MadBill wrote:Here's a (probably not original, given my penchant for reinventing the wheel) thought about highly supercharged engine cam timing: Since the charge density may be two or three times that of an NA engine, so will be its inertia, thus it should be possible to leave IVC much later without reversion detracting from the trapped V.E.
I tend to run intake cams at high LCA numbers in high-rpm,big-boost apps for that very same reason... never seen big power losses as might be expected,often there are substantial gains. Does improve the drivability quite a bit too (30+psi street app's).
Along the same lines, although charge density does not affect the speed of sound in the mixture, temperature does and a high boost engine, even with a good intercooler, will almost inevitably have much higher mixture temps. Thus a higher fps port velocity will correspond to a given optimum Mach number and so minimum port areas might need a re-think ...
Proper IC setups at 30 psi boost on gas most times have inlet temps no higher than the region of 95º to 105ºF..
-Bjørn
"Impossible? Nah...just needs more development time"
My wife's non-intercooled Buick Park Avenue (otherwise stock, but with an undersize driven pulley and 12 psi boost) shows as much as 225° M.A.T....
A pal has a modded Buick 3800 with a big water-to-air IC in an '88 Fiero, I should get a M.A.T. reading from it for comparison.
What is the relevence to cross sectional area of the int. for a blower application as compared to a normally aspirated motor. As far as percentage of int. to exh. flow, would you increase the bias of the exh., and if so - how much? Also related, as far as cooling. Are there any modifications specific to the cooling system that are applicable (or specific) for a supercharged motor?
I think to many people think that with to large a port volume they will have poor throttle responce.
This is the other reason they go with the heads that have the smaller port volume.
I was always taught a N/A application was WAY more critical on head ports, IE velocity cross section etc than a forced induction application.
Because a N/A application has to move its own air. In and out.
A F/I application is providing its own atmosphere and the exhaust is being "helped" out of the cylinder on the cams overlap.
Also, why would you need and huge exhaust valve, isnt the exhaust volume much smaller than the intake volume after the intake charge is burned? Isnt this WHY the exhaust valve is always smaller?
Im just asking, I dont have NEAR knowledge of most in the post.
new engine builder wrote:I think to many people think that with to large a port volume they will have poor throttle responce.
This is the other reason they go with the heads that have the smaller port volume.
Isnt this theory still from the carb days? Because of poor carb signal? EFI is not affected as much by this.
I have a 248CC port on a 7000 rpm 383 and throttle response is EXCELLENT. It makes over 400lb feet at 2500 rpm at the rear wheels.Its a efi engine.
new engine builder wrote:I think to many people think that with to large a port volume they will have poor throttle responce.
This is the other reason they go with the heads that have the smaller port volume.
Isnt this theory still from the carb days? Because of poor carb signal? EFI is not affected as much by this.
I have a 248CC port on a 7000 rpm 383 and throttle response is EXCELLENT. It makes over 400lb feet at 2500 rpm at the rear wheels.Its a efi engine.
I'm not trying to be a smart a-- but why would you need cylinder heads with a port volume of 248 cc's on a 383 that see's
7,000 rpm's??
I.M.O,. a 383 that see's only 7,000 rpm's needs a set of heads that are around 195-200 cc's.
My first vote would be for a set of AFR 195 cc Eliminator heads.
Seeing as I make near 600 hp on pumpgas from 383 inches with a moderate cam, and 23* heads, cant be ALL bad. I dont see this engine making that power with 195 cc heads.
FASTFATBOY wrote:Seeing as I make near 600 hp on pumpgas from 383 inches with a moderate cam, and 23* heads, cant be ALL bad. I dont see this engine making that power with 195 cc heads.
Go to AFR's web site and look at some of their dyno results.
They have a pump gas 413 with the 195cc heads that makes 574 hp at 6,400 with a solid flat-tappet cam with a 750 carb.
FASTFATBOY wrote:Seeing as I make near 600 hp on pumpgas from 383 inches with a moderate cam, and 23* heads, cant be ALL bad. I dont see this engine making that power with 195 cc heads.
Go to AFR's web site and look at some of their dyno results.
They have a pump gas 413 with the 195cc heads that makes 574 hp at 6,400 with a solid flat-tappet cam with a 750 carb.
I am making at least that much or maybe a little more, I streetdrive this car all over. Besides I only got a 383, not a 413. And Just a little FYI, you can never trust an in house engine test.
I have seen AFR heads out of the box that flow nowhere NEAR what AFR says they do. As a matter of fact this is more the norm with AFR.
I will stick with what I have, its proven.
I can make a good bit more power with a cam change. It has a 254/254@.050 so I got room to grow.
