400 BB Mopar dyno test

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Brian Hafliger

Brian Hafliger

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We just finished a 2 part dyno session using a steel 383 crank, stock rods, stock block (.030 over), 906 heads with bowl cleanup and std size Manley valves.
We went with a Comp Thumpr cam, straight up, 9.8:1 compression, Holley 750DP, rpm intake and TTI 1 7/8 headers.
It made 427HP at 5700rpm and 443TQ at 4200rpm.

I will post the dyno sheet Monday.
 

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Thanks for sharing. That is very similar to my 400bb. I am using a 383 performer intake with a 1 1/2" 4 hole "offy" carb Spacer and 9023s thermoquad. I also have a street dominator and offy tunnel ram intake to try. Can't wait to get the rest of the car together.
 
efriedrich said:
Are you happy with the results? What were you expecting?
Click to expand...

Considering the stock rockers, and almost stock heads yes I'm happy. Made good tq too considering the header was a bit large and stock stroke is only 3.380.

I was worried we wouldn't make 400 HP with the stock rockers...it sounded really good at 6000rpm!
 
Nice! I have almost the same thing but setup for turbo. I have a bit larger Scott Brown cam though. Good torque numbers too.

1975 400 .060 over, Stock forged crank, Diamond custom pistons, Eagle H-beam w/L19 bolts, 440Source Girdle all Balanced. Mildly ported 906's 2.14/1.80 stock valvetrain, 9:1 compression, TorkerII, 750 Proform.

Expecting 850hp @ 10#'s with a S480 Blowthrough.

Will upgrade to Eddy heads in the future!

Keep us posted on any pulls with changes. What should I expect as far as Max RPM for the lowdeck? I have a 6000rpm pill in the MSD and thinking 5800rpm shift point.
 
427hp not bad at all.That car will be a street killer.Wait until toy feel the toque
 
ou812 said:
Considering the stock rockers, and almost stock heads yes I'm happy. Made good tq too considering the header was a bit large and stock stroke is only 3.380.

I was worried we wouldn't make 400 HP with the stock rockers...it sounded really good at 6000rpm!
Click to expand...

If you do not mind so much, is there a previous thread to this build?

What size Comp Thumpr cam?

What pistons?

Just a cleaning up of the heads ports? No porting?

Thanks Brian.
 
rumblefish360 said:
If you do not mind so much, is there a previous thread to this build?

What size Comp Thumpr cam?

What pistons?

Just a cleaning up of the heads ports? No porting?

Thanks Brian.
Click to expand...

No previous thread.
Thumpr series is: thumpr, muthathumpr and big muthathumpr...this was the smallest thumpr, 227-241@ .050.
Pistons are KB flattops.
Mild bowl work, just what you see in the pics with a good valve job and backcut on intake.
No other port work or mods were done. Very basic build, with good machine work and good parts (except maybe the stock rockers).
 
Thanks. Plans to bowl port the iron heads with current stock valve sizes?
 
rumblefish360 said:
Thanks. Plans to bowl port the iron heads with current stock valve sizes?
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No, this was just a quick budget build that anyone with some savvvvy can do. The bowl cleanup was minimal.
Most difficult part was milling the heads .050 and then milling the intake .060. The block ended up getting milled around .030 to zero deck.
I wanted to try smaller 1 3/4 headers but felt they would only trade HP for TQ and the power band was so good we figured it would be a waste of time, and time was super limited.
 
OK, cool, I hear ya on time. Time is also MONEY!
IMO, I gonna guess that a bowl porting at this level would ad 35HP, maybe more?
 
rumblefish360 said:
OK, cool, I hear ya on time. Time is also MONEY!
IMO, I gonna guess that a bowl porting at this level would ad 35HP, maybe more?
Click to expand...

Not without better rockers (more, accurate ratio). I think a possibly better scenario would be the 275HL cam, on a 108lca, 1.7 Hughes rockers, and RPM heads but look at the cost! Now if we ported the heads to get around 270cfm, you'll have around 700.00 extra dollars in them so the RPM's look better, have a bit of quench, are aluminum and have alot more potential than the 906's. But this was a budget build and I think we succeded! Depending on what parts you already might have, like block, crank, rods, etc....it can be a cheap to semi-cheap build and with a rocker arm change alone (like regular 1.6 PRW or Hughes)should be reliable for many many years if taken care of.

BB Mopars are very resilient and tough as nails IMO.
 
