I need professional advise. I started this project in 2001 and I’m still not done! I built a 355 TPI with the following components:

Edelbrock center-bolt aluminum TPI heads;

Crower valve springs – part # 68304;

Edelbrock 58mm throttle body ported to the plenum;

Edelbrock TPI lower base plate;

Edelbrock Hi-Flo runners - NOT PORTED TO PLENUM;

adjustable fuel pressure regulator;

30# Accel injectors;

Crower “special grind” roller cam (@ .050 – 213 deg intake/221 deg exhaust (264/273 advertised); lift @ .050 – .337 in/.350 ex. (Gross lift is .506/.525); 114 degree lobe sep; RPM range 2200 — 6000 with peak HP at 5500;

Crower 1.5:1 roller rockers;

Crower hydraulic roller lifters;

Diamond Flat top ultra-light forged pistons – compression ration is 10.1:1 if not a bit more;

Crower forged connecting rods;

Scat forged crank; and

Edelbrock tubular exhaust from headers to tail pipes.

The engine was built a number of years ago and then it just sat around until I found someone in LA who could tune the computer to match it. So I went to my Viper mechanic, DC Performance in LA, and he said he could dyno tune it for me.

This is the problem: at 3500 RPM the engine makes 343 lb/ft of torque at the rear wheels; but the peak HP at the real wheels is only 243 at 4000 RPM! It then flattens out and drops off. That’s 1500 RPM shy of where this engine should be peaking out at.

Before the build, for whatever reason, Crower recommended that we swap out the valve springs on the Edelbrock heads. So we were given Crower springs. According to Crower their springs’ installation height is 1.750”, having 129# of closed seat pressure and 350# of open seat pressure. Once we saw that the engine’s giving up at 4000 rpm, we pulled off the valve covers and tested the springs which are at 1.750” but with only 110# of closed seat pressure and 300# of open pressure.

I called Edelbrock and the stock springs for its centerbolt heads had an installation height of 1.800” with seat pressure of 120# closed and 320# open. So Edelbrock is of the opinion that the valve springs presently have an incorrect install height.

I called Crower and they seem to think the problem is caused by valve float since the power flattens out and dies after 4000 rpm.

SO; what do you guys think? Could I be getting the float with the minimal reduction in the closed and open pressure? Could the Cam be degreed wrong - too far advanced? Or could it be that the Hi-Flo runners aren’t port matched to the Plenum (although Edelbrock says that that’s actually okay)?

ANYONE HAVE ANY THOUGHTS/SUGGESTIONS????

 

Well to start, I do think that motor should peak closer to 4600-5000 rpm, somewhere in there. TPI doesnt peak real high to begin with but should make it up to the high 4000's on peak with aftermarket stuff.

I'd port the plenum to better match the larger runners.... get as much air goin through as you can.

That cam is fairly aggressive on the lobes so it should have a good spring. The crower specs look ok and its not uncommon for springs to loose some pressure after few heat cycles. If those crowers are at 1.8 install height and not a 1.75, you will see less pressure anyway. I'd get a spring with around 130lbs seat, but abit more the better. But you usually dont talk about valve float with hydraulic rollers until your up over 5800 rpm.

What lifters are you using? What size springs are they anyway? torque output looks good, but that peak rpm for hp is abit low. Power is not great either for those mods. I'd expect abit more than that.

Was the manifold matched to the heads? Runners matched to manifold? Any steps in the flow path could cause some turbulence and may hurt power/rpm ability

Finally how are they tuning this? Is it a MAF car or MAP?

 

Thanks; yeah the manifold and heads were port matched by Edelbrock since they're part of the TPI "package" - the only thing that isn't port matched is the plenum runner openings to the Hi-Flo runners. But Edelbrock said that having it the way will increases the velocity. However, I agree with you, I think a TPI could use as much air as possible.

The lifters are Crower roller lifters that are the stock version matched to the cam; I don't know what the spring is but the part number is 66330 - their the OEM style. The springs seem to have been installed to Crower's recommended height of 1.750", but the seat pressure is still off nonetheless.

It's a MAF and its being tuned on the dyno with, I beleive, the tunercat software. I have an emulator from Moates and chips, a wide band and all that. Yet with the custom tune, it's still choking at 4000 RPM and I can't figure out why.

