I have a 406 that I just built for my 1988 Firebird. The car appears to make peak power at a lower RPM than what I thought it would and I would like your opinion of the combination and where the bottle neck could be. This is the combination:

-406 SBC
-10 to 1 compression, verified by cc all the parts
-ETec 200 heads
-Ported HSR that matches the heads
-ZZ-409 HR cam 226/226 at @.050, .550 lift with 1.6 rockers, 112 LCA installed at 108 ICL
-1-5/8 Hedman long tube headers
-2-1/2 exhaust per side that joins into a 3" single exhaust
-52mm throttle body
-SLP cold air high flow intake
-Gutted MAS
-Tuned by me on a Mustang dyno AFR is 12.7 to 1 and flat
-Timing at WOT 32 degrees which neted best power on the dyno

During the dyno runs my WOT intake vacuum climbed to 2-1/2" of HG, the exhaust backpressure was 2-1/2 PSI measured at the 3" single exhaust part of the pipe. The car peaked at 404 RWTQ at 4100 RPM and 360 RWHP at 5400 RPM and then slowly dropped to 345 RWHP by 6000 RPM. I thought the car should have peaked around 5800 RPM to maybe 6000 RPM and have been giving this some thought and want some opinions on the low RPM peak. Maybe the heads are too small for a 406, Intake restriction too high, exhaust too restrictive, cam too small? I know the CR is slightly low but that should not effect peak RPM.

The car runs excellent but I am looking for more power, I would like to get 400 RWHP with this car. I took it to the strip last Friday and on a 90 degree night it went 12.13 at 113 MPH at a race weight of 3600 LBS but that is not that much better then the previous 355 SR combination.

Any thoughts on the combination and low peak RPM?

Thanks

 

Since your torque peak falls about where it should, but it falters beyond there, my first guess is valvetrain stability. Can you post a graph of a dyno run?

 

I dont think you have enough cam to peak that high. My custom grind was a 233 deg cam that was suppose to peak at 5800 on afr 195's on my 401". It was short of that due to turbine exhaust backpressure but i think you need another 5-8 degs duration to have a shot at 5800 and abit of work to those heads would help

A 400" motor does need good airflow to run hard upstairs. My friends 406 with ported afr 208cc heads uses solid roller aroud 248-252 deg to peak in the 6200 range. So i think more cam is required

 

That power is about right for what you have. Keep in mind a mustang dyno reads much lower than a dynojet. On a dynojet you would probably be around 390 rwhp.
Also when you buy a new cam and it gives an rpm range for it. That is usually for a 350. When you go up to a 400 it moves the power band down a good amount. Plus the cam only calls for a 2000 to 2400 stall converter so I couldn't imagine it reving to 6000.

Also post the graph if you can. We can see if there is any valve float or similar valvetrain problem just buy looking at what it does past peak power.

 

Sounds about right to me. Not that any two engines are ever the same, but years back on a 400 setup very VERY similar to yours the combo would push a pig-heavy 87 GTA through the traps around 114 MPH (near sea level). We shifted around 6000-6200 which was a little past peak power (5600- very similar to your peak HP RPM).

On an old Mustang dyno it laid down a whopping 266 HP. Yeah, right. Trap speed clearly indicated the dyno reading was out to lunch.

Agreed- if you put that thing on a Dynojet I think you'll see a bit higher number.

 

My first impression is that your 2.5" into a 3" exhaust with 2.5 psi of back pressure certainly doesn,t help, Id suggest getting exhaust dumps for use when racing



http://www.jegs.com/i/Doug%26%23039%...250AK/10002/-1
http://www.summitracing.com/parts/QT...50CP/?rtype=10



but the cams duration is too small,to allow that set up too breath efficiently near peak rpm, Id swap to a crower 00471 and youll get a noticeable improvement, keep in mind the holley stealth ram is a fuel injection tunnel ram and its designed to run efficiently in the 3500rpm-6500rpm power band



why not call crane,
1-866-388-5120
crower,1-619.661.6477
erson,1-800-641-7920
lunati 1-662-892-1500
and
isky 323.770.0930
and talk to the tec support guys about what they suggest but DON,T mention anything any other cam manufacturer suggests during the conversations, just present the info on the parts used in that combo, rear gear ratio, compression, etc and see what they suggest, then make up your mind.

