[Steve Shively]

I am restoring a 1968 Firebird 400HO 4 speed coupe. Original drivetrain was long gone when I bought it in 1983. Long story short, I found out through PHS docs what the car was originally. So through the years I have been collecting correct number & code parts to build it as close as I can to factory. A few changes will be made. Here are my ideas:

WQ 400 .030 over, stock crank, Eagle connecting rods, studded bottom end, fully balanced. Zero deck block
Heads are #16 big valve D ports
stock intake
#7028271 Q-jet
Long Branch manifolds
M20 Muncie transmission
3.55 posi

I want a bullet proof bottom end that will take my abuse! Not worried about high compression, will deal with properly with race fuel mix if & when needed.


So now I draw on your experience's building Pontiac engines. Best pistons for good quench & cam. Considering using a RA IV cam, but wonder if a 3.55 gear is enough for that cam. So many ways I can go, but this car will be driven, alot. I'm spending too much money for it to a trailer queen.

[Steve C.]

"Not worried about high compression"

"but this car will be driven, a lot"

My first thought is to use custom pistons to lower the compression for pump gas.


.

[leeklm]

If driven a lot, you may want to consider a stroker crank with 9.3:1 CR and 3.08 or 3.23 gears. Or go with a 5SPD OD or a custom muncie 4spd OD. This combo would build tons of pwr on pump gas. You could have 461 cubes and look like a bone stock 400 on the outside.

If going that route, I really like the stump puller cam with roller lifters from SD Performance.

I have 3.50 gears in my 68 and 28" rear tires, and really do not like beating it down the interstate at 75mph. I try to stay on the 55-60mph side roads when I do drive on the road. When accustomed to OD trannies since the 80s, it kind of sucks driving long distance at 3k+ rpm with loud exhaust and a car that already has a lot more road noise when compared to a modern ride.

Again, this is assuming you are truly driving the car, and not just 10 miles at a time like I do!

Sent from my SM-G965U using Tapatalk

[ponyakr]

Yeah, you've definitely got a LOT of options, nowadays.

Looks to me like you need to make some definite decisions about the exact details of what you want.

(1) Stay with the stock 3.75" stroke AND high compression, OR go bigger, so you can have lots of power, at a lower rpm, AND run on pump gas.

(2) Stay with a HFT cam, OR go roller.

(3) Use a trans with a 1:1 high gear ratio, OR, go with an OD trans, OR go with less rear gear. With more cubes, you could go with much less rear gear.

(4) Exactly how strong do you want the bottom end ? Are forged rods & a cast crank OK ? OR, do you wanna go with a forged crank, Eagle H-beams & Ross pistons. There are other rod choices, some cheaper, some higher. There are cheaper piston choices. My choice would be Auto Tec. But, I understood Adam Strang to say that he ran 10's in his Stocker, using TRW pistons. They're heavier, but plenty strong & have been proven now for several generations.

If price is absolutely no problem, I'd go BIG, with the strongest parts & procedures available. BUT, you can probably build what you want, for several thousand less.

So, it's your call.

[tom s]

I you build a bullet proof bottom end and have too high of CR to run on your choice of gas you will still knock the bearings out of it.Tom

[77 TRASHCAN]

I now Cliff has experience with these higher compression builds. I'd get his 2 centavo's before I bought too many parts.

I'm guessing you plan to use forged pistons, did not see that on list.

Zero decking, removing sharp edges in chambers, and on pistons, proper cam selection, AND dialing it in, state of carb setup....all make a big difference. Leave out one and it can hurt you.

[Steve Shively]

Lowering compression a possibility, not opposed to dropping to around 9-9.5 range. But would dropping compression limit cam choice? Quench with dished pistons would be a concern. Staying stock stroke.

[pastry_chef]

Get your head chambers CC'd, then choose a piston that provides close to 9.5 CR.

Ballpark cam.
Ultradyne hyd flat from bulletcams.com

Intake - H25
274
226 @ .050
137 @ .200
0.3120 lobe lift

Exhaust - H18
282
233 @ .050
143 @ .200
0.3120 lobe lift

[pastry_chef]

Another.
Howard's hyd flat (Brookshire lobes)

Intake -
H2243240
271
225 @ .050
139 @ .200
0.324 lobe

Exhaust -
H2333383
279
233 @ .050
147 @ .200
0.338 lobe

[ponyakr]

Some go with flat pistons & reduce CR by removing material from chambers.

