MBDiagMan

Quinny,

One more thing:

I have done lots of research of late as well as lots of analysis using Desktop Dyno. My goal has been to build an engine for a different brand car which will build lots of low speed torque for propelling a relatively heavy car.

My findings have been that for building low speed torque, most factory V8's already have much of the necessary ingredients. The L98 certainly has them. Messing with heads, cam and intakes only have an incremental effect on low speed torque. There are only two modifications that can offer SIGNIFICANT improvements in low speed torque. Those two improvements are; full length, small tube headers and engine stroke increase.

If you want to add some fun to your L98. Add a set of small tube (1 1/2" primary) full length headers and go from there.

My $0.02,

Calderone

Excellent info MBDiagman ! i've just bought 1 5/8 longtube headers hopin for more torque!

steven mack

O.K. You don't want to do a stroker call AFR and get there recomendations on a 350 build or go to their site on the net they can tell you how to get where you want to get to.

Quinny

Thanks guys, I think I have a pretty good picture now of what can be done.

Decent heads, aftermarket TPI runners and base, small-ish cam, decent exhaust.

I was planning on using 1 5/8" Tri-Y headers, but the only company in Australia who makes headers for a RHD Corvette only makes 1.75" 4>1 with 3" collector pipe - which is too big for what I want, so it looks like I will be up for a set of custom made extractors.

One other thing, it seems alot of cam profiles for this engine are split duration. Is split duration the best way to go or would a single pattern work as well?

I could go for the Comp 212/218 cam or 218/224 cam, or get a custom ground 218/218 or something along those lines.

GREGGPENN

Interesting....Who will make your headers?

You are correct in questioning the split issue. For a TPI setup with good exhaust, no split is required. In fact, a bit of reverse split can be used (i.e., 218/214). But, the specific split/lift/LSA depends on your final decision for intake/exhaust. (BTW: This is a secret. Don't tell anyone else. They won't believe it!)

MBDiag's suggestion about using more stroke and headers is a good one for increasing low-mid range torque. I personally think better headflow and some improvements to the intake are also beneficial. The Edelbrock intake would raise rpm ceiling for a stock motor...But, when you increase air flow/power (at mid/lower rpms), you need some extra air to support that. Whereas the stock 350 TPI is better sized for a 305 motor, the Edelbrock is better sized for a 350. Port it and it goes up. Ported, siamesed runners can go even higher. The FIRST has tubes big enough for a 400ci motor (or one with equivalent power). There are other options in between -- like the superram.

IMO, 5000-5500rpms is a better ceiling to shoot for. *** And, I'm in that 10% minority who believes you should look beyond hp numbers! That's why I suggested looking at other intakes -- if your situation allows it.

Read this article and I believe you will feel more confortable with the various intakes and how they affect the power curve.




*** That's because the torque is better for just about any intake at 3k rpms vs 2500rpms or less. Shifting at 5000-5500 gets you there.

Quinny

I will be using a company called Di Filippo - who specialise in custom exhaust systems for race cars - they can make whatever I need in full mandrel bent stainless.

A custom ground single pattern cam might be worth a look.

That article on the different intakes is brilliant - exactly the kind of info I am after. It looks like the Edelbrock setup did ok, but the TPIS setup was better.

Is the TPIS setup a direct bolt-on, or does it need modifications to dizzy, fuel rails etc to fit? If it is a direct fit, then it is definitely worth a look.

GREGGPENN

Bassani also makes 1 5/8" Tri-Y headers for L98s. And, so does Vette Tech (who also specialized in C4 racing). I've never seen feedback on Bassani's. VTech headers are a bit cheaper but may require a bit of beatin/bangin to make perfect fit. There is a HUGE thread on the VTech Headers in this forum.

Bolts right up. Base is exactly the same as an Edelbrock sans badging. Runners are bigger out of the box. IIRC, TPIS runners were honed for the tests in the article I linked. Edelbrock's were not. With indentical prep, they'd be closer. Consider price vs extra HP/TQ for your final decision. If you like the TPIS best in that article, you might just be happy with the Edelbrock's. TPIS or ASM runners do cost quite a bit more.