My mechanic is starting to think that it might be that the cam is degreed wrong - too far advanced. So I thought to post here and see what you guys think since you have WAY more experience with these engines than me or any of the builders out here in Los Angeles.

 

That cam is rather large for a 355 IMO, I had a Lunati ~270* (around 220-230 @ .050) cam in my 383 stroker and it seemed large. The car made HUGE torque, but had no top end. Even the edelbrock intake parts you have still choke a stock 350 TPI. If you go with a miniram or ported LT1 intake I'd be willing to be you would gain AT LEAST 60RWHP.

That's the only gripe I ever had with the TPI, the runners/plenum just don't have enough volume to fill the cylinders at high RPM. Just my two cents though.

 

My mechanic keeps telling me that the cam is my biggest hurdle. They seem to think that I need a longer cam - something on the order of a 222/234 at least @.050. But then I'll NEVER pass the sniffer test on the smog machine - at least I don't think I would. Right now, this thing has CARB numbers for everything and an oversized cat that's free flowing yet smog legal.

Either way, I think you're right about the TPI - problem is that when I started this project in 2001, a TPI was still the only way to go. AZ Speed & Marine was putting them in everything. Now, it's all about the LT1 and blah, blah. It's too much to convert to an LT now - I'd have to change the entire engine/computer - who needs that! I thought about getting an intercooled Procharger kit for it (about $4000 not installed) but since i have 10.1:1 compression, I can't. Even with a thicker head gasket my compression will be too high and it'll restrict how much boost I could run.

 

Cam isnt huge, its not bad for TPI actually. It will peak higher thats for sure, just needs to breathe.

Cam could be installed wrong, wouldnt hurt to double check it. Edelbrock stuff does do well with some porting. I had an accel base which is the same as the edelbrock, and it had alot of room to port out. Opening up that base should easily increase your power numbers.

IF it still chokes up, can you siamese your runners alittle bit? just at the top, cut the divider out about an inch to inch and a half and you'll see alot more topend rpm wise. That system may just like to peak at that rpm for some reason, but siamese runners will help

 

Thanks; I'm probably going to have them port out the plenum and I guess I should have them do what you said too.

I know AZ Speed & Marine used to sell siamesed runners - maybe that's the ticket - get them completely siamesed all the way down. It's just such a pain in the butt to deal with this stuff now.

 

I meant modify the LT1 intake to fit the TPI heads. It's a decently popular mod to give the motor a good bit of room to breath. You could also try the miniram, since it sounds like you have a lot of time/money into this - it may be worth while.

I still think with the performance parts and cam in that motor, which in turn increase demand for air/fuel - you just aren't going to peak any higher without more breathing room.

For the miniram: http://tpis.com/index.php?module=cat...niRam+Manifold

 

I didn't know you can do that - the Mini ram probably won't pass smog inspection, but maybe the LT1 mod might - I'll look into that. Thanks! Know where I can find out how to modify that manifold to fit the TPI heads? I won't need to change the computer will I - I can still use the TPI wiring harness, etc, right?

 

The stock harness/computer etc. will work just fine. The only thing that will change is the intake manifold and fuel rails. The website was www.lt1intake.com which seems to be down now. I believe there were a few threads on the LT1 intake swap subject though. Might have some luck searching for "LT1 intake swap" i'll look around in the morning and see if I can dig up some more info.

 

LT1 wont have egr so it wont be legal in cali. Miniram can be equipped with egr now but it doesnt have a CARB number

 

Some material for the LT1 intake route:
http://www.popularhotrodding.com/tec...ls1/index.html
https://www.thirdgen.org/forums/tpi/...e-350-tpi.html
http://sethirdgen.org/LT1.htm

This guy might be able to give you some pointers: https://www.thirdgen.org/forums/engi...d-replace.html

The LT1 intake will not be a direct swap, it can be done with normal tools though, just takes time and patience. You will save cash over the miniram with that route though.

 

What's the wideband on the dyno read for AFR above 4000?

 

True, swapping any other intake will fail it for a visual unless it comes with a carb number. So if you are worried about failing visual, your best/only bet is to gut everything you can out of the TB/runners/plenum to remain stock appearing. There is a decent tutorial on that around here too.