Probably some head porters here who know how it's done properly.

Some make up for lowered CR by using a steeper ramp cam, such as the Voodoo series. Voodoo cams seem to be real popular here.

The 262, which most here call a "702", should give you lots of low rpm grunt, with the short stroke.

https://www.lunatipower.com/voodoo-h...8-262-268.html

But some insist on more thump & more power above 5000 rpm, & aren't really concerned about low rpm torque.

https://www.lunatipower.com/voodoo-h...8-268-276.html

Here's a few more from the list of shelf grinds I've compiled.

https://www.lunatipower.com/street-m...8-276-286.html

https://www.summitracing.com/parts/c...IaAusEEALw_wcB

https://www.summitracing.com/parts/s...YaAjPfEALw_wcB (cheapest)

https://www.summitracing.com/parts/hrs-410141-12

https://www.crower.com/camshafts/pon...m-284-hdp.html (high $$$)

https://www.lunatipower.com/street-s...8-285-300.html

https://www.summitracing.com/parts/h...w/make/pontiac

When you order from the cam grinders, you can usually get any LSA you want. Most(not all) agree that a larger LSA, like 112°-114°, will provide better street manners.

[Old Man Taylor]

Originally Posted by Steve Shively

Lowering compression a possibility, not opposed to dropping to around 9-9.5 range. But would dropping compression limit cam choice? Quench with dished pistons would be a concern. Staying stock stroke.

Quench with properly dished pistons is not a problem. Here's a picture of my 428 piston that has about 0.038" quench height. CR is 9.7:1 and it runs on 91 Octane. Heads are 670's. My cam is probably too large, but I run nitrous with my tri-power. Cam is a hydraulic roller, 242/248 at 0.050" lift. I ran hydraulic flat tappets as large as 260/260, but the tri-power didn't like them.

[OCMDGTO]

If you're stuck on a stock crank and iron heads I would get a good set of forged rods and pistons, get the heads ported and a good sized cam. Search for Cliff Ruggles 400 build, he has a PROVEN recipe with a Crower HFT that makes very good power I belive with their 60243 cam. If you get too wild you will need to upgrade the trans, driveshaft, rear, & fuel system. My old/spare engine was a 400 w stock crank, Eagle rods, TRW forged pistons, Comp HR cam, Torque 2 intake, stock flowing 16 heads, & 750 Holley that ran 13.0s & was a great street engine. I always wished I spent the money for better pistons and head work. Good luck!

[STEELCITYFIREBIRD]

400's like compression make torque, RPM to make HP
Personally I think you have a good head chamber volume for a driver street 400
~10.-10.5:1 depending on piston dish etc.
engine 400 with flattops. m20 should pair well with gears in axle for street car.
RA4 cam too much for gear choice and cruising.
rocker ratio??
See what CR works out to, then choose cam, use Rhoads Lifters for sure.
Good choice of components so far I see.
Myself
If I am buying good pistons with thin ring lands , rods, balancing,line hone /main studs
put a 4.00" stroke in!!

pretty Light car does, it have A/C?
How will it be preferably driven,upper highway speeds , crawling on freeway or back road bending/blasting?

[Steve C.]

We want to know if an iron-head street/strip Pontiac should be built with 9:1, 8.0:1, or a 10.0:1 compression ratio? These are all values that are often mentioned during bench racing sessions. To many, our engine at 9.1:1 is at the threshold of what they call streetable on pump gas. We’ll see......

http://www.rockettbrand.com/download...ac-Sep2012.pdf


"If you were waiting for me to tell you what CR is optimum but "safe" for you, neither I nor anyone on this planet can tell you what is safe."

"Each case is different in that different quality gas is available, the vehicles are of different weight and have different transmissions and gears, different cams are used, the chambers are prepared differently, and so it goes."

From a three part series on compression by Jim Hand.


.

[Skip Fix]

Originally Posted by tom s

I you build a bullet proof bottom end and have too high of CR to run on your choice of gas you will still knock the bearings out of it.Tom

This!

Pump gas varies batch to batch brand to brand and blended different for different seasons. Throw a wide band on and see haw varied your AFR is from day to day with a carb and pump gas. For the minimal increased HP of 1 point of CR why risk it. I think in HO's old book it was 4%/1 point. so 16 HP on a 400 hp build.

