04' top swap project planning

**monkeydude3602000** · 09-14-2016

First post here. I recently picked up a 04 grand prix gt as a work car. Wasn't necessarily planning on doing anything to the car other than general upkeep and window tint. It's got a bit over 250k on it but surprising enough it's one of the nicest driving and problem free vehicles I've ever owned. Interior is very nice and body is straight just paint flaking on the plastic parts. Steering is super tight. No noises. No lights on the dash. Even had new tires. So far I've put 5k on it and besides coolant elbows, rear window regs, and the blower resistor it's gave me no serious issues whatsoever. This car had excellent service records and I'm the 3rd owner. So down to business. I started researching the top swap and I was hooked. I've always wanted a gtp and now I'm about to make my own.

I scored a killer deal on a complete series II top end. A set of heads, LIM, 3 that's right 3 Gen3 m90s, 3 sets of fuel rails and injectors (one set cleaned with new o rings), 3 TBs (even though I can't use them) most of the bolts, bracketry, pulley stuff, all except for balancer and crank pulley, an extra water pump, oil filter housing, several extra odds and ins, but here's the icing on the cake... a new set of headbolts and a complete unopened top end gasket kit. All of this for $200. Guy rounded all this up for a 97 gt top swap then some old broad totaled his car. Still can't believe he didn't want more.

The heads will be sent to a machine shop to be cleaned and checked and get a valve job. Contemplating on zzp titanium valves and most likely springs too as I plan to use zzp 1.9 rockers to hopefully help with kr and get a little more air moving. I will probably go with the #90 springs unless someone has a better suggestion.

Cam will remain stock. Timing set may possibly be replaced. Suggestions here?

I've selected the best blower. It is very clean (other guy had already cleaned it up and polished the rotors) it only needs a coupler which I'm going to take from one of the spare blowers. I may do some slight port work on the intake side. And I wouldn't mind blocking off the silencer holes too. I'm buying the modular pulley kit as well along with a new belt.

I'm going to use a zzp front power log and downpipe but that's all for now. 3" or 2.5" on the dp? I'd rather go 3 if it won't hurt me to leave room for improvement. I'll build a homemade CAI. Or possibly try to buy my buddies wizard intake off his gtp as he's thinking of changing it.

As for tuning I will be using a aem wide band, aero force scan guage to monitor KR and Trans temp and HP Tuners for tuning. Fortunately I have lots of friends including my boss that's very handy with setting up fuel maps and timing. And a local dyno.

Just for peace of mind I'll probably change the trans fluid and filter and add an external cooler. Car already has a 180 tstat. Going to stick with that and see how it works. The entire cooling system is new (previous owner couldn't figure out the elbows lol) but I'll probably give it a good flush.

So here's a few more questions... and yes I've read the write ups I'm just a bit unclear on a few things.

What's involved with using a 2 bar map with my stock ecm? Can it be programmed with HP tuners?

Does a 3.5 pulley sound like a safe starting point?

What are my throttle body options for an 04 GT? Pretty sure it's drive by wire. I want to do anything within reason to reduce KR. Will the stocker suffice? Will a same year gtp tb work?

Does this sound like a good build plan? Lots of reading I know but if you made it this far thanks for any advice in advance.

**Fivefingerdeathpunch** · 09-14-2016

I'm not sure how the adding the 2 bar MAP works with HP Tuners, never seen it done I guess on these computers. I know the LS stuff much better for tuning different MAP sensors.

The TB is the same for NA and SC on the 04+, there is no other options. You'll need an adpater plate for bolting it to a gen 3 supercharger and it would bolt up to a GEN V just fine if you had one.

Biggest downpipe they offer is needed, exhaust flow is key or just buy headers.

You will be running a high compression bottom end compared to a regular L32 engine in a GTP, so start bigger with the pulley size. Go with a 3.6 for starters.

To get a tiny bit technical here, there isn't really a "Fuel" map. Pretty much it's a Stoich AFR, commanded AFR and fueling is controlled by the MAF curve. The more air that it see's coming in, the more fuel it will give depending on throttle input etc etc.

I'd copy over a GTP high/low octane tables (HP Tuners lingo) and then reduce them the higher cylinder volume area's like .60+ by around 2º at first to play it safe with low timing. Somewhere around 13-14 starting is a good idea under WOT.

**monkeydude3602000** · 09-14-2016

Glad you replied. I totally missed the adapter plate part... I may swap to a Gen5 one day. I just didn't see the point in dishing out the dough for it right now when I still need to buy all this other crap. And as far as tuning goes I'm a bit Greek but ready to learn. So since it runs off mass air is the 2 bar map even required? Or does it still need it for timing retard under boost?

**WarStryker13** · 09-14-2016

Gen 3 won't work. I've gone through everything I can with mine, it would cost more in the custom parts required for proper PCV than a more efficient Gen 5.

Stay away from polished rotors in a blower, the coating is extremely important to the dynamics of it. the fuel rails won't work for you either, 97-03 had a return style fuel system, 04+ has a returnless fuel system.

My suggestion is to sell off the gen 3 blowers, all three, fuel rails, injectors, etc... All the stuff that you can't or won't use. Then take that money, buy a Gen 5 and headers, L32 injectors, an L32 MAP sensor, and a 3.8 pulley.

