What would the drivability of a 355 CID engine be with 210cc heads and a procharger D1SC? I would most likely be going with a relatively mild cam and let the blower build the HP and settle for a little less peak HP.

 

head runner on a blower car is much less important from a driveability stand point, there is constant pressure to assist in managing port velocity, Naturally aspirated vehicle do not have this pressure and rely on atmospheric pressure to balance the void when the blades are opened. this is where every restriction from the intake, filter, bends and location o0f filter become a problem. the blower should be completely happy with large heads and better utilize the flow capability of the engine.

I ran 220cc ports on my 355cid turbo car and I had PERFECT driveability, a few have ridden in it and there was no lack of low end torque as opposed to a smaller port head. that was with a turbo as a restriction on both the inlet and exhaust side. go for it.. 210cc is really still very mild in comparison.

Chris

 

But a turbo makes boost at idle, a blower doesn't, and it still needs to turn the blower.

Which is why I went with a stroker and 195 heads.

 

Well, I was getting concerned over the pistons I chose for my 383, but after a quick email to JE my concerns have gone away. So the 383 is back on.

BTW, thanks for the replies.

 

Actually, you have it backwards, a turbo does not make any boost at idle, the blower which is driven by the crankshaft DOES make boost at idle which is why it requires a bypass valve to keep from building pressure in the charge piping.

small head port volume on a blower car is in my humble opinion a waste of flow capability, especially on a 383cid engine.

That is not to say that you can't make any power with a smaller port head, you will just hit the port stall speed much earlier in the rev range and limit any upper RPM power that could have been had.

Chris

 

I think what Brian cunningham is referring to is the build up of boost that actually registers on the gauge. In that respect, I might see 1psi-3psi below 3,000-4,0000rpm but once you wrap it out a bit you do see the boost build up much quicker.

this can be overcome several ways... i.e. smaller pulley for quicker spool up time, with a restricter place (i don't like restricter plates though, they tend to cause belt slip). the Procharger which has a 4.10:1 transmission, allowing it to build boost "quicker". installing a wastegate on the intake track to bleed off boost as the engine speed increases (i.e. set it to see 5psi at much lower RPM's and setup a waste gate to "hold it" at your desired boost level).

the positive displacement head units will make boost "quicker" than the centrifugal.

I too want to go with a 383 combo (but waiting to see what Dart does with their block options as well). this combo can potentially "grow" to 427ci... regardless, I wanted to slap on the "biggest" heads i can find (the AFR 235's are looking appealing). this is for the same reason as Chris (icvette) suggested. I am not worried about the heads ability to have good velocity at lower engine speeds... i leave that up to the blower, rather, i am interesting in volume at this point. Less effort for the head unit, much more potential to hit my target HP numbers... and these cars waste tires at low engine speeds anyway.

 

Yes they do, you can only use so much bottom end power.



The above dyno sheet is from an LS2/402 with a ProCharger F-1A with off the shelf AFR 225 heads and our blower cam. This combo makes over 400 ft lbs of torque at 2000 rpm and 864 rwhp at 12.4 psi of boost. Here is a link to this car. http://www.exoticperformanceplus.com...Car.php?car=29 Bob

 

Well, since my original question was about an engine 50 CID smaller with only marginally smaller heads, and a smaller ATI head unit, I'm not sure exactly how comparable this is.

Also, to be clear, the orginal question was not meant to determine how much power/torque the car will make at WOT off idle, but how the part throttle response would be when the blower is not making boost.

The comment about these cars "waste tires at low engine speeds" does not make much sense to me, because even with the stock cam low engine speeds are not impressive to me.

 

That dyno chart is very near to mine when I was running the lower boost (11 psi) with a 408 and the D1R (similar to the F1R). Likewise, I am running the large AFR heads and a very healthy SR cam.

Wait until you see how far past the 4 digit mark you can push that combo when you more than double the boost.

 

While mine is not exactly what you plan to build, I feel that mine is ever so much further from the small heads and cam that you intend, and the driveability is still very good. You do not want to lug it in 5th at 35 MPH, but there is no bucking ("drama") so long as you are above 15-1600RPM, and as soon as you see 2000RPM it is gone.

With that being said, I am pushing in excess of 10 psi by 3000RPM, so a bit different than most. And my car delivered just over 480WHP NA (I had wanted more), so it is by no means one of the phenoms you see on occasion that can get real close or exceed the 600WHP mark NA.

With all of that, I would not be concerned with the off-boost performance.

 

If this is a daily driver, the 355 might be sluggish off-boost, which would make it a pain to drive around town and could affect mileage. That being said, some of the better heads(like the 210 AFR Eliminators) that have great low and mid-lift numbers would probably be OK, but some of the mediocre heads would less pleasant.

Also, I think you should realistically look at how much time you will spend in boost. If it's not a lot, then a set of 190 or 195 heads will be a better match without sacrificing much on the top end - they will be much crisper with better throttle response and highway mileage off-boost.

I have known a lot of people who went too large on heads (and CAMS!) and were disappointed (and beaten by lower powered cars), but I hardly know of anyone that went with a more modest head (or cam) and a blower and complained about the total power.

My 383 has 200cc heads and hit 632rwhp with a Vortech T-trim, but it is crisp and very fun to drive around town. My friend's 355 with a huge solid roller (252/260 @ .050) and 210cc heads, Accel EFI, is sluggish and not fun to drive around town. Admittedly, much of that is due to the cam.

Jim

 

Just curious, what are the specs on your cam? You're right in the range of my goal for this build with my 383.

 

Dave,

I am running a custom Comp Cams solid roller, with 2 Xtreme Energy Street Roller lobes - 230/236@.050, 112lsa, with 1.6 roller rocker the net lift is .573"I/.584"E. The lobe numbers are #4872 and 4873. I got it through Comp for about $260 plus shipping. I am very happy with this setup - it idles very smoothly (my car is a sleeper and idle is important to me) has a killer midrange and spins to 7000, although it runs out of steam at around 6300 sometimes it is useful to keep it in a gear a bit long, and not worry. Ti retainers for insurance.

FYI, the 632 was recorded with only 11.7# of boost. Now I reengineered my air inlet piping to large radius 4" mandrel tubing and beefed up my pulley setup so ai could run more tension, and I've been hitting a consistent 12.9#. Should be over 660 now.

Jim

My site: http://home.mindspring.com/~jim_fisk/id1.html

 

Nice car! I love it. And thanks for the info.

 

Thanks! Yours is beautiful - I have always loved that blue and white combo...

Jim

 

sort of a sleeper there.... tires look beef!

 

Trying to keep it as low-key as possible and still have some traction... rears are now MT ET drag radials. That helped a lot.

Jim

 

Nice sleeper!

 

BTW your car seems to be a hit in OT

http://forums.corvetteforum.com/off-...e-sleeper.html