[Steve Shively]

Car is a 68 Firebird 400 HO M20 Muncie, 3.55 ZN posi. No A/C, no power steering, standard disc brakes. Verdoro green with black vinyl roof, Pearl/Parchment interior.

[HWYSTR455]

Originally Posted by Steve C.

We want to know if an iron-head street/strip Pontiac should be built with 9:1, 8.0:1, or a 10.0:1 compression ratio? These are all values that are often mentioned during bench racing sessions. To many, our engine at 9.1:1 is at the threshold of what they call streetable on pump gas. We’ll see......

http://www.rockettbrand.com/download...ac-Sep2012.pdf


"If you were waiting for me to tell you what CR is optimum but "safe" for you, neither I nor anyone on this planet can tell you what is safe."

"Each case is different in that different quality gas is available, the vehicles are of different weight and have different transmissions and gears, different cams are used, the chambers are prepared differently, and so it goes."

From a three part series on compression by Jim Hand.


.

Exactly. What works for one combo may not work for another. Weight, gear, stall, auto/manual, you can't just say X, OR even say 'other people doing it' as a blanket statement.

As for SCR, iron heads, 9-9.5 is still the best approach. The difference in performance compared to say a 10-10.5 IS NOMINAL AT BEST. Most cams in the range you would be looking at to run all fall into that category of SCR. The SCR stated by cam grinders are JUST a guideline, and not meant to be holy-grail brick walls. They are very generic. Proof? Look at the description for a specific grind, and then go to diff applications, displacement, head design, blah blah blah, and you will see, it's the same across the board.

If you end up closer to say 9.5-9.75, then choose a slightly larger profile, you end up in the 9-9.5 range, go to the slightly smaller profile in the 'range' of profiles you're looking at. Done.

Considering the type of build you are doing, you really don't have to do anything 'special', plenty of examples out there. Good pistons & rods are a must IMO, and depending on how you plan to use it, a forged crank is good insurance.

Once you start looking at the cost of machine work and parts, you will probably find you will not be really 'saving' any money by using the stock crank compared to stroker, and the benefits are obvious.

I will say though that if you're using long branch manifolds, it will like a little more duration split leaning towards the exhaust, and generally more LSA too.

.

[Steve C.]

At our local speed shop 110 octane VP race gas is about $11 a gallon, give or take. Or bite the bullet and buy a 55 gallon drum and cart it home to save a bit. Then add in 20 percent or so to a tank of 92 pump gas ? I mentioned 110 race fuel above, 100 octane race gas might be cheaper but mixing that with 92 unleaded pump gas will take a 50/50 mix in order to get 96 octane. And this is about race fuel—there’s also race fuel 'concentrate' to consider. Different than parts-store octane boosters that are mostly slick marketing at work.

You can go forth, head swimming in octane knowledge to choose the best octane enhancer for flat top pistons and high compression

All this hassle to avoid forged pistons at $599 with the proper dish to lower the compression !


.

[i82much]

In addition to the cost and hassle of race gas, the other thing would bother me is that I'd like to be able to road trip with my car someday. How cool would it be to drive that Firebird up through the Colorado Rockies or something along those lines? To do that, you would need the convenience of running pump gas.

[MrWrestlingII]

Originally Posted by leeklm

If driven a lot, you may want to consider a stroker crank with 9.3:1 CR and 3.08 or 3.23 gears. Or go with a 5SPD OD or a custom muncie 4spd OD. This combo would build tons of pwr on pump gas. You could have 461 cubes and look like a bone stock 400 on the outside.

If going that route, I really like the stump puller cam with roller lifters from SD Performance.

I have 3.50 gears in my 68 and 28" rear tires, and really do not like beating it down the interstate at 75mph. I try to stay on the 55-60mph side roads when I do drive on the road. When accustomed to OD trannies since the 80s, it kind of sucks driving long distance at 3k+ rpm with loud exhaust and a car that already has a lot more road noise when compared to a modern ride.

Again, this is assuming you are truly driving the car, and not just 10 miles at a time like I do!

Sent from my SM-G965U using Tapatalk

This is basically my combo as well. 4.25" crank, SD Stump Puller Cam, M-20 with 3.42 gears and 28" rear tires. I'd prefer an overdrive, and will probably upgrade to one someday, but overall this is a really good combo. It's turning around 3,300 rpm at 70 MPH, but everything is balanced so well it's really not a big deal even up to 80 MPH.

I say stroke it, I did and have no regrets.