Official GT40P headed 300rwhp thread!!!

greenlantern · Apr 15, 2009

Mustang5L5 said:
Is there a significant benefit to some "home" porting?

My car is laid up and i have the heads and my Cobra lower intake off the car. Anything I can do to improve either one slightly while they are off the car and I have time?

I was going to put them on untouched, but if there are gains to be had by some simple porting, I would like to do it.

Absolutely, I purchased a set of windsor jrs and took them to a machine shop to have them disassembled. Spent a few hours a night for about 2 weeks off and on cleaning up the bowls and smoothing the exhaust ports. Compared to the last set of untouched box stock windsor jr heads I had these were a nice improvement. Be prepared to spend a little for the sanding rolls and the right tools. I used both air and electric die grinders.

99FiveOh · Apr 16, 2009

What did you prefer, electric die grinder or air? Seems electric would be easier, I know you need a big compressor to use a pneumatic die grinder for long periods of time.

aarons914 · Oct 10, 2009

Im researching either ported stock head/intake combos and Gt40p options and was just curious about how people are making 300rwhp or close to it with this combo. It seems very close to a stock cobra setup with the GT40 heads, intake, and TB, are the Cobras extremely underrated from the factory?

Joe Jr. · Oct 10, 2009

I've always wondered the same thing. I guess there just weren't as many 93 - 95 cobras made that people were trying to modifiy. There's all the arguments about the 40 heads versus the 40p heads.....I think both heads are good, its just that the 40p heads seem to be easier to find because of all the Mountaineers and Explorers they were put on and are being junked now.

did you read the 40p head discussions on corral.net? lots of good stuff there too.

Mustang5L5 · Dec 5, 2009

Bumping an old thread

WHat are you guys using for springs on your 40P's? I plan on running the TFS1 with Cobra 1.7 RR's with my 40P's. Just want to make sure i have a good spring.

tmoss · Dec 5, 2009

Comp Cams dual spring #978

Micks 88 GT · Jan 15, 2010

What plugs are you guys using for P heads. I have 306. The plugs I removed seem to not seat as low as some of the one advance shows available. The ones I pulled are Motorcraft Platinum AWSF 32EE. Thanks, this is a great thread!

Micky

95BlueStallion · Jan 24, 2010

Add me to the list guys. Im sending my GT40P's to Thumper tomorrow for him to work his magic on. I am going to run them N/A for a while with a Trickflow street heat intake, but I am undecided on a cam. I have plans to run a vortech, so I want a custom cam for boost, but that would kinda suck for the next year while I save up for the blower. My boy is due Feb 13th, so I have to be careful with my spending. I might just keep the stock cam, cause I hear it is good with boost and I can save $$$. I know I will be far short of 300 rwhp N/A if I go that route.

insane85mustang · Jan 28, 2010

ok i have a question?would i make 300rwhp with my combo?
351w .040 over
forged keith black flat tops (9.5-10:1)
280H magnum(230@.050,.512)
rpm air gap
600 holley DP
now i know a pro porter and he said he would help me with the porting and also set me up with a serdi valve job(7 angle i think he said).now if i get them to flow like 220 cfm and have 1.9/1.6 valves,what do you think i would make?also how much more with a custom cam?thanks

insane85mustang · Feb 14, 2010

99FiveOh · Feb 14, 2010

insane85mustang said:
ok i have a question?would i make 300rwhp with my combo?
351w .040 over
forged keith black flat tops (9.5-10:1)
280H magnum(230@.050,.512)
rpm air gap
600 holley DP
now i know a pro porter and he said he would help me with the porting and also set me up with a serdi valve job(7 angle i think he said).now if i get them to flow like 220 cfm and have 1.9/1.6 valves,what do you think i would make?also how much more with a custom cam?thanks

Well this is a completely different animal. You have the cubes to get you over 300 rwhp easily. This thread was more aimed at people trying to get 300 rwhp out of their 302 motors with GT40P heads.

To answer your question, I'd bet money you'll easily crush the 300 rwhp mark!

insane85mustang · Feb 14, 2010

yea i didnt think about it being just for 302's but i do appreciate you answering my question.i was wondering how much the extra cubes would help.i would like to get close to 350rwhp but i dont know if that is dreaming with the gt40's or not.thanks again

99FiveOh · Feb 14, 2010

If you get a stellar porting job on those heads and get the heads milled down to boost compression a bit, you should be able to obtain that power rating without issue. Something these guys on here have taught me is that you'll need a very good flowing, short runner or box intake to make good power with a 351.

insane85mustang · Feb 14, 2010

as far as porting goes,i have a friend that has the quickest and fastest olds powered car and lives about 10 mins from me.he told me he would help me with the porting and set me up with valves(1.9 or 1.94/1.6)and a serdi valve job(i think he said 7 angle).i was going to have them milled to maybe 60cc and also thought about porting the intake while i have it off.i have heard good things about the RPM air gap(loses a little up top to a victor jr but does better down low)so maybe that will be ok.this car will only see the track maybe a few times a year,mainly a cruiser and and show car but would like to have some power there as well.car will probably not see over 6k rpms either.just cant afford aluminums right now and can get most work done free or cheap,so i figure why not try it.thanks for the reply
p.s. i know the carb is small and will be going to a 650 or 750 dp in the future.

GMcanblowmyFORD · Jun 9, 2010

i have some 40p's im doing the same biggest valve possible and light porting, should flow like a champ!!

tmoss · Jun 9, 2010

If you put bigger valves in and do not change the size of the valve throat, your missing the ball......

XLR8TR · Jun 9, 2010

Agreed. Allowing bigger amounts of air in by using bigger valves won't matter if the runners aren't opened up to accommodate the extra volume.

95BlueStallion · Jun 10, 2010

Well boys I have my combo all put together with the Thumper GT40P's, but I ended up keeping my stock cam. Im not sure if I want to drop the coin on a dyno tune when I plan to run a blower next spring and will need to dyno tune it then for sure... Well see how much extra cash I can save in the next month, because Im sure there are a few people that want to see what the stock cam is capable of in a budget build like mine.

nmcgrawj · Jun 10, 2010

The_Mustang said:
If you get a stellar porting job on those heads and get the heads milled down to boost compression a bit, you should be able to obtain that power rating without issue. Something these guys on here have taught me is that you'll need a very good flowing, short runner or box intake to make good power with a 351.

302 parts on a 351 equals 302 power.

tmoss · Jun 11, 2010

nmcgrawj said:
302 parts on a 351 equals 302 power.

and so 351 parts on a 302 = 351 power?

Official GT40P headed 300rwhp thread!!!

greenlantern

Member

99FiveOh

aarons914

New Member

Joe Jr.

Mustang5L5

That is…until I whipped out my Bissell

tmoss

Gettin Wired

Micks 88 GT

New Member

95BlueStallion

My assy trans to myself

insane85mustang

New Member

insane85mustang

New Member

99FiveOh

insane85mustang

New Member

99FiveOh

insane85mustang

New Member

GMcanblowmyFORD

New Member

tmoss

Gettin Wired

XLR8TR

New Member

95BlueStallion

My assy trans to myself

nmcgrawj

Advanced Member

tmoss

Gettin Wired

Similar threads

Official GT40P headed 300rwhp thread!!!

Member

New Member

That is…until I whipped out my Bissell

Gettin Wired

New Member

My assy trans to myself

New Member

New Member

New Member

New Member

New Member

Gettin Wired

New Member

My assy trans to myself

Advanced Member

Gettin Wired

Similar threads

Privacy & Transparency

Privacy & Transparency