306 gt40P questions Need advice please!

GofastJD · Oct 25, 2010

Ok, I'm replacing a stock 302 and replacing with a 306 that I just bought from a guy on craigslist for $500 completely rebuilt from a reputable machine shop and motor builder, they replaced all the internals to it, with JE pistons, scat crank, obviously .30 over, etc,etc. has a x303 cam, gt40p heads, gt40 explorer lower and upper intake, motor supposedly only has 500 miles... looks really clean as far as gaskets, etc.

Ok... I am wanting to have a reliable street/not often strip car that can blow the doors off any other streeters out there.

with that said.. my questions are..

where do I start... should I be concerned with the springs on the gt40p heads? hopefully the machine shop took care of it... but you never know... trying to find out details from the machine shop tomorrow. but, is there a way to check spring quality?

what about the rockers? should I be running 1.6 or 1.7> or other? can I tell what i have somehow?

x303 cam? will this work for my combo?

I just ordered some gt40p shorty headers, and wondering what spark plugs I should run? they said use what a 94 cobra calls for?

Also, I'm probably going to just use my existing 19lb injectors and stock fuel pump. will that be good enough?

I'm going to run stock maf sensor, with egr eliminator

I have alot of questions on installation of this new intake. but will post on another thread

Thank you for your time and any help is greatly appreciated.

NIKwoaC · Oct 25, 2010

I'm pretty sure the only way to test springs is to pull them off and load test them. Not sure if there is a way to do it with them still on the heads.

If you can get a manufacturer and a part number off the rockers, you can probably look it up. The only difference between the two is that a 1.7 will give you a little more valve lift.

Not sure if there is a difference in spark plugs between GT40 and GT40P heads. I'd use whatever spark plugs are specified for the Explorer engines that used GT40Ps (or whatever performance equivalents).

Injectors will be fine. Never hurts to go to a bigger pump, though the stock one will probably work.

Stock MAF will choke that engine. Stock MAF chokes a stock engine.

tmoss · Oct 25, 2010

run a 94-95 70mm MAF and port your lower intake, there is a how-to in the Tech Doc section here:

EECTuning.org • Index page

GofastJD · Oct 25, 2010

lower intake porting

I don't see a specific how to on that link. Is there a gt-40 lower specific instructions, or should I just read all of the porting threads and put all that knowledge together.

also, on the 94-95 maf 70mm do I just look for any 94-94 5.0 Ford MAF from salvage? or somewhere, and what about my throttle body, and egr spacer?

tmoss · Oct 25, 2010

The article to use is the HO lower porting article - the Cobras/Explorers have the same issues. Use a Mustang 94-95 MAF.

NIKwoaC · Oct 25, 2010

You can easily fit a 70mm TB/EGR on an Explorer intake, might have to knock the sharp edge off the opening with a dremel, but otherwise very little port matching is required to get the opening right at 70mm. I run a 70mm on mine.

Look on ebay for the MAF meter, you want one from a 94-95 5.0L Mustang. There were some other Ford cars that used the same 70mm MAF, but I don't know specifics there. You might also consider a larger aftermarket unit (75mm+).

onefast89 · Oct 25, 2010

id prolly say step your injectors up, my N/A 306 makes 350 horse to the tire and im using ls6 injectors at 40psi rail pressure. comes out a little more than 30lb/hr. im runnin an x cam to and i stuck with the 1.6 rockers, the tiny bit of extra lift from the 1.7's wouldnt even be benificial because those gt-40p's wont flow much more higher after .542"

NIKwoaC · Oct 25, 2010

onefast89 said:
id prolly say step your injectors up, my N/A 306 makes 350 horse to the tire and im using ls6 injectors at 40psi rail pressure. comes out a little more than 30lb/hr. im runnin an x cam to and i stuck with the 1.6 rockers, the tiny bit of extra lift from the 1.7's wouldnt even be benificial because those gt-40p's wont flow much more higher after .542"

Your N/A 306 makes 350 to the tire where his might make 275. Apples to oranges.

What is your setup, BTW?

Cobra1741 · Oct 25, 2010

yes check the springs. go for double beehive. id probably get rid of the x303 and get a comp xe270hr-12 ot tfs1 or look at anderson n-21. in this car your not really going to blow the doors off alot of streeters. gt40 heads just dont flow enough. will be a fun street car!! and grab a bigger maf.

and the flow is going to fall off after .500 lift stay with 1.6 rr.

