# 400 vs 455 swap



## dueyd42 (Nov 30, 2016)

Have a 68 vert with th400, 3.08 posi with a nice hole in the 400 block thanks to nephew. It has 96 heads, edelbrock performer intake, headers, and Holley I can reuse.

Would I be better of performance and cost wise to go with a 455 short block and keep my stuff or get a 400 long block with some ported 6x heads and keep intake and carb? I like the idea of keeping the car with a 400, but if the price and performance with the 455 short block is much better I'm good with that too.

It will be a cruiser and not see the strip, but pushing 400hp and 450tq would be nice to shut those 5.0 d-bags up.


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## Sick467 (Oct 29, 2019)

It's a bit of a toss-up in my opinion. The 400 is more desirable these days since it can be stroked to the same CID as the 455, but the 400 has smaller crank journals and that lends itself to higher rpms and a stronger block. But if stoking the block is not in your future a mild 400 with 96 heads would not be as powerful as a similar mild 455 build with 6X heads. IMO, getting 400 HP out of a 400 block would mean a high compression build among other common mods (port-matching, headers, & larger than stock cam) whereas the 455 could produce the 400 HP without the higher compression numbers (but still wanting the other common mods).


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## PontiacJim (Dec 29, 2012)

dueyd42 said:


> Have a 68 vert with th400, 3.08 posi with a nice hole in the 400 block thanks to nephew. It has 96 heads, edelbrock performer intake, headers, and Holley I can reuse.
> 
> Would I be better of performance and cost wise to go with a 455 short block and keep my stuff or get a 400 long block with some ported 6x heads and keep intake and carb? I like the idea of keeping the car with a 400, but if the price and performance with the 455 short block is much better I'm good with that too.
> 
> It will be a cruiser and not see the strip, but pushing 400hp and 450tq would be nice to shut those 5.0 d-bags up.


Go with a 400CI block and stroker kit. More cubes allows for a much better pump friendly gas compression and you will trade high RPM 400CI HP for low RPM Torque, and torque is what moves the car. With the correct matching heads/cam/intake/carb/exhaust, you can have a very street friendly driver that will light up tires and put you back in the seat when needed.

*Jared *purchased a Len Williams short block and installed a set of Nitemare Performance prepped iron heads and has just recently got it road worthy, so check out his posts. Most Pontiac engine builders have a back log, so don't be surprised. Don't select an engine builder/shop unless you have other Pontiac members recommend them so you don't have any disappointments. If you can do much of your on assembly, you can save money and locate a good 400CI block and go with a stoker kit. Just make sure you know how many CC's the head chamber's are so you can order custom dished pistons to get your compression down around 9.0-9.2 for pump gas - a litle more if you go aluminum heads. Select a good shop to do your machine work and then you can do the assembly if it is something you can do.



455 Short Block



And.........









FAQ - General: GTO and Pontiac Reference Sources


Another excellent book is "How To Build Max-Performance Pontiac V8s" By Jim Hand. It's basically how to get the best performance using mostly stock engine parts when you rebuild your engine. Unfortunately the book is out of print so it's probably hard to get a copy. Note that he got his over...




www.gtoforum.com


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## Jared (Apr 19, 2013)

Looks like the 96 heads would work on either size engine as long as they haven't been shaved. Based on the factory CC you would be right around 9.5 : 1 on the 455 and less on the 400. The 6X heads I have on mine were dialed in to 96CC and I've had no issue running mine on pump gas. So far I am very happy with the Len William short block I built up for mine. For the money, it's a great option especially if you need a block. Mine took about 6 months to show up and was well worth the wait. Same goes for the heads I got from Nitemare. The heads were ported, had larger exhaust valves installed and were flow checked (based on numbers would support ~600hp, mine is set up for less). An added bonus of dealing with Darrin is the technical support you get from him. He really goes above and beyond to help you out. I had trouble with my initial start up and he spend over an hour on the phone (late evening on a weeknight) with me to make sure I could get it to run, and then followed up by email a couple days later. The best part about both these shops is all they deal with ins Pontiac engines. The downside is you wait for their expertise. This will not be a back on the road in three weeks type of deal. 

If I were you I would really think about what your goals for the car are before you make this decision. If you just want to cruise around, a 400 is probably the way to go. My car was pretty quick with the tired 400 that came out of it. It is blistering fast with the engine in there now. I had a budget in mind when I built mine and went way north of that. Some unexpected things popped up, and on a Pontiac, a few things can get pricey fast. I didn't realize I'd need a windage tray, front cover, and an engine harness until I dug into it. I really couldn't use much of anything from the old engine other than the front accessories and the bell housing.

