Probably that you are talking about a completely different engine

 

As I was saying earlier, I know a fella that had a 382 with a 27x@.050, 8:1 motor that spooled a 106++ mm turbo back 4-5 years ago. There is this thought that turbos don't like big cams...lol.

 

Lol....cam profiles won't change much just because its a sbc and a lsx .They are really not any different....haha there both about the same size v8's. A motor is just an air pump...

 

Yeah.. I agree, some people don't get it.... a friend of mine run 6 sec et's at 210+ ...and competes with the pro's.....all his cams are huge, and his car idles like a street car, also it spools two 47/88's stupid fast!....and he wins often...so I think he know what hes talking about....

 

I am building a simular setup with a GT55 and a 410 (4.040 bore) 9:1 compression
heads Are AFR castings ported to Stage 3 TEA, flowing in the high 330 range 5" downpipe,
Car will run on E85. T400 w/210 gearset and a 400 stall converter. Victor JR, tubular manifold 1/34 primary with 3" collector.
Has anyone tried a tighter lobe seperation on a high flowing system?

 

since we are going to talk all of this buddy ****-my good friend Andy Jensen-who currently has the quickest turbo car in the world has a cam in the 260's on his 427sbc,i went 4.50's at 160+ with a cam in the 260's with a 8200rpm shift point,Phil's car went 7.50's at 191 on relatively low boost with a cam in the 260's(that's on radials at 3300lbs)i've done a-b tests with bigger cams-yeah they still make good power-but not much better than the smaller cams and make the power band much narrower.

I'm tired of hearing about what your buddy has-if it's not first hand info(stuff you have done personally)it's not really info-just hearsay.

 

oh yeah,we made 1100 rwhp in a 370 with a 228cam-if you need a 270's cam to make 1800hp and 8000 rpms there is something wrong

 

Since were name dropping...Search Brian Carpenter and his mustang. He basically spec. the cam out for me this time around...and he still thinks it's on the small side?

 

[QUOTE=Shawn @ VA Speed;10725654]oh yeah,we made 1100 rwhp in a 370 with a 228cam-if you need a 270's cam to make 1800hp and 8000 rpms there is something wrong[/QUOTE/]

What was the rpm band and/ or shift points of that set-up?

The something wrong was trying to make this power with an Lt1 and smallish AFR heads which is why a big cam was needed... The sbc needs to be 1700-1800hp and 8300-8500rpm

And if you took the time to read my new cam specs you would see that they are in the 260's........I was also asking for your opinion on this cam and the info I gave...Cam profile is about the operating range of the motor and the intended use also....these cams run just fine on the street ...just a bit noisy for my taste....which is why I was kinda looking for your opinion..

 

I think it was said earlier if you dont have first hand experience with it then leave it on the porch.

 

I guess so...if you want to look at it that way....but I also have plenty first hand experience on my own combinations.....the point was that not all engine builders, racers, and engine simulation software, etc. have the same opinion about this topic...Btw...How is my own motor not first hand experience???

 

Let me give you my opinion on your cam/combo,i assume you are running a class that requires you to run a 94mm turbo such as ORSCA EZ Street or something.At 8200-8300 rpms with that turbo on a 400'' motor will have some extreme exhaust backpressure.When you run big duration on the exhaust side of a high backpressure engine,as the engine comes to the end of the exhaust stroke the pressure in the exhaust will overcome the pressure in the cylinder and actually fill the cylinder up with exhaust(which is obviously less room for the intake charge)The other thing,i'm not sure what rocker ratio you are running but as you approach .700 or more lifton the ex side you can have problems with the cylinder pressure pushing the valve sideways and the valve not seating correctly(thus losing more power)I would like to take credit for all this info,but i didnt learn it on my own,but have found it to be true on turbo combos i have put together.Kenny Duttweiler actually was kind enough to share this info with me several years back.In my opinion that cam work work really good in a twin 88 engine,but you would be much better off swapping the lobes and making it a reverse split for your combo.

 

Almost forgot-I thought Brain Carpenter had a Proline engine in his car?

 

If backpressure is that high, can't he run a larger ex. housing?

The issue with the valve, would more spring pressure not be the answer?


BTW, I think all this is great. I like to see how others do it. I only have exposure to one guys setup, so that is all I really know.

 

Changing ex housing will not help much,you have to spin the compressor wheel extremely fast on that small turbo to make enough boost to make the hp he wants at 8200rpms,the faster you spin the compressor wheel the more backpressure you create.

The valve problem cannot be solved with spring pressure.The cylinder pressure actually bends the valve stem(not permanently)as the valve closes it doesnt hit the valve seat square-thus not sealing.This only occures at high rpm and high boost,as the engine comes down in rpm and boost the valve seats just fine-there is no permanent damage.

A couple ways to solve this problem-limit the exhaust valve lift to .700 lift
you could also have valves made with 3/8'' valve stems-of course that adds a bunch up unneeded weight to the exhaust valve.So we have used 3/8'' stem titanium exhaust valves to reduce weight-the titanium exhaust valves arent happy in a turbo motor so you need to replace them every 75 passes or so-but this allows you to use .800 lift cams with no issues

 

The actual valves bending...never heard that. My cam is only a .723 lift, so I don't have to worry about that. That would suck though, I'm guessing that would be a glitch you never would figure out.

 

Thanks for the info... My rocker arm ratio is 1.55.. that comes out to 669ish lift so I should be good there...This is a street car..lol...kinda, with a m6 back in it so I must have a lot of extra rpm to shift...I have found that its the only way to be competitive on the street against auto cars. It's too hard to try to short shift at this power level, and really the extra rpm just gives me more time/slack to make the shift happen...I just need one or two more seasons and a auto will go back in again, but I want to see how far I can go with the m6 again...I would love to tame it down in the rpm department, but I need it for now to make it work....any more ideas or info would be appreciated...Btw are you saying that it is possible to over spin the turbo so its falling off at those rpms in my set-up, and that I should make the power, but it will just start falling off? Also, won't the waste gate open to maintain a boost level and relieve some back pressure?....

 

Yeah..he brought another motor or two and is building one with the better parts and selling off the other one...kind of a funny three way deal..I think the second motor was a proline engine also

 

shawn,
is this the small block , bs3 efi car , that travis quillian tunes???

ash

 

What i'm saying is that to make the power you want at that high rpm with that small turbo your going to have to spin the compressor extremely fast,when doing that you gain a ton of backpressure-and that is whats killing the power.The higher the rpm the higher the backpressure.Yes the wastegate will relieve some pressure but it will take a great deal of exhaust pressure to spin the compressor wheel fast enough to make enough boost.