Hello all, it's been almost 8 years since I've been active on this message board under my old username. However, I have finally got back to the point where I have both the time and money to finally start working on my 3rd Gen again.

What I want to achieve is around 300 WHP out of my 305 LB9. I am a fairly competant mechanic, but I have been out of the 3rd Gen loop so long I don't even know where to start.

I'm looking for direction on what heads, cam and intake combo to run, and looking into engine management as well (ECM/PROM).

The car isn't a daily driver, but I am looking for a decently quick weekend car and plan on extensively upgrading the suspension as well, however my priority is getting the engine pulled, built, and ready to run by this winter.

Any suggestions would be greatly appreciated! Thanks.

 

Well For starters lets talk about your goal. You say you want 300 whp from your lb9. This might be pushing it as 300 whp = about 375 brake hp. Thats a pretty tall order from a 305 and I would definitely recommend going to a 350 if your firm on that objective. Now I want to say I'm not one of those "swap to a 350 305 are a waist of money ect" guys but if thats your goal thats just what makes sense here. Now if you were willing to go with 300 hp at the flywheel then I would say yea sure if your 305s in good shape thats doable.

However even before we get there is there any reason why you picked 300 whp as your goal? See the point I'm trying to make here is I see a lot of builds that start out like this with a hp number in mind for no particular reason. Its like women with their weight there so concerned with numbers when really its about appearance likewise here we should be more concerned with performance less about peek numbers. If were were talking about race cars things would be a little bit different but were talking about a fun decently quick street car.

Before I make any suggestions give me an idea of what exactly your trying to accomplish. For example:

looking for a decently quick car. What exactly do you mean here maybe you had a particular 1/4 time in mind or a 0-60? With these numbers we can start to formulate how much hp you will need and even what motor would be best at achieving that goal.

Street manners. How well street mannered are you hoping this car to be? Typically speaking for street cars I would focus on the low end because on the street thats where you spend 99% of the time. So things like 4k RPM stall converters and huge cams would be out of the question in favor of parts that will provide a broad flat tq curve across the lower rpms. Also things like emissions legality and fuel economy goals if you have any.

Other special request? Things like maybe a big concern to you is having a car with a really lopey idle ect.

Once we know what were trying to achieve then we can start selecting parts.

 

Thank you so much for your reply!


I picked the 300 WHP range simply because from the limited reading I have been doing that sounds within the realm of the LB9 in my T/A. However, I would be happy in the 275-300 range as well. Of course at some point in the future a form of low PSI F/I could make it's way on to the motor as well.

Again, with this being primarily a weekend toy, I'm not hugely concerned about MPG, however it would need to remain emissions compliant. Lopey idle doesn't bother me, in fact that's the one thing I wish my Hemi had!

If I had to shoot for a 1/4 mile time, I would like to be in the mid to upper 13's, however I'm not looking for a strip only car. I know that I will have to re-gear the rear end as well. I definitely plan on tearing into the suspension and make it a fun car to drive in the local canyons here.

Hope that helps!

 

Ok well now that we have your goals narrowed down a bit we can start talking parts.

First off your performance goals:

The Trans ams were a bit on the heavy side. I figure about 3500 lbs or so for an estimate. To get a car of that weight to run in the mid upper 13s that would require about 330 brake hp which is only 264 hp at the wheels.

Now that being said lets talk about motors. You state your goal is to remain emissions legal. Its going to be pushing it to make a streetable 330 brake hp on a 305 not to mention while maintaining emissions legality. The problem is this when your building an engine the force it will generate (torque) will be related to the displacement and its efficiency (which varies with RPM). To build more torque you either need to improve its efficiency (with things like headers for example) or the displacement. Now lets talk about hp. HP as you may already know is going to be the torque*the RPM divided by 5252. This means if a motor generates 300 ft lbs of tq at 4000 rpms its only generating about 230 hp but that same 300 ftlbs of tq at 6000 rpms yields about 340 hp. Because the amount of torque generated is going to be limited by the motors efficiency and its displacement, to generate more hp typically it means using "hotter" parts to shift the torque curve up in the higher RPMs. This will generate more hp at the expense of your bottom end. For your 305 we would end up having to do something like that to get it to produce 330 hp.

