turbo back pressure

[billet racing 1]

When I tore the motor down, noticed black coating on the intake ports of the heads. Seems to me we had some exhaust reversion. Machine shop agreed with me.
The set up. 496 tall deck, 9/1 compression, center rise water cooled exhaust, twin turbo, intercooler, 6,000 rpms, and 15 lbs boost.
So the questions(?).
Too much back pressure?
Increase turbo exhaust housing?
Cam adjustment?
Timing adjustment?
Any other suggestions?
Jerry

[BOOGEYMAN]

what turbo's and what housing are on there now? what size is the down pipe?

[billet racing 1]

older RayJay EE , Exhaust housing 1.0 , 3" exit pipe
Want to try a 1.1 or 1.3
Jerry

[Infomaniac]

I guess the cam is ground specific for a turbo? If so will you share the specs?
Not trying ti insult intelligence but just covering the basics. And FYI for anyone that is curious.
The exhaust valve must close when the pressure in the cylinder is equal to the exhaust system pressure or it will feed back.(much earlier than you might expect)

[billet racing 1]

Not afraid to share any info.
Cam by Comp cams. Ground specificaly for turbos. I think his name was Wayne/Duane? Gave him all my info. I will have to hunt down the cam specs. Think they are in the trailer, so may not have them till wed. Ran it by 058 before I ordered.
I was hoping for 6,500 rpms and specified that as well. Not sure I'm able to get all the potential out of this set up yet.
Running in a jet. 21' Daytona.
Jerry

[Unchained]

The rule of thumb for turbine housing back pressure is to keep it below 2:1 with boost pressure. Put a gauge in it and check the back pressure. My setup has 30# back pressure to make 20# boost.
From what I've seen with the turbo kits, the turbine housing is quite small and becomes a restriction in the exhaust. You pass a point where more boost will not make more power, just more exhaust back pressure.
Here's a comparison of a Gentry exhaust manifold and a Garrett large frame turbine housing. http://www.***boat.com/image_center/data/520/220gentryexhaust2.JPG
What does your exhaust manifold outlet look like as compared to the Gentry ?

[billet racing 1]

Yes, the exhaust manifold exit looks the same. I enlarged it a little to match the inlet side of the turbo exhaust housing. The turbo exhaust housing is not near as large as yours.
I made two spacer plates to put between the exhaust housing and the turbo housing. one side will have a pyrometer, and the other a pressure gauge.
This should tell me a little more.
I am computer challenged, so will have my kids sent you pictures, or help me to post.
Jerry

[Unchained]

While your at it with your spacer, thread it for an O2 sensor.

[randy77zt]

you could install a wideband o2 sensor and datalog your fuel mix-like an innovate motorsports system.my boat is an outboard but i have an old sportts car thats turboed with laptop efi system.car make 2hp/cubic inch.boats work will with turbos because rpms are always up

[MACHINEHEAD]

Billet, do the preasure check, its useful. Call Ken@ H-O Racing, I think I have seen a couple 1.3 housings and other various rayjay stuff. 1.3 w/EE would be my choice for 496 inches. 909-980-1451 Rancho Cucamonga

[STV_Keith]

As mentioned above, you want to get the ratio as low as possible of drive pressure to boost pressure. We used to do a lot of testing of that on the diesel trucks, and you can actually get them to have more boost than drive if you want it to, but it will usually cause the spool up to suffer some. But efficiency comes up.
Get a drive pressure gauge in there when you put it back together. A boost gauge works just fine. We usually tapped a 1/4" NPT hole, then went to 1/4" copper tubing for about 6' all coiled up (to dissapate heat), then a union to 1/8" plastic tubing to the gauge.

[Unchained]

Here's a solution to that back pressure problem,
http://www.childsdale-ind-prop.com/turbosandheaders1.jpg
http://www.childsdale-ind-prop.com/turbosandheaders2.jpg

[billet racing 1]

