1990 350 TPI

Bored over .040

Speed Density

Dart Iron Eagle 165 cc heads, with 72 cc chambers
Pistons' deck height is higher

Comp cam .488/.495 212/218 duration 112 lsa
Siamesed base 3.25"
Edelbrock headers
High flow cats
Borla exhaust
Pro magnum rocker arms 1.52
Ported plenum, cut air boxes, KN air filters

2600 stall

I have VE mostly done in the chip through labtop datalogging and eprom burning. PE is obviously off until I get to the wideband o2. But Why do I lose to chrysler v6's, mustangs, 4 cyl turbos etc at high rpms when I always beat them in the past with a stock car before the rebuild/mods? Is Speed density really like this, and should I just stick it out until I get to the dyno in a couple weeks for the wb o2? Or do you think there's something mechanically wrong with the car? I can't screech the tires either. Just weak throughout the entire rpms. Nothing appears wrong mechanically either. I've driven it 1,000 miles already. It idles steadily on the tach and labtop.

 

I really think if you haven't burned a new chip that that is your problem.

 

Your heads are two small, you need some 190's or 195's

 

While I do think you would be better off with bigger intake runners, those 165cc ports should be comparable in size to the stock heads. Plus those heads would still flow better than stock L98 iron heads, so blaming the heads might be barking up the wrong tree. Unless you are actually running less compression than you think you are, but you mentioned you have some domed pistons, so...... probably not that either. Only thing I don't see is some bigger runners, but you still should be seeing better performance than stock. Your cam looks really close to the Xtreme Energy cam 08-412-8 so I don't think the cam is too radical.... anyone else???

 

Last time I checked, all the specs were the same, better, or at least slightly better than stock. Therefore, I shouldn't be slower than I was stock. The pistons aren't domed either. I wasn't sure what the compression was going to be at the time of the build, but the machinist took the pistons and inserted the wrist pin in both the stock piston and the Trw forged piston I now use. Apparently, the Trw forged piston stood slightly higher which would "maintain or even gain compression despite the bigger combustion chambers." In other words he was saying that the piston deck height is higher. Correct me if I'm wrong. I'm just sick of being in the dark about why it doesn't perform.

I'm running out of ideas...PE isn't chip tuned but still, it runs ok, but it's just so damn slow.

 

That was my original opinion too, but I'm a little skeptical. Then again, like I said, I only have VE done on the chip and I have to go to get the wb o2 readings at the dyno soon. I hope you are right, but does anyone else have any experience with speed density and a buttload of mods at a time? The timing is at 6*

 

Screwed valves?

 

Scan that thing for trouble codes, knocking ... Check your engine's compression and now that the spark plugs are out check them to see if the mixture is ok.

 

What size valve are in those heads. And if its true that the intake on those heads (not sure what stock is exactly) then he would be better off with a higher flowing intake port on the head. The cam is pretty mild. Duration is a lil higher than stock, and the lift is up by a lot more than stock. Sounds like a good choice there. Could up to the 1.6 rockers though.

As far as compression, check to see what you have. 9.0-9.6:1 is what you'd wanna see. Personaly I think the heads are too small. 1.94/1.50 valves, with a 190-195cc intake should respond much better. Plus a ported aftermarket baseplate might help too.

 

hmmmm, i'm betting you have lower compression than you think. What pistons did you use? Even with a flat top, i don't see you being any higher than 8.8:1 However i don't know about your pistons you have. It doesn't sound right that they would sit higher than stock unless you have the wrong pistons, like for a different rod length. Do you have the part numbers for the pistons?

 

I am not sure of your problem, however I can say that it is not the cylinder heads not having enough flow numbers. I guess some people haven't heard that mrr23 made 539 torque and 350 hp with L-98 ported heads. And Sitting Bull has had such good results with porting, not to mention how he has helped tons of people re-use their stock heads for their budget engine. You do not "need" or "have to have" 195 cc. Too many members have already proved that wrong. If you are going to tell people that then you need to talk to a few other GM cylinder head experts on this board.

A 72 combustion chamber with flat top pistons will be lower compression than you think. in the 8's. A dome with .125 might only get you mid 9's on compression. However you could try Fel-Pro's head gaskets that are basically different size shims that are rubber coated. You could also have the intake and heads milled a few thousands. The forged pistons might have been the best choice, but they shouldn't steal that much power from blow by, weight or expansion rates.

