which is a better setup

[redws6]

right now i have bone stock LT1 with a flowmatser 3 inch catback. i was thinkin of either doin the lt4 conversion (heads, cam, intake etc...) or swap in the gm847 cam and throw on the lt4 itake. im not sure what i wanna do. future plans also include headers, and some other odds and ends. any feedback is appreciated.
thanks
chris

[Injuneer]

LT4 intake will not fit on yout LT1 heads without machine work to remove an interference between the LT1 valve cover rail and the top of the LT4 runners. And, after you have the machine work done, you will have gained nothing, since the LT4 intake is virtually identical to the LT1 intake, except for the provision of extra metal at the top of the LT4 runners, so that the intake can be ported to match the 0.100" taller runners of the LT4 heads. But, as cast by the factory, the LT4 intake does not even match the LT4 heads.

You've got sort of an apples or oranges choice... The LT4 conversion in cludes the LT4 HOT cam, which is a lot milder than the GM847. The LT4 conversion would be a well-balanced package with good low end torque and good high end power. The 847 would be a little less street friendly (not impossible to live with though) and would trade a little low end torque for increased top end power. Depends what you want to use the car for. Either setup is going to be happier with higher numerical rear gears. And you need to include at least info about your trans.. an automatic is going to need a higher stall convertor.

You can probably produce the same results, although maybe not the same balance of torque vs. HP simply by having your LT1 heads reworked, picking a more agressive cam, getting a set of 1.6RR's, etc. The LT4 conversion is a nice neat package, not necessarily the lowest cost approach. You also need to be aware that to get the advertised "425 (flywheel) HP" out of the LT4 conversion, you need LT headers, larger throttle body, larger injectors and very good computer tuning. The 425 HP claim fails to mention that the dyno testing done by MORE Performance to get those numbers used a $3,000 aftermarket computer.

[redws6]

thanks for the reply. so if i get the lt4 package the intake dont match up to the heads without machine work? or would the machine work just make the setup work better. and yeh i do have an auto. say i get the lt4 package, what size converter would be good? thanks for all the help. i want a good setup and just dont know how to go about getting it done right.
thanks
chris

[Injuneer]

If you bolt a factory LT4 intake on factory LT4 heads, it will bolt right on. There will be a mismatch on the ports. But it will be the same "mismatch" the stock LT4 Corvettes and LT4 F-bodys had. It just seems like GM ran out of money, and didn't put a lot of development work into the LT4 intake. The mismatch will work "OK" with the stock LT4 heads. But if you ever want to get really big HP out of the engine, you would need to port the LT4 heads, and do a fairly extensive port on the the LT4 intake. CNC Cylinder Heads in Pinellas, FL has one of the best combos on the intake side.

Can't help you with the specifics of the convertor for the A4.... my car was originally an M6. I suspect you would be looking at someting like a 2,800rpm, but you'd need to confirm that with someone who knows.

[redws6]

yeh i dont want anything too crazy, i just want my car in the 400+ hp range. does that co. in FL have a website?
thanks for the help
chris

[Injuneer]

CNC Cylinder Heads has a website, but there's not much info on it.

http://cncheads.com/

Let me alos caution you.... I have the CNC LT4 heads and intake. They sell complete heads, but I bought mine with only the porting done, no assembly. I had particular features that I wanted incorporated, like bronze valve guides, Ferrea intake valves, Manley extreme duty exhaust valves, etc., that CNC did not offer. The heads were completed by Second Street Speed in Perkasie, PA - known for their 1,000+HP LT1 engines. As recieved from CNC and assembled by Second Street, the intake side was one of the best they had ever seen on an LT1/LT4 head. And, Pete Incaudo at CNC suggested that we flow the heads WITH the intake. Doing that, flow actually increased, something they could not duplicate with a similar set of Lingenfelter LT4 heads/intake they had in the shop at the same time (off of George Baxter's 1,000HP 383 Vortech blown LT1).

So far, sounds good.... but the exhaust side of the CNC heads flowed VERY poorly in comparison.... only about 70% of intake, and nowhere near the Lingenfelter heads. When I tried to contact Pete at CNC, he suddenly lost interest in talking to me. He would never return phone calls or e-mails. And, there wasn't a lot we could do with the heads, since the "error" was basically hogging out too much material from the exhaust ports. We compensated somewhat by achieving 0.590 gross lift on bothe I & E, using 1.6RR's on the I side, and only 1.55RR's on the exhaust side. That way we could step up the lift on the exhuast side to see if there was any power to be gained. In the end, we left it with the 1.55RR's. But, bottom line.... Pete knows the intake side very well - he claims to have been part of the team that developed the LT4 heads/intake for GM, and speaks openly of the "compromises" that were done to the intake. The extent of machining that was done to my intake was extensive enough, and effective enough to indicate he knew what he was doing.


All that said, a couple years later, Second Street picked up a "new" set of Lingenfelter CNC's LT4 heads and intake, and they flowed better than my CNC's.... apparently LPE had made some serious upgrades to their LT4 porting. If you have the big $$$ that LPE charges, their LT4 head is very good. Alternatively, there are people who have extended the flow capabilities of the stock LT1 and LT4 heads to new levels. Check out Lloyd Elliot (ePort) or Advanced Induction:

Advanced Induction

I'll have to find the link for Lloyd.

[Formulaboy95]

Link for lloyd - eportworks.com

Eportworks