[mike_dmt]

Hi guys, it's been a while since I've posted on here. Life gets in the way of playing cars sometimes

So, I've got a 68 LeMans build on the back burner, and it's time to start getting the pieces together for it.

The idea is a street trim car with a couple turbos for fun. Automatic trans, in the 4L80 variety most likely.

I was starting to lean towards an LS, but I do have some parts on the shelf I'd rather use, if it's at all reasonable, so I was looking for some direction.

I've got a couple of 68 400 YC blocks and stock cranks. A set of 6X's and a set of 48's. I think the 48's might push the comp ratio a little too high?

From the reading I've done on this board, the stock stroke of the crank sounds like it would be ok up to a point?

The other parts I had in mind to source would be rods and pistons of the forged variety. The manifolds would likely be the airboat forward facing ones that I've seen here, and floating around the interwebs.

At the end of all that, I guess what I'm asking for is some advice based on the junk I have already laying around.

Sorry in advance for the long post

[ID67goat]

I think it all depends on your budget and how set you are with keeping it Pontiac....But based on what you want to do, it almost makes more sense to me to go LS. Lots of bolt on parts for turbos with LS, 4L80e will bolt right up, and computer will run the engine/trans combo.

[mike_dmt]

Yeah, the LS route would be cheaper and more reliable in the long run, for sure.

A Pontiac engine would keep it interesting though, there's already an ocean of LS swapped turbo builds.

Budget wise, I'm not looking to drop $10k on the engine, but a few $$$ are definitely in there for it.

The computer isn't too much of a concern, I was thinking to do EFI on it, so the trans can be managed from there as well.

[Scarebird]

If you are going turbo, sell the Pontiac stuff and go LS.

[Alex_F]

I am a diehard Pontiac guy and have turbo charged 2 working on a 3rd now. That being said I am also helping a buddy on a ls turbo project. The parts available for ls stuff is unreal, it doesn’t matter what your doing they probably make a kit for it or someone has already done the homework on how to. But at the end of the day it will end up being just another belly button car( everyone has one.) Build the 400, stock crank and 6x heads will work perfect. Throw some decent forged rods and pistons at it and some billet caps if you want to get wild. Those airboat headers look nice and you can’t beat them for the money. Get a good sized single or some twins and you’ll be happy. You wouldn’t believe how many people are shocked when they look under the hood and see a real Pontiac.

[ErikW]

Originally Posted by Alex_F

I am a diehard Pontiac guy and have turbo charged 2 working on a 3rd now. That being said I am also helping a buddy on a ls turbo project. The parts available for ls stuff is unreal, it doesn’t matter what your doing they probably make a kit for it or someone has already done the homework on how to. But at the end of the day it will end up being just another belly button car( everyone has one.) Build the 400, stock crank and 6x heads will work perfect. Throw some decent forged rods and pistons at it and some billet caps if you want to get wild. Those airboat headers look nice and you can’t beat them for the money. Get a good sized single or some twins and you’ll be happy. You wouldn’t believe how many people are shocked when they look under the hood and see a real Pontiac.

This

[Scott65]

How much power are you planning to make? Plan for less than production block splitting levels, or plan for an aftermarket block. All this after figuring your budget... To me (and I've considered it) this comes down to whether you make the decision from an emotional or logical place. Unless your budget is unlimited or not a determining factor.

[mike_dmt]

Thanks for the replies, fellas!

I don't really have a specific horsepower number in mind, and it's not going to be a race car. That's more of the direction my current build is going.

The budget is always a factor, but power with a level of durability costs money. I'm ok with that. This one will be more of a Power Tour candidate. I haven't ever done it, and it's on my list.

I've seen the 4 bolt billet caps, and was interested in some more info on those. Can a 2 bolt block be machined for them?

[ErikW]

Yes

[mgarblik]

If you don't have any particular emotional attachment to the Pontiac engine platform, it's very hard to make a case for building one vs an LS based engine. They are plentiful, cheap, and make decent power. Just like throwing an old SBC in any given Pontiac back in the day. Cheap, plentiful, decent power. Incredible aftermarket support for the Chevy stuff. The cool factor, and having something unique and different, opening the hood and having a real Pontiac engine in a Pontiac car. Only you can determine what that is worth to you.

[Sirrotica]

Since the LS engine was built on the platform of taking all the corporate strong suits from every division, it probably exceeds every divisions original design. Since the division engines wire actually designed back in the late 40s early 50s and appeared in the mid 50s after wringing out the designs, there has been a bunch of water under the bridge up until 1992 when the LS engine design was commissioned.

Roughly 45 years difference from inception of the divisional engines, to the corporate engine. I don't think anyone is surprised at the engineering differences as well as the metallurgy, machining, tooling, casting updates etc.
Hard to compare 45 years of advancements without tipping the scales to the newer technology. You're definitely comparing apples to oranges.

The good thing is some of the more recent advancements can be built in to the old iron to update it.

As Mike has said if you have no loyalty to the older platform, hard to convince someone to spend more money on old technology rather than just open a catalogue, and buy what they need. I own both ends of the spectrum, but personally I'll never put an LS into old iron that came originally with a Stratostreak engine between the frame rails. but I'm old and stubborn too.......

[70 bird]

You can go fast with either. Its up to you.

[AIR RAM]

Originally Posted by mike_dmt

Hi guys, it's been a while since I've posted on here. Life gets in the way of playing cars sometimes

So, I've got a 68 LeMans build on the back burner, and it's time to start getting the pieces together for it.

The idea is a street trim car with a couple turbos for fun. Automatic trans, in the 4L80 variety most likely.

I was starting to lean towards an LS, but I do have some parts on the shelf I'd rather use, if it's at all reasonable, so I was looking for some direction.