If you're married, I would start being really nice to the spouse now and figure out how on board they are on this. My wife was extremely supportive which made my life a lot easier between the time this took and the money I spent on it. My wife's only interest in the car is that we go out for ice cream in it on nice days.


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## dueyd42 (Nov 30, 2016)

Thanks for the replies. I was looking hard at a Len Williams 400 or 455 long block. Think the 455 will get me closer to where I want the car to be.

Was contemplating his short block 455 and reusing my 96 heads, but now would just be easier and maybe as cost effective to go with a done long block. The car is fairly new to me and have no idea what all may need to be done to the heads to get them up to snuff. Unfortunately I don't have the time, tools, or skill to build it back up myself, but I do have the time to wait for one to be done correctly for me. As you mention PJ, not alot of Pontiac guys around here so leaving the shop with the least amount of work to button it up for me may be advantageous.

Jared, the wife is on board with whatever the car needs. She wants me to make it how I want it now so we don't have to worry about it later. Her budget number she threw out was actually higher than were I was looking, so I may just hold her to that.

What are yalls thoughts on the Edelbrock Performer intake and the Holley 750cfm carb I plan to reuse on the 455 long block? Depending on cam selection, would this work well enough? Should I look for a Quadrajet?


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## armyadarkness (Dec 7, 2020)

Im biased, but here's a good thread! If you're not a tuner, I'd avoid the Holley. The Qjet is great (although arguably still tricky to tune), if you can guarantee that you get a good one.








EDELBROCK AVS2 FOR PONTIAC - STOP HATING THIS CARB!


Since I see weekly carb postings on this site, and no one seems to love Edelbrock carbs or include them in the GTO options, I figured that I'd make a post to at least enlighten folks about why this carb can be great. First of all, Edelbrock has improved their carbs and they now have an AVS2...




www.gtoforum.com


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## armyadarkness (Dec 7, 2020)

I think jared is about to swap on an eddy carb


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## geeteeohguy (Feb 2, 2008)

Have heard nothing but great reviews about Len Williams for a long, long time now. Reasonable prices and his engines hold up over the long haul and run as they should. 
Agree that there is no better carb for a Pontiac than the properly set-up Q-jet. For power and economy. Best of both worlds.


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## PontiacJim (Dec 29, 2012)

dueyd42 said:


> Thanks for the replies. I was looking hard at a Len Williams 400 or 455 long block. Think the 455 will get me closer to where I want the car to be.
> 
> Was contemplating his short block 455 and reusing my 96 heads, but now would just be easier and maybe as cost effective to go with a done long block. The car is fairly new to me and have no idea what all may need to be done to the heads to get them up to snuff. Unfortunately I don't have the time, tools, or skill to build it back up myself, but I do have the time to wait for one to be done correctly for me. As you mention PJ, not alot of Pontiac guys around here so leaving the shop with the least amount of work to button it up for me may be advantageous.
> 
> ...


The Edlebrock Performer might be a bad choice if you go 455 (400 stroker engine). The Performer has smaller runner passages and will be the limiting factor in air flow. Your engine might stop pulling at a lower RPM than it has potential to do because it can't get enough air into the engine. The Performer RPM would be a better choice if going with bigger cubes. I read that the Q-jet will work on the RPM Performer, BUT, I read you may have to open up the manifold slightly for the secondaries throttle valves as they may hit the intake.


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## Jared (Apr 19, 2013)

armyadarkness said:


> I think jared is about to swap on an eddy carb


I should be doing so today. I currently have a 650 Eddy on there and it's being swapped out with a 850. I wasn't able to get an AVS2 due to no availability of their carbs right now. I bought a rebuilt Performer off of Ebay supplied by a rebuild shop in MN (had great feedback on his rebuilds). Personally, I don't like the Qjet carbs. They are hard to set up and tune for a novice like me. The Edelbrock carbs are simple to dial in and I've had good luck with them.

I have a Torquer II on mine. While that is typically not a popular choice on here either, my engine seems to like it.


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## Jared (Apr 19, 2013)

A little more insight on Len Williams shop. He runs the business very old school. All communication is over the phone and by mail. If you decide to go with him, you send a pretty good deposit by check to get on the list and then you wait. As said the short block I ordered took ~6 months to arrive. This all being said, he's a nice guy and supplied me with a very nice short block


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