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Tuned Port 400?

Old 11-04-2018, 11:13 AM
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Tuned Port 400?

Hey, all. Been a while since I've poked around. The old 'Bird's still awaiting the wrench, I've just been busy as crap due to a combination of prepping the garage and overtime at work.

Anyway, after reading about all the various neat stuff and combinations involving my TPI, I got to thinking, what about dropping the system on top of a 400 block? The small chambers of the 305 heads combined with the large bore of the 400 will yield a ton of compression but nothing some piston dish and cam selection can't handle.

Just curious if anyone's bolted a TPI setup onto a 400 and if so, what were the results?
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Old 11-04-2018, 01:21 PM
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Re: Tuned Port 400?

400 shortblock
305 heads
TPI set up
none of that compliments one another.
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Old 11-04-2018, 02:25 PM
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Re: Tuned Port 400?

1.88" intake on the 305 vs 1.94" intake on the 350. It's a bit of a difference but I'm doubtful it'd make that much of a difference for a torquey street engine. Unless the 350 heads really do flow that much better than the 305's, but I can't really find any flow data on OEM heads.

Most 400's were made during emissions and I'd be surprised if those OEM heads would outflow later fuel-injected heads. Unless they had enough meat in the castings to allow considerable porting...

I'm looking to make 400 lb/ft torque and anything over 300 horsepower. Yeah, it's nothing exceptional but huge figures aren't what I'm after. I'm looking for a setup that kicks *** off the line, feels nice to drive with an automatic and doesn't suck too much from the wallet. I've got a fair bit of body work and other stuff to tend to as well and I don't want to sink my entire budget in just the engine.

And, well, I find it hard to ignore the allure of a bigger engine.
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Old 11-04-2018, 02:27 PM
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Re: Tuned Port 400?

Can you even add steam holes on the 305 heads ?
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Old 11-04-2018, 02:35 PM
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Re: Tuned Port 400?

Originally Posted by Yeret View Post
I'm looking to make 400 lb/ft torque and anything over 300 horsepower. Yeah, it's nothing exceptional but huge figures aren't what I'm after. I'm looking for a setup that kicks *** off the line, feels nice to drive with an automatic and doesn't suck too much from the wallet. I've got a fair bit of body work and other stuff to tend to as well and I don't want to sink my entire budget in just the engine.
300 hp at the crank is not an issue. 300 hp at the wheels with 305 heads will be very tricky, I'm skeptical.
When people talk about a setup that rockets from a stand I remind them of the article from a decade ago when the Holley Stealth Ram came out. A magazine (Car Craft maybe) did a very good writeup where they tested the IROC with the TPI setup and then changed the intake to the HSR and then revisited the drag strip. Even though the TPI made more torque the HSR was faster because they couldn't use all of the torque from the TPI. The IROC even had drag slicks for all the tests.

Last edited by Tibo; 11-04-2018 at 02:41 PM.
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Old 11-04-2018, 02:50 PM
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Re: Tuned Port 400?

I was under the impression that most SBC heads could be drilled for steam holes but I'll admit to making the assumption that 305 heads could be.

If 305 heads can't be drilled, it woudn't be too big of a deal to purchase a set of 350 heads (I have the post '87 manifold bolt pattern so I'll have to stick to post '87 heads, unless the center holes in the manifold can be drilled straight or the center holes in the heads can be drilled at an angle). The only reason of sticking to the 305 heads is because I already have them and it would save me some scratch. Of course, if they turn up to be cracked then that changes things...
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Old 11-04-2018, 10:03 PM
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Re: Tuned Port 400?

I replaced a 350 TPI with a 400 block many years ago and was not really happy with it. The machine shop I used drilled the steam holes in the stock 350 heads(sure it can be done with any sbc heads) so that I could use the TPI intake setup, and did a complete valve job. I used 10:1 hyper pistons, a small cam with typical other bolt ons and had great low end torque but felt the setup was slower and had a considerably smaller power band....seemed to lose power after 4k rpms. This just my experience using a 400 with TPI .
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Old 11-04-2018, 10:51 PM
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Re: Tuned Port 400?

I have a 400 TPI in my K5 Blazer and it is great. But I also have an RV cam and have it set up for low rpm power. It rolls off before 5k. I can post more details if interested. It is also full sequential and coil per plug.
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Old 11-05-2018, 10:13 AM
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Re: Tuned Port 400?

Even though the TPI made more torque the HSR was faster because they couldn't use all of the torque from the TPI. The IROC even had drag slicks for all the tests.
mine was also faster everywhere vs tpi. Made less peak torque but made more everywhere above that point and more hp and rpm. Thats why it was faster. 60 ft was as good and better. Wasnt because i couldnt use it, on slicks it would not spin


A 400 with 305 small valve heads is not worth it imo. You need atleast 1.94ís from a 350 head. Youíll make more trq than any L98 but donít expect much power, it just shifts lower rpm. Youíll need bigger heads and intake to make more power.
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Old 11-05-2018, 01:12 PM
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Re: Tuned Port 400?

You need atleast a 64cc head on a 400. A lil more say 72cc would be probably more suitable. NOT a 58cc head.
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Old 12-30-2018, 06:26 PM
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Re: Tuned Port 400?

Originally Posted by kurtis72 View Post
I have a 400 TPI in my K5 Blazer and it is great. But I also have an RV cam and have it set up for low rpm power. It rolls off before 5k. I can post more details if interested. It is also full sequential and coil per plug.
If you don't post it up here, I would like to hear about it! I have a '79 K20 with a stock 400 and a TPI sitting on the shelf. I was thinking MS to control it. I understand these guys views on it for their cars, but I think in a truck it is a different story. My truck has a hard time getting to 4k rpm's anyways...
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