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Discussion Starter · #1 ·
Hi Everyone here !!!
Performance bug has bit again, with great success we modified a
stock L98 with a set of AFR Heads, Accel/Lingenfelter Super Ram intake
and all of the proven LPE Combo.

This time we have a 1996 Yukon and we plan on give some power to the
1996 stock L31, We want to keep thing simple but the cam/head selection
might be a bit difficult.

First thing we will do is put a set of 1 5/8 long tube headers.
http://www.summitracing.com/int/parts/pte-h8059/

Since is a Vortec, we think the best head is AFR0912
http://www.summitracing.com/int/parts/afr-0912
65cc to bump the compression (for the cam)

We will add a true roller timing set
and a set of 1.6 or 1.5 (not sure) full roller rocker arms.
Brand new set of Lifters
Chrome Moly Pushrods

Here comes the difficult part :
We love the kickass sound of the Big Mutha Thumpr camshaft
We already know that most of them are more sound that performance
but we are using the Yukon as a cruiser and won't be hitting the track
at all but we would love more power there.
Here's what we got : COMP Cams: Big Mutha Thumpr™, 299THR7 <BR> Very Rough Idle, Street/Strip
For Chevy 305-350 c.i. Cyl '87-'98

We have the stock injection, will not go carb.
We have the stock intake, but looking for the upgrade.
We might upgrade injectors as well. no problem.
We might need high stall converter no problem, 2800-3200 Vigilante
will make the trick. We don't want to touch the gears we have 3.42.

What do you think of the Head selection?
What about the thumpr camshaft?
Intake/Injector upgrade or should i leave it stock?

Thanks in advance !!!
 

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More for Less Racer
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The injection is not going to like the 107° Lobe Separation of that cam, at least not the stock injection tune. Maybe you'll be able to find someone who knows how to deal with that, IDK. Going to need modification, that is for sure

I can't remember, is Yukon SFI, or TBI

Generally, the high overlap that gives a cam that big thump is the exact thing injection doesn't like at all, it confuses the sensors.

Everything is in line,...except that cam pick.

Thumpr's are cams for Wanna-be's and Mullet heads. Far cry from the LPE stuff you did before.
 

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Discussion Starter · #3 ·
Thanks Eric, yes we thought about tuning it with pcmforless.com
the injection has a spider with a injector on center , we haven't seen it yet.
I Knew i was in danger about the thumpr ! :) lol hehehe
" Thumpr's are cams for Wanna-be's and Mullet heads "
That made me laugh :) hehe yes i've been reading that for years
but the sound is soooo cool, but you are right, maybe LT4 Cam ?
i want to go more aggressive, we don't go much offroad
The corvette is a street/strip track so we used the 219 cam with a 3200 converter.
We want to start now ! Thanks for the fast reply , btw is there any cam that give us some lope?
 

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Wrench Turner
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The stock injection is good up to 375/380 HP,so'with some tuning,it should be ok.The Vortecs have adv 64cc chambers,so,while the AFR is a better head,it's not gonna raise your compression & for that cam,you do need to get it up there.That cam in that big heavy vehicle is a big mismatch.Your DCR is gonna down around 7:1.Cylinder psi is gonna be 133.This thing won't be able to get out the way of it's own shadow.If you wanna run this cam,you need to get the CR up to 10.5:1 & some gear behind it.It can be tuned,but,it won't be easy.You would make a lot more power & torque with a better cam choice.The LT4 Hot cam would be a lot better choice for power,as would many others.
 

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Discussion Starter · #5 ·
Thanks Joker, yes , you guys are right, i will forget about the thumpr
i really like the sound but won't be practical.
I'm willing to upgrade intake but i haven't found the upgrade
for example for my L98 i had several options like the miniram, super ram
and a few more, but for this trucks i cannot locate a natural option
but the "marine version" checking at ebay they seems to be rare.
Not sold to the LT4 Camshaft, i used to have a ZZ4 cam on the L98 before the 219 and did not impress me at all, i want more. Looking for a proven formula
for trucks, what's everyone's favorite combo?
Thank you
 

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Wrench Turner
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The Ramjet & ProFlo XT are both good options for the L31.They can both be tuned with your current PCM.There will be some clearance issues on the A/C & tstat hsg that have to be worked around.They both are 1000 cfm systems & injectors can changed to suit your needs.The kits are expensive,but,you already have a controller,distributer,etc,so,you can put 1 of these systems together for a lot less than the cost of a complete kit.If you shop wisely,you can build either for less than $1500.There are also other systems out there that convert carb intakes to MPFI.
 

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Discussion Starter · #7 ·
saw the ramjet, looks real cool and seems to make lots of power !!!
i don't care about AC, i might use a delete pulley.
Thanks for the suggestion!
 

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Discussion Starter · #9 ·
ot trying to beat a dead horse but we are close to upgrade our ´96 Yukon.
i've been trying to find out the best combo for the Yukon but everytime some new details comes into mind
and might change the plans a bit. The upgrade is a fact. I've done a great upgrade on my L98 87 vette
with a 219 LPE cam, SuperRam intake and base, AFR195 heads, 3200 vigilante, 3.45 Dana 44 and much more.
Once you are bitten by the performance bug i cannot leave the Yukon alone.

