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80 or 85mm throttle body

This is a discussion on 80 or 85mm throttle body within the External Engine forums, part of the LSx Technical Help Section category; i'm in the process of building a 5.3,3.905 bore,04 ls6 cam,1.8 roller rockers,ls2 intake port matched to texas speed stage ...

  1. #1
    Junior Member JROBINSON1016's Avatar
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    80 or 85mm throttle body

    i'm in the process of building a 5.3,3.905 bore,04 ls6 cam,1.8 roller rockers,ls2 intake port matched to texas speed stage 2.5 cnc'd 5.3 heads.

    since the factory throttle body is 78mm, 80 mm would only be 2mm difference,& 90mm wouldn't be optimum for performance,so i'm wondering if an 85mm throttle body would be the best choice for this set up

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    Moderator Firebirdjones's Avatar
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    Not much of a change really. If it were me I'd just port the stock 78 piece and put it on an LS6 intake, and ditch the LS2. Cheap and easy.

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    Junior Member JROBINSON1016's Avatar
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    not lookin to do an ls6 intake.....
    a 78mm throttle body is biggest you can go on it due to the opening
    & when you figure in the 600+ bucks it costs its not really cheap & you're stuck with a 78mm throttle body
    sure you can bottle neck it with an adaptor but whats the point
    back to my question
    80 or 85mm

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    Moderator Firebirdjones's Avatar
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    You can do an LS6 intake for the same cost that 85mm throttle body is going to cost you They are used all day long for $300-$350 and will run circles around that LS2 intake. If you are worried about bottle necks that would be the first thing I would address.

    Not to mention we are talking about a 5.3 with an LS6 cam according to your first post, not like it needs a big throttle body. Worked fine on the LS6 engines. A ported stock sized 78mm on an LS6 intake will support more ponies than that 5.3 is going to make.

    Just trying to save you some coin and make a little more power in the process

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    Junior Member JROBINSON1016's Avatar
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    yes it's a 5.3 thats bored to 3.905 which equals 348 ci,which is actually a bit more than a factory ls1 ls6 which is 3.898 ci,besides i already have the ls2 intake vs. buying a used ls6 intake,i'm pretty sure it'll do just fine port matched to my cylinder heads,& flow numbers really aren't that very dramatic between the 2 that i can justify buying another intake,i mean whats it going to cut about 2-5 rwhp overall,& i can run an 80-85mm throttle body vs a stock ported piece, which is still the question at hand

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    Moderator Firebirdjones's Avatar
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    Actually they are quite a bit different in flow numbers. To get the LS2 to flow as well, and possibly better than the LS6 it takes extensive port work form someone that knows what they are doing, and will cost upwards of $400 to get it there. Only then will the larger throttle body opening be of benefit with an LS2 setup, so you have to spend some coin to make it worthwhile, plus the added expense/necessity of using the LS2 fuel rails on top of that. Difference in RWHP is reported to be as much as 10 between the two with the LS6 on top throughout the entire rpm range when in stock form, not just peak numbers, that's all been pretty well documented over the last few years. I have flow graphs here somewhere I can post if interested. The difference is actually pretty shocking considering most think the larger throttle body should be an advantage, when in fact the poor design of the LS2 intake is the hindering factor.

    Because of these differences and added expense to get the LS2 to perform is the main reason why people running the LS6 intake skip over the whole mess and go straight for the FAST setup. There are also mods you can do to the LS6 for even better numbers.

    In any event, since you're already into the LS2 and looking at throttle bodies, I see no reason why you couldn't step up to at least an 85mm throttle body since you are going to spend the same money no matter what size you choose. May as well get an 85 and run with it.

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    Junior Member JROBINSON1016's Avatar
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    noooow we are on the same page FBJ.........
    i pretty much picked up the ls2 intake for the fuel rails,injectors,map sensor & all the bolts & hardware,for the price the intake was pretty much a freebie afterwards
    the ls2 injectors are much better than the stock ls1 injectors
    also i've been doing my own port work for many years,& do pretty well if i do say so myself
    so i believe i can port match & open the ports to be more consistent in size as well
    which seems to be the biggest problem with these intakes
    as far as how gm put them together & the poor seam alignment with overlapping edges goes, i tend to do some plastic welding on the seams before the port work
    so all in all i believe i can take care of the majority of the problems with the intake
    & if i ever want to swap intakes down the road a fast would of course be the next step

    in the end with a compression ratio of 10.9-11.0:1,stage 2.5 cnc heads,ls6 cam with 1.8 rollers, long tubes & tune i'll have a very well mannered streetable motor that gets pretty good mpg & can still put down 450 hp

    ya gotta love it when a plan comes together............


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