 

THANK YOU SO MUCH! In fact, I've been reading about the mini; stealth; and even the super ram all night long and concluded that I'm going to get screwed if ever comes a time that I need to actually go to a smog inspection shop. That's the problem. However, I'm almost willing to give the stealth a shot since it's so inexpensive compared to the alternative - of course, I'll have to figure out how I'm going to get my strut tower brace to fit around it, but that's a different story....

 

I don't know what the AFR is at 4000, however it's within whatever limits it needs to be since the guy is adjusting the fuel trims etc. so that it runs at its best. Is there a number I should keep an eye out for? You think if I boost the fuel pressure it'll help?

I'm starting to worry that there may not be anything wrong and that's what a TPI motor is destined for - peak HP at 4000 RPM. But vettes made more power and at higher RPMs so I still can't figure it out. I wish I knew an engineer...

 

Vettes only made 250 HP to the flywheel with a 6spd transmission.... Like 210 to the wheels on a good day, running cool. The Autos only made 245 to the flyhweel and have more loss, so they see around 195-198 RWHP stock.

I hate to burst your bubble, but you are doing very well to see a 40+ hp gain at the wheels with those Edelbrock components you have listed. While they are an upgrade from stock, they are not that great of an upgrade when it comes to power.

My 3815 (Edelbrock TPI Vortec) manifold was hideous flowing before I touched it...With stock long tube runners, I made like 280 RWHP and 360 RWTQ. With all the port work, siamessed SLP runners, and reworked tuning, I made 355 RWTQ and 356 RWHP. It felt like it had another engine under the hood from 4K on.





Its the NATURE of long-tube runner TPI setups. To get some power out of it, you need to do something like I did. Siamese port some SLP runners, Siamese the plenum, grind out the EGR diverter, and siamese port the lower manifold (my 3817 needed lots of work there).... I put down 356 RWHP with a heavily modified .030" over 305 TPI and it made the power at about 5,900 rpm, IIRC.



I needed a decent torque converter, decent gears, and a non-slipping transmission that actually shifted correctly. I put a nice 4L60E behind it and ran a 14.5 @ 94 in a 5,500 lbs G20 van. Not bad for 3.08s, a 1,600 rpm torque converter, and 310 CID. The rev-limit was at 5,750 in this video and I later stretched it to 6,500 after getting the tuning dialed in and a fresh transmission that didn't flare the 1-2 shift.


http://s243.photobucket.com/albums/f...t=101_1468.flv

 

Great. So now I have to port out the Edelbrock stuff...Are those runners you have one piece throughout - or do they have a seperator in the middle? In other words, are they "siameased" from end to end?

I researched the MinRam system all night and this morning I spoke to Street & Performance (http://www.hotrodlane.cc/). They said that the TPI can make great HP and Torque with the right combo - properly ported, like you said - even better than a MiniRam or LT1. Here's a great article written in Car Craft back in 1991 where the various EFI options were all compared on the same test motor (differnet EFIs and makers) - it's very informative: http://www.hotrodlane.cc/injectionselection/page1.html

Anyway, Street & Performance thought that my set up should still be making way more power and that there's definately something wrong. So I'm starting to think that the cam wasn't installed right if it isn't valve float (which I've heard it may not be since 110# of seat pressure is more than enough through 6000RPM).

I guess at this point I'm just going to have them port the Plenum to match the runners and perhaps "siamese" the runners for the first inch or so. I'm not going to mess with the base plate because that's supposedly "matched" to the runners and the heads by Edelbrock - right? (I'm starting to think that Edelbrock doesn't make as good a product than some other comparable manufacturers, which ruins my day since their stuff isn't cheap!)

If the cam wasn't installed correctly, then I'll consider a new one. I might as well since the labor to install a new cam and correct the installation of this one is probably going to be the same. Street & Performance suggested that I speak to Gerry Henderson at Comp Cams regarding my set up - evidently Henderson's been working with TPI engines longer than anyone there. Maybe a 224/232 with a 114* lobe sep, provided that, with a backup prom tune, I would still be able to pass the sniffer test if ever I needed to.

WHAT A PAIN!

 

I suggest you take a stroll over to the 'Southern California Area' forum and check-out what some of those people have done with modded TPI engines.

Bill

 

Yeah the tpi is natured to peak out at 4000 rpm's. Mine did. That's before I ported my plenum, but havnt had it on a dyno afterwards. But u DEFF need to port that sucker out. Because the runners and heads will only flow as much as what is before it, such as plenum.