Top swaps are notorious for kr problems, because of the higher compression ratio they're a pain and heartache to tune and keep from chipping a piston.

Trust me from years of research and thousands of questions answered by the old timers and veterans of the GP, they haven't steered anyone astray yet, after almost a full decade.

**monkeydude3602000** · 09-14-2016

Here's another crucial question I forgot to add... which fuel rail will I need to use. Series 3 motors have no return correct? So can I just cap the return on one of the series 2 gtp rails I've got? I seen where the write up said to use the fuel rails from the same series so will capping the return cause problems?

**WarStryker13** · 09-14-2016

It might work, but it might not feed fuel correctly, since the fuel can't flow past the injectors and just sits under pressure.

**Fivefingerdeathpunch** · 09-14-2016

If the L67 injectors have the same connector end as L32 injectors which I think they do, they should the same size injectors and work.

**monkeydude3602000** · 09-14-2016

Nevermind on that last one lol I see it was answered before I asked... OK so realistically what can I expect to get out of the Gen 3 blowers? And what about my LIM? I know it can be modded but is it extensive. I'm not scared of a dremel. I was really trying to keep cost down on this one... I have a buddy running a 3.4 on a n/a bottom end with 0 KR but now that I think about it he has a cam and headers. Both of those things are going to push me out of my budget though. Will I really have that much KR issues with the power log only and 1.9 rocker only running the 3.8 pulley?

**WarStryker13** · 09-14-2016

rockers will help, but realistically you would need a ported blower and LIM, and ported heads to run just a PLOG and downpipe.

The LIM will work with either engine, but I would go ahead and open up the inlet big enough for a Gen 5.

I got my Gen 5 for 250, most gen 3s sell for 150-200, depending on condition and if they're modified/ported or rebuilt.

A 3.8 won't give you that much in kr problems, but considering that a top swap is considered a "high level" modification for an N/A, it's always better safe than sorry.

**Fivefingerdeathpunch** · 09-15-2016

GEN 3's sells for under a $100-125 here now. I've bought them for $75-100 before.

**monkeydude3602000** · 09-15-2016

It looks like I could cover the cost of a Gen 5 anyway... if I can manage to sell all 3 blowers. So should I ditch the rockers and just put my money towards headers?

**WarStryker13** · 09-15-2016

Honestly, yes. Speed daddy headers from eBay run about 220.

**231FUN** · 09-15-2016

Originally Posted by WarStryker13

Honestly, yes. Speed daddy headers from eBay run about 220.

Which is less than what the 3" DP and plog will cost you if you buy new from ZZP

**monkeydude3602000** · 09-15-2016

So can I go ahaid and have the #90 springs put in for future 1.9 rockers? I've done springs before in a small block with heads on the motor and it wasn't real fun. I just hate to have to pull the heads again later to change stuff that I could do now while they are already off...

And speaking back on the compression issue. Can't I use a 5 layer cometic gasket to reduce compression a bit to allow more wiggle room for boost?

**Fivefingerdeathpunch** · 09-15-2016

Yeah you could run those springs if you want.

L67/L32 are 8.5:1 and L26's are 9.4:1 and I'm not sure how thick those gaskets are but I don't think you'd get much past 9.3????

**WarStryker13** · 09-15-2016

Honestly the best way to combat kr is the tune, but additional mods such as an intercooler, running E85, porting the heads and blower/LIM will help alot...and the heavier springs will also give you the option of a cam later.

Cam is nice. Lol

**231FUN** · 09-15-2016

If I was in your shoes I would do the headers/rockers/springs with a Gen V and the series 3 fuel rail/system and find a l32 MAP and use GM or Felpro head gaskets with your heads. Leave the stock 3.8 pulley on the Gen V and start your tuning/scanning from there. Can alaways add the modular pulley afterward when more $ is available if you have enough breathing room to pulley down

**monkeydude3602000** · 09-15-2016

Sounds like a plan. I really didn't know you could get headers that cheap... and if I'm starting with a 3.8 I'll just hold off on the mod pulley for now... I'm trying to make way for future improvement. Shouldnt be a problem to go ahaid with the rockers now too. I definitely want to add the big intercooler and a big cam in the long run and if I really get the itch for some extra power for occasional mustang chewing I may put methanol injection on it. I'm sure me and my gtp buddy will end up having dyno wars once start catching up. He's a shade over 300whp. I'd be happy to break 200whp right now honestly but I'm hoping to be able to get closer to 250 with a smaller pulley after I get use to tuning before I do any other major mods. Sound doable?

**WarStryker13** · 09-15-2016

With a top swapped GT, you will be making approximately 260 hp at the crank, with drivetrain loss that's close to 210 at the wheels, with stuff like poly mounts, a trans tune/minor upgrades, and a good suspension.

With a good tune, 3.4 pulley, and supporting mods, you should be close to 250whp. Ish.

The rockers will have to go bye bye with a big cam, you might be able to run a mild cam with 1.9s if you get the clearances right, but most people will only run stock ratio rockers or at the most 1.7-1.75 ratio rockers with the big cams.

But all in all, you've got a good start and a decent enough plan. Good luck.