Hello all,

I just got my car back and tuned last week. Ported milled 243 heads, ported FAST, 228-232 comp cam, Kooks 1 3/4 headers, supporting mods. The car dynoed 479rwhp and 430ftlbs. I am happy with the performance, but was wondering if a 1 7/8 header would pick up the power across the board? Any suggestions.

Thanks

 

Kooks 1 7/8's were the 2nd mod I installed after my Vararam and I noticed no loss of anything, actually the tires would spin at less throttle with a Diablo header tune only.

If you think you are going to go with even more mods (N20/Stroker) then yes, go ahead. Otherwise, you may not even notice it. Texas Speed did a dyno with 1-3/4's vs 1-7/8's on a smaller 346 and it lost no power at all down low. GM Hitech even installed 1 7/8's on a near stock LS2 and they said it was a gain of 20rwhp (untuned) and 32rwhp (tuned) with NO loss of low end.

http://www.gmhightechperformance.com...wer/index.html

But if it was me, I would do it.

 

Putting 1 7/8 headers on a car never having had 1 3/4 you wouldnt have lost any TQ compared to the stock manifolds. No one is saying that. The OP was asking if the bigger primaries lose low end TQ to the smaller primaries....not the stock exhaust manifolds. I have swapped out 1 7/8 4 times to 1 3/4 for cars that needed a boost in the low end and it picked up low end TQ every time. The minimum gain in the 3k range was 10-12rwtq.

Installing headers (any size) on any LS engine will lose nothing down low. It will gain across the board but it wont gain as much TQ as the smaller primary.

1 7/8 headers will not match the low end of a 1 3/4 header. Other tuners confirmed this. The only test I recall seeing from Texas speed was when Zack posted up the results saying they lost nothing in the low end. I think Zack went to MTI at that time or shortly after. He was saying it was no loss over stock but many cars running headers only had better low end. He never posted when people were showing thier dyno's with 1 3/4 with more in the 2500-4k range. The thread ended with people thanking him for showing the 1 7/8 did in fact lose over the 1 3/4. If I have to I will dig up the thread.

In the case of the OP, you will gain peak HP at the expense of low end. I will even guess for you.....6hp more up top and 10rwtq less down low.

Keep in mind that the averages are what you look at, not the single case that goes against the average. I've seen this one tested a dozen times. The fastest H/C cars run 1 3/4's on the list.

Now, I have to agree with Jay on mod path: If your mod path goes into strokers and FI (nitrous/supercharger/turbos) definitely look into 1 7/8 headers. The low end will not matter and the top end could pop 20-30hp more. RockinBlue did this swap when he went to FI but I dont recall the results. The objective makes sense.

 

You need to be moving a lot more air thru the engine in order to justify the larger header, ie, supercharging or turbocharging. Perhaps, with more cid, big heads and a radical cam you could make a case of them, also.

 

with the heads and cam absolutely go with the 1 7/8

 

Spin, what about on an LS3? Still use 1 3/4"? (With bolt ons only, no cam)

 

I'm running 1 3/4 LG's on my 427.

 

Someone could step up this year and do a back to back comparo on an LS2. Here, Livernois chose Kooks 1 7/8's on LS2's for thier head/cam dyno's.

http://www.gmhightechperformance.com...ads/index.html


I (personally) would be shocked to see any loss of power on an LS2/LS3/LS7 with 1 7/8's. I have mine for the larger shortblock soon and a shot of N20, but thats just me.

It sure would be nice to squash this with some current dyno testing. It would be really easy if you have a dyno.

 

Showing a dyno with a car that never had 1 3/4's on it says nothing about the difference so whats the point in you and others referencing the same GM high performance test? They didnt compare the bigger primaries to the smaller ones nor were their results stellar for a 232 cam. Vette docs just made 490rwhp without a FAST manifold with that cam and a set of trick flow 225's. 465 with the same cam proves 1 7/8's are better?

