Going backwards in size

[FieroRacer]

The SCCA F Prepared rules are very explicit about what you can and cannot do with an engine. Any block, crank, pistons, etc can be used (as long as you have the same crank throws, etc). You can bore up to .060 over, intakes and exhaust are open, etc. But the one restriction that is bothering me is the stroke. You CANNOT stroke the engine for this class. So that means I must go with the 2.8 stroke of 2.992 in my 2100lb Fiero (including a 6 point cage, full fuel, etc). There is no way around that fact unless I compete in the Modified class.

A 2.8 built to the SCCA rules can have lots of good stuff done to it, but it just simply would not breathe. The exhaust is not a problem, I am making custom, true equal length long tube headers tuned in length and diameter to the specific specs of the engine, cam, etc. It is the intake that is giving me fits. I live at altitude and travel to various road courses and autocrosses at varying altitudes, so a carb would be a royal pain changing jets and tuning weekly. I have one of the Torker II intakes with 2 adapters, one to fit the Blake Carburation tuned Holley 6397 NASCAR sprint series carb sitting on my shelf, another adapter to fit a modded 4.3L TBI to fit that same manifold. Improved breathing, but I think there is still a better way out there (that would keep me within the rules).

I had the opportunity to freshen up a Gen III 3100 a few days ago. My God, that intake is huge for that small an engine! That thing has GOT to breathe! So my thoughts turned to installing 3100 heads and intake on the beefed up 2.8. I compared the two crank and you know, it appears that except for the throws - - there is little, if any, any difference. So I started working through all the complications to make this combo work, but then I thought - - why not use the later 3100 block?

So here's my question. Were I to bore the 3100 out .040, get some good forged pistons that would give me 10 or 10.5:1 compression - - well than what would keep that setup from working using a 2.8 crank as well? I know I would have to use a longer con rod to maintain compression, but that would still give me my 2.992 stroke I need for this class (and a far improved engine). But then the question - - what length rod would I need? An engine built to the specs above and with the WOTcompetition heads and intake using my own custom headers and custom grind Comp cam - on paper that could be a pretty potent "2.8" for competition, I would think.

I throw this question out to the more intelligent and accomplished 60 degree folks for your opinions, as I am new to this engine (but learning) . . Can this be done, and if so what length rods would I need to use?

Thnx

[bszopi]

First off, welcome to the site! Second, would love to see some pics if you have any. And finally..

http://60degreev6.com/content.php/101-CR-Calc

Try our CR calculator to mess around with a bunch of stock values, as well as creating your own setup, and determine resulting compression ration and displacement.

[Guest]

You would just follow what GM did....

Use the same length connecting rod and use a piston with a lower pin hight. To get technical, GM actually went the other way, because they started with the 2.8L then stroked the engine to 3.1L where they kept the same rod length, but moved the pin hight closer to the piston top, to compensate for the longer stroke.

I like you plans so far, basically you will simply be de-stroking a 3100, to make a "2800". It has been talked about, but no one has done it yet to my knowledge, simply because no body so far has been limited by any sanctioning rules that had talked about doing it.
Stroke is just a small part of making power, the more air and fuel you can get through an engine the more power it will make, so your idea is on the right track.

Now, might I suggest a bit of grey area rule exploitation, at least from what you've mentioned it might be worth exploiting.
You say you can't bore the block more than .060" over, what if you used a block with a larger bore to start with? The 3400 block has a 3.62" bore size, which is up from the 3.503 spec bore of the 2.8 and 3.1/3100. Keeping the shorter stroke 2.8L crank, this will give you a "Short Stroke" 3.1L The thing should rev like no tomorrow and make a very good amount of power. I had thought about doing this previously, even had a 2.8L crank to do it, but just didn't get to building it, and I wasn't restricted by any rules, so with DD2K telling me the longer stroke made more torque down low, I've always stuck with the longer stroke. The short stroke 3.1 would require custom pistons. I wasn't overly sucessful in inding any stoke application pistons that would work for me at the time.
I also felt the 2.8 reved a little nicer than the 3.1, but I haven't had a chance to drive a 2.8 with a gen3 top end or a "2800". I believe the rod ratio of the 2.8L is a bit better than the 3.1/3100 anyway.

[SappySE107]

Are you going to use a flat tappet cam in a newer block? What are the specs? I like everything you said but potentially the cam and using longer rods. Just get 2.8 pistons instead.

[FieroRacer]

I have a built up 2.8 engine available, but was led to believe the 3100 heads won’t match up to that 88 Fiero block. But what I read above seems to indicate I can? The ‘88 2.8 is a distributor block, so would have to get a WOT external crank trigger, a new wiring harness and computer. But still cheaper than building a new engine . . .

