[wilmer496]

Guys, plenty of info out there on this topic so to just confirm my thinking before i start to spend money (bear with me)...

Have a -73 400 out of a Le Mans in my -67 Tempest. I did a stock rebuild on the engine some 8 years ago but cannot remember what pistons i put in it. Heads are stock 4X-4H, i added headers, a Summit 2800 cam, Eddie Performer intake, HEI ign and a Proform carb. Trans is a M20, rear axle gears 3.55. Car runs great but i want to spice it up some so i am looking at a head and cam upgrade.

As i have no idea what pistons are in the engine, i did a compression test and got around 8.0 / 115 PSI on all cylinders. That would be spot on for these 98 cc heads i believe. If i then replace the heads with Eddie Performer 72 cc's, i would get around 9.7-9.8 in compression. Does that sound right?
We have proper 95 octane gas available here!

Bumping up the compression with nearly 2 points, i will upgrade the camshaft. Not looking to build a screamer but some occasional spirited driving will happen. Also, i run a much needed air cond. Got manual brakes so slightly lower vacuum is not a problem. Any suggestions on a flat tappet hydraulic cam?

Thanks, Jerry.

[25stevem]

Yes, with Aluminum heads runnng even 10.5 comp is perfectly fine.

This chart is percent of power gain or loss.

[Formulas]

KRE D'ports 65cc crower 60916 cam good stock iron intake, i bet you would be happy compaired to what you have now
"IF" any of this stuff is available

[25stevem]

Just keep in mind that with any off the shelf aftermarket head for a Pontiac the your performer intake and maybe also your carb will limit Hp to between 400 and 415 hp.

You did not say what size your carb is, but a 600 cfm carb with your 400 cid motor is once again going to start to limit you to around 400 hp, your drivability will be great thought with 3.55 gears.

Compression wise here’s some info to help you out.

If your shooting for a 9.8 to 1 compression, and your motor is still at its stock bore size then you will need a total volume of 93 CCs with the piston at TDC.
So in CCs you need these factors .

Head chamber volume.
Piston valve notch volume or dish volume.
Deck clearance volume.
Head gasket volume
Intake valve chamfer volume, figure 3 CCs for a stock bore.
Piston ring land volume, figure 2 CCs for that.
Piston OD chamfer volume, if the piston has such

[Jim Moshier]

Hi Wilmer,

You said proper octane, but not everyone gets to it the same way In Thailand do RON (research octane) + MON (Motor octane) /be 2 Or AKI? I just want to make sure we know what you are running in octane. Do you have access to a stock Pontiac intake? 1968-1973

Jim

[wilmer496]

Boys, thanks for all the replies!

Formula: yes, everything is on back order 2-3 months. I will look into Crower cams, thanks.

25stevem: my carb is a 750 cfm, motor is .030 over. As for the CC factors, been awhile since the rebuild so i dont have those numbers. Therefore my thought was to go the lazy way by doing a compr test on my current set up.

Jim Moshier: those tech terms on gas you are using is way over my knowledge but RON sounds familiar. We have to types of 95, one mixed with cheap vodka, the other is an unleaded benzine. I have also a Mopar with a stroked BB, she runs great on the latter. If i am by "emergency" forced to fill with 95 ethanol, she pings.
I dont have any stock intake, most parts are hard to find locally. Are you saying i would be better off with that intake?

Thanks guys!

[Formulas]

yes the edelbrock performer is more restrictive than a good stocker, but if its hard to find parts where your at i wouldnt lose any sleep over it

its not a night n day thing at your engine size and HP level, but if you were to stumble on a non EGR 1967 or after Q'jet intake reasonable price grab it

[25stevem]

Here are some common CC values to help you out.

Cylinder volume at .030” is 831.2 CCs.

Total valve notch.volume for the common sealed power 2262 piston is 6.7 CCs.

Fel pro 1016 or 8518 head gasket is 9.7 CCs.

A common deck clearance for a stock 400 motor is .023”.
At a .030” over bore that comes out to 4.84 CCs.

Other CC values are in my previous post.

