinist.

You mentioned fuel mileage. Out of your list, the hot-cam will be the hardest on your fuel mileage. While it will be instrumental in producing a decent horsepower peak number, it will also sacrifice some of your low RPM fuel efficiency.
Careful tuning of your carburetor primary circuits and the vacuum advance mechanism of your distributor should allow you to achieve acceptable fuel efficiency at cruise. A four-hole carburetor spacer might also be helpful in maintaining good bottom end response.

89redliningRS

I was searching for LT4 hot cam threads and saw this. Just figured I would post my results for ya. I did my head/cam/intake swap at about your mileage. I'm down in the lower 14's with the LT1 cam, so there is a lot of room there considering the cam. My next step is a bigger cam of sorts, possibly LT4 hot cam, or a custom grind. Just need beehive springs and it'll be set for a bigger one. The LT1 cam pretty much has the vortec's maxed out on lift. I did mill my heads down .030 to keep compression reasonable. But I think 13's are in reach with one of those cams.

86LG4Bird

iTrader: (1)

Sorry I just noticed this thread a few months late!
With your supporting mods, you should have no trouble at all reaching 300 flywheel hp. Other than making sure you have enough compression and valve seal/retainer clearance, you can disregard all comments about working the Vortec heads, ie. any porting or cleanup work. Stock Vortec heads are capable of over 400 hp with the ports, pockets, and valve job just as they are.
You stated GMPP heads, which I take to mean they are the modified Vortecs that are already worked to accomodate ~.550 valve lift. Are they really GMPP, or just stock Vortecs?
Whether or not you mill the heads for more compression, I recommend running a .015" head gasket to bring the quench clearance down to a better number. Just make sure deck and head surfaces are flat.
Even if you're restricted within stock Vortec valve seal/retainer clearance, your idea of a Hotcam with 1.5 RR's and enough compression (I'd recommend at least 10.0, 10.5 would be better) will make 300 hp.