Here are the spec’s on the 2.8 block:
1. Bore – .030 over to 3.535"
2. Stroke – Engines MUST have stock stroke in FP, so that remains 2.992.
3. Pistons - Wiseco forged pistons.
4. Connecting Rods – Carrillo rods
5. Cam – custom ground, 7000 RPM, solid lifter, Comp Cam with 526 lift/284duration (exhaust) – 519 lift/274 duration (intake).
6. Compression – 10:1
7. Flywheel – a lightweight (9lb) billet flywheel with a Centerforce clutch bolted on to it.
8. Lubrication – higher pressure oil pump, larger capacity oil pan, modifications to both 2.8 crank and block, and a 2 qt Accusump.
9. Custom equal length (35”) 1 ½” primary tube headers with a 13” collector feeding into a 2 ½” exhaust

The biggest problem with this engine as it sits is that it has the restrictive Fiero intake, so the power curve falls off drastically right when the cam starts to breathe. It obviously needs more intake, and it appears that the WOT 3100 race/boost performance heads with the WOT Competition Ported 3100 Upper and Lower Intake would provide that. If I read the above posts correctly, I can almost bolt on the WOT race heads and intake and solve my problem without having to build another engine. Is this correct?

P.S. - I will submit photos within the next few days, but what all would you like to see in the photos?

[SappySE107]

The heads will bolt to the block no problem. If you have full cam specs i can simulate it in dynomation. Solid lifter would be the only real reason to stick with flat tappet so that much looks ok so far. I think I would still go roller lifter though but getting rid of the iron head setup would be a huge performance increase. If you spend most of your time above 5k RPM, the race heads are probably the best match. Otherwise, the Comp set is probably the best NA setup available for you. The Manley valves can be used if you need the strength for a fast ramp up rate cam.

[Guest]

The only possible issue I see with swapping the top end on the current 2.8 is that you will end up with somewhere around 15:1 SCR, just a guestimate. Putting the stock gen2 or 3 heads onto a stock 2.8 block that started with an 8.8:1 SCR will get to about 11 to 11.5:1 SCR, IIRC. Starting with higher SCR pistons will push the SCR even higher. You would need lots of bleed off from the cam you use to keep it running on pump gas.

[FieroRacer]

The heads will bolt to the block no problem. If you have full cam specs i can simulate it in dynomation. Solid lifter would be the only real reason to stick with flat tappet so that much looks ok so far. I think I would still go roller lifter though but getting rid of the iron head setup would be a huge performance increase. If you spend most of your time above 5k RPM, the race heads are probably the best match. Otherwise, the Comp set is probably the best NA setup available for you. The Manley valves can be used if you need the strength for a fast ramp up rate cam.

This IS a solid lifter cam custom ground by CompCams. The full specs as supplied on their build sheet are:
INTAKE EXHAUST
Valve Adjustment .018 .020
Gross Valve Lift .519 .526
Duration @ .020 Tappet Lift 274 284

Valve Timing @ .050 OPEN CLOSE
Intake 20 BTDC 44 ABDC
Exhaust 55 BBDC 15 ATDC

These specs are for cam installed at 102 intake center line

INTAKE EXHAUST
Duration @ .050 244 250
Lobe Lift .3460 .3510
Lobe Separation 106.0
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The header design with this cam and the 2.8 block bored to 3.543 and using the data for the Race heads and intake from WOT;
Using 65mm Throttle Body, and 28# injectors:

Primary Tubes (inside) 1.36 Collector Inside 2.14
Primary Tubes (outside) 1.75 Collector Outside 2.50
Primary Wall Thickness .21 Collector Wall Thickness .18
Primary Length 34.5 Collector Length 13.9

Of course, these dimensions would be impossible. Reality says to use .020 wall thickness and 1 ¾” diameter primaries, and 2.5 diameter tubing for the collector. All will feed into .020 wall thickness 2 ½” exhaust.

It is possible that I scan the build sheet for the block if needed, but it is on yellow paper so don’t know how it would turn out.

Here is a "teaser" photo of the car sitting in my garage. The Fiero in the drive is my street machine, and Cadillac powered.

[FieroRacer]

The only possible issue I see with swapping the top end on the current 2.8 is that you will end up with somewhere around 15:1 SCR, just a guestimate. Putting the stock gen2 or 3 heads onto a stock 2.8 block that started with an 8.8:1 SCR will get to about 11 to 11.5:1 SCR, IIRC. Starting with higher SCR pistons will push the SCR even higher. You would need lots of bleed off from the cam you use to keep it running on pump gas.

