Ls3 with 3.75" stroke
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That cam is way too small. Even for daily street use, I would use something in the 238/244 range. The big cubes will like the bigger cam, and still be tame on the streets. The 228 cam you mentioned, would be like a stock LS3 cam in a 5.3L motor. The .600 lift is fine. I would just give it more duration.
Did they ever put a 409 CID in a Pontiac? That would also be pretty cool. The pistons would be expensive, but it's just a 4" crank. The 6.0L iron block gives you lots of options.
Did they ever put a 409 CID in a Pontiac? That would also be pretty cool. The pistons would be expensive, but it's just a 4" crank. The 6.0L iron block gives you lots of options.
I came up with another option. If I start with an LQ4, bore it +.030", and use a 4.125" stroke crank, it will yield 421 cubic inches. This is another great Pontiac motor. For those that have suggested 416 or other builds that could probably be done a whole lot less expensive and similar power, you missed my point. The most important part of this build, to me, is that whatever I end up with, it must have been a CID that pontiac offered in the Grand Prix, plain and simple. I know this will cost me some extra money, but this will be my last muscle car. Technically not a muscle car, but that's another story. It will be a very fast car. Anyway, starting with an LQ4 and making a 421 will save money over starting with an LS3 and making a 428. Yes, I have given up power with the heads and intake, but I believe it to be a good sacrifice. I know with the longer stroke, it will not rev as high sacrificing upper end HP, but I believe it will be made up with low end torque. I still believe in the old adage, "HP sells cars, torque wins races." I think I will still be able to attain my goal with the added cubes and a cam in the 228/228-600/600 range. This should be a fairly mild mannered ride that's ready to kick some ***. Thoughts?
I don't want to pee in your wheaties but I will a little, a Pontiac "428" is actually 426.6 cubic inches (4.12 x 4.12 x .7854 x 4 x 8= 426.61), the marketing guys decided that 428 was better because other companies had 426's & 427's.... If you want to get hung up on numbers that's fine but just remember that the factory did not. Build whatever you want and call it whatever you want that's what Pontiac and several other manufacturers did.
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I don't want to pee in your wheaties but I will a little, a Pontiac "428" is actually 426.6 cubic inches (4.12 x 4.12 x .7854 x 4 x 8= 426.61), the marketing guys decided that 428 was better because other companies had 426's & 427's.... If you want to get hung up on numbers that's fine but just remember that the factory did not. Build whatever you want and call it whatever you want that's what Pontiac and several other manufacturers did.
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I don't want to pee in your wheaties but I will a little, a Pontiac "428" is actually 426.6 cubic inches (4.12 x 4.12 x .7854 x 4 x 8= 426.61), the marketing guys decided that 428 was better because other companies had 426's & 427's.... If you want to get hung up on numbers that's fine but just remember that the factory did not. Build whatever you want and call it whatever you want that's what Pontiac and several other manufacturers did.
You're not peeing in my Wheaties, I'm aware of what they did back then. The 326 is actually 336 CID. I'm 62 and have been into Pontiacs since my brothers went together and bought a brand new 1967 GTO. I was 6 and that car made a life long impression on me. I had a 68 GTO for 25 years.
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Thanks, that was one of my options in my original post, only I was looking at an .010" overbore with the 4.1" stroke crank. That will yield 427.8. I will have to look at the cost difference between the LQ4 and the LS3. I like the LS3 better because of the heads and intake. The only reason I would go with the LQ4 over the LS3 would be if the cost of the pullout was significantly less.
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I understand and I certainly don't intend any disrespect I just wanted to point the number discrepancies out in case you didn't know, good luck with whatever size engine you end up going with. IMO any LS over 400 cubic inches will outrun any of the old Pontiac engines you are referencing and they were certainly no slouches themselves.
That cam is way too small. Even for daily street use, I would use something in the 238/244 range. The big cubes will like the bigger cam, and still be tame on the streets. The 228 cam you mentioned, would be like a stock LS3 cam in a 5.3L motor. The .600 lift is fine. I would just give it more duration.
Did they ever put a 409 CID in a Pontiac? That would also be pretty cool. The pistons would be expensive, but it's just a 4" crank. The 6.0L iron block gives you lots of options.
Did they ever put a 409 CID in a Pontiac? That would also be pretty cool. The pistons would be expensive, but it's just a 4" crank. The 6.0L iron block gives you lots of options.
Just so you know, using actual geometry to figure CID, rather than "hot rod formulas," the LS7 4.125" bore with a 4.000" stroke is actually 427.6493 cubic inches. Can't get much closer to a 428 than that. But this combo will: a 4.075" bore LS3, with a Callies 4.100" stroke, will net 427.778498 cubic inches. IDK how much closer you can get to a 428, but that's MY-T close!!! Best of luck with your Chontiac!!!
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Thanks, I appreciate the real experience. Did the cam have a lot of lope at idle?
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Just so you know, using actual geometry to figure CID, rather than "hot rod formulas," the LS7 4.125" bore with a 4.000" stroke is actually 427.6493 cubic inches. Can't get much closer to a 428 than that. But this combo will: a 4.075" bore LS3, with a Callies 4.100" stroke, will net 427.778498 cubic inches. IDK how much closer you can get to a 428, but that's MY-T close!!! Best of luck with your Chontiac!!!
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I was looking at the LS7, but they are getting a lot more money than I want to spend on it. The specs on the LS7 are very very close to the Pontiac 428, 4.12" bore and a 4" stroke vs 4.125" x 4". This is actually much closer than the LS3 + .010" and a 4.1" stroke. I also looked at one of the aftermarket cast Iron blocks for the 4.12" bore, but that will add $3,800 to the cost.
Last edited by grinder11; Aug 22, 2023 at 08:51 AM.
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I was looking at the LS7, but they are getting a lot more money than I want to spend on it. The specs on the LS7 are very very close to the Pontiac 428, 4.12" bore and a 4" stroke vs 4.125" x 4". This is actually much closer than the LS3 + .010" and a 4.1" stroke. I also looked at one of the aftermarket cast Iron blocks for the 4.12" bore, but that will add $3,800 to the cost.
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Last edited by GR8ONE68; Aug 22, 2023 at 11:53 AM.
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You can get an iron 6.0L with LS3 (823) heads and intake. It would be something like an LY6 or LC8. I got one in Houston earlier this year for about $1100. It didn't come with the intake, but I got the truck style intake for about $160 with rails, injectors, and throttle body. Even with boring, the 6.0L iron block would probably be cheaper than buying a 6.2L long block. A lot of people bore the 6.0L out to 4.065", and use stock LS3 pistons. You could bore it enough to build a 421-428 CID engine if you wanted to. You might have to use a custom piston, but you can make just about any size engine you can imagine with an iron block.
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There's really no reason to use a 3.75" stroke. A 4" is the same price, and a stock 3.66" crank is 97.6% the displacement, and 2.4% isn't worth the money.
Then again, I've never been concerned with hitting a specific displacement. I am fine with my badge on the fender being a bit of a lie.
Then again, I've never been concerned with hitting a specific displacement. I am fine with my badge on the fender being a bit of a lie.
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You are incorrect about the 4.125×4.000 stroke being "much closer" than a 4.075 (.010" OS bore LS3) bore LS3 with the 4.100 stroke crank. I did the math above, and using true geometric mathematics, the above info is absolutely spot on correct. Unless you are now throwing being as close as possible to the 428 Pontiac's bore and stroke into this situation, when you've been adamant that having the same CID was your goal. Even though my math is correct, either configuration is so close to a "428" that your splitting an ants *** into 30 pieces, then trying to see a difference. Good luck in your pursuit.....