Dyno sheets were shown many times and are on LG's site too now. LG doenst offer a 1 7/8 because it doenst work on this displacement. I did the swap and the owners dyno'ed and had the 10-12rwtq difference every time. I dont see how it has to be done for each and every person that doesnt want to believe it when they simply have no proof to the contrary.

6.2 liter makes no difference and 1 3/4 should be the choice for any H/C car unless 10rwtq means nothing to you.

Here is a 1 7/8 vs 1 3/4 with no other changes.....do with it what you like. The 1 7/8 made 3hp more up top at the expense of the area under the curve. I did a swap from Kooks 1 7/8 to kooks 1 3/4 with the 1 3/4 showing the same lower rpm trend. There is only so much time I am going to waste on a topic when the only people saying the bigger primary is better have no dyno sheets of thier own. I dont care what gains a 1 7/8 make over stock exhaust manifolds. The topic is 3/4 vs 7/8.

http://www.lgmotorsports.com/gallery...?album=3&pos=9

AND BEFORE EVERYONE STARTS CRYING FOUL, THESE RESULTS ARE FROM gtoDOUG ON THIS FORUM FROM THIS THREAD: THEY ARE NOT LG'S TESTING AND DYNO.
http://forums.corvetteforum.com/c6-t...e-headers.html

Doug does all his own wrenching and tuning. He lives in Florida and doesnt work as a tuner so he has no agenda. He is like you and me so I see no reason to not think the results are real, nor do I have to rely solely on his results since I've done the swap on multiple cars and sometimes swapping out just the header for the same company's smaller primary header. I am insisting on this info being out there because there are people saying the 7/8 are betterr for H/C installs and they are not. Not by a long shot so i want to disprove the false info for the people making decisions.

Lastly, the test here was on a stroker and its obvious that even on that bigger displacement the biggerprimary does nothing so for the 6 liter and 6.2 liter, the smaller primaries are obviously the better choice.

 

Show your dyno proof. The bigger primaries are a mistake on a track and the street with a H/C car.

 

If you're making this a 100% drag race dedicated car and will NOT be driving it on the street, the RPM range that you want to target is much narrower. It's in this narrow, high RPM range that Spin says you will gain the approx 6 RWHP.

So yes, if you dedicate this car to the track, then by all means get the 1 7/8" primaries. Based on your choice of cam, it looks like you plan on driving it on the street so trading +6 RWHP at peak for -10 RWHP below peak doesn't sound like a good idea, but at least now you can make an informed decision.

 

I was in the 1 3/4 camp till I see that the highest hp 08 stock cars use 1 7/8.
http://forums.corvetteforum.com/c6-t...s-and-vid.html

Vette Doctors tryed 1 3/4 then 1 7/8 the 1 7/8 were easy winners across the board this is from Nick himself.
http://forums.corvetteforum.com/c6-t...rs-x-pipe.html

Also JB's 08 ls-3 has 1 7/8.that and the above are the strongest
header cars on here.
Also comparisons on the same dyno the Ls-3 with 1 7/8's made 18 rwhp and
15 rwtq more than two others with 1 3/4.
Also here is a HC cars with 1 7/8 vs 1 3/4

http://forums.corvetteforum.com/c6-t...rs-x-pipe.html
post 57

I have 1 7/8's on and have not been to the Dyno since the 1 3/4. I had knee surgery last week and my boost valve
is not closing. But I'll be there soon.
With Ls-3's there is no doubt in my mind 1 7/8's.

 

If this would be a fact, why doesn't LG Motorsports make a 1-7/8 header?

 

The facts are in my post
since you asked there is a member who put 1 3/4 on a 07 Z-06
He gained 10 rwhp!
Lg seems to have made thier headers for ls-1 ls-2's since they don't make 1 7/8 and where the 1 3/4
seems to be better. On the ls-3 ls-7 NO!

 

Maybe, but these were not. No reason too, as I had 1 3/4 These are true real world comparo's
that makes solid evidence. 1 3/4 header works fine but this proof above
and the fact that George from Kook's said when I bought my headers,
the same thing. They see them every day, He said LS-2 1 3/4
LS-3 1 7/8 OR when you reach the over 500hp level the 1 7/8's perform better.