I've been running stock rockers for years now. Id like to see what the rollers would do to that engine with no other changes.
 
72BBSwinger said:
I've been running stock rockers for years now. Id like to see what the rollers would do to that engine with no other changes.
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IMO, not much at all. The upgraded rockers show themselves right well with a high performance build of some stoutness rather than a OE re-build to moderate performance builds.

The upgraded rockers are accurate, less flexing and deliver the cams timing events and full lift as spec'd to the valves.

The OE rockers are a known flexing part with less than accurate ratio. Some have been found to be in the 1.40-1.43 area. Add the years of use and abuse, the ratio can drop.

Lift has a direct impact on HP

If your engine is dead bone stock, the return per dollar spent will be pitiful and low.

ou812;

I was just wondering out loud for a guesstimate. I do have a 400. I will be looking to a basic inexpensive rebuild with something in mind like what you did above. A bowl porting would be added.

Making use of what I have on hand, the only *performance parts* I have on hand are;

Aftermarket TQ
Holley Street Dominator
Headman E-lete (SP!) headers.

All of which cam with the engine.

The engine is a '78 P code. Not much to it considering the year it was produced for. Smog ridden equipment, broom stick cams and a D.O.A. compression ratio that can be run on yak urine.

I'm not sure exactly where I want to go with the build as of yet. There is no rush in doing so. (Other targets in my sight now)
The 400 is in a '71 Duster w/a 727, 8-3/4 rear. The gear ratio is yet to be decide, but, 3.55's are about where I want to be.

Cam wise (Also yet to be decided) would be something to be of an upgrade over the Road Runner cam. Considering that cam size, the intake duration being thought about wouldn't really be much larger at all. If at all. IIRC, it would be close to the Thumpers intake duration. But that is about the power band I'll be looking at.

All points headed towards a true street driving car.

Thanks Brian.
 
Real nice example of what a 400 can do even on a budget. Thanks Brian.
 
Rumble:
Everything has to work together. No matter the build, if you throw things at an engine, sometimes they work great and sometimes they are crap.

Given the parts you have, I would lean towards the XE274 cam for more drivability unless you don't mind the Thumpr idle.
If you use stock size valves, not much more bowl work can be done without hurting the port...you can thin the guide boss down some and work the S/T more but gains will be small...I would max the pushrod pinch before I did more bowl work.
 
This is great. I've always thought the 400 was a very under-rated engine.

Looks like a little milling here and a little more there really makes a difference.

I was going to approach the compression issue from a different angle- better pistons, but perhaps milling would be more cost effective, as it could be done locally.

I agree that high end or roller rockers are the third biggest mistake I've seen made on street engines versus the return on investment. 1 being over-carburation and 2 being a high-stall converter that doesn't match the cam and gears.
 
I don't think a better rocker arm is a bad thing...it doesn't take long before the pushrod can push it's way through the stock rocker arm at 6000+rpm and 280lbs. open pressure. I wouldn't chance it if I wanted reliability.
Yes, it's only a mild 400 so the 750 worked flawlessly. I did have to jet it up quite a bit, so a larger carb would make more power, but will also use more fuel and have less lowspeed TQ.
I'm guessing the smaller headers would have worked better for a larger heavier car, or a real tall gear. It's all in the application!!
 
Click'y da'link for the cam spec's;
http://www.compcams.com/Company/CC/cam-specs/Details.aspx?csid=708&sb=2

Yes! Combo is everything! Though the intake and carb combo is, well, a weird one. A old tyme Holley street dom is in what RPM range? IMO, the electric choke TQ, being a small primary unit, should be swapped out for the larger one.

I like the idea of the RPM & 770 Holley Avenger myself.
 
Great info and insight, Brian. Thanks for sharing. I too have a 400 block that will get built soon for a street/strip application, just have to decide which car it will go in.

Ma Snart
 
What is a reliable roller rocker to run on the street? I tried Harlands at one point and broke an adjuster after about 100 miles.
 
72BBSwinger said:
What is a reliable roller rocker to run on the street? I tried Harlands at one point and broke an adjuster after about 100 miles.
Click to expand...

I use both PRW stainless and Hughes. Crane is great too, not sure what they cost or availability but those 3 I don't think you can go wrong.
 
Been thinkin about Crane Golds or PRWs thanks. I think the Cranes would be lighter.
 
This is the type of build I'm looking for but with a 440. I wonder what the difference would be?
 
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