Do what I do. act like the engine is not even running and try to figure out why (if that makes sense). Check fuel pressure, spark, vaccum, leaks, injectors, spark plugs, wires, ground wire, Power enrichment, rocker arm adjust, etc. Do everything that you can think of.

 

I still think most likely it's the chip. But, I would also bet your compression is in the 8's also. I also would wonder if the cam was installed wrong. A cam installed wrong will ruin the performance of the motor. Was the cam degreed when installed?

 

problems like this are very difficult to diagnose. first off, how slow is the car really? we have no idea because you have no numbers. with 8.xx:1 compression, the smallish heads and cam you should be in the mid to high 14s at best (here come the flames). i see 350 TPI cars at the strip all the time that run low 15s, this is the norm for mild or stock L98 cars(yah yah i know all the "internet" L98 cars run 14.0 but this is real world not cyber BS). the bottom line is anymore alot of cars on the road can run a low 15 or so. honestly i think you are chasing ghosts, if the car idles good, runs good, revs decent, if you have good fuel pressure, and correct ignition timing, even with a speed density setup you arent far enough from stock that you are going to gain alot of power by burning a chip. not the kind of power you are expecting anyway. basically you just rebuilt a stock motor with a slightly better cam and a set of headers, and possibly less compression, dont expect this to be a firebreathing combo. so many people think TPI 350 cars are so fast when in reality the vast majority of them are just simply not fast at all. most 350 guys just refuse to believe that their cars are slow turds just like all the rest of us 305 guys. so lets all join the real world here and admit that this car is only good for a mid 14 at best stop trying to diagnose a problem that isnt there.

 

O ye of little faith. It is not internet bs when people post actual timeslips and dynos. 305 and 350's are different. I have seen publications of TPI long tube runner cars that can put hp numbers in the 300 range. If you are going to offer postings like that with a bleak out look, don't even waste your time posting it. People want help, not your car is "simply not fast at all."

 

The machinist said it would be higher than 8. The pistons increased compression so I don't have ****ty compression despite the 72cc heads.

 

hey Tibo, have you read this post at all? the car is basically stock. i'm not trying to be negative, i am simply stating the truth here, if you or anyone else cant accept that i am sorry.

BOTTOM LINE

we have no performance numbers from this car to go by, but since it is basically stock we will consider it so. do you not agree that most 350 cars are in hte mid to high 14s? go to the track sometime and find out for yourself. it is also a fact that many newer cars perform fairly well stock, a 15sec 1/4 on the street is not that uncommon anymore from many stock vehicles. so why should i make this car out to be something it is not? it is stock, it probably goes mid to low 14s, that is not that much faster than many cars on the street today so it stands to reason that he cant stomp on v6 cars and turbo 4s. i am not spreading negativity, i am just trying to dispell the "all 350s are fast" misconception and bring to light the reality that cars to day are faster and perform better. it is not that his car is junk or slow, it is just not that much faster many other cars on the street. thats why i dont think anything is wrong with the car, it probably runs just fine, it is just not as fast as he expected it to be.

 

He said that he was able to beat those cars prior to the engine build. That's a problem, especially when he was trying to move the other direction.

One problem with the car is that the owner doesn't know specifically what parts went into the shortblock (pistons). Therefore, nobody on this or any other board can tell him what, if anything, is "wrong" with his new engine combo physically, even if it was put together right (cam not degreed, valve lash to tight, air leaks, etc).

RocZ57, if you can find out what cc the piston is, along with compression height and block deck height, we can tell if anything is physically wrong with the build. The rest of the combination looks fine for a rather mild build and should do well against any of the stock combinations once it's tuned, providing the compression ratio is liveable. Even if the pistons pushed a few more cc's into the combustion chamber, it would have to be at the right compression distance from the pin to deck and overcome the 8cc loss in chamber volume.

 

Um, no, I was not aware of this, as it is not earth shattering to see worked over heads flow better than stock. And of coarse you will see good results with porting (if done right) and correct me if im wrong, doesn't porting involve the actual removal of material from the intake (and exhaust ports in some cases). If this is true then that would in fact increase the CC of the port. There fore transforming an utterly stock head into one that can flow much more air.

And as too

Dude you need to calm down. I have yet to see words here that state that L98's are "so fast" and have not seen anyone ( most 350 guys just refuse to believe that their cars are slow ) make such statements. The guy who started this post had a question, and to his knowledge has posted what he knows.