Talked with Ken at H-O Racing. He's the Pontiac Guru. Has done some stuff for me in the past. (4 GTO'S). Only have two now, and one is a parts car.
Any way, back to the turbo. Here are the cam specs. Spoke with Dean at Comp Cams for this.
Engine: Mark IV Chevy tall deck, 496CI, Merlin heads. 8.2-1 comp
Turbos: Race Aero set up. Exhaust manifolds are aluminum water jacket center risers. turbo, Ray Jay model EE series 600. exhaust housing 1.0
feed into an intercooler atop the intake. two 750 Hollys.
Current performance. 6,000 rpm 15-18 lbs boost.
In a 21' Daytona Aggressor Jet with A/B impeller
Speed 101-103. (Have NJBA time slips to prove it)
Cam, solid roller
intake exhaust
gross lift .731 .727
duration at .020 290 286
valve timing open close
at .050 intake 14 BTDC 62 ABDC
exhaust 60 BBDC 12 ATDC
cam installed at 114 intake center line
I love the setup. real quiet, hassle free. Felt we were choking the motor, and was hoping for around 6,500 rpms. Toasted the rings on it. During the rebuild, noticed exhaust reversion back into the intake runners. Another indication to me that we are choking this motor.
AT CFW we ran 6,200 rpms. Water was pretty rouph, and would like better water and more runs to verify. The OOPS. Have a Jessel external belt system. had repaired a loose keyway, and left the four adjustment bolts loose. Cam ran at 10 degrees retarded. Now I think I need to do a leak down, Hope I did not bend any valves.
Here's Pictures:


http://i81.photobucket.com/albums/j234/billetracing/STA70265.jpg (http://photobucket.com/)</p>


http://i81.photobucket.com/albums/j234/billetracing/STA70264.jpg (http://photobucket.com/)</p>


http://i81.photobucket.com/albums/j234/billetracing/STA70263.jpg (http://photobucket.com/)</p>

[billet racing 1]

Talked with Ken at H-O Racing. He's the Pontiac Guru. Has done some stuff for me in the past. (4 GTO'S). Only have two now, and one is a parts car.
Any way, back to the turbo. Here are the cam specs. Spoke with Dean at Comp Cams for this.
Engine: Mark IV Chevy tall deck, 496CI, Merlin heads. 8.2-1 comp
Turbos: Race Aero set up. Exhaust manifolds are aluminum water jacket center risers. turbo, Ray Jay model EE series 600. exhaust housing 1.0
feed into an intercooler atop the intake. two 750 Hollys.
Current performance. 6,000 rpm 15-18 lbs boost.
In a 21' Daytona Aggressor Jet with A/B impeller
Speed 101-103. (Have NJBA time slips to prove it)
Cam, solid roller
intake exhaust
gross lift .731 .727
duration at .020 290 286
valve timing open close
at .050 intake 14 BTDC 62 ABDC
exhaust 60 BBDC 12 ATDC
cam installed at 114 intake center line
I love the setup. real quiet, hassle free. Felt we were choking the motor, and was hoping for around 6,500 rpms. Toasted the rings on it. During the rebuild, noticed exhaust reversion back into the intake runners. Another indication to me that we are choking this motor.
AT CFW we ran 6,200 rpms. Water was pretty rouph, and would like better water and more runs to verify. The OOPS. Have a Jessel external belt system. had repaired a loose keyway, and left the four adjustment bolts loose. Cam ran at 10 degrees retarded. Now I think I need to do a leak down, Hope I did not bend any valves.
Here's Pictures:


http://i81.photobucket.com/albums/j234/billetracing/STA70265.jpg (http://photobucket.com/)</p>


http://i81.photobucket.com/albums/j234/billetracing/STA70264.jpg (http://photobucket.com/)</p>


http://i81.photobucket.com/albums/j234/billetracing/STA70263.jpg (http://photobucket.com/)</p>

[billet racing 1]

OK the pictures did not work. I'm new at the picture part. I can email them to someone, if you would like to post for me.
Thanks
Jerry

[earlbrown]

http://i81.photobucket.com/albums/j234/billetracing/STA70265.jpg
http://i81.photobucket.com/albums/j234/billetracing/STA70264.jpg
http://i81.photobucket.com/albums/j234/billetracing/STA70263.jpg

[billet racing 1]

THANK YOU
Jerry

[bumpstik]

Jerry-IMO-(no H), the cam is WAAAYY too big. Would rather see you with a 235/248 @ .050" on a 114-116LSA. ICL @ 108-110. lift is OK. 1.3 housings should help. If you want to do a little diagnosis, try putting .015" more lash on the intake rockers.Make 1 quick pass and evaluate. Try advancing the cam 10 deg. I know you said retarding helped,but I'D be curious about the other side of "straight up" also. You are doing this to help find what the engine wants for a cam. I'll check for some 1.3s tomorrow

[billet racing 1]

Left out some info
intake exhaust
duration at .050 257 253
lobe seperation 114
Jerry

[MACHINEHEAD]