Quinny

I am in Australia, so the car is right hand drive, pretty much any off-the-shelf headers will be for a LHD car... which kind of limits the options

I will check out the difference in pricing. I don't know of anyone in Aus who sells TPIS parts, so I may have to import it. Edelbrock is a bit easier to get hold of, but the TPIS definitely carried power a bit better in the 5000-6000 range without sacrificing low end torque, which is useful assuming I select the right cam. That may have something to do with the honing. Even the Edelbrock made an additional 20hp with no loss in torque right up to 6000rpm, so that is certainly better than the stock intake.

GREGGPENN

It does. It does. It does!

Honing increases runner or base bore size by about .050". Plus, the bores are MUCH smoother. I suspect honing accounts for a most of the difference in the article.

Edelbrock's would respond equally well (if not better) to honing. In fact, depending on runner thickness, they might be able to enlarge Edelbrock's as big or bigger than TPIS/ASM runners. But, honing is expensive.

Some creative home porting can go a long way too. (That's where the mega-ported/siamesed SLPs come in the picture. Done well, this option could match the siamesed ASMs in the "TPI Shootout" article.) Here's a pic of the set I did for my car -- compared to stock runners.



BTW: I originally got the idea from a forum member who has a business doing this.

pologreen1

To the OP
I spoke to Edelbrock a over a year ago about their, manifolds and runners, and they told me flat out that the runners are not going to make much diference even on a bigger base, but I have been waiting for an SR for years, so I bought that instead for the same price.
much happier, but you can port the heck out of the Edelbrock's they said.
good luck

Quinny

According to the article that Greg linked to, the Edelbrocks made 21hp more than the factory intake on a 383 from 4500 to 6000rpm - I reckon that is a bit of a difference. On a mild 350 it probably won't make 21hp difference, but it shows that it does increase breathing capacity above 4500rpm.

Calderone

Im currently researching for Heads,some nice heads will help too !
http://www.edelbrock.com/automotive_...rformer2.shtml

Quinny

I just read that TPI Shootout article again, and it doesn't say any thing about the TPIS runners being honed - it does talk about the comparison between the extrude honed stock runners and the TPIS ones though....

TJM

Ow!!! custom headers?? That's not cheap.

One quick comment. Stainless are nice, but L98 become real hot motors [ temp wise] when you feed them air. You might be better off with steel and get ceramic coatings? Lowers your engine bay temps.


This & a low restriction exhaust will bring your torque curve both up and forward = more Hp at higher RPM.

TJM

GREGGPENN

I reread it too. (It's been several months since I looked at it.) You are correct, it does not say the TPIS tubes were honed -- though they look awfully smooth in the pic. (That's why I assumed they were also honed, but maybe not).

If that's how large TPIS and/or ASM runners are w/o honing, then the difference is more dramatic that I thought and explains why they've done the best in aftermarket runner tests.

bjankuski

Your combination is good, the only thing I would change is the cam to a slightly smaller HR like the hot cam or TPIS ZZ-9 cam. With the TPI you will be out ouf breath by 5000 RPM so you need to keep the intake duration under 220 degrees for best results. I had a very similar combination and it made approximately 350 HP and ran mid to high 12's in the quarter.

89onlyZ51

TPIS/ASM tubes are made by mandrel bending aluminum tubing and welding to the flanges. That's why they look smooth inside - kinda like the inside of an exhaust pipe. It's thin tubing and can't be honed. The SLP/Edelbrocks are 1-piece cast aluminum, and the surfaces will have a porous look. The walls are thick and can be honed.

GREGGPENN

Redvette_22

Quinny, PM sent

Quinny

Cool.... revised plan:

*Stock rods and crank
*New pistons - 10:1 compression
*Trickflow 195cc L98 heads
*TPIS BigMouth intake runners and base
*Custom ground cam to suit engine specs - 218/218 .500" 112 LSA - something like that
*1 5/8" headers with twin 2.5" pipes
*Custom dyno tune

Along with a 3.07 or 3.54 (is there something in between for the Dana 36??) diff ratio - should be lots of fun to drive...