[25stevem]

To be more help to you note that at your bore and stroke size ( 4.150” by 3.750” ) it will take a 5 CC change up or down to shift the compression ration by a full 1/4 point.

This may help save you from making endless calculations!

[Stan Weiss]

Bore = 4.15"
Stroke = 3.75"

CR against Total Volume

Stan

[racegto65]

Originally Posted by wilmer496

Boys, thanks for all the replies!

Formula: yes, everything is on back order 2-3 months. I will look into Crower cams, thanks.

25stevem: my carb is a 750 cfm, motor is .030 over. As for the CC factors, been awhile since the rebuild so i dont have those numbers. Therefore my thought was to go the lazy way by doing a compr test on my current set up.

Jim Moshier: those tech terms on gas you are using is way over my knowledge but RON sounds familiar. We have to types of 95, one mixed with cheap vodka, the other is an unleaded benzine. I have also a Mopar with a stroked BB, she runs great on the latter. If i am by "emergency" forced to fill with 95 ethanol, she pings.
I dont have any stock intake, most parts are hard to find locally. Are you saying i would be better off with that intake?

Thanks guys!

If Crower is backlogged call and talk to George or Nick at Clay Smith. Just had them do a hydraulic roller cam foe a customers B/B Chevy and had it in 3 days

[wilmer496]

Originally Posted by 25stevem

To be more help to you note that at your bore and stroke size ( 4.150” by 3.750” ) it will take a 5 CC change up or down to shift the compression ration by a full 1/4 point.

This may help save you from making endless calculations!

There we have it!
Anyway, i will play around with your other spec's and see what i get.

Thanks again!

[wilmer496]

Originally Posted by Stan Weiss

Bore = 4.15"
Stroke = 3.75"

CR against Total Volume

Stan

Stan, pls elaborate on that graph.
As i am at 8 points on my current set up, it would indicate that i got 114 CC heads?
To my understanding, the 4X-4H heads that i got only came in 98 CC?

Or is the graph based on only bore and stroke, excl other factors such as piston dome, gasket thickness etc?

I'm learning!

Thanks, Jerry.

[25stevem]

Stans chart is " Total volume" , it states that in his second short paragraph.

Don't look at it as in just being chamber volume.

[Cliff R]

Unless you bought a forged piston you ended up with 8 valve relief cast pistons, which lower compression quite a bit plus end up WAY down in the holes at TDC. I've seen come down in there as deep as .050" with many around .030-.035". None of that is a good scenario for making compression or power with one of these engines. Even TRW/Speed Pro forged pistons are pretty short so not ideal in a 400 build without decking/squaring to reduce quench some.

Anyhow, if you can get to 10 to 1 compression the Crower 60243 cam is an excellent choice for one of those engines. With uported KRE 74cc chamber heads It will make 450hp without much effort, relatively smooth idle around 750-800 rpms, and fine on pump gas with correct tuning. The smaller 60916 wasn't too far behind at 440hp so neither one is a bad choice for that combo.

The Performer intake is OK in a 400 build, but will still pinch off some power compared to an RPM or factory iron intake. Since you are using a square flange carb the intake of choice is the T-II. 400 engines love those intakes, provided you have good head flow and well chosen cam to compliment it.

I don't talk much about 400 builds on here as there isn't nearly the interest in them as the bigger 455's and "stroker" builds, but I have some pretty stout ones out there and they are pretty "mild" at a glance. One in particular pushes a street driven 68 Firebird to high 11's at 114-115 mph. It's a pretty "basic" build, with KRE prepared #62's, Crower 60243 cam, 1968 iron intake/q-jet. It's backed by one of my TH350's, custom built converter and 3.73 gears........

[wilmer496]

25stevem: got it, thanks!

Cliff R: your suggested combo of KRE and Crower at 450 horses sounds great.
I checked KRE on the heads, 12-14 weeks wait... jeezz
I will also upgrade the conn rods so my engine will come apart soon anyway (will also verify what pistons i have). With all the info i got from you guys, i will figure something out. This will be fun!

[25stevem]

Just keep in mind that your not going to achieve 450 hp out of the Perfromer you have now.
You need a stock iron Intake that's port matched, or the Perfromer rpm.