300 Performance Questions
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Senior User
Joined: Jul 2003
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From: Minnesota
300 Performance Questions
Hello, I'm new to the 300 inline 6 engines. A buddy of mine just picked up a '79 Ford F250 4x4 with a 300-6, manual trans with granny low, and 4.11's all the way around. The engine runs great but he wants to get some more power out of it to keep up with some others in the mud. He ordered a set of 33x13.50-16 Super Swamper LTB's for it and we are going to put a locker in the rear end. But we are going to dive into the engine and do some work to it to give it more power. The first thing we planned on doing was to put the Offenhauser 4 barrel intake on it with a 600 cfm vacuum secondary Holley. Also we planned on putting a header on. But as for internals. The cam will get pulled out and a more performance grind will get installed. We were lookin at something in the 2000-6000 rpm range. But what I can't seem to find any information on is the heads. What are the valve sizes? Also, how much will bolting a 240 I-6 head on raise compression? But are the valves smaller on the 240 head? This should answer a few of my questions for now. Thanks
Posting Guru
Joined: Jul 2004
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From: Bored town OH
The 2000-6000 rpm cam is WAY to high for the 300. I would get a cam that works from Idle to 3500. the 300 doesnt have any power after 3500 anyways, it makes peak torque at 2000 RPMS. The 300 is the closest a gas motor will ever be to a diesel. you can bore it 30 over and put 390 pistons in it. For the head there isnt much. Port & Polish, and small block chevy valves. the 240 heads bump the compression up to 9:1 I think, not to sure though. Oh yeah Clifford makes 4 barrel intake manifolds too, and most people like useing holley 390's or edlebrock 500's. With the intake manifold, carb, headers, truck cam, small block bowtie valves, bore & 390 pistons, and a port and polish job, that 300 will pull most trucks backwards, especially with 4.11's and a granny tranny.
There is a thread at the top of this forum called need more power again and again. it has a ton of posts of mods for the 300.
There is a thread at the top of this forum called need more power again and again. it has a ton of posts of mods for the 300.
Postmaster
Joined: May 2002
Posts: 3,241
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From: Broken Arrow, OK
You've gotta go 0.050 over to use 390 pistons. Instead of a 240 head I think I would try an EFI head with a recurved distributor. The EFI head has a better chamber and will already have hardened seats for running unleaded fuel. I think you will have to have those installed on the 240 heads.
Senior User
Joined: Sep 2003
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Porting the head can add performance but not to the degree that you can run the 300 at 6K RPM.
The problem is the head doesn't flow very well and there are no aftermarket solutions to that. You can make some gains porting the stock head but not to the extent that you can turn the 300 into a engine that will be a monster above 4500 RPM
A 600CFM carb will be too large. Mileage and throttle response will suffer. Trust me on that as I'm living with a 600 CFM carb currently.
Also, the Chevy BBC 1.7 Rockers will add some gains along with a cam but once again you are limited by the stock head's crappy flow.
If you decide to use the BBC roller rockers, custom length pushrods and push rod guide plates will be needed.
The carbed head does flow better than the EFI.
The problem is the head doesn't flow very well and there are no aftermarket solutions to that. You can make some gains porting the stock head but not to the extent that you can turn the 300 into a engine that will be a monster above 4500 RPM
A 600CFM carb will be too large. Mileage and throttle response will suffer. Trust me on that as I'm living with a 600 CFM carb currently.
Also, the Chevy BBC 1.7 Rockers will add some gains along with a cam but once again you are limited by the stock head's crappy flow.
If you decide to use the BBC roller rockers, custom length pushrods and push rod guide plates will be needed.
The carbed head does flow better than the EFI.
Junior User
Joined: Feb 2005
Posts: 56
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From: Parma Heights, Ohio
no one has said anything about valve springs????valve springs are a must. your stock springs have a valve seat psi. of 60psi 70 at most, not good for compresion. especially over 9:1. they have a open psi of 140psi. again not good for rpms over 3,500 thats one of the resons why the 300 doesnt make high rpm power. that bad for a truck with 4:11 gears.
my sugestion would be to get some crane cams valve springs for a small block ford. they have them for $80, and have a seat psi of 120psi and 250 over the nose. those valve springs fit the original retainers. get rid of your rotaters if you have them. you dont have to machine the head. unless u want them at the specsified installed height of 1.7in.. stock installed height of the 300 is 1.67in..
thats what im doing to my engine, along with shaving the haed .050..
its getting paint right now...
my sugestion would be to get some crane cams valve springs for a small block ford. they have them for $80, and have a seat psi of 120psi and 250 over the nose. those valve springs fit the original retainers. get rid of your rotaters if you have them. you dont have to machine the head. unless u want them at the specsified installed height of 1.7in.. stock installed height of the 300 is 1.67in..
thats what im doing to my engine, along with shaving the haed .050..
its getting paint right now...