 

Numbers dont seem bad and i dont know if a dynojet will read all that much higher. Alot do but some dont. We have one Mustang dyno that reads 22% lower than other dynos and another that reads within few % of a dyno jet! Its all in the calibration and such.

All on dynojets, 320 whp and 3700 lbs went 108 for me in hot air 3000 ft da. In cold air at 3450lbs and few less hp probably 300-305 and 3450 lbs it went 112. 375 whp and 3450 went 116 in 2500-3000 ft. In my experience 360 and 3600 lbs an 113 traps is about right depending on the location and air.

Its good for the combo but if you want more power and rpm the cam should go up up up

 

Numbers dont seem bad and i dont know if a dynojet will read all that much higher. Alot do but some dont. We have one Mustang dyno that reads 22% lower than other dynos and another that reads within few % of a dyno jet! Its all in the calibration and such.

All on dynojets, 320 whp and 3700 lbs went 108 for me in hot air 3000 ft da. In cold air at 3450lbs and few less hp probably 300-305 and 3450 lbs it went 112. 375 whp and 3450 went 116 in 2500-3000 ft. In my experience 360 and 3600 lbs an 113 traps is about right depending on the location and air.

Its good for the combo but if you want more power and rpm the cam should go up up up

 

Given what you built already,I'm sure you know there are no cake and eat too situations. What you gain in the top end your going to give up in the power curve lower rpm range of the bottom end. So you end up raising the launch rpm to maintain the 60'ers. That is if you can still with your current set-up,still hook the car effectively.
I've been mph'er before and lost a race,but more often than not,the 60'er's or 330'ers has won the race in E.T.

I'm just saying,while your considering down on power on the top end.

 

Thanks for the replies. This information comfirms what I supected, too small of a cam, and heads to support 6000 RPM on a 406. I did make a mistake on my intake restriction, it is 2.5" of mercury not water for a restriction.

The dyno chart is nice and smooth after the peak power, I am not having a valve train control issue. My seat pressures are 140 LBS at 1.8 " installed height and open pressures are 340 LBS at .600 lift.

I built this engine with spare parts that I had laying around the shop and my one goal was to run 11.99 or better in any weather. To do that I need about 20 RWHP gain. If a optimize my curret combination I believe I can get there. I believe I need to reduce the intake vacuum to near zero with a 4" MAF and custom piping that I currenly own along with a retune with that combination. The exhaust cutouts may also be an option but I have had bad luck with them in the past, they always seem to break.

I do not really want to tear the engine down since it is brand new but I do have a ZZX cam (240/240 @ .050 .595/.595 lift with 1.6 rockers, 112 LCA) laying around that I could try. I decided to try the smaller ZZ-409 cam since I only have 10:1 CR and was concerned that the ZZX would not perform well with the 10:1 CR. What do you guys think of trying the ZZX cam?

Again, thanks for taking the time to read this.

 

its probably going to be an improvement over the current cam, Id sure swap, don,t get to worried about the port size the extra cam duration will help that restriction once the exhaust is less restrictive as scavenging will improve

 

2.5" (Hg) restriction on the intake is pretty big. Like running -1.5 PSI of boost.

For what it's going to cost you to buy a bigger MAF and reporgram are you sure you wouldn't rather convert to speed/density and forget about the MAF?

I know "cold air" systems are sexy and all, but I've seen more than a few speed/density cars (not even at your power level) run quicker and faster with nothing more than a K&N shoved directly on the front of the TB. Sucking hot underhood air and everything. They still ran faster. No way to do that if you have to mount a MAF somewhere in the intake tract.

My personal rank-order of intake system importance on a 1-10 scale is as follows:

1. As little restriction as possible. Importance: 10
2. Cold air. Importance: 4
3. Ram air. Importance:1 unless you're going high speed racing at Boneville or something, then it's a 2.

 

Zzx is a good cam for a 406. The 200's will support 6000 rpm but 210-220 would be better. No problem its enough to go 11's just may need more gea and launch rpm to take advantage

 

Plenty of intake port volume, cam should be more like 236/242 -110 for HR.