The problem with doing that is these "hotter" parts are not typically emissions legal and it takes away performance from the area you spend most of your time. A better choice may be to swap to a 350. Legally many states offer provisions to swap motors as long as it was a motor that came in that car and you retained all the emissions components. Since third gens came with l98s you would probably be able to get away with this as long as you retained your TPI and other emissions equipment. It would be much easier to produce 330 hp while still maintaining street legality and driveability.

So with all that said would you be opposed to the idea of swapping in a 350?

 

I would really like to keep the LB9 simply for nostaglia reasons. This particular car has been in the family since the early 90's and I'm only the third owner. At the time I took it off the street to start this project, it had just a hair over 100K on the clock. For me, I really would prefer to keep the LB9.

That being said, what would be a reasonable number to expect out of a streetable 305?

 

I think your goals can be doable. Guys here have gotten 305's in the 12's which is about 300whp.

If you have some money to spend, i'd do this just like any other 350/383/400 build... heads/cam/intake.

More budget would be ported aluminum L98 vette heads...run you about 700-1000 bucks complete and be more than enough to make that power. Other option is Trick Flow 175cc small bore heads. Need to stick with a 1.94 valve or smaller to get enough piston to valve clearance and valve to cylinder wall clearance. Reduces shrouding effects too.

Cam i'd go custom hydraulic roller for the application. Peak at 6000-6200 if possible. Rev up to make the power. Stock bottom end should be good for 6300-6400 rpm shifts so peak few hundred rpm below that. Something around 216-218 deg I think will work, low 500's lift should be fine with those heads.

Intake, i'd do siamesed TPI runners and ported base to keep it smog legal and nostalgia like. If you could swing it, I'd go stealth ram or superram. That would be a nice combination of parts.

 

Like I mentioned before, at some point I want to go with a form of low PSI F/I (most likely remote mount turbo). However, I just pulled the lower intake and heads off yesterday and was very happy to find zero rust in the cylinders and even after 100K+ miles there is visible cross-hatching left on the walls.

Since I want to go F/I in the future, I was looking at upgrading the pistons and conn. rods to forged. I might as well add a little displacement and have the cylinders bored out. Do you think the factory crank would be good for 6-8 PSI?

Also, could I get away with having the factory LB9 heads ported? I know that the Vette heads will save a bunch of weight, but with a future turbo, will it make that much of a difference?

I'm not opposed to swapping the manifold, and I've heard that the Edelbrock lower is a pretty decent piece with lots of room for porting.

 

If your set on boosting then just get forged pistons, fresh overbore, and new rods with strong rod bolts. Check the stock crank to see if it is in good shape, have it rebalanced with the new stuff and throw it all back together. It will handle 15psi with good tune let alone 8. I think 12-15 psi is gonna be what you want to run to really feel a strong difference in the motor

Port the stock heads will work. Just shoot for 8 to 1 compression or so with Iron heads, 9 to 1 with aluminum for boost.

Mild cam to match the heads/intake/boost combo and you're set. Ported stock base would be nice, so would an aftermarket base, but with boost you can just turn it up and gain power that way if needed.

It will feel better all motor with aftermarket TPI and ported heads with mild cam in the time being... stock base on that setup will restrict everything and wont feel much better.

 

Well one conflict I see is that if your serious on going with a forced induction set up the parts you would chose for a N/A motor vs a forced induction motor are different. So honestly I would tend to hold off on the whole project till your ready to go all the way. N/A well built I think you could conservatively expect about 280 brake hp with just under 400 ftlbs of tq while still remaining 100% emissions compliant. With forced induction its a whole new ball game but this is another area where I see a lot of this is what I want to do and am planning on doing but then life happened and you've got a half finished project. I just see a lot more work involved than just installing a bunch of forged components.