Also, credit to AFR. They have always had great flowing heads in the mid lift range. That is where their SBC heads really shined above others, and they obviously carried that into the Gen III heads.

 

I wish you would have written this up about a year ago.

 

Patrick, I see you no longer have a stock rotating assembly. Can you shed some light/give some insight on whether this (high compression) can be done on a stock shortblock with success? Not everyone looking to make 500/looking for a high hp reliable combo can justify building a forged bottom end only to run a totally n/a setup.


My true question being: How likely is it that a shortblock with good compression (all cylinders within 1.5% of each other), and higher mileage (mine has 80k on it) make similar power to a forged rotating assembly (which presumably is actually a bit heavier, but you're adding significant strength to it)? Hell- would a stock assembly with notched pistons to account for the added lift cam/milled heads make **dare I say** more power?

 

That was a nice run...extremely high MPH for only 452 rwhp.

 

He made that pass on the bottle, if I am not mistaken.

 

That sounds about right. My motor makes 558 rwhp and the best trap speed to date is 131MPH.

 

ya, it was on the bottle. If I ran that NA I would leave the 224/228 baby cam in LOL

 

He's has the forged motor for quite a while now. Ideally a lighter rotating assembly would make greater power. That's why you always here of guys who forge their 346s and lose power using the same heads and cam.

Although the forging has benefits also. Valve reliefs allow greater PtV clearance, provide a greater range of milling, milling leads to greater quench, and of course allows for larger nitrous applications. I think the benefits out weigh the downfalls.

Answers?

 

Not very good. In fact, in unported form, they're worse than an LS6 intake. With porting, they're better than an LS6 intake, but still 10-15 rwhp worse than an unported FAST 90. Just because it has a 90mm throat does not guarantee that it will flow lots. Most of the flow losses occur at the runners (which are very difficult to port).
When your head lifts, the gasket blows or something breaks. I'm not real sure about the question as to whether you mean actual cylinder pressure during combustion or cranking psi or dynamic compression or WHAT?
Nitrous was not hard on my motor because of high SCR or DCR or timing. My tune was good and I was only running 20 degrees of timing with a 150 shot. Nitrous was hard on my old motor because I was spraying for a mile instead of a 1/4 mile.
Yes, you can continue to pull timing, but to make maximum power on the spray, you want maximum cylinder pressure to occur around 13-15 degrees after TDC. If you keep retarding your timing, you risk having peak pressure occuring beyond the 13-15 degree window and power will be reduced.
Welding chambers works as well or better than milling, but there are very few head porters that will finish a welded chamber to the proper configuration without charging an arm and a leg. This is not a budget process. There is so much power to be gained and lost in the combustion chamber. Doing it half-*** or wrong will ruin a great set of heads.
If it's a multi-layer steel gasket in the .040" range, they have been know to seal as well under higher CP as stock MLS gaskets.

 

any lightweight trick pieces used in your new short block pat, that might have helped/contributed with your overall power numbers? just curious.

 

Nice write up!

 

The key here is not only in the heads but the drivetrain as well. Keep it light. factory 10 bolt, single disk clutch w/billet flywheel, oem wheels. I could swap heads and intake and cam with Patrick and I wont come close to his numbers. The parasitic loss from my heavy drivetrain smashes the numbers. Also dont be thinking that these are off the shelf AFR 205's because they are not. They have extra work done to them as Patrick has explained.

 

No lightweight parts. In fact, if this was a stock shortblock, it would probably make a few ponies more (because of lighter weight and tighter clearances). I'm not complaining though as my shortblock has ARP fasteners throughout and very durable forged pistons and nitrous-friendly rings.

 

Hey Pat nice job.
You wrote up a story that a few of us including yourself have known for some time now.
Many don't realize its about combo and you have to pick the right parts for a 500+ RWHP 346/347.
I want to add what Pat is saying about the manifolds and how they flow.
Lets use some fake numbers just for comparison sake.
Lets say a head at .500 flows 275. At .550 Flows 300 at .600 flows 315 and at .650 flows 330. Now when you bolt on the ported fast it can not keep up with the head and becomes a bottle neck in comparison.
So now through the manifold at lets assume this manifold ported. At .500 maybe we can see 265. At .550 we get 280 (a nice gain from .500)
at .600 we get 285. At .650 we get 288. The gains are becoming less because the manifold can't keep up with the head. But because the head is still flowing up top it can still see a positive number through the manifold. You pick up 15cfm's from .500-.550 but only 8cfm's from .550-.650 where the head is really making its best CFM's.
I don't think he was saying 280 is the max a good manifold will flow but that about the point where it start getting really hard for the manifold to keep up and produce more air.
Also people are saying that AFR did this and that to these heads.
In all reality had Pat been going for a peak number he would have wanted to keep the heads flowing better past .575 Instead he gained a bunch down low to possibility loose a bit up top. Instead of his head flowing say 315 at .625 and maybe 285ish through the manifold he chose to have it flow 300 at .575 and 280ish through the manifold.
5 CFM's doesn't sound like a lot but in a all out peak number game that could have been an additional solid 10 RWHP at peak. (with the right cam and parts etc.)

 

nice writeup...
Good stuff.............

 

Patrick G is the man!!!

 

Patrick, how much of an increase in torque would you see with a 4.00" stroke? Would a 382 change other factors?

 

Going from a 346 to a 382 with no other changes would give the motor around 45 more lb ft of torque, but the hp would probably be unchanged (although it would peak earlier). Going 6 degrees bigger on the cam would allow the engine to peak at the same rpm and it would make more power.

 

Thanks for the answers, here's some more questions.

I was meening at what point does the added cylinder pressure of nitrous become too great and cause problems? I know there's lots of circumstances such as octane, distribution of fuel / nitrous, timing, compression, head bolt / stud clamping force, gasket selection, etc.... Let's say what's the most you could run on your combo provided all hardware stayed the same, but allowed for variables such as optimal tuning and octane?

Is this for your size jetting or all jetting? Let's say a 150 vs 250? Let's say you are below the 13-15 degree window. Basically it would reduce the effect of your jetting? Basically a 250 rwhp jet would become not so accurate say a 225 jet (random #)? What about the opposite end of the spectrum and having the timing above 13-15 range?

I'm pretty sure Patriot does this on some of their heads. I remember Gunnar selling 035 heads with 62cc welded chambers. Ideally though welding chambers shouldn't effect PtVC? Or does it depend on how much metal is added to the chambers?

I was also wondering about why you didn't decide to stick with the LSK lobes. You said it was unnecessary. Yet, wouldn't having the faster ramp rates allow you to take advantage of your great flowing heads? Even if it was .005 seconds more technically a larger amount of air would enter the cylinders. More air + adequate fuel = more power. What makes it unnecessary?

I like you combo, but let's say someone concentrated on the opposite flow wise. The low / middle flow numbers didn't matter so much and went for the higher numbers. I'm thinking of a nice solid roller setup when I put my engine back together. I know Tony Mamo's has a very high opinion of the solid setups as he runs one in his 383. What do you think about them? I've read some good results on here and would like to try it out.

 

STICKY pleasssssssssssssssse. i need to read that for months i really like wht patrick g done .
you are the man pat.