 

Go to stealthram, you'll be happy with it.

 

Not when he cannot pass the visual part of the CA smog test.

 

I agree that the Edelbrock components are not the best flowing pices, but 4000 RPM power peak? Nah, I'm not buying the magic on this one. Go with your first suggestion- valve springs. The seat and open pressures you've got now are like what you'd use on a mild flat tappet cam. That "custom grind" roller might not have much duration, but I bet the ramps' acceleration/deceleration rates are more than those springs can handle at elevated RPMs. Springs don't lose as much pressure as you're seeing- they're either the wrong ones or you're not measuring the installed height correctly.

Wondering how the Edlebrock installed springs could have been 1.80 but your current springs are at 1.75. The spring doesn't determine the installed height- the locks, retainers and spring cups/shims do. Did somebody install extra shims when the Crower springs were installed? What closed the installed height down that extra .050" from Edelbrock's original spec?

Anywho.....The other two things that kill power in the upper RPMs are:

1. Inadequate igntion. Are you SURE of the condition of every part in your ignition system?
2. Inadequate fuel system. This one is much easier to check. Do you have consistent fuel pressure all the way up the RPM range at WOT? If so, strike it off the list. If not, you got fuel delivery problems.

I would definitely match the sides of the plenum with the runner openings. Not sure how far off they are with the Edlebrocks, but they were WAY off with the SLP runners I used to use back in the day.

 

Thanks Damon. I don't think they've checked the fuel pressure yet but that's next on the list. As for the ignition, I'll have them look into that as well.

The reason the Crower springs are installed at 1.750" is because that's what Crower's specs call for, so I don't know why I'm losing that much pressure - 19# on closed and 50# on open. Notwithstanding, the guy at DC Performance said that 110# and 300# (although less than spec) is still enough to keep the valves from floating until passed 6000 RPM. But you do have a point as far as the ramps - so I'll bring that up to them Monday. Also, what do you think about whether the cam was degreed wrong??

From what I remember, the Edelbrock runners were a good deal bigger than then the plenum's openning - but Edelbrock claims that that disparity is okay because it lends to higher velocity. However, common sense suggests that it really lends to turbulance and restriction. So I'm going to have the plenum opened up to match the runners.

Bonehead Performance in PA (http://www.boneheadperformance.com/M...creen=EH_PRICE ) could port out the plenum, runners and base plate for $800 - I don't know if that's worth doing or if I'm better off buying a whole new base plate/runner combo from AZ Speed or SLP - but then I'd still have to have the plenum opened up to match the runners.

I'm just worried that the entire Edelbrock combo is crap (which is what I'm starting to think irrespective of my little problem with the potential valve float). The only reason I got Edelbrock's set up was because they claimed it was part of a performance "package" when coupled with their 58mm TB and their aluminum centerbolt TPI heads (which I also got). Plus, the "package" came with CARB Nos. But now I'm starting to think that their "package" isn't that great to begin with and that I never really needed CARB numbers for the intake component because it would've probably passed visual inspection with an SLP unit. So, I think I might've SCREWED myself when I bought into Edelbrock's hype!

 

My 305 (bored 0.030) did 254 FWHP@4800, and 334 FWTQ@3000 and this was after ported plenum, AS&M runners, accel manifold, ported+polished heads, cam, edelbrock headers, flowmaster 3" catback exhaust, gutted cat, STOCK TUNE...

Im sure tuning would give a good deal more HP but maxing out at 4000 i'm not sure if that's normal... Guess I wouldn't know though but the stock numbers are out there and i think it's higher than 4000 rpm?

 

The holes in the sides of the plenum where they meet the runners are only about 3/8" thick. Any "velocity" you gain there is lost as soon as the air tumbles into the runners. Port to match. You need as much flow as you can get- what you got now is like having a little restrictor plate at the top of each runner.

 

It's the LT4 that doesn't have the EGR.

Jake

 

you'l be amazed, maybe you should switch mechanics and give Dyno Don a visit in the So Cal forum.

 

I agree....sounds like a someone new needs to be working on this project.

 

What i meant was the LT1 intake swap would not retain EGR for the L98, so no EGR means no pass cali requirements.