I posted this in another forum but wanted some more opinions.

I recently had the 408 installed in my Silverado and this weekend I had it tuned and dynoed. I was disappointed to see that it only made 250 HP and 280 TQ.

The specs are as follows:

408 ci w/8.7 cr
P&P 6.0(317) heads
224/231 .595 .595 114 cam
Stock exhaust manifold
Stock intake
Stock exhaust(cats, pipes, muffler)
2800 stall converter

I was told it was low because of the low compression and the dyno(Dyno Dynamics) itself. Apparently this dyno shows 17% lower than a DynoJet. The reason for the stock components, lower compression and cam are do to the fact that I will be adding a turbo. I just wanted to know what it put out before the turbo goes in.

Does building it with F/I in mind make that much difference? If I had built it with 11:1 cr, a N/A cam, LT's, intake, CAI etc. what would it have put down?

 

I would hope there is a turbo in that things future....it still seems a bunch lower than I would expect. I would be looking for at least 350 to start from that combo. I would get some headers and exhaust, that would probably free up a bunch, it can't breath right now.

 

That Dyno has been very consistantly reading low numbers. You 8.7:1 compression is going to make a lot less power (expecially in the low end) as a higher 10 or 11:1 CR.
Dyno numbers don't really mean crap anyway, seriously. Compare your first pull graph to the final tuned one and look at your gains.
Your low compression is going to allow you to run very high boost, don't go too small there.

 

It's a shame, but I would plan on some smaller cc heads asap and then sell your 317's. Should make a big difference. Good luck!

 

your numbers are close to what i put down in my stock 5.3.

 

The engine was built with 20 lbs of boost in mind. I did not replace the stock manifolds or exhaust because I have a STS kit. I thought about going to a trick kit but I would still keep the stock manifolds.

I already talked to my engine builder to see about switching heads so I could up the cr and run less boost. Maybe 9.5 cr and only 15 lbs so that my around town feels more peppy. The builder suggested LS6 heads to up the cr and a smaller cam. I might be putting up my WCCH up for sale soon, lol.

Do you think I could run 15PSI with 9.5 cr safely? Also, how much more power would I make with more cr and a cam change?

I know. It feels almost the same as the 5.3 I had in it. That is why I am so disappointed with the results so far.

 

boost is a measurment of restriction... saying a motor is built for X amount of psi isnt saying much. as long as the motor has good internals you can push a decent amount depending on the tune. the tune is the biggest part of this. your motor is down on power since you have a huge bottle neck. you have a cam and ported heads on an other wise stock supporting setup. if the setup was free'd up you would help alot more. also the dyno could of been calibrated poorly so you would see lower then opt numbers.

i wouldnt worry about raising the CR any. that amount is only going to gain you roughtly 30 hp...its not enough to notice.

 

From what I understand, 9.5cr and 15lbs is doable. It would really help your low end and gas mileage. Ideally your compression is low, but since those are WCCH 317's it would be ashame to ditch them. You definitely are down on cylinder pressure but fi would take care of that. If you are thinking of running 20 lbs. you may just want to maximize your timing for now, maybe advance your cam and wait it out.

 

The tune is dead nuts on. Timing was increased as much as possible which was a lot because of the lower cr. At one point increasing timing no longer made more power on the dyno.

 

dont feel bad man , my truck only put down 600 rwhp with 10 psi and spray but that . i know it has alot more than that , the tune is what i really wanted out of it.
i just dont know why my truck could only make that much boost. after making 15 psi easily before then after i left it still wouldnt make more than 10 psi. swithced back to a 3.0 from a 2.7 pulley and boom right back up to 14 psi.

sorry for the hi jack , but that dyno is putting down lower numbers than what are normally posted on this forum.

sorry