OK, using the table in this forum as suggested by BSZOPI above
(http://60degreev6.com/content.php/101-CR-Calc) and using the following values:

Bore - - - - - - - - - - - - - - - - - - - - - - - - 3.535
Stroke - - - - - - - - - - - - - - - - - - - - - - - 2.996
Head gasket Bore - - - - - - - - - - - - - - - - 3.622
Head gasket Thickness - - - - - - - - - - - -- .060
Combustion Chamber Volume - - - - - - - - 28.6cc
Piston Dome Volume - - - - - - - - - - - - - - 0.0cc
Piston deck Clearance - - - - - - - - - - - - - .020

The result was: Static Compression Ratio - 12.46:1
I got these figures from my engine's build sheet and the 3100 specs from the same table.

Keep in mind that I will be using the WOT Competition 3100 heads, and they claim that there will be a "slight compression loss due to the redesigned combustion chamber" ( a good thing, in my case, but how much is "Slight"?).

In any case, I should be OK with my current bottom end and the WOT race heads, and their upper and lower plenums - if my calculations are anywhere near accurate.

This was brought up elsewhere, however on that list the responder said that the CR would increase to around 13 to 13.5:1 (according to his program) from the 10:1 currently registered on the 2.8. Well, even a compression ratio of 13.5:1 would not be difficult in the regime I would be racing the car in (the Quad 4 that was run in it for a decade had 13.5:1 CR), nor would having to use a high octane race fuel be a problem (ditto). But I wouldn't want to run with any higher CR for the sake of engine longevity.

Waiting for SappySE 107 to plug in my cam profile to his dynomotion program, am curious what the results will show.

[SappySE107]

I amj not sure the iron head 2.8 has a piston/deck clearance of .020". I cannot use those cam specs because I need seat to seat, not .020 even though that is how solids are speced. With porting you are looking at 29-30cc combustion chambers.

[FieroRacer]

Attached is the CompCams build sheet for this cam. I don't know if there are any spec's I missed when I transposed them to the above post, see if this helps.

[SappySE107]

That works, because I have the comp cam files to go with the software. Pretty nice ramp up rate on the lifters. Looks like you will peak about 6k RPM and then loses power. I would run the Competition 3100 heads with the PAC 1518 springs for that cam as the velocity will do you more good than the increased flow of the Race heads. Its all about usable power and I believe SCCA is autocross, unless it covers a lot more than that.

I would definitely go 11:1 or higher with this cam.

[FieroRacer]

The car is being built to SCCA Solo II rules for F Prepared, but quite frankly we have a new road course not to far from my house with long straights and the car will see a LOT of higher RPM's also. The cam was supposed to be a 7K cam,

I tried to send the build sheet for the engine, but it keeps saying the file size is too big. So I folded it in half and just scanned the parts list - - you can get the idea just how built this engine is from that.

I plugged in some different numbers to the CR calculator, and built a table from the results. No matter what combo I used, it ended up between 12.5:1 and 14:1 compression ratio. The number I used in my initial calculation for the piston deck clearance (.020) came directly from the CR calculator for the 2.8HO. Not sure that with the custom pistons it is different, but in any case I used all the numbers from the 2.8 for the engine/block, but for the 3100 for the heads (including the head gasket, etc).

Am I too far off? The CR is an important factor here . . .

Oh, another teaser picture from 2000 when the car was running the Quad 4

[FieroRacer]

Even with the restrictive Fiero intake and stock exhaust and stock chip/tuning, this 2.8 engine produced some degree of power. This engine just can't breathe, and should do a lot better (especially with that cam). Here is the chassis dyno sheet, note the low air/fuel ratio.

With the headers I am building and any kind of better breathing - from the carb to the 4.3/5.0 TBI to the 3100 heads and intake we are discussing (any one of them) - there would be a vast improvement. From what I can see, the 3100 should be the best breathing choice of the bunch. I would expect with a fuel/air ratio of around 12:1 and with better exhaust (along with some creative tuning) this engine should peak at around 180- 200hp and over 200lbft torque according to an engine calculator. One set of figures has it at 221/228 (with 13.5 CR).

Keep in mind that this is powering a 1950lb car (2100 with roll cage).

[SappySE107]

That was something else I may not have mentioned. 1 3/4 primaries are too big for this motor. You won't be anywhere close to the power output needed for that size. 1 5/8 would be a much better idea. 16:1 is way too lean. 12.5:1 is a better starting point for dyno tuning. 14.7:1 is stoich.

I forgot to add headers in my sim. It pulls to 7k now, but def want 1.625 primaries instead of 1.750. Also, you have to account for the exhaust runner from the seat to the end of the port for your primary tube length. I think its about 3" off the top of my head. Been a bit since I measured. Im not sure if the 37.5" I used is optimal or not but I saw 260-270 and 7k peak.