Where's the power?
 

I've been noodling on my current engine for a little over a year. It's running pretty well, but I just can't seem to get the power out of it that I think it should have.

For instance, from an under 20mph roll if I punch it, it will downshift and the tires will squeal but it won't break loose like I would expect. Punching it around 45mph on the freeway on ramp downshifts to 2nd, but it feels more like a station wagon than a performance car.

My setup:
68 400/#16 heads
Dished pistons for lowered compression. The builder never told me what the compression was, I assume it's around 9-9.5:1.
Crower 60916 cam, matched lifters and springs. The shop degreed the cam on install.
Stock rockers
Ram Air Manifolds
13" Continental Stall
3.55 Posi

'68 Q-Jet rebuilt to Cliff's #1 recipe. I'm running 42 rods and 74 jets in the primaries based on Cliff's recommendations. The secondary rods are CE, but the ends have been turned down.

'68 Distributor recurved by SunTuned running a Pertronix. 12 degrees initial, 36 degrees total. I've tried 9-12 degrees initial and 12 gives me better throttle response. I haven't heard any pinging. I'm running ported vacuum off the thermostatic switch on the manifold. I've verified that it's working.

I think this combo should run like a scalded ape, so what am I missing?

Well have u done a cranking comp test just to see what that is? Where did they set the cam at? CE rods are .041 stock so u have a even richer rod then that turned down? How fast is the secondary flaps opening etc. Sounds rich to me on WOT ,least for the carb.

Your converter may be tight for the RPM range of the cam, just from a quick look at the specs. What RPM can you flash the converter to? Once you get the stall matched to your rear end ratio, then maybe some 1.65 rockers will help. I'm positive that you are bogging on your converter and it is feeling like a dog until the revs come up, just as the trans shifts to the next gear and you are back on the low side of your powerband and it feels slow.

Dumber things have happened (I've done them), but make sure your throttle is opening all the way. (when you press the pedal down all the way)

Doing a compression test is a great idea as well.

That sounds like a well thought out combo - should run pretty dang well...

Haven't done a cranking compression test yet. I'm not sure what he set the cam at, I assume straight up. My engine build was such a drawn out process when it came time to pick it up he didn't give much info on it.

I am getting some black smoke out the back when the secondaries open so I'm sure they are too rich, not sure by how much. What rods should I be running? I got the secondary rods from Cliff years ago for my old combo and haven't fiddled with them since. The secondaries kick in smooth, I've probably got about 7/8 of a turn on the air valve spring.

I can't remember the flash RPM on the converter off hand, I'll double check this weekend. This engine does definitely like the higher RPMs so it's possible my converter may need to be restalled.

Throttle is opening all the way, that was one of the first things I checked.

ive asked the same question as my combo is almost identical to yours and on the dyno i have not come close to the 400-420 hp that they say is possible with this combo, my compression is the same as yours and that appears to be to low for this cam, now i have done some tuning, added set try y headers and 3 in exhaust and am going back to the dyno on the 15th weather permitting, 3.73 gearing to replace the 3.23 are an option i am considering, overall i am not overly impressed with my combination but it is getting better than it was at first, time wise my previous set up with smaller 2801 cam was same or slightly better.Getting closer to 10/1 comp may be a winter project for me.search 60916 cam for opinions given to me.

Sounds like you should try a leaner secondary rod set. If your CE rods were turned down, that could be giving you a over rich condition which may be half or all of your problem.

Good thread
 

My setup in my 68 Firebird is similiar to yours and would like to see what others
suggest. My car does currently have 3:08 gears and I know that will take a little
out on launch, but I like the low rpm cruising manners on hwy.

If I may ask where do you have timing at? initial and total.

Have you tried a leaner secondary rod??

The 13" continental I just installed from Cliff actually helped me over the unit
that was installed when I purchased car.

Gerry

Sounds like it could definitely be a culprit. I should still have to stock secondary rods laying around. Might as well give them a shot and see if they wake things up.

Right now I'm running 12 degrees initial with 36 total.

A cranking compression test is definitely in order.
Warm engine, throttle wide open, all plugs out, hot battery and good starter for the most repeatable results.

Probably should double-check the camshaft timing. Just dot-to-dot on the gears doesn't cut it.

Most likely undergeared for your application.

I'll just about guarantee that you're too rich in the secondaries.

HTH!

Some good comments, start with the basics. I'll throw a few comments out as one who raced a 400 for several years that had a real 385-400 HP based on a conservative dyno and track mph.