Bumpstik, remember the 496 at westech with single 850 and 2 rayjays and no waste gates? The one that could not be tested below 5000rpm due to a excessive boost condition (22psi) and 900lbs/tq. Maybe Brules memory can be jogged about when that engine was tested to get cam specs. Maybe March 06. I think the cam was a Xtreme Marine Hyd Roller grind with some extra LDA and was not real big like 236/244-114. If Billet has a solid its more like 247/244 in hyd. land. Still pretty large IMO

[bumpstik]

B R-- I calculated your specs before I replied. M-H--That (Westech) was one of the engines I had in mind when makeing the cam recommendation. Also following other high boost/high HP turbo buildups and the cams, even @ 2000+ HP are relatively mild.

[Unchained]

Also following other high boost/high HP turbo buildups and the cams, even @ 2000+ HP are relatively mild.
I'd be interested in an opinion of what would be an optimum turbo cam too.
I've downsized cams a couple times since going with Turbos/EFI a few years ago.
The one I am running now is a Bullet solid roller,
116 lobe center
.662 lift
Duration at .050 is 262
Intake lobe degreed to 114 ATDC
I was considering having it ground down to less duration yet.
Since the previous cam which was .730 lift I have gone to less of a valve spring and the roller lifters have held up better.
I've been running 20# boost, 7000 rpm. 540 CI
I just tore it down for inspection and the ports were clean all the way to the valves so I guess I'm not getting any reversion.
I was surprised to see that there was no fuel staining at all in the 5" +- from the injectors to the valves. Must have been real good atomization.
When I ran a blower/carbs the inside of the intake and ports were all stained red from leaded race gas.
Thanks for any input

[MACHINEHEAD]

Bumpstik, did you find some 1.3 housings for BR? That may be a quicker way to find out which direction to go in camshaft. Also, why do you think that some cam grinders like to use a larger intake lobe for turbo use, like 226/216@.050. Where do you think that all started? Seems like a single patern would work best and use housing A/R to reach your best average FT/LB/TQ number. Not like there are that many choices for rayjays anyway. Just your thoughts.

[bumpstik]

Sorry---no 1.3s! Must have sold it @ a swap meet. Got 2 .8s and a 1.0. I have no idea why some cam co.s are using shorter ex. events. Possably in the early days of turbo experimenting, a short ex.event was needed and thus became "the truth". Possably hi-tech, hi rpm engines like Indy and F1 need it. My thinking is that if you put in 50%more air (8# boost) or 100% more air(15# boost),you are going to need more time, in terms of cam ex. lobe degrees, to get the greatly expanded volume of A/F mix out of the engine. And, unlike a mechanical blower, you are exausting against back pressure.This is why I like to put more timing on the ex. lobe and advance the lobe (which is what happens when the Lobe Separation Angle is increased) when compared to a natually aspirated cam design. In addition , overlap is reduced, thereby reducing the amount of exhaust back pressure ( in exposure time) the intake charge must fight in order to start filling the cylinder. Overlap is further reduced by using more moderate durations than what Billet and others are using. Rember ,also, the exhaust side is the 'engine' that gets the compressor turning, and I believe, additionally benefits from greater ex.duration and earlier opening.

[billet racing 1]

All sounding good. A little longer in the exhaust duration. Maybe thats why a little cam retard helped by 200 rpms on the top end.
As soon as I can get the exhaust pressure measured properly, I will post up some more. Aslo need it to warm up a bit. Damn its cold. Don't really want to be working in the garage when I have to put my beer in the fridge to keep it from freezing.
Jerry

[MACHINEHEAD]

Who is rebuilding Ray Jay stuff. Have some EE housings that need to be blue printed. Tried replacing the Z gap ring but started to smoke shortly there after. Have a 523 inch chevy build in my future. And I was thinking today about how I was going to get 800 hp on pump gas, with 1 carb. I think Im going to go the easy route. 2 Turbos, bumpstik cam, little carbs=800hp!

[billet racing 1]

Turbonetics in Simi Valley is who I was directed to. I needed to raplace a compressor housing recently. They did a good job, just took them 3 months. Customer service was the ships. Never returned calls or let me know what was going on. Was suposed to have 1.3 housings, but they never materialized either.
Again workmanship-good. Service-bad
But I may have to deal with them again. If they are the only ones with the parts.
Jerry

[Unchained]

Turbo city in Ca used to be a big distributor of Rajay turbos, they exchanged cartidges too. I bought a new one from them back in the early 80's.