I'm about to start the biggest modding project I've ever done...slowly but surely turning my low mileage 99 WS6 into my idea of a fun part-time daily driver. I'm going to drive this car about 5k miles a year for the foreseeable, so I am not really looking to get into major internal engine mods. Once I have the mods below done, I plan to find a local shop to get a proper dyno tune. Round 1 mods are...
1) SLP lid and bellows (already on the car)
2) GMMG catback
3) SLP revised-design LTs

Does anyone have any thoughts as to how much HP over stock this will add? Safe to assume around 35 rwhp total? Maybe more or less?

Round 2, I'll add...
1) LS6 intake
2) Ported OEM TB
3) SSRA
4) Is it worth it to modify the OEM hood by removing the baffles in the hood?

If I do all of this, with a proper tune, how much RWHP can I expect from an A4 car? I am hoping for 350. Is there anything else worthwhile adding, that will not affect the driveability or adversely affect MPG too much? I am not looking to make an 11 second or better car out of this thing...I have other cars for that Any input is appreciated...could also use some decent advice on plugs and wires to use, as I might as well change them out too while doing this.

 

Ideally dyno the car and base line before doing any mod's. From what I recall when new A4 99 TA's would put down 285-300whp. There was probably ~5 whp hp of actual variance in the cars and 5-15 who variance in the test procedures used by the DynoJet operator & test procedures.

HioSSilver is the Uber bolt on guru maybe will comment. He's had a,450+ whp bolt on LS6 at one point and excels are wringing out the bolt on hp. Ask him about the "Super Duggy Box" it makes the ram air / CAI stuff look restrictive. Not sure I'd want to expose to heavy rain etc but thats true of most good CAI RA set ups.
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Phase 1
1) SLP lid and bellows (already on the car)
2) GMMG catback

Sounds like 10-12 whp

3) SLP revised-design LTs

I like 1 7/8 best for even bolt on LS. If they are 1 3/4 that's still very good. A lot of the benefits relate to the Y pipe desk.

Which Y pipe. Some are terrible. The Flowmaster type are excellent.

This Flowmaster style is excellent

Flowmaster brings exhaust in parallel

This Jethot style Y pipe is garbage. The exhaust pulses are directed at each other. Prone to ping, hurts power and torque. JUNK


Phase 2
1) LS6 intake -much better than an LS1 intake. LS6 needs the LPE 90mm snout mod for better flow. Fast 90/92 are also good. 102 Fast is popular but pissy to tune for excellent drive ability in many cases.
2) Ported OEM TB - 92 mm WARR Performance TB is very good. Works well with Fast intakes or 90mm snout LS6.

Maybe others can offer insight
3) SSRA - sounds good, I have no experience with it.
4) Is it worth it to modify the OEM hood by removing the baffles in the hood? - I don't know. I cut the bottom out of my lowered airbox and added an SLP CAI with the Fast toys extension.

Other stuff
While it can be some hassle a 10-25% under drive pulley /dampen definitely helps. With the A4 idle I would want to over drive the alternator with the OD pulley if going 25% UD.

90mm + intake track is good, so 85mm MAF works well or as many harder core folks do go speed density if you have an excellent tuner. Definitely dyno tune.

Electric water pump helps. I've not got one but they are well proven to help with hp.

Adding a stall converter will get you a big bang and fun with the A4 than all of these other mods. A Yank SS2800 to SS3600 stall would rock depending on your tolerance for stall. I'd go at least 3200 stall. My vette has a Yank 3200 and it's an outstanding good driving converter. A friend has a Yank SS3600 in his 00 cams and it rocks and drives very nice not quite stock but very good.

Plugs and wires, I like the OEM wires with the heat shields MSD is good. Check new wires with voltmeter resistance and continuity if you want to make sure it's a good site before installing. I like the NGK TR-55'S gapped at .050. Have ran them that way for almost 20 years. They are good for about 20,000 miles. If you don't want to fool with 20k mile plug changes, a good quality platinum plug should work well for the bolt on set up.

I would do all the maintenance before moding. Coolant flush and change, fuel filter, transmission fluid and filter change change etc.

BTW - 350 whp is very doable with bolt on's. With electric water pump & 1.8 or 1.9 rockers some say they have hit 400whp + with bolt on's and Super attention to details. 375 whp could probably be done with less expense.

 

Thanks for the input! The Y pipe is the revised SLP design with high flow cats...supposedly it flows decently, with better ground clearance than their original design. GMHTP did a before and after dyno test of them with the SLP Power Flo catback on a bone stock car with no other mods, and they picked up 33 RWHP without even a tune. No idea how accurate that is.

I will look into the LPE 90 mm snout mod...hadn't come across that before. I could do a FAST 92, but didn't know if the extra $$$ is well spent on a fairly stock car. I don't want to go as big as a 102 because driveability is key. If I take this on a 5.5 hr ride down to Key West for a weekend, I want something easy to drive.

I have considered a converter, as admittedly this is my FIRST A4 4th gen. My big thing is, I don't know **** about converters and have a ton to learn. I personally do not want to add a shift kit because I like smooth shifts. With a converter I need to add a bigger trans cooler, correct? As for maintenance, the coolant is fresh, and I plan to do a transmission and rear end service as part of this. The exhaust is scheduled at work for next week...I work for a Cadillac dealer and am lucky to have a 98 WS6 owning ASE tech at my disposal!!

 

One side note about the pulleys. I have considered an UD pulley/dampener. I do not want to mess with the alternator however, as the icing on the cake for this car is going to be a very powerful, old school Xtant stereo build. Frankly, I may need a bigger alternator than stock...adding capacitors may not be enough at night...

 

Drive ability is king in my book too and car has to be able to do a nice long road trip like you mentioned. The ws6 tech at the Caddy dealer will probably be a whole lot of help with doing and planning mods.

99 Black Bird TA flow test data, pictures of LS6 90mm snout

The price of used Fast 90/92 seems to be coming down so it's very possible you can find a good deal on one.

The LPE snout works good in my experience especially if you already have the LS6 intake. The some folks like the look of the Fast intakes better. My flow test of 90mm LS6 vs Fast 90 was basically a wash. The Fast 90 would be easier to port. Most folks will say go fast 90/92.

FWIW - Regarding shift kits, my experience is limited.

1) Had a 4L60e built at a shop and took a Transgo shift kit along. Shop owner took one look at kit and said "Well at least Transgo isn't as bad as the B&M shift kit but I still don't want to use it." He had developed his own shift kit and it was firmer than stock without being harsh. The shop owner was on the money.

2) Had a Th400 rebuilt for my 72 Vette at another shop because the owner mention in #1 had passed away. Mentioned shift kit to shop #2 owner. "Let us do that our way. The B&M is harsh and I don't like it. Transgo is better but ours is the best of the three. The 2nd shop owner was on the money too.

3) Fiance's son has a B&M in his Camaro. He likes the hard, mule kicked you in the back of the head 1-2 shift. I hate it, way too harsh for a street car.

Your WS6 acquaintance may know of a shop that does an outstanding custom shift kit.

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Shift kits are good upgrades (TransGo & Sonnax) and can be tailored to desired shift firmness. Those neck jerking shifts are usually due to drilling out the 2nd and 3rd apply feed holes WAY to big in the separator plate.

A very good upgrade for the 4l60e that does not come in a shift kit is the sonnax 2-3 shift valve.

 

Sonnax - that maybe part of what the shop owners mentioned as their way. It's been ten+ years and I don't recall.