400-420 HP is going to require some airflow,probably more than some average D ports are going to provide unless ported really well by a guy with a flow bench. Figure stock D ports are around 215-220 cfm @ 28". Using the Superflow formulas with the PERFECT cam,compression ratio, intake, carb you are looking at the 400-440 HP range. Again PERFECTso probably 11-12:1, roller cam etc etc. a 9.5:1 with that cam is not going to get you there unless you up the airflow in and out porting the heads a lot, round port heads, aluminum higher flowing heads(D or round port).

Some folks think 9.5:1 in a 400 is starting to get a little low, a shorter seat duration cam with the same 0.050 might do a little better to not bleed off your compression. As the others said a compression check will give you an idea there, also might suggest if the cam was degreed in correctly.

Also as some of the others briefly mentioned -gears. A 400 is going to need more gears and more convertor to use the higher rpm range. We swapped from a 455 to a 400 shot block when they changed my class to keep my RAIV heads(mroe airflow than a D port)-same cam, same intake, same carb, same exhaust and with the 3.42 it felt like a dog compared to the 455. 4.10s, 4000 stall and it would run with most street/strip 455s.

The #16 heads are small valve that could be hurting HP as well.

Easy things first; x2 on the secondaries. If that doesn't cure it.....

Compression test: Since there was not much info on this engine and you have been fighting this from the start, there is a distinct possibility you have LESS compression than you think. Pistons may be down in the hole .020, UNTOUCHED cylinder heads with possibly MORE combustion chamber volume than you think, cam not installed where it should be, etc. I like to use cranking compression as a ballpark indicator as to how an engine will run at low rpm and whether or not pump gas will be an issue. If you're in the 160's, you will probably need to crank up your ignition timing.


BTW, Have you tried ADVANCING your ignition timing to 16 deg's?

Good luck!

valves
 

My 68 400 has #16 heads as well, and are factory originals.
Mine has the larger valves and I would think the OP does too.

I did measure when motor was redone 7 years ago.

my timing is similar to yours as well. My total comes in around 3400ish rpm.

Thinking my next area of concern is to get rid of current exh setup. Believe a
nice setup with a mandrel bent head pipe and a crossover my help. currently
head pipes look too narrow at curve.

Well,if you're talking about chassis dynos and rear wheel hp figures,there's no way that sorta 400 cid combo will crank out 400 to 420 RWHP,as that's like 500+ hp at the flywheel.

Chassis dyno that sorta 400 cid combo should be somewhere between 300 to 340 RWHP max.

Now at the flywheel,yeah a 400 cid combo like that may be able to make right at 400 hp,but it's probably not gonna hit 420 hp,not without more cam,compression,head flow or something of that sort like Skip mentioned.

That's not necessarily so,sorry.

There are three distinct #16 head castings,a small valve high compression version (1970 2bbl 400),a big valve high compression version ('68/'69 4bbl 400),and the round port SD455 heads.

So they easily could be big valve #16 heads.

Anyhow,I agree that a compression test is a good idea,never hurts to do that.

Also agree it sounds like it could use some further tuning.

Sometimes it takes some serious work (and a little luck) to get these things to run their best.

Good luck with it.

Bret P.

I've got the '68 big valve heads on my car.

I'll try some different secondary rods and do a compression check first. Haven't tried advancing the timing more than 12. Seems rare that a Pontiac likes more than 36-38 total, but every setup is different.

I know the power is there somewhere, I just have to find it.

My 455 ran at 11.2 - 11.5 A/F with CE secondary rods. Moved to a CH and it is at 12.5 - 12.7 A/F. Try in that range. http://quadrajetparts.com/rochester-...ter-p-166.html

Probably wont want more total timing,though it might want more initial timing,you know,to give it that low RPM "pep" you say it seems to be missing,but then you'll probably wanna shorten up the actual advance curve to keep the total timing in check.

FWIW

Bret P.

An easy thing and quick thing to try is to use manifold vacuum for the advance instead of ported. You might be surprised. It will idle higher when you change it, so turn the idle back down.

My mistake, as it turns out I have turned down CH rods in the secondaries (on the right). In the middle are some stock BE rods which appear to have the same diameter tips as the CH, just shorter. On the left are some CT rods I had laying around which are way too big (.0774). I think I pulled them from a '71 Buick Q-Jet.

http://forums.maxperformanceinc.com/...1&d=1347073650

I guess I'll order up a few other sizes to try, but I'll try the stock BE rods in the mean time and see if it helps since they have shorter tips.