GofastJD · Oct 25, 2010

ported the lower intake

Well I ported the lower intake and cleaned it all up, i probably shaved about a 1/4" off the bottom ports, took me about 3-4 hrs of non-stop grinding with an air tool carbide bit, and then smoothed it out with a softer bit. I just eye-balled for the measurements for now, going to put a caliper on it later before I'm done.

with the combo I have, and adding to it a 70mm MAF, new springs, and 1.6 RR, also just bought some stainless gt40p headers, running h-pipe no cats, dumped thru 2-chamber flowmasters, pulleys, cold air intake, and going to program a chip with a dyno. What do you guess the hp will be? and how much do you think to the wheels? torque? etc.

I don't know where you live but I used to have a 13 sec street stang and it would beat quite a bit of the sport cars out there.

If I can get it to hook up, especially in 1st gear, run a high 12 sec 1/4, pretty sure that would smoke most of the cars out there in my town.

GofastJD · Oct 25, 2010

70 mm MAF

Ok, just bought a 94-95 MAF 70mm on EBAY for $50 bucks delivered. What else should i do?

Would like to get to 300 hp with gt40p heads

My buddy just spent a ton of dough on a 347 stroker combo and dyno'ed at 307hp

Hoping that I can get there at a 1/3 of the price.

so far $500 for motor/ gt40p heads, explorer intake

$250 for gt40p headers
$50 on motor mounts
$200 on T5 good tranny

How close do you think I am right now to 300? and remember i'm going to be putting it on a dyno and programming a chip for it as well.

Cobra1741 · Oct 25, 2010

lol i live in dallas. ALOT of high powered cars down here... mainly need a low 12 second to be running anyone haha. my gt40 unported heads and e303 put down 265rwhp and 304 ftlbs, 3.73's, steeda control arms, drag springs, ported cobra intake, CAI, 24lb injectors, increased compression to 9.7:1 or so not 100% on that, and mine is basically a 8.7 1/8th mile car... i would say even with the porting it will be very very tough to put down 300 to the wheels with stock size valves and a cam that seems a little "big" for those heads. did you mill the heads to increase the compression?? i would say you can put down 280-290 rwhp and 310-315 rwtq but numbers jump around all the time. the track time will give you what you need to know!

a 347 only putn down 307?? low compression? something wrong there lol.

GofastJD · Oct 25, 2010

yea i was thinking i would probably hit a 75 nos shot later. there's guys on here that have a custom cam and are getting 300 with gt40p heads and other mods of course n/a

Cobra1741 · Oct 26, 2010

yea the custom cam could definately get you there!

GofastJD · Oct 26, 2010

how much for a custom cam and how/where would i get one?

GofastJD · Oct 26, 2010

i just figured out that i have stock roller rockers 1.5 they have a 5 stamped on them. Is this going to be ok with my setup or should i fork out the money for upgrade.

I guess the best thing would be tfs 1 cam, springs, and 1.6 RR ? what do you guys think>?

Cobra1741 · Oct 26, 2010

custom cam grinders- comp cams, FTI ed curtis cams. custom cams are 300 at comp cams and 300-350 i think from ed curtis.

the 1.6 rr and tfs1 will work well but wont get 300rwhp.

tmoss · Oct 26, 2010

Cobra1741 said:
and the flow is going to fall off after .500 lift stay with 1.6 rr.

So what - the idea is to get the valve lifted faster and flowing faster. I run 1.7s on my intake side and 1.6s on my exhaust.

Cobra1741 · Oct 26, 2010

tmoss said:
So what - the idea is to get the valve lifted faster and flowing faster. I run 1.7s on my intake side and 1.6s on my exhaust.

yea true. i heard that comp cams had a pretty aggressive profile which gives you that fast ramp rate. you think id see a gain if ne by putn 1.6's on the intake side of my e303 with gt40s??

tmoss · Oct 26, 2010

most often there is only one way to tell for sure - try it and see. It can respond positiively to any combination as the best, 1.7s all around, 1.7s on the intake, or 1.7s on the exhaust. Depends on what your combination of parts needs most. My car was more inlet deficient so it responded to them on the IV.

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