Back to topic. If you have the stock runners, then those are a bottleneck, and as far as i can see the heads are a bottleneck as well. Larger runners, port the heads, and get the actual CR, or you will be flying blind till then. Take a look into the chip programming as well, for that will really screw it up too.

 

Usually when porting the intake side of the heads, the goal is not to remove material to make them bigger, but to clean up restrictions and crap formed from the casting process, etc. (unless it is some full blown race port). Profiling the valve guides and smoothing the intake bowl helps flow, too. Now all of this will probably make them bigger, but I just don't think that the size would be too much of a factor. When I port my heads, I try to just remove as little as I can to make everything nice and smooth because I am not an engineer or expert on these things, so I personally am not out to recreate or redesign the intake port.

 

Guys this post is actually getting ridiculous. I think a lof of problems occur during the actual rebuild of the shortblock. Whether you guys build your engines or instead trust the local ******* engine shop down the street is up to you. But I really think some shady things go on at some of my local machine shops to say the least. And about stock 350 tpi's running and not running, it all comes down to how well an engine was taken care of. Not all engines wear the same and are treated the same, because there are hardly any new stock 350 tpi engines around today and that's the truth. So throw all the comparisons of this 350 ran this and that one ran that out the mother****ing window.

RocZ, go over your timing first and make sure that's not a problem, do detailed searches on the board on how to check for timing problems/adjustments. If this is all fine, check out your entire fuel system, get a fp gauge and see what's happening when your foot is in the floor. If this checks out okay, then do a leakdown test, immediatly so you can check the condition of your ring seal. THIS is what makes or breaks about half of the engines that don't run right. Yeah it's a pain, but it IS A MUST. Remember do a leakdown test, not a compression test. I had a 383/SR/AFR/219 cam engine that made an embarassing 256rwhp, because of cracked piston rings. It should have made about 340rwhp. So you can see what it takes for an engine to be a stone. The leakdown test was all I needed to know to determine what killed my old engine.

 

Compression is not an issue. Compression is almost 10:1 believe it or not. I forgot the part number on the pistons, so take my word on it, and the machinist's word, and another machinist that sold me the heads/pistons together. They are flat top trw forged. Higher cc. It's from the books too.

I'm in the process of doing all suggestions. Most I had in mind already. Fuel pressure at wot is a new one but I don't know how that can suddenly go bad after six months of sitting in the garage, but I guess weirder things have happened.

 

Actually I don't think the heads are a bottle neck anymore. They flow better than the L98 heads. Sure they aren't flowing AFR or other obviously better heads, but according to http://www.chevyhiperformance.com/te...98/index4.html

They flow better than l98 vette heads by 15 cfm more at .5 and better all the way on down. Yea they're not hte best heads in the world, but they're sure a better step up than stock. Therefore I don't believe they are a bottleneck any longer, the runners and siamesed base maybe.

 

Another thing too, I did a compression test on cyl 1 after it got together. It was at 171 psi, which is higher than stock's 160 or so.

 

for reference my 305 did 165-175 when it was stock. but that is cranking compression. cranking compression is pretty much only good for seeing if all cylinders are sealing evenly. lots of things affect cranking compression, like cam size and timing. so do the leakdown, it really is the best way to check your health. all the static compression in the world is no good if it all blows into the crank case due to poor ring seal.

 

for reference the only way to achieve 10:1 with 72cc chambers, flat tops, and a standard head gaskets is with 0 deck height and no valve reliefs. We all know all flat tops have valve reliefs. I still think you are in the 8's but since you said you KNOW it is 10:1 I would say your problem is you are smacking your valves into the piston, because your pistons don't have valve reliefs. So what head gaskets are you using, that will help me understand your compression better. I hate to be an a$$ but if you are using a standard head gasket you don't have 10:1 compression.

 

I used the felpro 1003 or 1004, I don't remember which but they are similar specs.

 

Did it ever accur to you that mrr23 made that power using nitrous? He doesn't make it advertise those number with nitrous but those number weren't made N/A.

 

are you using 93 or higher octane?

 

Yes to 93 octane. Chip tuning almost a week away.

 

Just got back from the dyno run. It is NOT chip related.

The wbo2 displayed extremely lean down low as high as 18:1 and extremely rich up high as much as 10:1 at 3800 rpm.

Burning chips made no noticeable responses or differences. I'm thinking inconsistent compression across the cylinders.

Part throttle after VE tuning makes good air fuel ratios according to the o2 sensor and labtop. But the variables on the VE table are smaller than the stock's tables. Any thoughts on everything above?

The car is still very loud too...