I've got a couple of 68 400 YC blocks and stock cranks. A set of 6X's and a set of 48's. I think the 48's might push the comp ratio a little too high?

From the reading I've done on this board, the stock stroke of the crank sounds like it would be ok up to a point?

The other parts I had in mind to source would be rods and pistons of the forged variety. The manifolds would likely be the airboat forward facing ones that I've seen here, and floating around the interwebs.

At the end of all that, I guess what I'm asking for is some advice based on the junk I have already laying around.

Sorry in advance for the long post

Make sure you DONT buy the Air boat version and purchase the car version... I beleive the Air boat version sticks out a bit more and the car version hugs the block closer.

https://www.stainlessheaders.com/sea...ults?s=pontiac

They make them for the LS as well...

I thought about going LS for about a nano second... I just hate to see corporate engines in non corporate vehicles. There is no denying the Greatness of the LS engines... heck if God had an engine on his chariot, he would be running an LS. I even have an LS3 car now which I love... however, I'm bent on building a Pontiac engine for my 69 Bird. It will be a Pontiac 496 to run a single bore throttle body, twins with 15-20lbs boost, Multi Port Fuel injection, and PCM controlled... Daily street driven in Miami Traffic. I initially set out to build my cast iron 455 block but ended up getting cold feet. I would have been limited to 6-8lbs of boost and there where just to many people saying "DONT DO IT"... lol... so when I came into some funds I picked up an MR1 block for the bases for the build. Yeah I know, the lines get blurred when you go to an aftermarket block...

SPEED SAFE, NICK

[gtokid1968]

Pontiac ALL the WAY!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
I would never put a Chevy in ANYTHING!
Just like belly buttons and A!! Holes!
B,O& P all my life.
Use what you have or sell it and buy a Cheby and put an LS in it.
JM2C!!!

[mike_dmt]

I'm more of a Pontiac guy, I don't see myself getting in to chevys any time real soon. I wouldn't hate a C-10 or a split bumper some day, but one would have to fall in my lap.

So, am I understanding that the stock blocks can only handle 6-8 pounds of boost?

[Tom Vaught]

Mark at Luhn Performance did a dyno test on a 455 engine with a Vortech T Trim Supercharger, (I was there) and he made 862 HP and even higher torque numbers and the engine never went over 5300 rpm at 13 psi of boost pressure.

So I know stating that a 455 engine can handle only 6-8 psi of boost pressure is not true at all.
That testing was documented by Don Keefe and was written up in one of his magazine articles many years ago.

That is a FACT.

Tom Vaught

[Scott65]

Tom, could you in good conscience recommend to the OP to put 862 horsepower on his stock Pontiac block and crank? Expected lifespan? 6-8 psi may be a very appropriate range for this to keep things together.

[Tom Vaught]

Originally Posted by Scott65

Tom, could you in good conscience recommend to the OP to put 862 horsepower on his stock Pontiac block and crank? Expected lifespan? 6-8 psi may be a very appropriate range for this to keep things together.

The engine that Luhn Performance ran was not a aftermarket block, it was a basic early 70s 455 engine block with some good rods and I believe one of Wade and Mark's BOP forged cranks.

So to answer your question, after we tore it back down for a engine inspection the only issue we noticed was some main cap fretting, (that Mark later fixed with longer precision fit alignment dowels, same two bolt main cap block).

I plan on doing something very similar on my aluminum head FACTORY 455 block (2 bolt main) using another T-Trim Vortech Supercharger at (9-10 lbs of boost) in my street convertible. Should be good for a easy 600 HP with a mild camshaft and factory crank. I would not worry about running 5300 rpm or 13 psi of boost but do not want to twist up the car (64 GTO) to brag about another 860+ HP engine. SO YES, NO PROBLEM IN MY MIND AT ALL.

Tom V.

[mgarblik]

When working to turbocharge an engine platform designed in 1952-53 vs one designed in 1994-95, there better have been some improvements in the 45 year time span. The biggest improvement IMO, is in the stability of the block structure with the deep skirts and the 6 bolt main cap retention. Second would be the lifter valley area. The head deck is hardly better, still retaining a 10 bolt pattern. ( tiny bit of extra clamp load from the little inboard fasteners) If course the heads breath much better stock. But as the power level and boost really increase, an LS will turn into aluminum cole slaw just as easily as any other engine. I have seen plenty at the race track split in half and barely recognizable as a GM engine vs a Hemi or Ford. It's that "moderate" HP range where the LS really shines, cost wise vs a Pontiac. To make a Pontiac V-8 run reliably at 1000 HP, your going to have to spend some real money on it. With an LS, a trip to the junk yard and a moderate budget, and your there. It hurts me a little to write this, but it's what I see in my classes and at the drag strip. I personally wouldn't run one, but I understand why some people do. The TV shows all use them because they exist to sell parts for their sponsors. Not a lot of plug and play parts for a traditional Pontiac.

[Jay S]

If you want to use the parts you have. The 6x would be cheaper and easier to do. But you could run some dished pistons with the 48s and get the compression to a level attractive for boost. I think the 3.75” stroke is a good choice too.

If your looking at boosting stock heads, 8 lbs of boost is not stressing the short block that much. Totally different than someone’s stroker 340 cfm e head combo with 8 lbs of boost.

The problem with boost is it is addictive. Lol.. A little more is almost enough. Keep the boost level matched to the level engine mods and run it. IMO, Moderate levels of HP from turbo’s in a Pontiac is good power for the buck. The short block really will not require anything much different than a well built naturally aspirated Pontiac. MLS head gaskets and boost ready FI systems have made boost not that difficult on about any vintage vehicle. About the only thing you have to create is the hot side manifold on the turbo.

Btw...LS versus Pontiac..Some things get meaner as they get older