Dave69Z

I recently dyno'd my solid roller stroker in my Formula. It was down on power and peaked at only 5600rpm. I would have thought it would have peaked much higher say about 6300-6500rpm. Below is a little information about my combo....where are similar combos peaking?


My motor is a 392 ( .010 overbore and 3.875 Cola Crank). The compression is approximately 11.4. I have lightly worked AFR 190s flowing 297 at .600 Int and 237 at .600 Exh (flowed with pipe). The intake has been cut for a 58mm throttle body and has been port matched with little runner work at all.

I have a Cam Motion Solid Roller with Crane Solid Rollers...I don't have the cam sheet with me right now but the spec were something like 245/250 (give or take a degree) at .050 and .608/.611 lift with 1.6s. I am running a Comp Pro Magnums with a Comp Stud Girdle. I am running an Digital 6 and MSD wires as well. Power was going through a Moser 9" with a 35 Spline Locker, Gun-Drilled Axles and 16" Nittos.

I recently had my car dyno-tuned by Speedworks in Lewisville, TX. Started at 423 with a PCM4Less tune and ended at 431 (not sure if that says a lot for PCM4Less...or bad for Speedworks Tuning)....pretty weak and down at least 20-30rwhp. Ran cleanly, didn't really have any spikes....but plateau'd at 5600rpm and dropped power slowly from there.

Even though it did not sound like it floated the valves or had a miss, etc... is it possible the motor doesn't have enough valvespring or needs a rev kit?

Where do I find my missing horsepower?

Any suggestions or help is greatly appreciated.

Dave

kmook

First question that comes to my mind is what springs are you using? Also do you have any logs while you were on the dyno?

Nonetheless, general engine troubleshooting should be in a general technical forum. Moving...

Josh-'04 GTO

I'd second kmook's comment about the valvesprings. That is a pretty rowdy cam, and will need some heavy duty valvesprings to prevent valve float. How did the air/fuel look? What about the timing? I assume you have a good intake/exhaust setup...

Mindgame

I agree with your expectation in seeing a ~6500 rpm peak.

Tough to diagnose stuff over the internet but it very well could be in the tune.... and it's even more likely that it's somewhere else.
Any way you could post the dyno graph or any other information that might help.

-Mindgame

Dave69Z

I need to look for the information about the springs. They weren't too stout. Something like 180lb / 450lbs and I am also using titanium retainers.

The AFR was right around 13.1 on most runs and just a little leaner on the max power run. I have Hooker LTs and true duals with a Dr Gas X-Pipe and Bullets. I am have a Ram Air Box that came with my Predator Hood (my worst purchase for the car).

I was not real impressed with tuner, I was not there but for a run or two. I don't know if he logged it or not...I doubt it. It had a blended gas with an octane of about 95 as I was trying to rule out false knock, etc. If I remember right he finished with 37 degrees of timing. I will have to look at the program.

I will try and hookup my scanner and get a copy of the Dyno Graph posted.

Thanks for the input guys.

Dave

Mindgame

Dave,

FWIW, and based on my experience with solid rollers like yours I'd say your springs are adequate for the job.

Look forward to seeing more information from you.

-Mindgame

Dave69Z

Here is the best dyno of the day.

Dynograph

Thanks again,

Dave

Mindgame

Dave,
Do you have another tuner in your area? How far are you from LG Motorsports??

What you need is some feedback (data). If no more power can be found in the tune (and I believe there's more there) then we have to accept the fact that this engine is peaking early due to a loss of engine airflow. In other words, the heads, intake, are a restriction and they'll have to be worked to realize maximum potential. Looks like a combination where the head is too small and peaks way too early but it's tough to tell without seeing high "resolution" data throughout the dyno run.

I'd get a second opinion on the tune 1st, then go from there.

-Mindgame

JordonMusser

I actually stopped by speedworks not long after you left..

anyway, I agree with mindgame.. There is a restriction somewhere, although I disagree with just about everybody else

there is no way in hell that small of a cam with those heads is gonna peak at 6500 in a 392 cube motor. my solid roller motor with MUCH bigger heads and a little more cam peaked at 6100 tops.


what CC are the intake runners, and who flowed/ported them?

Mindgame

I agree, knowing the intake runner size would help alot. Most of the smaller AFR heads you see that have been worked for strokers have pretty much been hogged out and have low velocity for their size. My peak with a set of Brodix Track 1's (actually ~224 ccs) was 6400 rpm with a 244 @.050 cam. Then again, this was using a Brodix HV1000 intake. The intake alone is worth some revs compared to something with a smaller runner.

So it's tough to say but yeah, I would think "restriction". More data would be needed to confirm this though.

-Mindgame

Josh-'04 GTO

MG and Jordon are on the right track about the heads. I just ran a dyno simulator on your setup and peak power came in at about 5700-5800 rpms, well short of the 6300-6500 you were expecting. Moving the setup to a 350 cubic inch motor bumps the peak power to 6500. I would probably take another whack at the runners and try to dig up some more airflow.

Dave69Z

Thanks for everybody's input.

I had the cylinder heads worked by BJ's Cylinder Head Service in Tulsa, OK. The started out as 190cc AFRs and the runners themselves were not worked very much. Most of the work focused in and near the bowls and a valve job. The work done was his "street / strip" porting.

Here is a link to BJ's Cylinder Head Service's webpage :BJ's Cylinder Head Website

I scanned the flow sheet I received when I picked up my cylinder heads. Here is the link to it: Flow Sheet

Sorry about the size....on the sheet Cylinder #1 is the untouched flow numbers at every .100 of lift. Cylinder #2 and Cylinder #3 is after his initial work. Cylinder #4 and #5 are combined, they are read together to get the flow at every .050 of lift.

Will those flow numbers not support 450-460rwhp? Is more port volume that necessary on an under 400ci / under 7000rpm motor?

The only other restriction would be either the intake manifold (only cut for a 58mm TB and port matched to heads..very little work done to the manifold) and or the crappy air box that came with the Predator Ram Air Hood. Mentioned to James that I wondered if it was a restriction, but didn't try and push for quick dyno with the air box removed.

Thanks,

Dave

JordonMusser

I would always reccomend having a cylinder head flowed by somebody other than the porter.

but I would guess that a 190cc port would be a little small for that combination. mine were closer to 218cc.

I would also consider the intake manifold as a restriction, I always try to get that damn injector "pinch" as straight as possible.

I am sure mindgame will post his thoughts

Feel free to ask James @ speedworks to overlay your dyno graph on mine. I dynoed there through the exhaust(single 3" borla) and it made 471/45X if I remember. HP was down because I didn't open the exhaust, but I was too lazy

Dave69Z

I actually saw you there at Speedworks back in the beginning of June when I made my appointment for the tuning, I came over from Arlington with my dad from the Hot Rod Power Tour's last day. My parents did the Long Haul in an Ex OK Highway Patrol Z28.

Thought by the time the day was over I might see you there again..apparently we would have had the tuning session taken a while longer.

Dave

94 NO TOP Z

"I have lightly worked AFR 190s flowing 297 at .600 Int "
that seems like a lot of flow for some mild bowl work. I'm not familiar with what the LT1 AFRs are capable of but, the stock casting usually get 275-280 at 0.6" with a pretty good full porting. It kind of sounds suspect.