 

I would tend to put more faith in a legit Corvette expert such as LG before someones dyno sheet where anything is possible as we all know, some believable and some not. I have KOOKS, but I also think all mods are subject to what you as an individual think is the correct choice and may or may not be factually proven. It's kinda one of those he says this while she says this.

 

With Lg's the design might make the 1 3/4 better for them.
The Kook's and ARH are what I'm seeing all three great product.
I'm just going by unbashed results as no one has a stake.
AR or Kook's doesn't care what size they sell only reason they share results
is to relay what they get with test results. I'll know more when I
dyno. The Kook's 1 3/4 is great header and did me well so I'm
hoping the switch, results warrant the trouble and cost.
Cost was 1895. for the coated AR's and I sold my Kook's for 1100.00
Things I can tell so far is the 1 7/8's and 3" is louder with The Z0-6
cans open. My boost Valve is not working but off boost it feels
good. Things I looked at for the switch
1. I was getting a lot of cat heat during boost.With a lot of pressure sound Cats would not last IMO
and the AR moves the cats back another 12" more downsteam than the KooK's they should see less heat.
Plus the AR cat is different with bigger holes and less restriction
It' was obvouis when I inspected both. Then I see a few boosted
cars showing better with 1 7/8's. Not many examples on that and alot of great ones with 1 3/4 so
that is what I need to prove to myself.
But NWC-6 and both with 2008's were tuned and dyno by Tom the master. Getting with in 2 of each other around 423hp and 418 TQ
Then same tuner same dyno same MO, only 1 7/8 made a solid
441hp with 435tq. No rigging no interest to. Just the facts.

 

Great info, thanks.

I actually spoke to Kooks before ordering my 1 7/8's and they were very convincing to go with the 1 7/8's when I told them my plans.

 

I went through all those threads and saw but one dyno sheet comparing the different primary sizes. C6dvl running 1 3/4 ran a 132 trap speed. JB's car never had the 1 3/4 and I dont see how that qualifies the 7/8 as the better primary size for the job. Cartek uses 1 3/4 exclusively and has lots of track proof. I dont care what a tuner says....they're biased.

I dont want it to turn into an argument. You and I have to have the biggest laugh on this topic since we have run the entire spectrum of header wars and now it not company, its primary size. The fastest track LS3 has 1 3/4 and the fastest C6 6 liter and 6.2 liter FI car have 1 3/4. The fastest bolt on car LS2 has 1 3/4. Track proof is still not saying anything because it isnt testing back to back runs with different primaries. I use it to illustrate the silliness in polls and dyno sheets. Since all points of view have been shown then in my eyes its a stand-off if we use that kind of data as proof.

I think anything else is just opnion by those who defend what they own. I tried once to show a back to back on header swaps on my car and ultimately bowed out when the tuner didnt want me to post dyno sheets since they saw a conflict with the header they sell even though I was just renting a dyno. Even if I posted the results, foul would have been cried by the unhappy owners of the 'other header'. One thing we have to agree on is that surgery is a bummer. Feel better Rob. Dont take the rest of it so seriously.

I have no problem when a guy shows proof with a dyno or track run. Its the peanut gallery with an opinion on things they never tested that get to me. Having a poll on whats better is simply showing which company had the best sales because people vote for what they have, not whats better for thier application.

 

I have a unused set of kooks 1 3/4 and the header itself is the only thing that would have to be swapped out to show the proof. Where are you? I can swap them out and see if they are right. Cartek tried this size only swap and found the 3/4 to run the fastest at the track. Please show the proof to the contrary because the manufacturer doesnt have a corvette with track runs as the reason for the reco and a tuner doing the testing is the authority. I am willing to do all the work myself. As always, if I'm wrong, I want the better header for my application on my car.

I did the swap with all Kooks parts more than once and the results for every swap showed the 3/4 to make more power under the curve every time....wait I'm repeating myself so what's the point. It isnt what people want to hear after they bought the other size.