Now this are the facts and doubts :

- What's the stock '96 L31 Compression ratio? thinking on using 0.026" compressed inch head gaskets to bump the compression a bit
- Will this Compression Ratio good for the LT4 Cam?
Not sure what will be the CR with this heads
- Im between AFR0912's 190cc or Edelbrock 60975 170cc E-tecs (we won't be using the stock heads anymore)
AFR has bigger valves but might be overkill with the stock intake and 19lb poppets. Is it worth to swap heads with this alum versions? We might add a VMax spacer later.
All of this will be coupled with a Vigilante 10.5 3600 stalll and 1 5/8 Long tube headers and 1.6 Roller Rockers , we have 3.42 gears.

Thanks !
 

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Wrench Turner
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4,952 Posts
ot trying to beat a dead horse but we are close to upgrade our ´96 Yukon.
i've been trying to find out the best combo for the Yukon but everytime some new details comes into mind
and might change the plans a bit. The upgrade is a fact. I've done a great upgrade on my L98 87 vette
with a 219 LPE cam, SuperRam intake and base, AFR195 heads, 3200 vigilante, 3.45 Dana 44 and much more.
Once you are bitten by the performance bug i cannot leave the Yukon alone.

Now this are the facts and doubts :

- What's the stock '96 L31 Compression ratio? thinking on using 0.026" compressed inch head gaskets to bump the compression a bit
- Will this Compression Ratio good for the LT4 Cam?
Not sure what will be the CR with this heads
- Im between AFR0912's 190cc or Edelbrock 60975 170cc E-tecs (we won't be using the stock heads anymore)
AFR has bigger valves but might be overkill with the stock intake and 19lb poppets. Is it worth to swap heads with this alum versions? We might add a VMax spacer later.
All of this will be coupled with a Vigilante 10.5 3600 stalll and 1 5/8 Long tube headers and 1.6 Roller Rockers , we have 3.42 gears.

Thanks !
Advertised CR for the L31 is 9.4:1,however,if you use advertised specs of 64cc heads,12cc dish piston,& .028 gasket w/ a .025 deck hgt,most calculators put it at approx. 9.2:1.That being said,the Vortec heads usually run closer to 62cc,so,it can be anywhere from 9.2: to 9.4:1 depending on your actual parts.If iwere gonna install aluminum heads,i would try to get my CR up close @ least 10.5:1.The stock CR would be OK w/ the Hot Cam,but,it would be better if you could bump it up some & take advantage of the better heads.FWIW,I've never used the V Max spacer,but,from what I've heard & read,it's a total waste of money & time,along with the TB spacers & Cold Air Intakes.
 

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Why not try to go with what you know works.... Afr vortec heads...same single pattern LPE 219/219 cam, some tuning and you're rolling. Monster torque and power strong until 5500. The Vortec intake is a similar large runner / long tube arrangement like the ASR. I'd investigate the tuning aspect first. Some times there is limited performance tuning support for OBD2. My quick research suggests there are companies out there that do it for you when you send them your PCM. I'd call them, they'll know what works based on customer feed back.
 

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Wrench Turner
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Tuning is not so much of an issue.If you are gonna use the stock Vortec intake & injectors,they will support approx 375 to 380 HP in stock form.There have been guys hitting 400 HP thru tuning & increasing fuel psi,but,after 380 HP or so,you start getting into lean WOT conditions.That tells me that the intake flows air better than it can supply fuel.That's why the V Max is considered a waste.If you are looking more HP than this,you will have to go aftermarket EFI.The stock injectors flow approx 23 lb/hr @ 58 psi.Theoretically,that will only support 368 HP.By increasing fuel psi& tuning,this rate can be improved,but,it's not an easy thing to do.The best way to tune is in person,or,by using a data log sent to someone with your PCM & all the mods to your engine.
 

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Discussion Starter · #14 ·
thanks guys, there is the possibility of installing the beehive springs
on the vortec heads but im not sure if its a big hassle !
since i was reading this article

http://www.crankshaftcoalition.com/wiki/Vortec_L31_cylinder_head#Upgrading_and_compatibility

Maybe i should stick with the AFR route and forget about it
use non self align rockers which i like better and lose some weight.

I know there is a spider update as well it has better injectors
but i cannot find the link, i have it somewhere.
 

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Wrench Turner
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The Vortecs will support more HP than the stock intake & injectors can supply.The beehive springs are a drop in.The upgraded spider is a big improvement by replacing the poppets with mini injectors,however,it does not give you more flow.They can be purchased thru GM or most part stores.There are companies that offer spiders that are flow matched & offer more fuel.Wester's Garage is 1 that comes to mind.The marine intake is another option,if,you can find 1. CFM Tech also has a cast iron intake that can be used for an MPFI conversion.It is basically a carb intake w/ injector bosses drilled into the runners.
 

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All springs should be shimmed to the correct installed height and clearances always need to be checked. My cam has .497 lift and .530 if I use 1.6 rockers

Comp 08-412-8
 

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Discussion Starter · #20 ·
Today we have received the VMax spacer , beautiful thing !
We are planning on install it, but we have a doubt.

When the head swap day comes, we will have to dissasemble the intake?
i mean separate the vmax spacer from the lower intake?
As far as we know this vortec intakes are different than classic SBC Intakes since
they have a plastic top or cover, when we swap heads we are going to be able to remove
the full intake as a unit or we will have to take the spacer off and then assemble the whole thing again?

Thank you
 
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